VWDiesel.net The IDI, TDI, and mTDI source.
Engine Specific Info and Questions => IDI Engine => Topic started by: greg123 on May 20, 2007, 03:31:12 pm
-
I'm building a diesel special soon, not VW but very similar in many respects, AX 1.4 idi diesel (excellent engine, bad alloy block). I'm using a petrol GTI cast iron block and thinking about putting the later 1527cc head on the 1360cc block, which will drop compression to 20:!, via a larger pre combustion chamber.
I also am thinking about full ceramic treatment. I have read a research paper which showed that fuel economy of 5% better was achieved by dropping compression down to 15:1, of course starting in the cold may be hard but I'm not too concerned about that especially not at 20:!.
Wanted to start a theory & pratical discussion on lowering compression ratio, enlargin the pre chamber and *possibly* reduce pumping frictional losses by increasing the bore of the entry hole to the pre chamber cup, anyone messed with this stuff?
Oh by the way 1st stage is to see what mpg I can get from this motor, it did 71mpg in stock form before, I have several improvements to make and a couple on the vehicle as well (narrower taller tyres, better fluids, aero engine guard, electric brake vacuum pump if I can find one). 2nd stage may be a turbo to see how quick I can make it, so a low compression and coated engine would be good prep for that.
I don't want to confuse with leaking rings/valves/worn out low compression, I'm talking a 100% fit and fettled engine, but working on bigger pre-combustion chamber size which is a different thing to an engine that won't start because all the compression is coming out the breather, obviously that's a big waste of power!
Greg.
-
my polish mechanic talked about these russian trucks that would first start on gasoline, then switch over to diesel... they had lower compression than 15 i think... i wonder how it worked though... gasoline isn't a good lubricator for the pump... so that would damage our engines. but what about say 50/50 mix in order for it to ignite ? then you would need a purging system once the vehicle is all warmed up...
if you can find a way to heat up the motor before each start you won't really have an issue. the high compression ratio is mainly for cold starting.
at 15:1 compression ratio i think you might be able to use an m-TDI pump on the car... of course you will need TDI injectors though... but the piston's might not work properly as TDI ones have special swirl chambers machined right inside...
71 mpg is great!!! imo lower compression ratio will give better power/fuel economy...
-
my friend who is a farmer has a bunch of old tractors, many that are diesel, but start using gasoline, by having a type of bleed valve, where some compression is bleed out so the gas can ignite, it still detonates like a diesel, but then you switch over to the diesel pump by turning a valve, once its warmed up, so i know it can be done, especially if i think its a Farmall, that did it at least 50 years ago.
just curious though, wouldnt a higher compression make it more thermally efficient? therefore be better on fuel?
-
Any gas/diesel combination engine I've witnessed has required the use of regular spark ignition to start on gasoline. These engines also use a regular carburator when running on gasoline. Once the combustion chamber was warmed sufficiently the diesel injection pump is activated and the carburator bypass valve is opened allowing free flow of air into the engine and it operates as a normal diesel.
Gasoline has a much higher antiknock index than diesel, so it is much, much harder to ignite from the heat of compression than diesel fuel. The higher the octane of the gasoline, the less prone to ignition due to heat or pressure.
In short, to start on gasoline you'll need a carburator and spark ignition, or a compression ratio much higher than a regular diesel, which isn't the point really...
Getting back to the point, the compression ratio at which a diesel will reliably start depends alot on the surface area to volume ratio of the combustion chamber. Very large engines tend to start and run much better than small ones at low compression ratios due to the lower surface to volume ratio and the resultant lower heat losses to the combustion chamber walls. Direct injection engines also start better than indirect injection engines, again due to more favorable surface to volume ratios. I believe the the 17:1 figure of optimum efficiency was achieved on one of recardo's very large, slow speed single cylinder test engines, not really the same animal as a modern small diesel.
A 1.5l 4 cylinder will probably start an run acceptably with a 20:1 compression ratio in a relatively warm climate. Andy2's car starts a bit poorly with ~18-18.5:1 compression ratio and I'm told lacks torque at low rpm and boost pressures. If you are going for ultimate economy, very low compression might not be the hot ticket. If you're going for power it is, the decrease in compression ratio lowers the cylinder pressure for a given boost pressure and the added boost more than makes up for the lack of compression, once the turbo(s) spool, of course.
Modifications to the prechamber oriface are similarly a double edged sword. The hole needs to be small enough to insure good air velocity in the chamber during compression to aid in charge mixing, particularly at low engine speeds. It also must be large enough to minimize pumping losses. I would assume that larger orifaces would yield more gains in the upper range of RPM/power and smaller orifaces would perform better at low speeds. For an economy motor that will spend most of its time at low speeds the stock oriface is probably a good compromise.
-
Gasoline has a much higher antiknock index than diesel, so it is much, much harder to ignite from the heat of compression than diesel fuel. The higher the octane of the gasoline, the less prone to ignition due to heat or pressure.
In short, to start on gasoline you'll need a carburator and spark ignition, or a compression ratio much higher than a regular diesel, which isn't the point really...
Gasoline engines have an average compression ratio of 10:1, much lower than the 23:1 of a VW IDI diesel. The higher the compression on a gas car, the more prone it is to knocking, thus requiring high octane fuel or race fuel when a certain ratio is reached (12.5:1 and higher). Gasoline is much easier to ignite on compression alone, which is why gassers fear pre-detonation.
Anyway, I don't think starting the engine on gasoline is a good option in this case, a lot of modding is required (bleed valve, carburator...).
-
well gasoline might not be the greatest option, but i'm sure there is something out there (other than quickstart...)
i thought that the higher compression ratio requires more work to achieve, therefore lower compression ratio relieves that stress... so it's more efficient to have higher compression ratio's?? why do race gas engine's use higher CR's then???
-
I'm building a diesel special soon, not VW but very similar in many respects, AX 1.4 idi diesel (excellent engine, bad alloy block). I'm using a petrol GTI cast iron block and thinking about putting the later 1527cc head on the 1360cc block, which will drop compression to 20:!, via a larger pre combustion chamber.
I also am thinking about full ceramic treatment. I have read a research paper which showed that fuel economy of 5% better was achieved by dropping compression down to 15:1, of course starting in the cold may be hard but I'm not too concerned about that especially not at 20:!.
Wanted to start a theory & pratical discussion on lowering compression ratio, enlargin the pre chamber and *possibly* reduce pumping frictional losses by increasing the bore of the entry hole to the pre chamber cup, anyone messed with this stuff?
Oh by the way 1st stage is to see what mpg I can get from this motor, it did 71mpg in stock form before, I have several improvements to make and a couple on the vehicle as well (narrower taller tyres, better fluids, aero engine guard, electric brake vacuum pump if I can find one). 2nd stage may be a turbo to see how quick I can make it, so a low compression and coated engine would be good prep for that.
I don't want to confuse with leaking rings/valves/worn out low compression, I'm talking a 100% fit and fettled engine, but working on bigger pre-combustion chamber size which is a different thing to an engine that won't start because all the compression is coming out the breather, obviously that's a big waste of power!
Greg.
Are you in the UK?
My father's AX does 86+ MPG imp on a run and abot 68mpg on the village farting about. It has a funny problem with the I/P where it surges like a turbo. [May have rcently stopped actually] Bosch or Citroen don't know what it is but I suspect something stretched inside. Strangely a couple of months ago someone gave two AX's away because the better one had developed this same fault and failed the MOT and she didn't have the time to r & r ... Missed them :cry: Dad's is running a CAV setup and these run with lower injection pressures than Bosch. I suspect that tuned up it will be more like a Renault 5 turbo Gordino (showing my age) and leave most Golfs behind.
IMO good injectors running less pressure are better mpg wise.
-
Yes I am in the UK. The 71mpg was on a motorway run between 70 and 80 for around 400 miles, with a little running around. I doubt 86mpg is obtained 2 up at 70+mph, are the figures obtained over several tank fulls by brimming the tank, zero trip counter, wait till empty, brim tank at same pump method? Using this method over several thousand miles the best we had was 65mpg as an overall, at least 1/3 of that being urban. I have never driven anything else that comes that close, the nearest being a Montego 2.0di turbo which would do 55mpg average but I could not better the average much on a run.
You are right about the engines, they do run very well and go very well. However serious power would need a turbo as they are in the 54hp range for the 1.4 if memory serves correct and I calculated I will need 165hp to get a semi respectable 5 sec 0-60 time (grip allowing!).
I have had some surging during warm up issues on the CAV pump, other than that an unsuitability for veg oil, no issues. I have a bosch pump for one sat here, not tried it as most of them (all the ones I have run) have been cav. The 1.5 only came with cav setup. I also have a brand new EPVE turbo pump from a pug 1.9, I should be able to fit this easily - plan to use it if I turbo the engine. I have the injector lines and pulley to make it fit. I might just use it anyway and see what happens, it will run fine as a na pump! If the timing for the td 1.9 and the na 1.4 are similar I can't see an issue other than having to reduce max fueling a bit?
Question is, will I see gains in mpg from a 'worked' (ported and engine full ceramic treatment) 1.5 diesel head and the 20:1 compression ratio.
If lower compression wasn't better for efficiency, surely lorry engines would be running 25:1 rather than dropping them to scrape 15:1 at present? A di will still work fine at higher compression ratio....
I guess the 1.5 head is for certain going to be better if I move away from the economy project to the 'power' project, if I build the engine with good studs and gasket and coated as a starting point it could evolve into either right?
Are you in the UK?
My father's AX does 86+ MPG imp on a run and abot 68mpg on the village farting about. It has a funny problem with the I/P where it surges like a turbo. [May have rcently stopped actually] Bosch or Citroen don't know what it is but I suspect something stretched inside. Strangely a couple of months ago someone gave two AX's away because the better one had developed this same fault and failed the MOT and she didn't have the time to r & r ... Missed them :cry: Dad's is running a CAV setup and these run with lower injection pressures than Bosch. I suspect that tuned up it will be more like a Renault 5 turbo Gordino (showing my age) and leave most Golfs behind.
IMO good injectors running less pressure are better mpg wise.
