Help me compare emissions for EGR vs non-EGR

[RustyH]

My wife's car (she loves it) is a 1990 Volvo 240, California version, so it has EGR. The EGR is fairly early in its technology--there is a vacuum controller, but no temperature sensor on the EGR. I have recently cleaned the EGR valve, so I believe it to be operational. Car runs fine if you like slow, 114 HP, 136 ft-lbs. Here are the EPA fuel efficiency ratings:

Regular, non-EGR, city, combined, hwy: 18, 20, 23
EGR: 17, 19, 21

I understand the EGR lowers combustion temperature in the engine to reduce NOx production, however the EGR is worse with fuel efficiency.
So, over a 10 year period of time, say 10,000 miles per year, which is worse for the environment (amount of pollutants)? Please include the energy and emissions to produce the gasoline, and whatever else I'm missing in my thoughts about emissions.
And, yes, I agree that a newer, fuel-efficient vehicle would be best, but let's stick to the question. Thanks.

 

[supton]

What area of the country? CA has bad smog issues. I've seen some musing about how they could stand to have more NOx due to the weekend effect (heavy trucking goes down on the weekends, the worst smog is on the weekends--there's more to it than that, but that's the quick explaination). Elsewhere, no issues, then...?

Or, what is worse, CO2 (global warming) vs NOx (smog). What do you think is worse? That appears to be the question if I'm understanding it.

 

[A_Harman]

Global warming is Bovine Scatology. CO2 emissions are a natural result of life's organic processes.

NOx is a contributor to photochemical smog, and that is more relevant to smog in the LA basin of California. The rest of California doesn't have a problem. Wildfires contribute many times the pollutants to the atmospheric problems in California than cars do.

 

[Danno]

Originally Posted By: A_Harman
Global warming is Bovine Scatology.


Thread winner!

 

[supton]

Look, I'm sorry for bring up global warming; I didn't mean to derail the thread. I was trying to get more info out of the OP as to what he considered "bad". Some groups of people consider CO2 a pollutant, others do not--but depending upon where you fall the 2mpg penalty counts. Or not.

 

[RustyH]

Car lives in Idaho (near Boise). For city driving, 10000 miles/year, 10 yrs, the EGR will consume 5882 gal gasoline vs 5555 for the Non-EGR, difference is 327 gal. I read that more modern EGRs don't seem to reduce the fuel efficiency like this one reportedly does.

 

[supton]

Emissions are measured in grams emitted per mile, not grams emitted per gallon. So the EGR model is going to put out more NOx per mile, regardless of mpg's. Wild guess says other emissions rise too, despite lower CO2/H2O emissions and higher mpg (but I could be wrong on that count, it's possible that HC's are the same).

My belief, apart from any science, is that the CO2 bit is more damaging. Almost as bad as the hit to the wallet. But not quite. A bit more NOx? I drive a diesel, so I already don't have a huge fear of NOx emissions. I'd rather have the higher mpg at a slight cost to emissions, possible global warming, and saving a bit of a non-renewable resource.

CA due to its geography apparently needs different emissions controls than the rest of the country. Fine. The rest of us don't need such tight controls.

What I've never gotten around to finding out is what it costs to dismantle and recycle a car. That is not exactly emissions free either.

 

[bdcardinal]

Originally Posted By: supton
CA due to its geography apparently needs different emissions controls than the rest of the country. Fine. The rest of us don't need such tight controls.


Not so much the geography as the concentration of vehicles. Look at a picture of the LA skyline form the 70s versus now and you can see why we have the pollution controls here.

 

[Trav]

Quote:
CO2 bit is more damaging.

Really? Plants work fine with CO2 but don't do well at all with the effects of NOx.

 

[dailydriver]

Originally Posted By: Danno
Originally Posted By: A_Harman
Global warming is Bovine Scatology.


Thread winner!


...and some even blame those same said bovines' flatulence for global warming!

 

[artificialist]

Often the California car will have more than just an EGR valve. Often the exhaust systems have precats, which raise backpressure and cost fuel efficiency. Other times the California car will have lower compression and that also has a negative impact on MPG. Cams are sometimes different. ECU programming will be different, and that can also have an impact.

