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#15
by
8v-of-fury
on 10 Oct, 2013 15:43
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You want to inject as much fuel as you need as soon as you can get it in there. The faster it is in there and burning the better all around.
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#16
by
TylerDurden
on 11 Oct, 2013 13:49
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Not necessarily... what do you think causes clatter?
Diesels work on combustion, not detonation... it is why VW went to pilot injection, or 2-stage injection... eh?
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#17
by
745 turbogreasel
on 11 Oct, 2013 15:04
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Split shot just burns cleaner.
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#18
by
TylerDurden
on 11 Oct, 2013 16:38
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Again... what causes clatter...
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#19
by
TylerDurden
on 11 Oct, 2013 16:48
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....Traditionally, light and medium duty diesel engines for motor vehicles have used “indirect injection” (IDI). With IDI, fuel is injected into a red-hot pre-combustion chamber (“pre-cup”) or a swirl chamber for less noisy combustion. IDI engines use a “throttling” pintle-type nozzle to introduce a very fine “pilot-injection” of fuel for less abrupt ignition. Once ignition starts in the pre-cup, the rate of fuel delivery is increased, and a rich expanding/swirling flame is then “blown” through an orifice into the main chamber to drive the piston downward. Delivery of fuel then tapers off until combustion can no longer be sustained in the excess of air (as much as a 40:1 ratio at idle), making the IDI diesel a relatively quiet and economical diesel engine—but still not acceptable to many American motorists, or for the EPA.
Killing the Clatter… Prior Efforts
Various mechanical designs have been tried to reduce diesel ignition clatter:
Most passenger diesel engines traditionally have used the Ricardo® style “pre-cup” IDI design or similar with a “throttling” pintle-type nozzle to help reduce ignition noise.
Peugeot diesels using distributor-type pumps incorporated a “quietidle” device as an early attempt at rate-phasing to suppress noise: At low “throttle” settings, a small portion of fuel delivered from the pump was routed to an accumulator of sorts, reducing the initial amount of fuel injected per crankshaft degree to help reduce clatter.
Some Mercedes-Benz engines used a so-call CHIP (for “center hole in pintle”) nozzle for similar reasons. Combustion started with pilot-injection of a very fine pre-spray from a tiny hole drilled up the center of the nozzle pintle. As the nozzle pintle lifted further, maininjection took place. Often the center-hole became caked with carbon, resulting in all-too-familiar ignition clatter—and vehicle owner heartburn.
Volkswagen’s 1.9 Turbo-Direct Injection (TDI) engine clatter was softened by use of a two-spring nozzle holder assembly. With fuel pressure applied, the first spring compressed and the needle lifted enough for a pilot-injection of fuel and ignition; once the second spring compressed, main-injection completed the event.
http://www.cdxetextbook.com/asearticles/quietdieselevol.html
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#20
by
8v-of-fury
on 11 Oct, 2013 18:52
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Yupppppppp.
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#21
by
carrizog60
on 13 Oct, 2013 01:41
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aaz came with 2 stage nozzles as well.
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#22
by
Blocksmith
on 13 Oct, 2013 11:07
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I see what that article is saying, but how does that relate to larger plunger size? It seems to me that the article concerned a DI vs IDI comparison, not a plunger size comparison. I know that DI's need more advance, but if we just stuck with one motor type and compared only the pump plunger size, it would seem to me that having a larger plunger would enable the same amount of fuel to be injected more quickly (all other things being equal), which would translate to needing less static advance rather than more since the injection lag would be decreased.
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#23
by
TylerDurden
on 13 Oct, 2013 11:58
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... it would seem to me that having a larger plunger would enable the same amount of fuel to be injected more quickly (all other things being equal), which would translate to needing less static advance rather than more since the injection lag would be decreased.
I agree.
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#24
by
carrizog60
on 13 Oct, 2013 15:05
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if the same amount of fuel was injected it would need less advance but usually plungers are changed to increase fuel delivery...more fuel will need more time to burn,so more advance.
ok,i officially confused myself
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#25
by
8v-of-fury
on 14 Oct, 2013 08:31
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Very true. One does not install larger plunger and larger nozzles to inject the same amount of fuel..
You can inject more, faster, and more efficiently than before. BUT, you need to do it sooner because there is jsut that much more fuel.
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#26
by
TylerDurden
on 14 Oct, 2013 09:03
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AIUI:
It's not as simple as just more fuel earlier, we can do that without a bigger plunger.
When things get tricky is when we install a bigger pump and for that, we get overfueling and/or unburnt fuel.
For the first issue, we want more air, so we stuff more in with a supercharger.
For the second issue, we advance the timing... but if we get clatter, injection shaping needs to be implemented with two stage injectors and/or camplate change.
The above can only get us so far, after which, fancy injection control is easier with computer thingys.
As for "cleaner" there seems to be a tradeoff between soot and NOx emissions, so VW raised injection pressures to reduce soot and added a CAT to reduce the resulting NOx.
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#27
by
TylerDurden
on 14 Oct, 2013 13:55
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Well, there was an interesting version with a fancy plunger:
Anybody seen one...?