-
Just a comment, been thinking and maybe this is correct:
Providing there is enough heat and the air is swirling well in the pre-combustion chamber, allowing the diesel to ignite easily, further increases in compression will only result in increased losses in performance due to pumping and air friction losses - the extra heat energy gained won't improve matters since it was alreayd above diesel flashpoint.
So a rule of thumb all things being equal is, find the lowest compression ratio it will happily run at. I also theorise that lowering cr by dishing the piston or similar would reduce in far less oxygen/air volume in the pre comp where the diesel is injected, meaning a bad burn. So I would say that decrease in cr should only be done via a bigger pre comp volume, thus the amount of air in there is the same and indeed there is increased room for the mix to swirl before hitting the walls of the chamber, the advantage being lower pumping/friction losses.
Next question, why do mfr's produce high cr idi's if lower is better. I think I may be able to suggest that cold starting (poorer with lower cr) cost (don't have to ceramic coat the engine etc) and reliability (when compression drops a bit a low cr engine may not run, but a high cr engine will still run - albeit breathing heavily and sounding tired - but will still manage another 50k!) so for mfr's a higher cr may be needed.
An enthusiast who has a good condition motor and can cope with/doesn't have to worry about freezing starts (there are ways round this anyhow, cold start fluid injection system/pre heater mods/block heater/a garage) may be a different kettle of fish right?
Comments please!
-
Read this too:
http://tinyurl.com/2nz2to
-
well gasoline might not be the greatest option, but i'm sure there is something out there (other than quickstart...)
i thought that the higher compression ratio requires more work to achieve, therefore lower compression ratio relieves that stress... so it's more efficient to have higher compression ratio's?? why do race gas engine's use higher CR's then???
Yes, higher CRs are more efficient, which is why race cars use them. More hp and torque for the same displacement. However race cars have to use very high octane to prevent damage from the high CR. That fuel is much more expensive, and may still use lead to achieve those numbers. When I raced, the pump at the track said something like 4 grams, or maybe milligrams of lead per gallon, with 104 octane. It also cost $3.75/gallon back in 1994. That is one of the reasons diesels are more efficient, along with running lean, and the main reason they have more torque for the same displacement.
-
Gasoline engines have an average compression ratio of 10:1, much lower than the 23:1 of a VW IDI diesel. The higher the compression on a gas car, the more prone it is to knocking, thus requiring high octane fuel or race fuel when a certain ratio is reached (12.5:1 and higher). Gasoline is much easier to ignite on compression alone, which is why gassers fear pre-detonation.
I will respectfully disagree. Gasoline is subject to accidental "knocking" at compression ratios higher than 10:1, but that does not mean it will ignite easily or reliably in a diesel. The major factor in gasoline engine preignition is the presence of the combustable mixture in the combustion chamber during the compression stroke. Diesels suffer no such "flaw", the fuel is introduced only at the desired moment of ignition, so pre-ignition is a non issue.
Fill a gasser with any heavier fraction (diesel/kerosene/jet A) by accident, even a small amount, and you will experience preignition that must be heard to be believed. Gasoline easily forms explosive mixtures with air but is not particularly succeptable to autoignition due to high temperatures. Be careful not to confuse flammabilty with octane (or cetane) rating, they are not interchangable terms. Diesel has very high tendency to autoignite, or low octane rating and cannot be used in a homogeneous charge (premixed fuel/air) gasoline engine as it will ignite long before the spark has a chance to fire it.
-
Is a higher compression ratio more efficient? For any given engine, increasing compression ratio leads to higher chamber temperature. For the same head then heat transfer across to the coolant is greater. therefore less efficient. Definitely more power but I think not more efficient.
Having said that the efficiency peak lies somewhere on a bell-curve; too much or too little compression then it drops off. I suspect that higher injection pressures help to hide defects in injectors a bit like strong valve springs give/maintain a good seat for the usual short life of the car.
Greg that mid 80's mpg is obtained doing between 60 and 70 mph cutting across from Gloucester to Ipswich via 50 roundabouts mum and dad fully loaded up for a weekend with my sister. A tank of fuel lasts so long that he doesn't normally check mileage. :lol:
Yea I mean't with a turbo added. :wink: Dad thinks there was a version with a turbo.
The other amazing thing is that he can put 15 bags of cement in the back and still pull a trailer with the same. This is one car that American dieselheads would have loved... Mind you my FIAT127 1300GT used to beat xr3i's Alas it was murderd by vandals.
-
Well, if you have more power with the same fuel/air mixture, then you have greater efficiency. Higher temps mean greater pressure, meaning more force on the piston.
-
I am talking purely diesel here, not petrol - but to answer a few points below I disagree that higher the cr the more efficient, or you would see petrol race cars with 25:1 cr. You don't, as they would detonate all over the shop and produce little or no power. A drop from 25:1 to around 10:1 - 13:1 is required to achieve good power in a petrol engine. Which shows there is an 'optimum' cr for a petrol, which allows for a quick ignition and fast burn resulting in peak pressure reached early in the cylinder cycle and more 'work done' on the piston. Higher octane petrol allows for earlier ignition and more pressure build up before the piston travels down, greater overall force on the piston. Just to confuse matters not many people realise there is a BIG difference between static and DYNAMIC compression ratio, the former is what we talk about, the latter is the only thing that matters. A cr is just an influence on pressure in the cylinder prior to ignition, a race petrol has massive valve overlap meaning that half the air leaks out of the valves at low speed resulting in low cylinder pressure even with a high CR - a low cr and it may not even run. As revs rise and the valve timing means better cylinder fills the effective pressure gets better, but this is balanced by reduced cylinder filling due to speed, if memory serves at 6k roughly half the air per stroke is entering the cylinder due to the small amount of time allowed for the cylinder to fill and the inertia effects of the weight of the air etc, compread to low speed. This of course is balanced by the fact that though a less efficient fill of the cylinder produces less power per stroke there are 4 times as many strokes - so overall power goes up. As the cylinder pressures fall on a high rpm race engine the high cr helps to keep pre-ignition pressure up and get a fast burn going - needed to extract any useful power from the small amount of time the flame front has before the piston hits BDC. Additionally petrol engines are throttled, with low throttle openings little air goes in and thus cylinder pressures are low, why some petrols like WOT to start better. LPPG is an interesting fuel as can tolerate 15:1 cr, or a far higher turbo boost and has other engine benifits. Including charge cooling - if injected in liquid form.
Diesel has around 14% more energy per gallon than petrol, which is why partly it gets better mpg. I belive the rest is down to the fact it can burn in an air rich environment (petrol requires a measured balanced environment - cannot burn as lean and requires to be vaporised which is hard to do 100%) so I still don't see high CR as anything other than an aid to getting the diesel to fire and swirl. A tried and tested way of getting tired old diesels with no compression to start (witnessed this on a lorry engine in a digger recently) is to start a big fire of petrol soaked rag just below the intake, then crank the engine - it sucks in flames and red hot air from the fire and guess what - fires right up! A blowlamp pointed into the intake of a small diesel has similar effect. This goes to show that a diesel fires on heat + air, not necessarily compression - the compression is just a method of giving us enough air and the head in one place round the injector.
I have read the ceramic coating thread and much other research on the web and think I will go that direction anyhow which should help with air temps at point of ignition.
I'd like more discussion on the efficiency effects of lower CR if anyone has further to add? I know I added about petrol systems above, but I guess that should mainly be for another thread as petrol is really a different animal to diesel in many ways, only the mechanical componants are similar (pistons, valves etc) the chemical bits of what's going on in the cylinder are very different.
At uni when doing automotive engineering I recall some single cylinder variable cr (rais and lower the block, crank stays in same place) engine that was built to study this, in my opinion it was flawed as it did not alter the cr via the swirl chamber capacity (or piston bowl capacity in a di) but I would like to dig up the research if I can. The main thing I remember is that if it was low cr it wouldn't start - but we know that ;-)
Greg.
Diesels
Yes, higher CRs are more efficient, which is why race cars use them. More hp and torque for the same displacement. However race cars have to use very high octane to prevent damage from the high CR. That fuel is much more expensive, and may still use lead to achieve those numbers. When I raced, the pump at the track said something like 4 grams, or maybe milligrams of lead per gallon, with 104 octane. It also cost $3.75/gallon back in 1994. That is one of the reasons diesels are more efficient, along with running lean, and the main reason they have more torque for the same displacement.
-
Higher temps great, but they come from considerable resistance placed on the piston dring compression and friction losses driving the air through the swirl chamber entry hole. Energy doesn't come for free and if we presume the same amount of fuel is burnt (eg same % of unburnt fuel in both cases) then the only power extracted is the same, from the explosion down stroke. This would seem to me to indicate a 30:1 cr would drag more power off the engine, not increase it. If a power gain is seen, it must be due to previous insufficient cr to generate enough heat to ignite the fuel properly, or not enough velocity on swirl to mix it - rather than a product of the pressure it's self.
Comments please ;-)
Well, if you have more power with the same fuel/air mixture, then you have greater efficiency. Higher temps mean greater pressure, meaning more force on the piston.
-
I wish there was an easy way to experiment with C/R by using different glow plugs or something... a skinnier glow plug would be about as easy as it gets.
-
I think exploding the fuel gets the most energy out of the fuel but does not get the most work done. Burning gives a more sustained push with the gases which works for longer on the crank. Ceramics of course would slow down the losses from higher heat. The CAV set up shows how high injector pressure is not neccessary for an efficient burn. Like the early 1.5 VW diesels.
Greg, I nearly put a 1.6 TD in my mother-in-laws mk1 Polo! No brake servo put me off :lol:
-
It seems that the general consensus here is that compressing the air on the compression stroke represents a net energy loss. This isn't entirely true. At the end of the compression stroke, if no fuel is added, the air compressed within the combustion chamber will expand again and drive the piston back down, think of the air as a spring. The pressure in the cylinder will then be much the same as at the end of the intake stroke. Very little work is done and therefore the losses are minimal. The losses would consist of the heat lost during compression the some energy lost to moving the air through the intake and exhaust valves.
