EGR: The good, the bad and the ugly??

[racprops]

My nearly lifelong understanding is if the factory put it on an engine it is there for a very good reason.

My understanding is that EGR helps with MPG….and I have read that adding even more can make even more MPG. This is by displacing the incoming air/fuel charge.

I also read that adding more can induce the throttle plate to be made to be more open which can at lower high vacuum and that vacuum lowing can lower the pumping losses.

It is a funny fact that we are told that we will get the best MPG when the vacuum gauge is at its highest….when the engine is now fighting that very vacuum…

A diesel engine has no pumping losses as it has no throttle plate, and thus no engine vacuum and no engine braking. An engine driven vacuum pump is then needed for vacuum controls and lucky me I already converted to hydro boost brakes, so no vacuum brake booster.

The ugly is all the crud that gets into the manifold and the ERG Valves…and I think on the intake valves??

Too bad there is no filter to remove the crud and thus run EGR cleaner.

So the question is to EGR or not to EGR??

Which will give the best MPG?? Note my main aim is the most MPG not performance, not HP and NOT high RPMs.

What about water injection instead or with EGR, can water replace EGR or better clean up the crud?

Inquiring Mind wants to know.

Thanks.

Rich

 

[0xDEADBEEF]

I think in theory water mist would make a good substitute for an EGR.

In practice I think you will have a harder time tuning it and making it work right than just leaving it alone.

 

[Pinger]

I also read that adding more can induce the throttle plate to be made to be more open which can at lower high vacuum and that vacuum lowing can lower the pumping losses.

It is a funny fact that we are told that we will get the best MPG when the vacuum gauge is at its highest….when the engine is now fighting that very vacuum…

It isn't vacuum as such that is the problem. Vacuum (like compression) is recoverable - on the compression stroke the vacuum while not quite sucking the piston upwards does offer less resistance.
The problem is the turbulence at the throttle plate where energy (ultimately drawn from the crankshaft) is squandered as noise and heat and can never be recovered into useful energy. The turbulence is unavoidable (at that smaller throttle opening) as the air passing it reaches velocities high enough to create the turbulence as it chokes the airflow as intended to limit how much air enters the manifold and thus how much power the engine can develop.

 

[Erik the Awful]

The sole purpose for the EGR valve is to reduce oxides of nitrogen (NOx) in the exhaust.

[storytime]
Back in the '50s and '60s fuel mileage usually wasn't a concern - except for people who spent all day driving. Mechanics figured out that they could lean out a carburetor until the engine misfired, go back two jet sizes, and so long as the driver wasn't involved racing or driving for extended times at high speed, the engine abided while nearly doubling the fuel mileage.

In the '70s in the northeast part of the country, the rain became acidic, to the point that if you walked around in the rain and then washed your clothes, your clothes would develop holes. It was a serious problem. They quickly figured out that the NOx in auto emissions was making the rain acidic.

Burning a fuel mixture lean results in very low hydrocarbon pollution, but the oxides of nitrogen are high. This is why a lean mixture stings your eyes a bit. Even burning at the stoichiometric ratio (14.7:1) results in significant NOx. Running rich is the only way to eliminate NOx, but then you get high hydrocarbons.

The EGR is actually a bit genius, and it only came about after the introduction of the catalytic converter. Here's a simplistic explanation: instead of trying to maintain a "perfect" ratio, the fuel injection system swings between running rich and lean - that's why you look for swings in your O2 sensor voltage. When it's running rich, a bit of unburned fuel loads up in the catalytic converter, allowing the NOx in the cat to be neutralized. Then the engine swings lean and the rest of the unburned fuel mixes with the lean mixture and burns in the cat. That's why your cat always runs hot. The constant swinging from rich to lean and back means that your engine is able to dissipate the heat from running lean without damaging itself.

EGR doesn't boost your mileage, but if it isn't running right, it can negatively affect your fuel mileage. I'm sure @L31MaxExpress can give a little more insight and correct me if I've misstated something.

 

[Pinger]

EGR in reducing NOx relies on the 'ratio of specific heats' being lower for exhaust products than for air - 1.3 vs 1.4. This lowers peak temperatures - a fundamental ingredient in NOx production.
The ratio of specific heats is also known as a 'polytropic index' which is used in thermodynamic equations that govern engine operation. It gets complex at this point but when you see the effect that varying the polytropic index has in the equations' results, it's obvious that its effect is significant.

