-
#15
by
Gearhead
on 28 Feb, 2008 11:28
-
Ok, now I'm confused. If you go from 130bar to 155bar, then you'll still have injection pressure less 200psi, correct? What's triggering the secondary injection?
-
#16
by
Mark(The Miser)UK
on 29 Feb, 2008 18:25
-
I eventually put a 84 rabbit NA and NA injectors on my 92 Ecodiesel. It was starting to die and not getting good fuel economy. I can't comment on fuel economy, because I never did get the timing right on it. But the car ran fine.
I think that VW might have lowered the injection pressure on the AAZ because of the newer dual spring design.
I do wish that we could get conclusive results of what increasing or decreasing injection pressure will do. I had heard that increasing the injection pressure means less power, but more mpg, but that's not what I seem to be reading here.
I don't see much difference in the high pressure side of the NA and turbo injector pumps, so Giles answer does make sense. I would guess that as the 130 bar injectors age, and decrease in opening pressure, that they could, in extreme circumstances, cause problems with the turboboosted engine.
Another thought is this: One problem with injectors and nozzles is that instead of injecting a smooth stream of diesel into the engine, it will stutter. I would guess that a higher injection pressure would help this problem as well, especially in turboboosted engines.
Wouldn't a stutter be similar to the TDI pre injection? I guess it depends how many vibrations you get in?
If lower break pressures resulted in worse fuel economy then that doesn't quite tally with the 1.5 engine.
The higher revving ability of the 1.5 also implies IMO that slower combustion is not an issue either.
The only answer is to have two sets of injectors both in tip top condition and to do some test drives.
Whilst higher break pressures will give 'better ' atomization. Is that wanted in general driving? More detonation? Which although extracting most energy from the fuel into the chamber will also lead to higher temperatures and so greater temperature gradient across to coolant which would lead to more rapid heatloss...'Ceramics'??
Just a few thoughts...
Is exhaust size/restriction a bigger factor?
Why did VW stop issuing Quantum TD exhausts as 2" all through and revert to only issuing 1.5" centre pieces with reducers as standard (corresponding to the old Dasher sized exhaust??). I shall shortly be doing a test on these two exhaust sizes to see if that is the source of economy reduction of 60mpg down to 45 mpg... :?:
-
#17
by
gldgti
on 01 Mar, 2008 14:27
-
to answer this secondary injection question... we really need some facts:
rate of the injector spring; static pressure in the injector lines; predicted peak cylinder pressure; preload on the spring.....
not to mention the area of the end of the pintle..... its about .5mm diameter right? so then the area of the end of the pintle (the only place pressure could provide upwards thrust) is pix(0.5x0.5mm)^2.... 0.196mm^2.
force = pressurexarea, therefore if the peak cylinder pressure is say (to be optimistic), 130bar, thats 13MPa
F = 13x0.196
= 2.548N.
Now, i might be a sceptic, but wouldnt you want a bit more than 2.5N pushing on the other side of the needle to keep it closed.... in all cases!
someone correct me on the peak cylinder pressure, since i'm guessing given that the peak cylinder pressure under load at 5000rpm for the 1.5 engine (nonturbo) is 98bar.
before everyone fires up and says that the peak cylinder pressure is HEAPS higher in a turbo engine - it is higher, but not equivalent to as much more air as you put in....the pressure just lasts a lot longer through the stroke.
-
#18
by
Mark(The Miser)UK
on 01 Mar, 2008 20:50
-
Blueing the surfaces and rotating the needle, leads me to believe that the middle taper is the seal. Diesel pressure acts on the larger taper. If SA of that taper is 'X' and opens at say 130bar then the pressure needed to open needle from chamber which is acting on part only of the middle taper with S.A. of say 'X'/20 would be 130 bar x 20 or 2600bar or38,000psi wouldn't it :shock: EDIT Clicking on the picture shows stain of limit of what I imagine is combustion gases
-
#19
by
hillfolk'r
on 01 Mar, 2008 21:00
-
i'm running 1.6 idi and want more power, so i bought mercedes 300td nozzles and asked a injector specialist to raise the pressure to 180.
I had to remove the pump before fitting the new injectors and now the car won't start, i'll put back the td 155 injectors to check if it works.
If not something strange is going on here :roll:
yea wheni used the same ip (12mm )from my1.6 on my tdi-m,it was a *&^&*^%$&%$&^*()) to get it to pull a prime
i had to leave 2 lines loose ,crank till it spit,close them,,get it fired on 2 cyls,then crack the other 2 while it was sputtering on 2 cyls
then it cleared out after that
i just figured it was cause of higher breakover on the tdi injectors,makes sense
-
#20
by
dillenger1
on 02 Mar, 2008 04:32
-
So with the 155 pressure do i have a possibility of the pump blowing a seal?As it was originally and NA IP.Sounds like most would say that the 130 press. is better for economy wether yer boosted or not.What are the dangers of detonation(using 130 w/turbo)?Is this just a performance issue?