Efficiency gains or losses due to raising/lowering the compression ratio should focus more on the dynamics of combustion than the negligable frictional losses due to compressing air. As far as I know, the higher the compression ratio, the higher the efficiency but the point of greatly diminishing returns occurs somewhere around 17:1. Higher compression ratios will very slightly increase efficiency but at the cost of greatly increased mechanical stress on the engine. Most automotive engine manufacturers use higher ratio's to improve starting and slow speed operation but not necessarily to increase efficiency. In the end, the factory compression ratio would probably be optimal. Slightly lower ratios will probably yield minor losses in efficiency.
-
I wish there was an easy way to experiment with C/R by using different glow plugs or something... a skinnier glow plug would be about as easy as it gets.
Custom thicker heatshields?
Ooh, good idea. Or just some shims to shim up the existing heatshields. Using copper should still allow a crush seal.
You will be altering the spray pattern a bit though -- effectively widening it, I think. Hopefully not enough to make a difference.
-
Gasoline engines have an average compression ratio of 10:1, much lower than the 23:1 of a VW IDI diesel. The higher the compression on a gas car, the more prone it is to knocking, thus requiring high octane fuel or race fuel when a certain ratio is reached (12.5:1 and higher). Gasoline is much easier to ignite on compression alone, which is why gassers fear pre-detonation.
I will respectfully disagree. Gasoline is subject to accidental "knocking" at compression ratios higher than 10:1, but that does not mean it will ignite easily or reliably in a diesel. The major factor in gasoline engine preignition is the presence of the combustable mixture in the combustion chamber during the compression stroke. Diesels suffer no such "flaw", the fuel is introduced only at the desired moment of ignition, so pre-ignition is a non issue.
Good point. If we were to inject gasoline at the desired moment of ignition, it would work. IIRC, isn't it how FSI engines work? They have a pretty high injection pressure (there's between 435 and 1595psi of pressure in the fuel rail).
Efficiency gains or losses due to raising/lowering the compression ratio should focus more on the dynamics of combustion than the negligable frictional losses due to compressing air. As far as I know, the higher the compression ratio, the higher the efficiency but the point of greatly diminishing returns occurs somewhere around 17:1. Higher compression ratios will very slightly increase efficiency but at the cost of greatly increased mechanical stress on the engine. Most automotive engine manufacturers use higher ratio's to improve starting and slow speed operation but not necessarily to increase efficiency. In the end, the factory compression ratio would probably be optimal. Slightly lower ratios will probably yield minor losses in efficiency.
Isn't there a vw paper that states that the most efficient compression ratio for a diesel is 18:1 or 18.5:1? I remember fspGTD saying something about that.
I wish there was an easy way to experiment with C/R by using different glow plugs or something... a skinnier glow plug would be about as easy as it gets.
Custom thicker heatshields?
Ooh, good idea. Or just some shims to shim up the existing heatshields. Using copper should still allow a crush seal.
You will be altering the spray pattern a bit though -- effectively widening it, I think. Hopefully not enough to make a difference.
Some time ago I bought a gasket set for my 1.6TD. It came with thin heatshields. I didn't know the kit included heatshields so I ordere a set separately. The separate set was a lot thicker, maybe twice as thick and looked much more heavy duty. Unfortunatey I can't compare the two since the head the thin ones were in cracked so I replaced it along with the injectors and used the thick heatshields.
The 1.9TD metal headgasket is a nice OEM way to slightly decrease the compression ration as the squish are is greater due to the cylinder bores being larger. So now I guess my compression ratio is lower due to the thicker heatshields and the 1.9 HG.
-
No, amazingly a tank full of petrol in yoyr diesel doesn't run. The 'direct injection' and high pressure petrols still squirt the stuff in during the intake stroke! They still rely on a spark to ignite it.
Good point. If we were to inject gasoline at the desired moment of ignition, it would work. IIRC, isn't it how FSI engines work? They have a pretty high injection pressure (there's between 435 and 1595psi of pressure in the fuel rail).
-
doesn't the old diesel manuals state that you can add up to 50% gasoline in extremely cold cases??? the only real problem i see with gas is that it's not a good lubricant like diesel, and has less energy. probably why the old trucks used to be able to be started on it, then switched over to the 'good stuff'
-
20%. Lubrication longer term would be an issue, a more immidate issue is that petrol won't ignite if injected in a diesel motor ;-)
Old trucks didn't start on it in that sense, they ran as a petrol engine with high cr when cold and a diesel engine with low cr when hot. When running as a petrol engine they had plugs and a carb, when running as a diesel the fuel was injected with a ip. I think some people are also getting confused with the 'TVO' or diesel type (parrafin) tractors that were NOT diesel engines, a hot petrol engine could run on lower grade fuel (inbetween petrol and diesel) but wouldnt' start on it, so they started on petrol and when hot switched to TVO. The whole system was run completely as a petrol engine, plugs and no IP. It wasn't an amazing idea and hasn't been used much in modern times. The most modern vehicle I worked on with that system was an old MF tractor form the early 50's I think. I used a moped engine to test this system, it ran okay when hot on parrafin but wouldn't even start when hot on it, I had to switch back to petrol to get it to start even when hot. I also had to alter the jetting for the parrafin running compared to petrol, which is understandable.
Greg.
doesn't the old diesel manuals state that you can add up to 50% gasoline in extremely cold cases??? the only real problem i see with gas is that it's not a good lubricant like diesel, and has less energy. probably why the old trucks used to be able to be started on it, then switched over to the 'good stuff'
-
Been thinking on your idea, how about - for experimental purposes only - taking out the glow plugs completely and blocking the holes with bolt (set screw) and washer making sure the threads are only as long as needed, or for that matter a sawn off old set of glow plugs sawn off just past the seat.
It would be hard to start but I'm sure it could be got going by a bit of cranking/bump start/liquid in the manifold, once running it should be fine. Quite how we would establish efficiency without then driving it 500 miles I'm not sure... Unless you live on a hill and can put up with it for a week? ;-)
I wish there was an easy way to experiment with C/R by using different glow plugs or something... a skinnier glow plug would be about as easy as it gets.
-
It would be hard to start but I'm sure it could be got going by a bit of cranking/bump start/liquid in the manifold, once running it should be fine. Quite how we would establish efficiency without then driving it 500 miles I'm not sure... Unless you live on a hill and can put up with it for a week? ;-)
If the engine has good compression and a good battery, it'll start without additives. I was able to start my 1.6NA with three burnt glow plugs, in -40 weather, unplugged. I took a lot of cranking but it did start.
If you found a way to heat the intake air only during startup, I think it could help. Something like locating one or two GP on the intake manifold. The amount of space they would take in the manifold would be negligible compared to the space they take in the cylinder head.
BTW, disable HTML in your profile, that way your quotes will work properly :wink:
-
This is gonna sound kinda nutty, but provided the owner lived in a warm enough climate, say... close to the equator, could an IDI start and run reasonably well with a ~16:1 CR? From everything I've gathered, it's not CR that'll make or break diesel performance/efficiency, but quench. Which is why a head gasket that's too tall can hurt an engine way more than the lower CR seen in the TDIs. From the 1.5L SAE paper, the main reason for a higher CR was cold starting concerns, but w/o those, how much farther could we go down in terms of CR?
Also, what about running a grid heater, pulling the glow plugs, installing spark plugs, and running E85 with TBI/MS&S above ~4-5k rpm? Diesels don't have the greatest air utilization rates, but there should be plenty for higher octane fuel and gasoline as long as there's spark. We could rev the engine a make plenty more power above ~4k rpm, while still maintaining the characteristics that make diesels efficient at low load.
-
I wish there was an easy way to experiment with C/R by using different glow plugs or something... a skinnier glow plug would be about as easy as it gets.
I've done the math. Removing the glow plug completely only lowers the compression by about 0.5, so 23.5:1 becomes 23.0:1. The volume of the glow plug is suprisingly little.
-
You'd think so wouldn't you? However try that on a Peugeot 1.9TD, the things never start without glow plugs - even if hot! Well they would eventually when hot but they do NOT like it. My older Peugeot 2.5l idi in my motorhome is a worse design and dates back nearly 30 years, however it starts first swing and once it's been started for the rest of the day it doesn't need glow plugs. So I think there is a bit more to play than just the cr, such as the designed energy of the swirl etc which may be low at low cranking rpm necessitating glow plugs for some engines - even when hot.
If the engine has good compression and a good battery, it'll start without additives. I was able to start my 1.6NA with three burnt glow plugs, in -40 weather, unplugged. I took a lot of cranking but it did start.
If you found a way to heat the intake air only during startup, I think it could help. Something like locating one or two GP on the intake manifold. The amount of space they would take in the manifold would be negligible compared to the space they take in the cylinder head.
BTW, disable HTML in your profile, that way your quotes will work properly :wink:
-
I was going to ask if anyone knew the volume ;-) Okay that is not such a helpful idea then!
I've done the math. Removing the glow plug completely only lowers the compression by about 0.5, so 23.5:1 becomes 23.0:1. The volume of the glow plug is suprisingly little.
-
My first car on the road was a Polo 895cc, it was a very good car really and did 70-80 on the motorway fine. I remember the brakes though, you certainly wouldn't want a faster/heavier vehicle on them ;-)
Greg, I nearly put a 1.6 TD in my mother-in-laws mk1 Polo! No brake servo put me off :lol:
-
It seems that the general consensus here is that compressing the air on the compression stroke represents a net energy loss. This isn't entirely true. At the end of the compression stroke, if no fuel is added, the air compressed within the combustion chamber will expand again and drive the piston back down, think of the air as a spring. The pressure in the cylinder will then be much the same as at the end of the intake stroke. Very little work is done and therefore the losses are minimal. The losses would consist of the heat lost during compression the some energy lost to moving the air through the intake and exhaust valves.
I respectfully dissagree. Yes it would seem that if you compress the cylinder that takes work, but the highly compressed air would then push the piston back down releasing the same amount of work. This is perpetual motion, which can't exist.
I believe the practical illustration of just how big the losses in energy due to compression can be illustrated as follows: Take an engine with good compression and crank it over by hand - or on the starter. To spin it at starter motor speeds takes in the order of 3HP just to crank it, that is nowhere near idling speed! Now adjust the exhaust valves so they are cracked open a bit all the time (don't foul the pistons!) and thus the engine has no compression. The cylinder still pumps the same volume of air - so pumping losses are still the same, but doesn't have the compression and similarly doesn't have the 'reclaimed' power on the downstroke after compression. It's quite remarkable, the starter spins the engine over twice as fast using half the current - sounds like a turbine! This is why a hand crank engine has a decompression lever, to allow you to spin the engine up to cranking speed without the considerable power looses of the compression cycle (same amount of air is always pumped, even on decompression lever operation as that lever allows air in and out of the cylinder freely).