In other words, EGR isn't always what lowers MPG in California spec cars.

Actually, with gasoline engines, EGR can save fuel. You can reduce intake manifold vacuum without adding fuel. That would reduce pumping losses at part throttle, and may raise MPG. This is also why diesel EGR sucks, but that is for a different discussion.

 

[A_Harman]

Originally Posted By: RustyH
Car lives in Idaho (near Boise). For city driving, 10000 miles/year, 10 yrs, the EGR will consume 5882 gal gasoline vs 5555 for the Non-EGR, difference is 327 gal. I read that more modern EGRs don't seem to reduce the fuel efficiency like this one reportedly does.


OK, I'll take a stab at this.

327 gal of gasoline at 6.2 lbs/gal = 2027.4 lbs of additional fuel burned over 10 years. Assuming the fuel contains mostly octane, C8H18, when burned will produce products according to the chemical equation:
12.5 moles O2 + 1 mole C8H18 => 8 moles CO2 + 9 moles H2O

CO2 has a molar mass of: 12 + 2*16 = 44 lbs/mol.
C8H18 has a molar mass of: 12*8 + 18*1 = 114 lbs/mol.

The number of moles of additional fuel burned: 2027.4/114 = 17.78 moles

The number of moles of additional CO2 produced is calculated by the molar ratio of octane to carbon dioxide in the above chemical equation. i.e.: Every mole of fuel burned will produce 8 moles of CO2: 17.78*8 = 142.27 moles

Mass of additional CO2 produced: 142.27 moles CO2 * 44 lb/mol = 6260 pounds

 

[Cujet]

RustyH,

EGR, can, on some engines/vehicles result in slightly improved MPG's. As artificialist noted, engines with EGR, operating at partial load, need greater throttle opening for a given output. This results in lower pumping losses, slightly higher cylinder compression (due to increased volume) and the need for more advanced ignition timing. It also reduces the combustion temperature and burn rate, potentially increasing thermal efficiency.

No question that there is a "down side" to EGR. Most older systems/engines/ecu's are not all that well configured, don't meter exhaust gas all that accurately and the exhaust gas often contaminates an otherwise clean intake manifold and intake valves. It also adds to soot loading in the oil.

Today, we can use EGR to cool combustion temperatures significantly, with high flow rates. This helps us operate engines with incredibly high compression ratio's on lower octane fuels.

Also note that EGR is often not used at full throttle.

I'm not a fan of many older engines encumbered with emission controls. They are often sluggish at part throttle, non responsive, less efficient and so on. People forget just how responsive many performance oriented engines were in the 1960's. They were fun to drive, not because the ultimate output was so high, but because they were so lively.

I don't have an answer for you with regard to MPG. I'd suggest that the EGR engine's tuning/configuration is less than ideal and that's the reason for the lower MPG. An objective look at BSFC could be interesting.

 

[A_Harman]

Don't generalize too much on the benefits of EGR. High pressure loop, cooled EGR when applied to heavy duty on-highway diesels caused an increase in fuel consumption of ~10%. This was due to the necessity of running higher turbine inlet pressure than intake manifold pressure to force EGR flow to go to the intake manifold. The extra pumping work caused the increase in fuel consumption.

On gasoline engines, this pumping work penalty already exists due to exhaust back pressure and intake manifold vacuum at part load conditions. But hot exhaust gases dumped into the intake manifold cause a gross amount of intake charge heating unless the EGR is cooled. Exhaust temperature can easily exceed 800F at road load conditions, so it doesn't take much to greatly increase intake charge temperatures that would be ~100F on a naturally aspirated engine. Some intake charge heating would assist fuel evaporation, but that benefit basically ends when the IMT exceeds 180F. Then the mixture becomes too prone to detonation, and spark must be retarded, erasing any fuel economy benefit due to slightly lower pumping work from charge dilution and better fuel evaporation. Cooled EGR is the key to being able to run high EGR rates to increase the benefit of charge dilution without causing excess intake heating. But I don't know if anybody is currently using cooled EGR on naturally aspirated gasoline engines.

