Why EGR valve got so popular even if it create more harm than good? 1

[Nico3d3]

Everything is in the title. It seem that in almost all diesel engine, the EGR valve is clogging the intake until there's so much restriction that the engine begin to smoke a lot, starving for air. Next thing you learn, your engine is creating even more pollution than it would've create without any EGR valve. Why every constructors are still using such a crude system?

 

[MikeHalloran]

Huh?

What Diesels have EGR?



Mike Halloran
Pembroke Pines, FL, USA

 

[Zapster]

To meet emission standards.
See the link below for some information.

http://www.myturbodiesel.com/1000q/egr.htm

On my VW diesel, I used a vag-com to minimize the EGR flow. I have never had a problem with intake goo; however, I only have 110,000 miles on the car. In addition, I suspect that I am pumping a little more pollution out than a unmodified computer controlled TDI VW; however probably much less pollution than a TDI with a fouled manifold.

 

[Lou Scannon]

Heavy duty diesels (except Caterpillar) have used cooled EGR since 2002, in order to meet emission regulations.
Light duty European & Asian diesels have used cooled EGR since the late 90's, also to meet emission regulations. Any light duty diesels sold in the US since ~2002 have also used cooled EGR to meet emission regulations.
I'm sure there are better informed experts on diesel combustion in this forum than myself, but I'll do my best to explain.
The main purpose of EGR is to dilute the mixture in the zone where combustion is occuring (of course it dilutes the mixture everywhere, but the zone of combustion is where it matters). The purpose of dilution is to reduce peak temperature, by adding inert matter mixed with the reactants, that absorbs heat without adding to the heat release. NOx formation is a strong function of peak temperature, which is why this strategy is very effective.
The purpose of cooling the EGR is to increase the density of the inert matter, so the manifold and cylinder pressures can be reduced for given EGR mass flow rate. Also, this not only reduces the peak gas temperatures, thereby helping with NOx reduction vs non-cooled EGR, it also reduces the peak temperatures and thermal loading on critical components like pistons and exhaust valves.
EGR is now a fact of life for diesel engines in tightly emission regulated markets. Increasingly, it will also become the norm for high power density (i.e. boosted) spark ignited engines in these markets also.

 

[Nico3d3]

Zapster, I have a VW diesel too, I had to reprogram the ECU to deactivate the EGR because my intake was completely clogged. I used the vag-com adaptation like you did on your car, for a while, but I learned later that it almost doesn't change anything if you only use vag-com to tamper with the EGR. You need to reprogram the ECU, if you want to make sure you won't get any intake clogging. This is usually done when you add a performance chip to the car.

I know it is there to reduce NOx emission but the point is that it's doing more harm than good. Why is it still necessary? Every modern diesel use urea aftertreatment to remove NOx so it seem that the EGR valve is redundant.

 

[dicer]

What Diesels have EGR?

Pretty much all of them made now. Well for automotive applications anyway.
EGR is a great way to ruin HP and fuel economy. It is counter to anything that is done to increase power in a reciprocating internal combustion engine.
It is done to remove oxygen and cool the combustion process. To reduce Nitrous oxides. I guess I better stop here.

 

[SomptingGuy]

"Every modern diesel use urea aftertreatment to remove NOx"

Not true. For heavy duty diesels, there are two NOx reduction strategies: urea or EGR. Broadly speaking, USA companies favour urea; Europeans favour EGR.

Diesel engine manufacturers are bound by legislation.

- Steve

 

[Lou Scannon]

"USA companies favour urea; Europeans favour EGR."
Hmmn, last time I checked, it was the other way around. Have things changed since 2007?

 

[SomptingGuy]

Maybe I got it the wrong way around (?). But there are two competing approaches to the same legislative problem.

- Steve

 

[SomptingGuy]

... or maybe I'm thinking of the future rather than the present (?).

- Steve

 

[Nico3d3]

Nobody ever tried water/methanol injection to reduce combustion temperature? It should be simple enough, just use a bigger windshield washer fluid reservoir and inject the washer fluid in the intake. Washer fluid is composed of methanol and water... The water would also help the intercooler as its evaporation would cool down the airstream. The methanol would probably help create a more complete combustion, reducing black smoke.

 

[romke]

at this moment most european truck manufacturers use urea to reduce emissions (since it is cheaper and less technically complicated), but when more stringent emission regulations are introduced EGR and DPF will be unavoidable. EGR nowadays is restricted to areas (city centres)where extra emission regulations sometimes are called for.

 

[patprimmer]

Nico3d3

How will adding more fuel reduce black smoke.

You obviously live in a cold climate and presume everyone else does.

Water injection may help to remove carbon deposits, depending on where they are.

A small siphoning problem or excessive flow can cause hydraulic lock in a diesel a lot easier than it does with a spark ignition engine.

It sounds like a decoke of the EGR area should be a regular service item like changing oil and filters. My car (not diesel) actually has a fine mesh filter on the EGR supply.

Regards
Pat
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[Nico3d3]

What makes you believe I live in a cold climate? Maybe the addition of methanol to the water will prevent it from freezing but that was not the main goal. I thought methanol would act as an accelerant promoting a more complete combustion. Kind of like some people are doing with propane injection on their diesel.

 

[SMOKEY44211]

If you can catch it before the EGR valve and/or passages become compleatly clogged, water injection is an effective way to remove deposits. Principle of operation is the same for SI and CI engines. --------Phil

 

[Zapster]

Smokey44211, I thought that the way water effectively removed carbon deposits was when it flashes on the deposits. I can’t picture adding so much water that it flashes downstream of the EGR valve.

 

[patprimmer]

In warm climates we simply use water and detergent in windscreen washers so your presumption of the normal content was in fact presumptuous.

Adding extra fuel to a diesel at full throttle will overfuel and result in black smoke. Alcohol is a fuel and consumes oxygen as it burns.

Alcohol in the water of a water injection system is useful to prevent the growth of algae which can block nozzles.

Water injection is very effective at removing coke from the chamber, but not from upstream of the inlet valve.



Regards
Pat
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[BrianPetersen]

On the latest-generation diesel engines (example: North American specification 2009 VW Jetta TDI) they are using a low-pressure EGR that takes the exhaust from after the particulate filter, which ought to solve the clogging issue.

 

[ivymike]

...possibly with the downside of a sulphuric/nitric acid ingestion issue, depending on how the dpf is catalyzed.

 

[patprimmer]

Well sulfuric/nitric acid ingestion should reduce carbon deposits as there will be less metal left to deposited it on ;-)

Regards
Pat
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