They theory behind *why* I would guess as follows: A fair bit of energy upon compression is lost as heat and escapes through the engine. Some of the compression escapes as blow by - the higher the compreassion the higher proportion. On the down stroke the hot air from compression has had time to cool some and by the time the pistion gets to the maximum torque half way position the cylinder pressure may be half what it was on the upstroke at the same point. Increased compression increases friction on the engine by placing greater loads on it. There are also inertia losses from speeding up the air more and trying to push it into the cylinder head, where it 'piles' up, requiring a change of inertia and direction on the down stroke - all at the expense of power. I guess there are frictional losses in the air as it's forced into the pre-cup that manifest as heat, a proportion of which is lost by conduction to the engine.
If one could have air going in and coming out at the same temperature and a block/head that had 0 heat transfer properties as well as engine internals which didn't increase friction as the load increases, then the higher compression shouldn't count. Of course such an ideal engine doesn't exist.
As I see it, increased compression results in extra heat, some of which heats up the air in the pre cup and some of which is lost into the engine with corresponding loss of efficiency. I think mfr's run them high as the efficiency loss may not be huge (I'm thinking 5% between as low as it will go and run compred to say 25:1) and it ensures cold starting running.
In trying to build an 'efficient' car, that possible 5% from a low CR, with around 5% tops from ceramic coating, 5% from aerodynamic mods, 3% from low friction fluids and 5% from narrower low resistance tyres may take my 71mpg and make it 87mpg ;-) Add in a turbo and the increased efficiency it brings, or low resistance exhaust/ram air inlet/porting to work on pumping losses and perhaps some more? Goal is 100mpg... Remove brake vacuum pump and go electric, greatly reduced parasitic load there - spinning a brake vacuum pump at 1500rpm (camshaft speed, 3k engine) for 2 hours on the motorway when you don't use your brakes is a big load!.
As far as I know, the higher the compression ratio, the higher the efficiency
This is what is often said, the purpose of the thread is to challenge it. I think I have made enough points so far, anyone with any more reasons 'why' a high cr is supposed to be more efficient? Given that a lower CR will perfectly heat, swirl and ignite the mix? I go back to my point about the tdi's, why don't VW put the cr up to 25:1 on them? I suspect because all they 'need' to ensure a good fuel burn is around 15:1, so they make it 18:! or something to ensure good starting in cold - knowing that any further increase just lowers efficiency and reduces hp and mpg as the power to do the compression and produce that heat which is lost comes from the power stroke, sapping the engine.
-
During cranking the starter has to deal with singular compression events, getting over the "humps" is quite difficult and takes considerable torque, hence the need for a powerful starter. This cannot be compared to the conditions at higher engine speeds. The flywheel inertia at higher speeds is sufficient to drive the crank over the "humps" and the energy stored in the compressed air is returned to the crank on the expansion stroke. Indeed there are losses from all of the points mentioned, so this is anything but perpetual motion, but the losses are not total, which is the point I was trying to make. The compression losses may begin to go exponential as the compression ratio and air heating increases. Single stage compressor efficiency does something like this beyond a certain point.
-
Although at higher rpm, wouldn't heating losses be less as the air has less time in contact with the cooler metal? I seem to remember a long time ago some one tested an all ceramic engine. I don't remember much else though.
-
Well you can roll your car down a hill, engine off, in 3rd gear, with and without the exhaust valves cranked open (perhaps safer in a petrol as need them cranked open a fair bit to ensure no compression at speed) and notice the same result, far less drag without the compression. This proves the point I think. Alternatively we could slap a head on an engine with the pre-comp filled in, so very high compression, and see how well it rolled down a hill in gear.
Regarding the 'humps' when cranking - if the starter has put the enerty into a mix of inertia and gas compression, regardless of the speed if that energy is still there unless it has leaked away anywhere. As you point out, there isn't enough energy released after the 'hump' of the compression, meaning net effect of high comp = high loss of energy. I accept that this is multiplied at cranking speed due to there is more time for the compression gasses to soak heat away and cool down (lowering pressure for the downstroke) and blow by the rings/valve seats, however all this still goes on at higher speed, just not 'as' much.
During cranking the starter has to deal with singular compression events, getting over the "humps" is quite difficult and takes considerable torque, hence the need for a powerful starter. This cannot be compared to the conditions at higher engine speeds. The flywheel inertia at higher speeds is sufficient to drive the crank over the "humps" and the energy stored in the compressed air is returned to the crank on the expansion stroke. Indeed there are losses from all of the points mentioned, so this is anything but perpetual motion, but the losses are not total, which is the point I was trying to make. The compression losses may begin to go exponential as the compression ratio and air heating increases. Single stage compressor efficiency does something like this beyond a certain point.
-
Yes, which is why losses at cranking speed will be up to 100% if you crank it slow enough (all the heat and compression goes away after a few seconds) but those losses are still around the 20-30% mark at normal operating speeds, 40-50% going out the exhaust and 20-40% coming out as useful power (depending on design, fuel used etc).
Although at higher rpm, wouldn't heating losses be less as the air has less time in contact with the cooler metal? I seem to remember a long time ago some one tested an all ceramic engine. I don't remember much else though.
-
Just an update on the research so far, with members help and the time on the net etc (inc looking at some patents, Atkinson and Miller cycle engines etc) it seems to be to me that lowering the compression as far as it will go WITHOUT harming combustion (negating cold starting) can have UP TO 5% better efficiency (power/economy) and similarly a FULL engine treatment of coatings can have UP TO 5% improvement.
So there would be between 5% - 10% to gain from coating (in bulk probably about £100 per engine, to us £300 per engine it can be had for) and difficulties cold starting/starting when engine gets 'tired' a bit. Which probably explains on both counts why mfr's don't do it much, though they are starting to now. 3 hybrids are running Atkinson/Miller cycles (Toyota and Subaru among them) and I read on this board Subaru are running ceramic coated piston tops from factory now - though that's far from a full internal coat (probably more to protect piston crown than to aid efficiency since most WRX buyers don't buy it for fuel economy....).
Just my 2p so far for those interested ;-)
-
We'll probably start seeing far more miller/atkinson cycle since it really, really helps w/ low load efficiency in gasoline engines, which is where they really can't compete w/ diesels, and the most gains will be seen. Peak efficiency hasn't changed much over time and the difference between gas/diesel there is negligible.
-
A good discussion covering a lot of the theoretical aspects of CR and its effects on efficiency and performance. From a practical standpoint I can offer a bit of anecdotal information. Having had a number of VW diesels… of all the na’s, the best running (acceleration and hill pulling), and the highest mileage (55mpgUS road car), was a well-worn 1.6 Jetta. The compression centered closely around 350psig and the pump was set to .045” at several service cycles (so it wasn’t a fluke adjustment). It’s Achilles heel as you might imagine was cold starting; it was a bear to get going when the temperature was at or below freezing! Used a block heater at home to minimize the problem, and finally ended up using an Orpin switch to crank with 2 batteries in series, couldn’t find any hi-performance starters in those days. Drove the thing on many long trips, for a lot of miles, never having a problem other than it used oil at a qt/800 miles. Couldn’t guess what the effective CR was… but from what I’ve read and experienced I believe lower CR (within limits) will result in more power and better economy (for IDI VW’s ), if you can solve the cold start problem (move to Miami?). Regards
-
That's particularly interesting as if the engine is well worn it will lose efficiency from blow by and leaking past the valves. So if you are getting good economy one could expect even better if it was done via a bigger pre-comp chamber without the associated losses of a worn engine.
A good discussion covering a lot of the theoretical aspects of CR and its effects on efficiency and performance. From a practical standpoint I can offer a bit of anecdotal information. Having had a number of VW diesels… of all the na’s, the best running (acceleration and hill pulling), and the highest mileage (55mpgUS road car), was a well-worn 1.6 Jetta. The compression centered closely around 350psig and the pump was set to .045” at several service cycles (so it wasn’t a fluke adjustment). It’s Achilles heel as you might imagine was cold starting; it was a bear to get going when the temperature was at or below freezing! Used a block heater at home to minimize the problem, and finally ended up using an Orpin switch to crank with 2 batteries in series, couldn’t find any hi-performance starters in those days. Drove the thing on many long trips, for a lot of miles, never having a problem other than it used oil at a qt/800 miles. Couldn’t guess what the effective CR was… but from what I’ve read and experienced I believe lower CR (within limits) will result in more power and better economy (for IDI VW’s ), if you can solve the cold start problem (move to Miami?). Regards
-
Man, you guys make me keep waffling. The improved MPG of a lower C/R really temps me to enlarge the prechambers, but I'm afraid of losing cold start performance (not on the new engine, but 150Kmi later). Maybe you could pull off a 20:1 C/R with Total Seal rings for longevity?
-
This is based on guestimate, but with a fresh head (eg valves ground in) and new rings and a honed/rebored cylinders, you should have excellent seal for at LEAST 100k if you change the oil. I'm thinking 20:1 should be fine, unless you live in a VERY cold climate, where a block heater would do the job for clean home starts. I'd be nervous of it starting easily at 17:1, I'm afraid this is a case of 'try it' and 'be brave' lol.
Man, you guys make me keep waffling. The improved MPG of a lower C/R really temps me to enlarge the prechambers, but I'm afraid of losing cold start performance (not on the new engine, but 150Kmi later). Maybe you could pull off a 20:1 C/R with Total Seal rings for longevity?
-
libbybapa
How was the performance of your low CR. motor?
-
Ok, this is starting to sound good. What's the best way to reduce the C/R to 20:1? Turn the precup interior on a lathe?
-
Ok, this is starting to sound good. What's the best way to reduce the C/R to 20:1? Turn the precup interior on a lathe?
what does the thicker gasket give us? Or can we use 2 togeather or is there something in Cu sheet?