-
#21
by
jimfoo
on 02 Mar, 2008 08:02
-
Considering they use the same pump, though modified, for TDI pressures of 180 or 220 bar, no it will be just fine. The max pressure of our pumps is 350 bar.
-
#22
by
Tintin
on 02 Mar, 2008 08:44
-
Opening pressure of the injectors do not have any effect on the sealing of the pump, even to 500Bar, that changes anything on the sealing.
The Opening pressure is only the point where the injection begins and finish, during the injection the pressure goes up much much higher than 130, 150, 200Bar or etc..... On the PD engine, the first stage is set at 220Bar, and during injection, the pressure goes to 2000Bar, I dont know for the 1.6IDI, but I think that It's around 600 or 800Bar, I'm not sure, but I,m sure with 10mm, 11mm head It's higher than the factory.
Giles rightly, and now if you set the injector too much low, example of 100Bar, the begin and the end of the injection between 100 and 150Bar will be badly pulverized and you can see also a little bublle in the return line, white smoke at idle (air in fuel)........ and I think also that a too high setting change nothing on performance or etc.... just a good balance with the specification from bosch It's perfect, quick opening and quick close.
PS: if one takes the example of an PD engine, with a large injection precison, very efficiency injection, practically of not black smoke with a chip tuning, however the opening pressure is not higher than the old diesel engine :wink:
EDIT: I'm not a guru, It's just mi opinion.
-
#23
by
Mark(The Miser)UK
on 02 Mar, 2008 10:19
-
Blueing the surfaces and rotating the needle, leads me to believe that the middle taper is the seal. Diesel pressure acts on the larger taper. If SA of that taper is 'X' and opens at say 130bar then the pressure needed to open needle from chamber which is acting on part only of the middle taper with S.A. of say 'X'/20 would be 130 bar x 20 or 2600bar or38,000psi wouldn't it :shock:
EDIT Clicking on the picture shows stain of limit of what I imagine is combustion gases
Clearly what I meant to say was ..."pressure needed from combustion chamber"
Quickly doing some math[es] for surface area of cones ie PIxRxS came to ball park 19:1 assuming stained area is area acted upon by combustion [10/10 for a bl**dy good guess, especially for someone who is beginning to doubt his own sanity :wink: ]
-
#24
by
Giles@PerformanceDiesel
on 02 Mar, 2008 10:44
-
The only seals that see the higher pressure are the timing gauge plug and the part around that. The rest of the pump is low pressure.
Andrew
there are a number of things to address in this thread.
1: opening pressure does affect fuel economy, in this context
2: Peak pressure in the compustion chambers will exceed opening
pressure of the injector nozzle on the turbo motor with the 103 Bar
Injector.
3: This secondary injection is caused by the excessive pressure
lifting the needle off it's seat and relieving the pressure in the
injection line and therefore injecting a small amount of fuel after
initial combustion takes place. This will cause poping and white smoke.
4: yes this will also have the adverse affect of overheating the needle of
the nozzle and contaminating it with carbon.
5: there is never a steady stream of fuel being injected, it is a pulse
only mili-seconds long.
6: As the pump seeing this higher pressure are you asking if the pump
can see the combustion gasses? if so then it is possible for the gasses
to get into the injection lines but the delivery valve will stop it from
going into the injection pump. Except when the delivery valve has
a bleed off cut out on the retraction coller or the delivery valve seat.
Hope this helps
Giles
-
#25
by
blkboostedtruck
on 02 Mar, 2008 11:02
-
you guys are sharp! but i still have not learned the answer to what we want?
for example N/A pump with LDA installed- N/A 130bar injectors can those injectors be recalibrated to 155bar and get the same results? to run on a TD motor!
did i explain that well enough?
or is it better to use the 155bar rated injectors that has the correct spring inside for that higher pressure
let me know if that helps ?
thanks Duane
-
#26
by
Giles@PerformanceDiesel
on 02 Mar, 2008 11:05
-
Hi again
didn't answer that before.
YES you can reshim the NA injector to Turbo spec's no problem
we do it all the time.
Giles
-
#27
by
subsonic
on 02 Mar, 2008 11:06
-
A lot of this is over my head right now, but I am understanding the basic concepts of the conversation. So here is a question, at what point will additional boost call for additional or higher breaking preasure? In my case I will be running the dual spring 1.9 injectors set at 155. I intend to run the boost up into the high end of 20psi. say 25-30ish. Will there need to be a breaking preasure adjustment to compensate for the additional boost?
-
#28
by
blkboostedtruck
on 02 Mar, 2008 11:51
-
dilinger will have to chim in it's his project! he wants me to rebuild, poptest his N/A injectors up to 155bar and i was not sure about that and wanted to find out if it's a way to go?
Duane
-
#29
by
dillenger1
on 02 Mar, 2008 14:10
-
I was under the impression that it would take a NA pump a little longer to make the 155 bar.All things considered can i make up for this time by increasing internal pump pressure?I guess what im trying to say is what needs to be done to get my NA pump converted "completely" to TD.Ive got the LDA on Ive backed out that pesky post that was in the way,Ive got a10mm head and plunger assem. installed also.If i up my internal pressure will this cause leaks?