 

[OVERKILL]

Originally Posted By: A_Harman
Don't generalize too much on the benefits of EGR. High pressure loop, cooled EGR when applied to heavy duty on-highway diesels caused an increase in fuel consumption of ~10%. This was due to the necessity of running higher turbine inlet pressure than intake manifold pressure to force EGR flow to go to the intake manifold. The extra pumping work caused the increase in fuel consumption.

On gasoline engines, this pumping work penalty already exists due to exhaust back pressure and intake manifold vacuum at part load conditions. But hot exhaust gases dumped into the intake manifold cause a gross amount of intake charge heating unless the EGR is cooled. Exhaust temperature can easily exceed 800F at road load conditions, so it doesn't take much to greatly increase intake charge temperatures that would be ~100F on a naturally aspirated engine. Some intake charge heating would assist fuel evaporation, but that benefit basically ends when the IMT exceeds 180F. Then the mixture becomes too prone to detonation, and spark must be retarded, erasing any fuel economy benefit due to slightly lower pumping work from charge dilution and better fuel evaporation. Cooled EGR is the key to being able to run high EGR rates to increase the benefit of charge dilution without causing excess intake heating. But I don't know if anybody is currently using cooled EGR on naturally aspirated gasoline engines.


Ford used a (coolant cooled) EGR cooler on many engines in the 80's including the 5.0L. I don't think it would have brought EGR temps down to coolant temps however.

EGR flow came up through the centre of the head, into the LIM, up through a passage between the LIM and UIM, and then into this spacer which fit between the throttle body and the UIM. The spacer had coolant compartments on each side with coolant from the heater rail run through it.

 

[RustyH]

Thanks for all the interesting replies and the chemistry lesson.

 

[camelCase]

tl;dr


It's well known EGRs lower fuel efficiency. You're wasting space that could be filled with a fresh air/fuel mixture with exhaust gases.

The benefits of EGRs can be heavily debated from both a lab stand perspective as well as real world operation.

I, personally, hate them and remove them when I can. It's quick and easy to fabricate some block off plates with some sheet aluminum/steel/etc and something to cut it with.

 

[dailydriver]

Originally Posted By: A_Harman
Don't generalize too much on the benefits of EGR. High pressure loop, cooled EGR when applied to heavy duty on-highway diesels caused an increase in fuel consumption of ~10%. This was due to the necessity of running higher turbine inlet pressure than intake manifold pressure to force EGR flow to go to the intake manifold. The extra pumping work caused the increase in fuel consumption.

On gasoline engines, this pumping work penalty already exists due to exhaust back pressure and intake manifold vacuum at part load conditions. But hot exhaust gases dumped into the intake manifold cause a gross amount of intake charge heating unless the EGR is cooled. Exhaust temperature can easily exceed 800F at road load conditions, so it doesn't take much to greatly increase intake charge temperatures that would be ~100F on a naturally aspirated engine. Some intake charge heating would assist fuel evaporation, but that benefit basically ends when the IMT exceeds 180F. Then the mixture becomes too prone to detonation, and spark must be retarded, erasing any fuel economy benefit due to slightly lower pumping work from charge dilution and better fuel evaporation. Cooled EGR is the key to being able to run high EGR rates to increase the benefit of charge dilution without causing excess intake heating. But I don't know if anybody is currently using cooled EGR on naturally aspirated gasoline engines.


What is your opinion of the system on '98-'00 LS1 f bodies, yea or nay??
Even when operating perfectly, do they hurt mileage and performance on our cars?
I know most eliminate them ASAP, especially when installing long tubes (headers, for those not in the know), and of course the C5s and latter '01-'02 f bodies did not even have them from the factory and still met or beat even CARB emissions standards.

 

[wirelessF]

I'm just lucky my Silverado LM7 does not come with a EGR valve like the other truck engines. Surprising since it's Canadian built with California emissions.

 

[eljefino]

Originally Posted By: camelCase
tl;dr


It's well known EGRs lower fuel efficiency. You're wasting space that could be filled with a fresh air/fuel mixture with exhaust gases.


would be at full throttle but EGR is taking the space of vacuum that the engine has to otherwise work to avoid. It's not making power, but that power isn't demanded. It's a part-throttle cheat.

Hasn't yet been pointed out, but some cars just use cam/ valve overlap to sneak a little exhaust gas into the intake all the time anyway.