Reading my previous postings (other threads) My most economic TD by far has lower compression. How much? I dunno but definitely easier to turn by hand and with old injectors gave 62mpg imp on a run compared with 48mpg best with a 'good condition' 'burn no oil' 100k engine. I make that ball park 30% more economic. Only other difference was the larger exhaust from a 5 ganger Quantum. Divide by 1.2 to get US wine gallons :mrgreen:
-
what does the thicker gasket give us? Or can we use 2 togeather or is there something in Cu sheet?
Thicker gasket will lose quench-effect. It is important in gasser world, how about in diesel? I think even more important?
-
Not sure adjusting HG thickness alone is optimum solution, or if changing cup dimension to keep ratio of cup to compressed cyl. volume app. the same would be best. Seems I remember a thread where one of the hot rodders had figured out how to use some other cup (think it was GM) in the VW head! Here is a Cu shim gasket supplier that (according to list) seems to have pattern for VW 1.6's (diesel?). If not, I'm sure they could use an old HG for pattern. If shimming the head alone will give satisfactory results then the different thickness's available should allow someone to built just about any CR engine they desire. Regards
http://www.headgasket.com/gaskets.html
-
Definitely don't want to mess with the head gasket. If you use a thicker head gasket, a bunch of oxygen never makes it into swirl chamber. Need to have (as near as possible) 100% of the available oxygen in the swirl chamber when injection occurs for a good burn.
-
There was the thread about modifying the central groove that runs down the piston to get better high rpm performance. It would also lower the CR.
-
Definitely don't want to mess with the head gasket. If you use a thicker head gasket, a bunch of oxygen never makes it into swirl chamber. Need to have (as near as possible) 100% of the available oxygen in the swirl chamber when injection occurs for a good burn.
[/size]
Why do you need all or nearly all the oxygen/air in the swirl chamber? With a turbo there is always a xs anyway
-
I just remember from other threads on this board that thicker head gaskets are not a good idea.
-
I just remember from other threads on this board that thicker head gaskets are not a good idea.
[/size]
Are you including the 3 hole /notch standard gaskets or specially commissioned ones?
I wonder how much longer an engine will last if the compression is lowered. Less strain on bearings etc?
-
Regarding - why does increasing Cr (or rV) not increase overall fuel economy?
Remeber there are two efficiencies here, which are COMPLTELY different, thermal efficiency (formula that uses Compression ratio) and mechanical efficiency.
For a better THERMAL efficiency, high CR is always better. But it is just a theoretical number. Mechanical efficiencies are based not on compression ratio directly, but more about material properties and engine speeds and loads and VE.
As an engine goes faster, mechanical efficiency drops, as does VE (cylinder filling). Lower compresssion can increase mechanical efficiency due to less forces (friction > heat) onto contact surfaces.
Think of it as two lines on a graph, compression ratio x axis, efficiency y axis. as comprssion increases, mech eff goes down. So top left to bottom right. Thermal eff goes up, so botom left to top right. We have a big X. Very simplified, i know but it is just an illustration.
Middle of the X is the best point for efficiency. Seems to be 17:1 according to many sources on a diesel, but would expect 18:1 would be as low as you can go on these engines...
What was the numbers for the increase in compression volume too get 18:1 again? I think I have an idea... :P
-
I just remember from other threads on this board that thicker head gaskets are not a good idea.
[/size]
Are you including the 3 hole /notch standard gaskets or specially commissioned ones?
I think he means stacking gaskets. It's common procedure with gassers but the cr and pressures within the cylinders are much less.
-
Something to consider with the "well worn" engines. They are also burning oil which does produce power.
I'm not sure how much the swirl chambers can be modified. There was alot of engineering put into them to maximize air/fuel mixing etc.
-
Unless it's really really bad I don't think it can add more than a mpg or so. Even at 5L per 2500 miles, that'd still only add a couple mpgs...
-
what do you guys think of this, the valvecut out in the piston is now deeper, he also have custom cams, its calculated and its reduced to CR16,9
this is a stock picture:
(http://img166.imageshack.us/img166/5206/dscf0006230205gm7.jpg) (http://imageshack.us)
(http://img234.imageshack.us/img234/2650/dscf0007230205zk9.jpg) (http://imageshack.us)
this is the modified
(http://img217.imageshack.us/img217/5569/dsc00094cr169op1hi8.jpg) (http://imageshack.us)
Greetz, Benjamin
-
Looks interesting Benjamin; but are there any performance/mileage figures to go with it?
-
Funny pictures, all my old VW diesels have different oil supply and return hole placements. What do we have here???? Regards
-
he didn't keep the little stem thing that usually connects the 2 valve indent things... which aren't really valve indents, since they def don't line up with the valves, atleast not on a vw. what is that motor for anyway? is it a mercedes or something?
-
Wow I been away too long, where to start....
C/R's gas well established between 8:1 and 12:1.
is more better NO the higher c/rs in race appalcations are for the long bleed ( duration) of the camshafts on the intake lobe I have good experance with this, my last engine for my Bonniville (small block chevy) was a 400 ci with 9:1 comp and i have a dyno sheet for 550 hp. 580 tq.
at 4300 and 3200 rpm
on diesel from 15:1 to 24:1
the higher on pre-comp only this is for starting issues the more movement in air means more heat generated,
Di engines are usally at 17:1 or 18:1
again more is not better.
on this note i finshed with my injection pump experament with results:
stock idi no turbo 1992
untouched 1600 psi breaking 55mpg
reset to 1850 psi 58 mpg
set to turbo 2250 psi 53 mpg with black smoke and low top end
timing at n/a settings .088 mm
changed timing to turbo 1.00 mm
untouched at 1600 59 mpg
reset to 1850 61 mpg
turbo 2250 53 mpg with black smoke and sputter
so
with a stock engine i found with 1.00 mm stroke on the pump and 1850 breaking the best mpg hope this helps
Craig
-
on this note i finshed with my injection pump experament with results:
stock idi no turbo 1992
untouched 1600 psi breaking 55mpg
reset to 1850 psi 58 mpg
set to turbo 2250 psi 53 mpg with black smoke and low top end
timing at n/a settings .088 mm
changed timing to turbo 1.00 mm
untouched at 1600 59 mpg
reset to 1850 61 mpg
turbo 2250 53 mpg with black smoke and sputter
so
with a stock engine i found with 1.00 mm stroke on the pump and 1850 breaking the best mpg hope this helps
Craig
It's really nice of you to share such info, thanks!!!
Those psi figures are the injector's breaking pressure right? Do you think we'd get similar results on a turbocharged engine?
Reason I'm asking is because I have 135bar mercedes injectors (1958psi) timed to TD specs on my 1.6TD.
-
on this note i finshed with my injection pump experament with results:
stock idi no turbo 1992
untouched 1600 psi breaking 55mpg
reset to 1850 psi 58 mpg
set to turbo 2250 psi 53 mpg with black smoke and low top end
timing at n/a settings .088 mm
changed timing to turbo 1.00 mm
untouched at 1600 59 mpg
reset to 1850 61 mpg
turbo 2250 53 mpg with black smoke and sputter
so
with a stock engine i found with 1.00 mm stroke on the pump and 1850 breaking the best mpg hope this helps.
Craig
[/size]
Good contribution Craig :!:
The 1600psi is only 108bar. All else the same it looks like peak mpg might occur around 1700psi or 115bar. From the results it may be 65 to 70mpg. Factor in a freeflow exhaust and then a lowered compression and then 80mpg might be hit. :shock:
-
yes breaking psi and this engine has 440,000 kms and not sure of the current state of the rings on the pistons but it started better at 1.00 mm on timing then it did at .088 mm
-
Greg,
Did you find a way of altering the compression ratio without machining anything yet?
For the purpose of tests on mpg?
-
maybe that's why my MPG is suffering with 160 bar injectors... have you tried running 1.05mm injection timing for turbo injectors??? i'm currently running 1.06mm or so...
i wonder if there is any validity in VW upping the turbocharged injectors breaking pressure to 155 bar, to ensure a safe fuel atomization??? has anyone tried N/A injectors on a TD???
-
Yes I have put 135 bar injectors in a TD. With out changing anything else: smoother idle, measurabley less power on top end, no appreciable difference in fuel economy.
-
Greg,
Did you find a way of altering the compression ratio without machining anything yet?
For the purpose of tests on mpg?
For testing it has to be varied combinations of head gaskets. We're not talking 100's of miles... just say 20miles, fuelling from a measured 'baby bottle' in the engine compartment.
-
Yes I have put 135 bar injectors in a TD. With out changing anything else: smoother idle, measurabley less power on top end, no appreciable difference in fuel economy.
I wonder if 1mm on TD pump is wrong with n/a pressures. Andrew has his 99 cents dynamic tester to confirm this :wink: Smoother idle sounds like a great advantage.
-
I guess its time to re-read the SAE paper on the TD motor and see why the 155 bar pressure was used on the TDs. Using the 135 bar injectors with less advance may work better than the same injectors at 1mm, but are they working better than the correct injectors for the engine, with the pump set to the specified pump timing.
I didn't leave the 135 bar injectors in very long. It was a non-availability thing for the TD injectors. I still have the 135 bar injectors sealed in a plastic bag. If i get bored, I'll get GTD nozzles and recalibrate them.
i don't concider a smooth idle a desirable thing, at the expense of power. As long as all four are fireing at idle, I'm ok with that. My engine spends very little time at idle.
-
hmmm smoother idle... sounds to me like what the TDI's do with their dynamic timing
-
I guess its time to re-read the SAE paper on the TD motor and see why the 155 bar pressure was used on the TDs. Using the 135 bar injectors with less advance may work better than the same injectors at 1mm, but are they working better than the correct injectors for the engine, with the pump set to the specified pump timing.
I didn't leave the 135 bar injectors in very long. It was a non-availability thing for the TD injectors. I still have the 135 bar injectors sealed in a plastic bag. If i get bored, I'll get GTD nozzles and recalibrate them.
i don't concider a smooth idle a desirable thing, at the expense of power. As long as all four are fireing at idle, I'm ok with that. My engine spends very little time at idle.
I see what you mean about desirability of power... However
1) Standard power standard TD bars isn't maximum power available.
