Egr - PeachParts Mercedes-Benz Forum

JamesDean · #1 08-18-2006, 01:01 AM

question: I know disabling/removing the EGR vlv on diesel MB's will net the car better MPG and overall performance...will it do the same on a gasser? (m103?) are they any performance/effiency reducing devices that I could disable?

thanks

kris

sixto · #2 08-18-2006, 01:45 AM

AC

Sixto
... stay tuned

ConnClark · #3 08-18-2006, 12:25 PM

EGR on a gasser doesn't have the same effect as it does on a diesel.

In a diesel you have no throttle and run with excess air. The more excess air you have the more power you extract from the fuel. EGR heats the intake charge allowing less of it to fill the cylinder. It also reduces the specific heat ratio of the gasses in the power stroke. This reduces your power some.

In a gas engine your engine is throttled and the power is controlled by how much air fuel mixture is allowed into the cylinder. The exhast gasses from the EGR just act as filler. Without egr your engine pulls more of a vacuum. This vaccum is a double edge sword. A vacuum helps evaporate the fuel droplets into a vapor. A vacuum also makes your engine work harder to suck in a charge. These offsett each other for the most part so adding EGR on a gasser really doesn't hurt you much if any.

Brian Carlton · #4 08-18-2006, 01:25 PM

Quote:

Originally Posted by ConnClark

These offsett each other for the most part so adding EGR on a gasser really doesn't hurt you much if any.

Adding EGR on a gasser always causes a loss of some efficiency and fuel economy sufferes slightly. Sometimes it's noticeable........1.5 mpg or so........sometimes it's not...........less than .5 mpg..........but it's never zero.

Old300D · #5 08-18-2006, 03:24 PM

EGR valves on gassers won't hurt performance as the recirculation is only done under partial throttle. But fuel efficiency may indeed suffer a small amount.

Brian Carlton · #6 08-18-2006, 04:00 PM

Quote:

Originally Posted by Old300D

EGR valves on gassers won't hurt performance as the recirculation is only done under partial throttle. But fuel efficiency may indeed suffer a small amount.

The EGR hurts "performance" in the sense that it detracts from throttle feel. It's like losing the power of 1/2 cylinder on a V8. Disconnecting it will give you a "noticeable" feeling of additional performance for about two minutes until you accept that new level as the standard.

cjlipps · #7 08-21-2006, 12:12 PM

I'd like to clarify/correct a portion of ConnClark's post. EGR is strictly an emissions control. Exhaust gasses are introduced into the intake in an effort to "poison" or inhibit the combustion process with products of combustion. This has a detrimental effect on combustion, actually lowering combustion temperature thereby reducing the production of oxides of Nitrogen (NOx) in the exhaust. It definitely affects performance and economy, though to what degree is difficult to quantify. (Anything you put in the intake that is not a fuel or an oxidizer-and exhaust gas is a poor example of either- will hurt performance and economy) If there is any heating of the intake charge it is negated by the lowered combustion temperature. It should not directly affect vacuum but may have an incidental influence on it since the throttle position at a given speed/load may be slightly different with/without EGR. CC is correct in stating that the engine has to work harder to overcome higher vacuum but under normal operation with a healthy machine, higher vacuum always translates to better fuel economy. After all, the "economy" gage is just a vacuum gauge with no numbers.

ConnClark · #8 08-21-2006, 02:26 PM

Its true that EGR does poison combustion to some extent. This poisoning slows the flame front and provides a more even distribution of heat throughout the combustion chamber lowering NOx. This slowing of combustion robs you of some power, however EGR also cools combustion by absorbing some of the heat. Some of the heat absorbed would be transfered to the block. Heat absorbed by the block is not energy used to generate power. EGR keeps this energy in the working fluid for the piston to extract it. Once again we have a power trade off thats hard to quantify.

You are incorrect about adding something to the intake not being a fuel or oxidizer robbing fuel economy and power. If you were to add a nobel gas like helium, neon, or argon instead of EGR you fuel economy and power will go up due to a higher percentage of energy being extracted from the combustion.

The point is EGR is not as bad for a gas engine as it is for a diesel.

#9 08-21-2006, 09:47 PM

Quote:

Originally Posted by ConnClark

The point is EGR is not as bad for a gas engine as it is for a diesel.

EGR's have also been on gassers for many decades. They have been refined and tuned to work with them.

EGR is a relatively new concept for diesels. The EGR system on our OM617's is downright stoneage compared to gassers of the same era. They have been nearly non-existant on highway diesels until 2002 emissions standards forced engine builders to consider their use. Cat resisted (and still does) using an EGR, and any diesel tech can tell you what a cluster-F*** their twin-turbo setup is.

4 years later, and EGR's are almost on par with gasser systems. Although, I still see issues with EGR coolers rotting from the inside-out (Mostly on Detroit Series-60's).

A good example of how emissions can choke diesels is the Cummins ISX. Just look at the intake tube at the restriction to allow greater EGR flow. Pre EGR, the ISX was a great engine, now it's junk. They even had a 600hp option, now 550 is the highest offered.