:::RHMT::: Real Home Made Turbo
General Category => Engine Management => Topic started by: kgx on October 24, 2009, 12:24:00 AM
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i've been doing some reading lately on the subject of using cooled EGR at high boost as knock suppression and augmentation of the fuel mixture.
i removed the EGR from my MR2 years ago, but now i'm actually considering putting it back on.
this is one of the items i stumbled upon:
http://www.me.utexas.edu/~sae/Files/Cooled_EGR_and_alternative_fuels_V1.pdf (http://www.me.utexas.edu/~sae/Files/Cooled_EGR_and_alternative_fuels_V1.pdf)
essentially it shows that using cooled EGR at high engine speed/load not only pushed the knock threshold back by ~20%, but also resulted in a decrease of engine brake specific fuel consumption (BSFC) of about 10%.
i read a few days ago that saab engineers were able to run pump gas at 14.7:1 under full boost not only without detonating, but without losing power. seems like an interesting concept.
part of the effect is attributed to the CO->CO2 reaction, which is normally a slower component of combustion but is accelerated by the presence of water vapor in the EGR. leftover unburnt HC's are also given some credit for it.
obviously, EGR is good for part-throttle driving, since introducing spent exhaust into the intake dilutes the incoming air charge (and therefore reduces engine speed) for a given throttle angle, resulting in lower pumping losses.
i think i may give this a try next spring when i take the car out of the garage again. if i can help my BSFC with E85, every little bit counts. i get decent mileage on the highway (~26-27) but this might get me back up around 28-29 and help out with those times when i just can't keep my foot out of it.
the simplest setup i can think of to implement it currently control-wise would be to couple another PWM solenoid to the boost controller, then use that solenoid to feed vacuum to the EGR valve actuator relative to boost. i could even have it dump into the turbo inlet and let the turbo do the mixing.
question is, how the hell to cool it off? a diesel EGR cooler would get eaten pretty quick with SI engine exhaust, both from the heat and the corrosive compounds formed at those temps.
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egr does work but there are better ways. I do not beieve in running dirty shit back through my motor for any reason. Take a high millage motor apart on look into the egr ports.
I dont understand why you think a diesel egr cooler wont work on a gas motor (heat wise), my truck will run 1500 on the egt's easy, mind you I pulled the egr system off it but still.
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EGR has no place on a performance motor, it for gay ass emissions :mexi:
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EGR in it's vanilla form is to introduce exhaust gas back into the engine at part throttle and mild acceleration conditions in order to cool the combustion rxn and therefore inhibit the production of NOx gasses.
People have played around with massive EGR @ highway cruise, accompanied by liberal spark advance and sometimes leaning past stoich. It's reputedly good for a large increase in FE, I have no clue.
EGR as a method of knock suppression is not a new idea, MacInnes was a proponent of it decades ago. Bit of a shitty system to maintain... any of the OBD2 Fords would be great test candidates for it as you can map your EGR valve's lift at engine speed vs load, but then again look at Ford EGR system failure rates if you think that's a hotshit idea. :(
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EGR has no place on a performance motor, it for gay ass emissions :mexi:
+1
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I dont understand why you think a diesel egr cooler wont work on a gas motor (heat wise), my truck will run 1500 on the egt's easy, mind you I pulled the egr system off it but still.
the nitric acid that can be produced in gasoline exhaust is what worries me. the temps are a second order concern.
also, given the failure rate of many diesel EGR coolers, i think they would have an even harder time coping with petrol exhaust.
EGR has no place on a performance motor, it for gay ass emissions :mexi:
for OEMs, sure.
the ideas i'm talking about are sound. 10% reduction in BSFC without a reduction in power is quite good. I'm running E85, so 10% better efficiency for equal power, and being able to run crazy stupid lean (some have run engines as lean as 25:1 in cruise) is HUGE with E85.
reducing pumping loss by using dilution to throttle the engine is also very effective at increasing part throttle economy.
what's the point of having cake if you can't eat it too?
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In reality: works as advertised.
Protip: don't take advice from someone who's never done it and never will.
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I dont understand why you think a diesel egr cooler wont work on a gas motor (heat wise), my truck will run 1500 on the egt's easy, mind you I pulled the egr system off it but still.
I think most of the issues with EGR coolers on a diesel come from the buildup of carbon clogging them. Which should be much less of an issue with gasoline exhaust in my eyes.
the nitric acid that can be produced in gasoline exhaust is what worries me. the temps are a second order concern.
also, given the failure rate of many diesel EGR coolers, i think they would have an even harder time coping with petrol exhaust.
EGR has no place on a performance motor, it for gay ass emissions :mexi:
for OEMs, sure.
the ideas i'm talking about are sound. 10% reduction in BSFC without a reduction in power is quite good. I'm running E85, so 10% better efficiency for equal power, and being able to run crazy stupid lean (some have run engines as lean as 25:1 in cruise) is HUGE with E85.
reducing pumping loss by using dilution to throttle the engine is also very effective at increasing part throttle economy.
what's the point of having cake if you can't eat it too?