So could more power be tuned in to the n/a bar TD setup you had?
2) Smoother idling means less mounting wear probably.
3) n/a pressures mean less wear on pump and less work done on compressing.
4) Whats the physics of changing bars downwards?
i) larger droplets?
ii) Is it the same volume of diesel squirted slower?
iii) Earlier or later start of burning?
iiii) Longer burn doing more work on the crank?
5) I dunno.... :roll:
-
Mr. the Miser,
Who mentioned anything about the length of the test, or over what period? I am not sure i see the point of your remark...
I have an idea for reducing Cr without changing headgaskets, that can be changed to suit.
Also remember thicker headgaskets will destroy the quenching effect, not desirable.
-
"I see what you mean about desirability of power... However
1) Standard power standard TD bars isn't maximum power available.
So could more power be tuned in to the n/a bar TD setup you had?"
Like I said, we need to look at the SAE white paper and see what the reason for increasing the break pressure was. I don't think the VW engineers were stupid and overlooked a very obvious performance enhancement. The only screw up I'll assign to them is the pea shooter exhauste.
I can put forth an educated guess why the idle was better, more advance at idle.
As for my own ride, its deffinately making more power than stock. It has: full 2.5" exhauste, GTD nozzles that i calibrated to 155 bar, closed waste gate, boost pin at the highest fueling, and diddled with governor. Full blast boost is about 22 psi while the EGT occasionally tops out above 1300F. It has embarassed many a V8 gasser and quite a few rice boys. The only change I did was to put the 135 bar injectors in and the power measurabley dropped. IE its top speed was significantly lower over a known distance. But i had a great idle.
I have a hard copy somewhere of the TD SAE paper. I'll try to dig it out and look at the break pressure thing and see if they disclose the reason. There is an outside chance that they did not put a reason why they increased the break pressure because of proprietary reasons.
-
sounds to me like the timing should be around 1.05mm and maybe a little more timing advance in the upper rpm range??? (with the 135 bar injectors..)
-
Mr. the Miser,
Who mentioned anything about the length of the test, or over what period? I am not sure i see the point of your remark...
I have an idea for reducing Cr without changing headgaskets, that can be changed to suit.
Also remember thicker headgaskets will destroy the quenching effect, not desirable.
My reference to length of test was only a suggestion. To run tests when you are way off maximum efficiency for perlonged periods say a complete tankful is somewhat thumbtwiddlingly slow. As you get closer to the goal; proof by perlonged testing may be desireable. Rather than re-engineer slabs of ally to alter compression ratio; slipping in gaskets temporarily is time efficient. Not intended to be permanant or for testing maximum powers. Unless you always go to the same gas station filling tank needs plenty of iterations to average natural variations in squirting fuel in ...and even then it varies.
...I thought this thread was about changing things to get different results :shock:
-
when putting n/a injectors (135 bar) in a td without adjusting the timing to work with the injectors you effectily advance the injection timing that is why the topend had no power the injection was to early at max rpm with a td you could go to 163 (max limit) and you should get better power...
But at what expence... with a turbo the engine will use all the fuel you put to it, Personly I will start with propane injection on my n/a to see if it helps me I'm still looking for a td to play with the possibility of nitrous ??
:twisted:
Craig
-
Mr. the Miser,
Who mentioned anything about the length of the test, or over what period? I am not sure i see the point of your remark...
I have an idea for reducing Cr without changing headgaskets, that can be changed to suit.
Also remember thicker headgaskets will destroy the quenching effect, not desirable.
OOps sorry what was your method of changing compression ratio without changing gaskets? :?
What's the quenching effect?
-
I think i can vouch for not using thicker head gaskets to test for engine efficiency.
I put a TD motor together with new pistons, bearings, head, valves, and gaskets. However, The block and crank were from different motors. I was in too much of a hurry to measure piston protrusion, so I went with a three notch gasket. I figured since its a summer only diesel, what could be the harm.
As a result, this thing has always had a less than pritty start. i checked the compression, and all cylinders were in the mid 400 when the engine was below freezing temp. It doesn't burn any oil, and will start without the glow system working, even down to 40F. Its ugly, but it goes. Even today @ 85F, I expect it to do some start monkey business when I go to lunch.
So we have:
Good stone cold compression
Burns no oil
Has seen nothing but synthetic since the first two pans of dyno oil
Starts about the same, with or with out a glow system.
The only thing I can figure is it has the wrong gasket thickness.
Although it may be doing me some good at high booste, at part throttle cruiseing, its probably not doing me any favors.
rather then pull the head and change the gasket, I'm going to build a 1.9 mechanical head, measure the piston protrusion, put in the proper thickness metal head gasket, and bolt on the 1.9 head.
This is not an invitation to solve my starting issues. It starts just fine for me. It is an observation on the posible outcome when testing engine efficiency with a thicker head gasket. Its probably a less than optimal condition.
-
I think i can vouch for not using thicker head gaskets to test for engine efficiency.
I put a TD motor together with new pistons, bearings, head, valves, and gaskets. However, The block and crank were from different motors. I was in too much of a hurry to measure piston protrusion, so I went with a three notch gasket. I figured since its a summer only diesel, what could be the harm.
As a result, this thing has always had a less than pritty start. i checked the compression, and all cylinders were in the mid 400 when the engine was below freezing temp. It doesn't burn any oil, and will start without the glow system working, even down to 40F. Its ugly, but it goes. Even today @ 85F, I expect it to do some start monkey business when I go to lunch.
So we have:
Good stone cold compression
Burns no oil
Has seen nothing but synthetic since the first two pans of dyno oil
Starts about the same, with or with out a glow system.
The only thing I can figure is it has the wrong gasket thickness.
Although it may be doing me some good at high booste, at part throttle cruiseing, its probably not doing me any favors.
rather then pull the head and change the gasket, I'm going to build a 1.9 mechanical head, measure the piston protrusion, put in the proper thickness metal head gasket, and bolt on the 1.9 head.
This is not an invitation to solve my starting issues. It starts just fine for me. It is an observation on the posible outcome when testing engine efficiency with a thicker head gasket. Its probably a less than optimal condition.
[/size]
Saurkraut, Having changed so much how can you be sure it's the gasket?
Are you saying 400psi is bad?
Many workshops just put in the 3 notch as a matter of course to save measuring as you did.
Difference between a thick and a thin gasket is 0.3mm...
So maximum possible affect with a wrong gasket is 0.3 x (76.5^2)PI/4 =1.3cc;
but depending on engine may be only 0.65cc [or nothing :wink: ]
1588 cc TD has 23:1 pressure ratio. Stroke is 86.4mm
(76.5^2)PI/4 x stroke, is swept vol... 397cc
calculation of combustion space
(397 +s)/s =23; 23s = (397 + s) ; s=397/22 = 18cc
Biggest compression drop is:
(397 + 1.3 + 18.)/(1.3 +18.) ... =21.6:1;
or 22.3:1; [0r no change] :roll:
A poorly seated re-ring could achieve this drop!
Add a second gasket; a (1 notch)...
1 notch gasket is 1.3mm thick...
1.3 x (76.5^2)PI/4 = 6cc
(397+6+18 )/24 =17.5:1
A 3 notch engine using 2 '1 notch' gaskets (6cc-1.3cc)
(397+ 4.7+18 )/22.7 = 18.5:1
Good for experimentation and then replaced with a taylor-made version metal or otherwise.
EDIT... Achieving compression ratios between 18.5:1 and 21.5:1 are not so easy without special gaskets ....
Unless an intact 'old one' has compressed slightly :?
EDIT... EDIT A real time engine's compression may be lower to start with so in practice those compressions are attainable. [Pays to have a tight spec. engine and a broken in specimen alongside]
-
Are we debating the same side of the compression issue? I am really trying to say that running a thicker head gasket is not a good idea. I screwed up and did it myself, and I'm trying to save others from making the same mistake.
For clarification, there were months between changes. The entire process took over three years. Each change was verified with a befor and after acceleration run over a known distance. If it did not yeild an improvement in EGT, Boost, or speed, it was undone.
This motor was not slapped togather, and a bunch of changes done before the key was turned. The motor went in bone stock. The only difference between it, and a brand new motor was the 3 notch gasket, and 1st oversized pistons. The pistons were even fitted to the block according to the honeing group number.
As far as I'm concerned, the engine performs to my satisfaction. It goes like a scalded cat when I want it too, cruises on the highway just fine, and gives good fuel milage to boot. I just wouldn't enter it into pritty cold start contest. That is not its strong suite.
And, quite the contrary, I think mid 400 psi (i forget what it was exactly, 460 or so, with very little difference between cylinders) is just dandy compression.
If many work shops blow off piston protrusion measurements, it doesn't make it right. It just shows there are alot of schlocky mechanics out there that are doing their customers a disservice. Once agian, I don't think the German engineers were stupid, and made a mistake in specifying piston protrusion numbers that related to engine performance.
And yes, i can work a calculator too. If an engine's piston protrusion calls for a 1 notch, and a three notch is installed, the compression change is very small. It yields very small chainges. Its not the way to go for lowerering compression. Its a mistake I made, and I'm trying to communicate that this is not the way to go if you want to lower compression.
But what is changed significantly is the squish area between the head and piston. When the squish area is correct, the head and piston act as if they are in thermal contact, and some cooling bennifit is enjoyed by the piston. When the gap is increased, this bennifit disappears.
So my point is, going to a thicker head gasket to lower compression is not a good idea. You don't achieve significant results, and unintended consiquences arise.
I'll try to find more information on squish band, and i'll post it here.
-
Saurkraut,
I'm not trying to accuse you of slapping the mods together; I'm just trying unravel the secrets of why some engines are more economic than others. Nothing against extra power either :) But I'm only really looking for smooth running compared with a farm vehicle and great economy. Perhaps I just want 'sufficient' power. What with all these speed cameras we have here in the UK. 1 bad week and the driving licence could disappear!
Are you still running the 3 notch gasket? If so then:
You actually don't know whether your 'play it safe' with a 3 notch was in the 33% correct bracket?
I suppose all will be revealed in 100,000miles time when you change the gasket :wink:
With the lower power you felt you were getting did you try and add extra fuelling elsewhere to compensate?
