Hi,

I've read many posts about EGRs here, and I know it is a controversial topic. But, I was reading the newspaper today and saw this definition of an EGR valve by the Auto Doctor:

"The purpose of the EGR valve is to cool down the internal engine temperature and lower the very harmful NOX coming out the exhaust. Lowering the internal temperature keeps the spark plugs, piston and valves at correct temperature as well. The EGR valve and operation are essential for long-term engine life." (Junior Damato)

Assume that EGRs in diesels and gasoline engines do the same thing, I make the following points:

1. The exhaust coming out of the engine is hotter the intake air. The first things that comes to mind is that it is not possible for the hot exhaust to cool the engine. So why send it back to burn again? It would be like inhaling your own breath.
2. However, hot exhaust theoretically continues no oxygen. Less oxygen in the intake air causes the combustion process to burn cooler.
3. But, more oxygen makes more horsepower in a diesel since the molecules of diesel can more easily find a molecule of oxygen combine with.
4. So, if we disconnect the EGR, we would be causing the engine to operate at a temperature higher than what is was designed for.
5. Or, we get more economy and horsepower without an EGR valve.

What's your opinion?

The engine produces higher temperature when the fuel mixtures are lean. This high temperature combustion produces nitrogen oxides (NOx). By introducing small amount of exhaust gas (about 7%) into the intake manifold, you are diluting the mixture with non-combustible gas that will cool the combustion process and reduce NOx emission.

Do you want more horsepower or do you want cleaner air?

David

You get more power and more heat and more NOx emissions without the EGR. Not really a problem on a diesel.

The exhaust gas, slightly cooled, replaces some of the combustible mixture in the cylinder, interfering with the oxidation of the fuel and lowering the temp. More oxygen would raise, not lower, the temp, so air won't work here. "Used" air -- mostly nitrogen -- reduces combustion heat since it doesn't contain much oxygen.

Gasoline engines are more of a problem -- since the advent of the EGR, the valve timing has been changed to get more power and economy with the EGR. Blocking it off can result in condiderably more heat, enough in some cases to overheat the exhaust valves and cause them to fail. Also can cause serious pre-ignition under high load.

Eliminating the EGR won't bother a diesel -- the European models are identical and don't have EGR that I know of.

For gasoline engines, leave it on and make sure it works.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I've owned a Toyota 1C diesel engine (Japanese Surplus), and it didn't have an EGR. It wasn't very old, probably 10 years old. So, I suppose that blocking the EGR wouldn't hurt a Mercedes diesel since similar models in Europe don't have EGRs.

People tell me that the diesel Beetle is not sold in California because it cannot meet the California pollution standards. I would think that a car that burns it fuel more thoroughly would also lower its pollution levels.

psfred

Peter
When I was asking a tech at the dealer's about the EGR valve he said that it only opened at periods just above idle and at low load. Do you know if this is true? Further if it is, what is the thinking behind any particular injection of recirculated gas?
Thanks
David Sure wouldn't mind seeing some more discussion of this.

David,

That's an interesting point you brought up about when an EGR works. If the point is to reduce NOx emissions by lowering engine temperature, don't think you the EGR should recycle gas when the engine is hottest? That is when the engine is under heavy load, rather than at idle or little load. Any thoughts?

I don't know. I know that the same approach of EGR was examined and rejected by big marine engine manufacturers on account of the high wear implications of recirculation. Judging by what I saw in my intake pipe above the EGR valve I didn't like it either. below the EGR reentry point it was shiny clean; above the stuff was millimeters thick and on through the intake manifold.
I know that Cummins's approach to the problem has been to keep the charge air aggressively cooled; a huge cooler as fitted on my truck. But I understand that rumor has it that Cummins will be fitting EGR in the nest few years along with common rail injection. I don't like the idea of terrible cold air going into an engine because of the potential for a non-prompt commencement of injection. On Marine engines that we run now the charge air goes in at 80C and there is very little knock due to lag or diesel knock. Many of these engines have their charge air cooled or heated by the cooling water so you can see what I mean
David

I don't know. I know that the same approach of EGR was examined and rejected by big marine engine manufacturers on account of the high wear implications of recirculation. Judging by what I saw in my intake pipe above the EGR valve I didn't like it either. below the EGR reentry point it was shiny clean; above the stuff was millimeters thick and on through the intake manifold.
I know that Cummins's approach to the problem has been to keep the charge air aggressively cooled; a huge cooler as fitted on my truck. But I understand that rumor has it that Cummins will be fitting EGR in the nest few years along with common rail injection. I don't like the idea of terrible cold air going into an engine because of the potential for a non-prompt commencement of injection. On Marine engines that we run now the charge air goes in at 80C and there is very little knock due to lag or diesel knock. Many of these engines have their charge air cooled or heated by the cooling water so you can see what I mean
David

That is true; EGR is only used at light/part load. It is effectively disabled at idle and full-load. On a diesel engine, the highest O2 surplus occurs at light and part load conditions--this extra oxygen is used in the manufacture of NOx. Under heavier loads, this extra O2 is consumed and NOx production drops off as well--EGR is no longer necessary to keep the NOx emissions within spec.

-Joe

Now I've got it
Thanks Joe
David

David:

The EGR on my Volvo stuck wide open -- huge clouds of inky black smoke and no power to speak of at low speeds. Very noticable. Once up to speed and turbo going (it was bad, too!), no effect.

At full throttle there probably isn't enough oxygen left to make NOx -- when you get soot, the oxygen is all gone, and temp drops off. This is the only reason over-fueling a diesel (increasing maximun fuel delivery) doesn't melt the exhaust valves.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

diesel beetle does meet California clean air standards. there is a sticker under the hood indicating that.
they are not sold in California due to some thing about fleet and overall pollution.
diesels are also sold on a limited basis elsewhere.
I think vw could sell all the diesels it could make due to the markets interest in them.

__________________

79 240D my current toy
42 years a Diesel addict

240D sold
250SE sold
220D sold
280C sold
280S sold
300D (2) sold
300CD sold
300DT sold
300SD sold
380SL sold

Particulate emissions are a huge bugbear at the present moment in the USA. Diesel soot is a bad thing, of course, since it contains carcinogens and is all breathable (goes right down the lungs). The irrational part is going after light duty diesels rather than the old over-the-road smokers -- an old Mack or Peterbuilt probably produces more smoke running up from a light on Highway 41 here that my 300D will produce in a year, and that is if it is in good shape!

The solution is oxygenated fuel (biodiesel!) -- the city ran the busses in town on peanut oil mix for a year -- wonderful odor of roasting peanuts instead of stinky diesel smell, and almost no particulate emissions. Instead, the bureacrats are trying to ban light duty diesels.

The real kicker is that gasoline engines ALSO produce particulates, composed of manganese oxide and other residual metals from the fuel, and these particulates aren't any better than the ones from diesels. To say nothing of the unburned hydrocarbons, carbon monoxide, and NOx emissions that are much higher for gasoline engines that diesels.

Go figure!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Yes our government is about to protect the citizenry by going after the big rigs. In a year or two all will have to meet tighter emissions by having egr or other devices. The problem with egr on a diesel is not the extra heat but the soot that gets recirculated back into the engine. This creates added wear on the engine along with mixing with blowby or turbo oil leakage to build up a big mess and stopping up the intake passages. Egr also results in less power output and lower fuel mileage because combustion is not as efficient. I would advise all Mercedes owners to disconnect the egr if they value their engine life.

__________________
1995 S-350
370K + SOLD
1952 220B Cabriolet
39K kilometers + SOLD
1998 E300D
310K +
2012 E350 BlueTec
120K