 

[0xDEADBEEF]

The question is if you could achieve the same thing using water. I do think it is possible. There's probably some math to calculate the amount of water to inject that I don't know.

 

[Caman96]

your clothes would develop holes

We considered that fashionable back then.

 

[L31MaxExpress]

The sole purpose for the EGR valve is to reduce oxides of nitrogen (NOx) in the exhaust.

[storytime]
Back in the '50s and '60s fuel mileage usually wasn't a concern - except for people who spent all day driving. Mechanics figured out that they could lean out a carburetor until the engine misfired, go back two jet sizes, and so long as the driver wasn't involved racing or driving for extended times at high speed, the engine abided while nearly doubling the fuel mileage.

In the '70s in the northeast part of the country, the rain became acidic, to the point that if you walked around in the rain and then washed your clothes, your clothes would develop holes. It was a serious problem. They quickly figured out that the NOx in auto emissions was making the rain acidic.

Burning a fuel mixture lean results in very low hydrocarbon pollution, but the oxides of nitrogen are high. This is why a lean mixture stings your eyes a bit. Even burning at the stoichiometric ratio (14.7:1) results in significant NOx. Running rich is the only way to eliminate NOx, but then you get high hydrocarbons.

The EGR is actually a bit genius, and it only came about after the introduction of the catalytic converter. Here's a simplistic explanation: instead of trying to maintain a "perfect" ratio, the fuel injection system swings between running rich and lean - that's why you look for swings in your O2 sensor voltage. When it's running rich, a bit of unburned fuel loads up in the catalytic converter, allowing the NOx in the cat to be neutralized. Then the engine swings lean and the rest of the unburned fuel mixes with the lean mixture and burns in the cat. That's why your cat always runs hot. The constant swinging from rich to lean and back means that your engine is able to dissipate the heat from running lean without damaging itself.

EGR doesn't boost your mileage, but if it isn't running right, it can negatively affect your fuel mileage. I'm sure @L31MaxExpress can give a little more insight and correct me if I've misstated something.

A few points I will add. EGR came numerous years before the catalytic converter. Catalytic converters also came years before feedback fuel systems using 02 sensors. Chrysler had about the first EGR system IIRC. It was merely holes drilled into the exhaust crossover into the intake passageways with stainless steel orifices threaded into them. GM added EGR in about 1972 or 1973 using a vacuum operated valve. GM calibrated the early catalyst equipped carbs richer than the previous generations, disabled vacuum advance under normal engine operation, then added an air pump to lean out the mixture going into the cat as well as help burn up carbon monoxide and hydrocarbons. The biggest contributor to acid rain was actually burning coal to create electricity not cars although cars did have a small contribution.

 

[PlayingWithTBI]

If you wanna gain MPGs, ditch the EGR and add Hywy Lean Cruise. It leans out the mixture and adds spark Advance. It adjusts AFR and Spark Advance based on MAP, As MAP changes, it'll automatically add/subtract so you don't burn a hole in a piston. AND, no dirty exhaust going through your intake

 

[racprops]

If you wanna gain MPGs, ditch the EGR and add Hywy Lean Cruise. It leans out the mixture and adds spark Advance. It adjusts AFR and Spark Advance based on MAP, As MAP changes, it'll automatically add/subtract so you don't burn a hole in a piston. AND, no dirty exhaust going through your intake

I was planning on Highway mode, in fact it was a thread on ThirgGen.org back in the late 90s that caused my selling off a OLDS403 I had rebuilt for my then 78 Chevy Van and going back to a Chevy SBC SO I could run a 85/90 TPI system.

I got three of them. And started building a special low RPM SBC engine.

But life got in the way and I ended up buying my current 93 G20 Van. Only a failure of an oil line to an oil cooler ruining the current 350 has caused and allowed me to go forward on this project.

So Now it Is a 383 and will be running a 4L80e Motor Home transmission though a US Gear Dual Range Overdrive.

I plan on running a 16197427 PCM with the 4L80e Chip BNKM.

I have seen a few posts on here about Highway Mode and this is one of the main reasons I joined.

I need three things, 1) how to convert the TBI injection system of that PCK to the MPI 8 Injection system, and:

2) How to either turn on Highway model or how to program a 427 for it.

3) How to build a reasonable water injection system and best flow rates.

Rich