That squish thingy sounds interesting. My thoughts are that a larger area of compressed air above the piston with no fuel in it would help to cool the pistons seeing as the greatest heat is eminating from the prechamber fire.
So the compression wasn't affected much then mid 400's sounds excellent compared to some people 's 250 to 300!!
What's the size of the 1.9 head chamber? I'll see if I have the info somewhere!
-
I've worked backwards from a bunch of available information on the various VW diesel engines and get around 18.5:1 for a 1.9 head on a 1.6 block. I don't have the stuff at my finger tips, but i'm faily confident in my mathematicle abilities to be satisfied. If someone else want do do the research and comes up with 19:1, i will not be up set. Its in the ball park, and it will do what I want. There are poeple that have gone befor my in this endevour. I am by no means the pioneer here.
My main goal for ruducing the CR is to reduce the load on the rods, bearings, head and whetever else, so I can run more boost and fuel. Its a summer only diesel, and it still should start with a lower CR. It might start even better with the piston clearence set properly. If the fuel milage drops, I will not be concerned. Its a diesel power go kart in my eyes. A nifty toy.
Since I have blown off the piston protrusion measurement, I have no idea where the gasket situation is.
What I do know is this engine has always had a less than gorgious start, even with everything bone stock, and all the glow stuff PERFECT. With everything essentially brand new, and set spot on, and nothing else weirded out, it points to the only variable I did not verify: piston protrusion, and hence the proper gasket.
Ive been all over the fuel thing. Was even running 24+PSI with a soot cloud that blacked out the light and warmth from the sun. Its a little more conservative now, but in no way pedestrian.
I hope to get to this head swap soon, and I'll gauren-gosh-darn-tee that I'll measure piston protrusion. Its was appearently a big enough deal for the engine OEM to go through a few hoops to get it right, and thats good enough for me.
As a matter of fact, i'm gonig to determine what the squish is, and i might make it tighter if i can get away with it.
Here is some squish stuff that took me only a short time to find. I don't think the detonation thing applies to us, but piston cooling, and turbulence are right up our alley:
What does having the squish clearance close do? It makes the compressed charge between the squish band and the top of the piston (at the top of the stroke) thin, thus allowing for quicker heat transfer between the piston and the squish band. This clearance change will produce MORE HP, MORE TORQUE, and the engine will not have to work as hard. You will be able to run a richer setting, come off the turns faster, launch better, pull a bigger prop, run cooler and run faster! This is probably one of the 3 biggest failings of the Novice Boater!
One of the most important items in the design of a good combustion chamber is the squish band. I believe that a flat squish band produces much more power than an angled squish band. The flat squish band head has a flat area (squish band) around the perimeter of the head which comes in close proximity to the piston at top dead center. This squish band is designed to keep the layer of combustion mist very thin, in order to let heat travel quickly from a hot piston to a cooler combustion chamber (head). The thinner this layer (the closer the head clearance), the better this heat transfer is accomplished. If your head has its squish band to far away from the piston at TDC and the compression ratio is high, you will get pre-detonation (knock). You can tell if this is happening by looking at the squish band. If it looks like it has been lightly sand blasted, it is pre-detonating. Most people when they see this pre-detonation automatically raise their squish band piston clearance. That is the WRONG WAY!
Quench, or squish area is typically the flat area on the top of the piston that's almost level with the top of the block deck. It must have a corresponding flat area on the deck surface of the head to qualify as quench.
If you look at a combustion chamber, you will usually see these flat areas, and they will have the volume of the actual combustion chamber between them. When the piston is compressing the mixture, as the piston nears the head, the flat areas on the head and piston come together and force the mixture from those areas to "squish" into the chamber, where the spark plug and burning mixture reside, so you achieve a more complete burn.
The quench area also runs cooler than the rest of the chamber / piston. These lower temperatures are where the "quench" comes from.
When properly designed, the quench areas can have a tremendous effect on the quality of combustion, and allow higher compression ratios, and due to this they are considered "artificial octane" by scientific types.
Bottom line is "properly designed, quench is good
-
This squish effect seems to be directed at gassers. They have a larger readymixed combustion field that is prone to detonation at the more desireable higher compression ratios. Does not seem relevant to diesels and a 20% gain on a gasser is still way below the efficiency of a diesel.
Improvements in maximum power at high speed can be found with 'smaller' inlet valves!
What's the compression ratio of a 1.9 diesel?
The purpose of experimentation is to vary the 'variable'; so how can you get other compression ratios if the 1.9 head doesn't give you an improvement? [Other than the improvement in maximum power for more fuel]
-
To say squish / quench doesn’t apply to diesels is making a very bold statement. If we take a look at the tops of the pistons, and the bottom of the head, we see allot of flat areas that like it or not, are more than probably, acting as squish / quench areas.
Squish helps turbulence, which improves combustion. We like to call the swirl chambers “precups” or “prechambers”. VW calls them swirl chambers. I wouldn’t be at all surprised if the swirl in theses chambers gets a big boost at the end of the compression stroke as the air is forced out of the areas were the piston and the head are very flat, and in very close proximity to each other.
Lets look at quench. The main reason we put EGT probes in our exhaust manifolds is to keep from melting pistons (and a host of other things). The top of the piston and the head are very close. These areas are also very large. I not ready to say that this close proximity is providing no quench either. Increasing the gap between these surfaces may cause the piston to run hotter.
I am reluctant to say that VW didn’t design in quench and squish into this engine.
What I will say, with all the information I put forth, lowering compression with thicker head gaskets is a bad idea.
“The purpose of experimentation is to vary the 'variable'”
I’m not sure what your asking here. I think I pointed out that I’m not throwing a bunch of stuff against a wall and see what sticks.
-
The close proximity areas in the vw diesel are only compressed air and not compressed mixture....
The air flow [volume/rate] through the entrance to the swirl chamber cannot be 'boosted' towards TDC because the piston travel is slowing down; hence the 'Dead' part of the term.
Can there actually be a detrimental effect because of the vaccuum affect of bringing two surfaces close and then pulling them apart quickly?
These forae are full of punters who have changed one thing and inadvertantly altered something else. [Not saying you have, but can you absolutely exclude it]
One factor that you may not have taken into account is the Tom, Dick and Harry theory.
Huh?... Basically take 3 identical engines/cars from the factory; and the figures for performance reliability and economy can be very different.
ie Tom is a great car, runs well, occasional problems and owner happy.
Dick is always in the garage, never had the economy of Tom and could give the vehicle a bad name and the owner won't be repeat buying.
Then there's Harry...
The owner loves this car and reliability is #1. Economy great and never lets the owner down. Engine does not wear. It's demise will leave the owner very sad 15 years down the line when it is shunted and written off by the insurance co. ...
Whilst the above may sound a little abstract and non scientific it may be analysed by coincidence of machine tolerances that work together.
Having owned and driven 7 Quantum's; I can assure you that there is truth to this yarn. I also ran two identical Fiats from the 1980's which were far from identical.
My father bought 2 [UK] MINI pickups in 1959. One green and one blue. They were so different...
Throwing sticky stuff at a wall seems like a random event. Not the iterations that I'm proposing. I thought this thread was about finding out effects of compression ratio variation :?:
Sure you have what may or may not be the wrong gasket. It may or may not be the reason that you are getting the symptoms you describe.
What you gonna do if it was the correct gasket? When you change heads please add to the data the actual piston protrusion measurement.
You aren't interested in the 'smaller' inlet valves creating higher speeds? Not 'my' theory etc etc :wink:
-
"The close proximity areas in the vw diesel are only compressed air and not compressed mixture....
The air flow [volume/rate] through the entrance to the swirl chamber cannot be 'boosted' towards TDC because the piston travel is slowing down; hence the 'Dead' part of the term."
Were did this come from? Do you have a link?
-
"The close proximity areas in the vw diesel are only compressed air and not compressed mixture....
The air flow [volume/rate] through the entrance to the swirl chamber cannot be 'boosted' towards TDC because the piston travel is slowing down; hence the 'Dead' part of the term."
Were did this come from? Do you have a link?
What do you mean where did this come from?
This is general elementry physics.
In the IDI engine a piston travelling along the length of its bore pushes the air through a fixed orifice at a rate determined by 'PI r squared' (the piston area) It is directly proportional to the rate of travel of the piston. The rate of travel of a piston is at a minimum at either end of its travel and a maximum in the middle of its travel. The minimum speed/velocity is zero [even though the crank is rotating constantly].
In addition you refer to the squish band allowing the piston to be cooled by the head. In the IDI the head is being heated by the fire and compressed air in the swirl chamber whilst the piston is cooled by the incoming fresh air.
I again suggest that the squishy squashy stuff is related to DI gasser engines.; as your source suggests and my initial googling confirms. Please post links to diesel related squish /squash for IDI engine.
-
The piston periphery section 29 forms a squish area 31 of the combustion chamber 44 with the surface 48 of cylinder head 16. The squish area 31 allows more volume to be adjudicated to the lobes 20 and 22 and promotes rapid air motion into said volumes as the piston reaches TDC on its compression stroke for faster mixing and burning with the flames exiting out of the prechamber through the transfer passage (which have not yet been described).
-
"I'm not here to help... I'm here to Pro-Volke"
This is becoming more and more obvious.
"saurkraut wrote:
"The close proximity areas in the vw diesel are only compressed air and not compressed mixture....
The air flow [volume/rate] through the entrance to the swirl chamber cannot be 'boosted' towards TDC because the piston travel is slowing down; hence the 'Dead' part of the term."
Were did this come from? Do you have a link?"
I merely asked were this came from. It looks to me like its talking about the differences between compression ignition and spark ignition. I wanted to see it in its full context.
"What do you mean where did this come from?
This is general elementry physics.
In the IDI engine a piston travelling along the length of its bore pushes the air through a fixed orifice at a rate determined by 'PI r squared' (the piston area) It is directly proportional to the rate of travel of the piston. The rate of travel of a piston is at a minimum at either end of its travel and a maximum in the middle of its travel. The minimum speed/velocity is zero [even though the crank is rotating constantly]. "
Geez, I apologise. I didn't know that you were a Physicist. How ever, the same is true for gas motors, the pistons slow down as they approach TDC. I've degreed modified cams in turbocharged gas motors and set ignition and rotary valve timing in racing two stroke engines and I'm well aware of this phenomena.
“I again suggest that the squishy squashy stuff”
This is a response that engenders further cooperation.
I’ll see what I can find. Like I said, I did a quick search (it wasn’t google). I’ll look some more.
The “squishy squashy stuff” has been around a long time. I did not invent it. It’s a basic design function that shows up in just about every gas motor on the planet. The basic mechanical function of a diesel (pistons, connecting rods, crank, camshaft) is not so completely different from gas motors. It may be there too, but not had a whole bunch of attention drawn to it.
I just think it very peculiar that VW specified different gasket thicknesses, when we can clearly see it does not affect the compression significantly. Why did they do that? What is the important factor?
The reality of the situation is there have been a lot more gas motors that have been modified, and things studied more closely after modification
-
While not related to diesels in general, I did find a very interesting patent related to squish areas of gas engines, claiming to greatly increase efficiency as well as reduce/eliminate pinging even on low octane. I also found a forum where people have tried this idea, and it seems to work.
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6237579.PN.&OS=PN/6237579&RS=PN/6237579
-
The piston periphery section 29 forms a squish area 31 of the combustion chamber 44 with the surface 48 of cylinder head 16. The squish area 31 allows more volume to be adjudicated to the lobes 20 and 22 and promotes rapid air motion into said volumes as the piston reaches TDC on its compression stroke for faster mixing and burning with the flames exiting out of the prechamber through the transfer passage (which have not yet been described).
Risking the peril of provoking some prominent rockit scientist on this board, I humbly ask for a link to this excerpt. I'd like to read the whole document. The TD SAE paper doesn't go into this much detail.
-
It was mostly on the benefis of 4 valves as opposed to 2.
http://www.patentstorm.us/patents/5309879-description.html
-
Thanks!
-
Mr Saurkraut I concede the 'Squishy/squashy' bit was a little light relief :lol:
I still seem to have missed references linking s/s to diesels. in particular IDI diesels.
I do admit that in a single chamber setup the final few mm in of travel would produce accelerated movement of small quantities/(large q small vol) of air or mixture. But where it has to go round a corner into a fixed aperture swirl chamber it must be slowing down again as its being pushed by a slower piston that was previously pushing air through at a faster rate.
Maybe where we differ the most is that you are predominantly looking for more power [with probably a hope for a sustained fuel economy] and this may well suffer from thicker gaskets; whilst Im searching for better economy [and if it means I have to suffer with the temptations of greater power so be it] but I find that a slightly tweeked Quantum TD is quite responsive and defiinitelyhas more acc'n under load than its 1.6 gasser brother. Top speed in a Q TD? I've never been able to find it... 105mph and I gave up as our sneaky timed distance cameras we have here will shoot me down knowing my luck :shock:
Jimfoo
I looked at some of those patents through the Patent Storm site. But the content is hard to follow without the pictures. Unless you can see where they are located :?: ...
-
No, I was looking for them too.
-
In response to an earlier query as to why would vw bother to issue different gaskets rather than just a 3 notch...
Because vw block/crank and pistons all vary by their reasonable tolerances; one method other than more accurate machining which tends to be come prohibitively expensive; (imagine the cost if the engine was built like the Bosch pump) is to use different sized gaskets take up the slack. This was felt neccessary to try and standardise the performance. Remember the engineers thought it neccessary to offer 5 gaskets at first before reducing to 3 ... maybe 1 will be the way in the future.
-
Yes, its obvious why there are different head gaskets: tolerance stack up. It manifests itself in piston protrusion.
But what are they trying to control. I would offer that its not compression, as we have seen that the min/max gasket thickness changes compression very little. Are the trying to controll the gap between the piston top and bottom of the head for some other important reason?...
I even wonder what the manufactureing variability in the swirl chamber voluum is. Is that variable enough that the actual compression is a range of 22:1 to 24:1
-
Probably so the pistons don't strike the head. Remember that things like connecting rods and pistons expand when they get hot.
-
Probably so the pistons don't strike the head. Remember that things like connecting rods and pistons expand when they get hot.
If that was the only reason why would they have made 5 (and then 3) different thicknesses? It would have been cheaper to just run the thickest gasket if interference was the only concern
-
While not related to diesels in general, I did find a very interesting patent related to squish areas of gas engines, claiming to greatly increase efficiency as well as reduce/eliminate pinging even on low octane. I also found a forum where people have tried this idea, and it seems to work.
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6237579.PN.&OS=PN/6237579&RS=PN/6237579
(http://img264.imageshack.us/img264/1959/us006237579001jj2.th.png) (http://img264.imageshack.us/my.php?image=us006237579001jj2.png)
(http://img156.imageshack.us/img156/4590/us006237579002gh0.th.png) (http://img156.imageshack.us/my.php?image=us006237579002gh0.png)
Found the missing images :shock:
Don't ask me how 'cus if I told yer I'd have ter kill yer :mrgreen:
Definitely linked to DI engines only in this case according to pics :!:
-
It was mostly on the benefis of 4 valves as opposed to 2.
http://www.patentstorm.us/patents/5309879-description.html
And 4 valve diesel stuff
Don't ask :wink:
(http://img175.imageshack.us/img175/3329/4valvedieselci7.th.png) (http://img175.imageshack.us/my.php?image=4valvedieselci7.png)
(http://img175.imageshack.us/img175/2927/4valvediesel2rb3.th.png) (http://img175.imageshack.us/my.php?image=4valvediesel2rb3.png) :mrgreen:
-
Found the missing images :shock:
Don't ask me how 'cus if I told yer I'd have ter kill yer :mrgreen:
Definitely linked to DI engines only in this case according to pics :!:
On his website he claims for all internal combustion engines. I never found where anyone had tried it on one though, although some big diesel semi's had tried it, but the people hadn't told him the results. If you look at the how to make your 1.6 TD rev higher, or whatever it is thread, the mod there is supposed to create more turbulence also. So I bet it could be done on an IDI and achieve similar results, plus it will lower compression for better economy.
"US Patent 6237579 is applicable to any 2 or 4 cycle internal combustion engines featuring " Squish or Quench " concepts. The placement of one or more grooves or channels or passages in the squish area as shown & described in the first page of my US Patent 6237579 results in "Accelerated Laminar Total Clean Burn Combustion " out of any fuel ? Meaning to say, this simple but radical design change to squish areas & configurations enhances progressive turbulence in the charge close to the skin of the combustion chamber and further directs the (added) turbulence towards the igniter followed by multiple flame front propagation thus resulting in a radical change to " In-cylinder Combustion ". This technology is as radical a change to engine design as it was with the introduction of the ' quench ' concepts by Sir Harry Recardo almost 80 + years ago. ALTCBC improves " Torque & Power " through the entire operating range with lesser amounts of fuel. This simple design change "opens up" the combustion chamber to activity. Hi-Breds can now benefit from the enormus low-end torque produced out of smaller displacement engines to pull away with ease. Simplicity in design is the key to keeping costs down and pays on the long run !
After this simple design change ~ Obsolete Side Valve Engines which feature large quench areas have shown reductions of up to 42.5 % in fuel consumption ( BSFC) when fully loaded at 2000 rpm on the dyno further producing more torque & power at lower operating temperatures in comparison to a stock engine. ( ARAI Test Results )"
-
Maybe it is just the DI as I found this.
"My experiments over the years lead me to some definite conclusions & proof of improvements in the area of Thermal efficiency gains - Both DI Diesels & Petrol engines respond to this design change almost in the same manner - If done on the piston crown ! Provided the Piston has a Dish. You can run petrol engines incredibly lean without any hick-ups or heating-up or stalling !"
I e-mailed him to ask about IDI engines.
-
If my memory serves me correctly (which it may not) the threads on this site dealing with the grooving of the piston were to direct the burnt fuel towards the exhaust valve; which in turn was hoped to help through flow and thus increasing revs. I think maximising revs then encountered the problem of the follower in the pump launching off the cam and so leaving the injection piston behind....
-
Well here was the reply I got. Sounds like his idea is a groove across most of the piston over to the prechamber, just like our pistons already have.
"Thanks for your interests in Diesels !
i call IDIs ~ Flat chambers ~ as in most cases the head is flat so are the piston's tops ~ Except for some little directional grooves guiding the charge into and out of the key hole connecting them to the embedded pre-combustion chamber. i have milled a thin groove or call it a channel covering across 3/4th of the piston crown with the maximum depth close to the key hole thereby giving some direction to the compressing charge and to further channel its way up into the pre-combustion chamber through the key hole causing a more severe swirl in the pre-combustion chamber. ( All this is ~ Assumed ??? ) Once ignited the flame fronts with partly ignited diesel get a chance to go much further across the piston crown to meet the trapped fresh air. i have noticed a little compression loss due to the longish channel. All this calls for a lot of thinking and modifications to strike a compromise. The key hole as it is ~ Is enough to cause enough and more turbulence in the compressing air ~ It is like whistling with your lip formation !
This kind of longish channel did manage to get my IDI's start a lot quicker and idle smoother ? The smoke was gone so was the watering of eyes ?? due to CO ? The torque also improved ~ i did not have time to face the block & Piston to further increase the compression to the optimum ? Who knows ? ~ My friend hardly uses the heater plug once the engine has been started-up and has no complains ? i have seen M Benz older 5 cylinders IDI's having 4 channels on the piston crown like a star bust & a slight projecting nozzle having 4 or 5 holes at different levels aligning with the grooves ~ This extended bulb which is the pri-combustion Chamber really remains hot & glowing once started to heat up all the air passing through it ! ? i am sure MB & Bosch have many Patents on them ~ After CRDI with multiple injections took over ~ it is a different story ! Nobody realizes the complex expensive hard ware that supports Fifth generation CRDI ?
The grooves can achieve the same performance from Lower pressure First generation CRDI 's ( DI's ) ~ Can now Run on poorer quality high Sulpher Diesels ? Producing a lot lesser NOx !
Life goes on ! What type of a IDI's are we looking at ? Where do you come from & what is your back ground ? Stay tuned ! A lot more is sure to happen !
Happy Motoring !
sing !!!