Cooled EGR
 

I first read about cooled EGR in Daox's EGR thread:
Increasing EGR flow for better mileage, post #163.
Since then I've found out that later versions of my turbodiesel engine have cooled EGR, but mine doesn't. Recently, I found a used EGR cooler for my engine and plan to have it installed. I started this thread to gather information (and experience) on C-EGR.

Here is what a quick Google search turned up:
Effects of Highly Cooled EGR on Modern Diesel Engine Performance at Low-Temperature Combustion Condition - sae.org
Living with Cooled-EGR Engines

Here are some pictures of the EGR cooler, which I plan to install, from later versions of the 1.6 HDi engine:

http://ecomodder.com/forum/attachmen...1&d=1287945878

http://ecomodder.com/forum/attachmen...1&d=1287945878

The exhaust gasses go through the coolant in 30-35 small pipes. Quite a nice heat exchanger...
Here is the make and model, in case anyone is interested:

http://ecomodder.com/forum/attachmen...1&d=1287945878

I'll try to have a look behind the engine to see if it's there on my car.

Some or all of the jap versions of my yaris have the egr cooler. Mine doesn't. I read somewhere (might have been the tdi club) that the coolers are prone to filling up with soot or tar over time. The intake filled up on mine over time too due to the gases condensing in the intake and settling in it as a thick sticky tar.
It must also be pointed out that egr reduces NOx only. It apparently raises everything else a little....go figure why something would be invented that fixes one problem but makes a load more worse!

From my reading, cooled EGR is necessary to run higher amounts of EGR. If you don't cool it you have HOT EGR gasses going into the engine and causing pinging/knock which will retard your timing and lower efficiency.

The limit of how much EGR can be used, and the point at which the highest efficiency is is determined a lot by the individual engine and its design.

For a throttled engine (gas), I see EGR as being a big benefit as it can reduce pumping losses and optimize ignition timing at higher loads.

For a unthrottled engine (diesel), you obviously don't have the pumping loss issue. However, you do have the NOx problem and EGR will help with that. Any additional benefit from EGR would have to do with the actual combustion process. I know Tas had posted some charts in my EGR thread that showed the effect on diesel engines and EGR did improve efficiency. However, I am not exactly sure why.

Yes, EGR is messy and will need to be cleaned out every once in a while. I'd suggest probably 30k mile intervals. A small price to pay for what could possibly be a big efficiency enhancement.

I've wondered about using higher amounts of egr, and thought about running a second exhaust pipe from near the end of the existing tailpipe as the intake for the system. I figured I'd be able to reduce pumping losses quite a bit that way, and that the length of pipe would cool the gas quite a bit.

I guess I was onto something!

I left the car at the shop this morning, tomorrow afternoon I should know if it still works with the EGR cooler installed;) I keep thinking about whether it'll help with warm-up, since the ECU may not open the EGR valve when the engine is cold (condensation). We'll see. I plan to hook up a voltometer to the EGR valve one day to see under what conditions the ECU opens it and by how much (yes, my EGR valve has more positions than just open/closed).

Yeah, those skinny tubes inside mean a lot of surface area to exchange heat, but also a lot of area to acquire soot and tar. The cooler I bought was made in 2008, but I gave it a long bath in gasoline to clean it out (at least partially) since it already had some sooty gunk inside (the pictures in post #2 were taken after cleaning). I also asked the mechanic to clean out the EGR valve while installing the cooler.

Raising everything else a little may be worth lowering NOx, since the cat and DPF should take care of the rest.

I've got a Jeep Liberty CRD (diesel). The US version flows a lot of EGR, cooled, and the intake manifold is part of the valve cover making it extremely difficult to remove and clean, unlike VW TDIs.

My solution was to disable the EGR completely. I gained about 1.5 mpg as a result. EGR does help with NOx emissions, but it's a secondary pollution, requiring hydrocarbon and particulate matter to create smog. I figure I'm good because I already fuel the Jeep with 100% biodiesel.

If you think you will gain economy in a diesel engine with EGR you are sadly mistaken. I modify EGR diesel engines in over the road trucks to halt all EGR flow and it results in a 20% increase in economy.

My VW TDI also has a higher flow EGR with a cooler. I am going to try the same trick I did with the Jeep. Simply disconnecting the vacuum line does not work effectively as the ECU sets the engine light and it seems like driveability is affected. I am going to fake out the MAF input to the ECU so EGR will be disabled without the ECUs intervention. Not to mention alerting the emissions tester. Maybe I'll get a few mpgs as well.

Okay lets first get a few facts down

soot = incomplete combustion of fuel

higher intake temps = higher combustion temps = higher NOx emissions

higher combustion temps = higher heat loss to cooling system

To keep NOx emissions low in a diesel two main approaches are employed. Reducing peak combustion temps and reduce excess O2. Spreading the combustion evenly throughout the combustion chamber reduces hot spots where most NOx is produced. Reducing the O2 in the cylinder means the fuel spray has to travel farther to encounter enough O2 to burn thus spreading it out. The denser the intake charge the more mass the fuel has to heat and thus the lower the combustion temps. The colder the intake charge the more the fuel has to heat a given mass to get it into NOx production ranges.

The whole purpose of cooling the EGR on a diesel was so they could use it more effectively or use lessof it to control the NOx emissions and pack more excess air in the cylinder to reduce soot. The mixture of air and cooled EGR is more dense and thus more of it can be put into the cylinder on the intake stroke. This helps reduce the peak combustion temps and reduces NOx. This also reduces the heat lost to the cooling system and thus more power can be extracted from the fuel.

An ideal diesel optimized for efficiency would not uses EGR at all. EGR reduces the specific heat ratio of the combustion gasses and reduces the amount of power that can be extracted from the fuel. Instead of EGR spreading combustion throughout the cylinder evenly would be accomplished by controlling the velocity of the atomized fuel droplets so they would burn up just before they hit the edge of the combustion chamber. Additionally to maintain the ideal constant pressure combustion of the diesel cycle fuel would be injected in at a rate to ensure this. Since this is very hard and expensive to do it is not done.

In the case of a direct injection diesel engine EGR percentages are used to slow burn rate of the fuel. It aids in spreading out the combustion and thus heat evenly in the cylinder. The percentage can also be used to help approximate the constant pressure combustion cycle of the diesel cycle. IT reduces excess O2 content so there will be less for nitrogen to combine with to make NOx. It also increases charge mass that in turn reduces combustion temperature.

Increasing EGR percentages past a certain point are detrimental to efficiency however. It slows the burn rate of atomized fuel to the point it strikes the wall of the combustion chamber which in turn causes an incomplete burn. It slows the combustion rate to the point where the ideal diesel cycle constant pressure combustion isn't maintained. It reduces the amount of fuel that is burned by depriving it of O2. It also reduces the specific heat ratio of the combustion charge.

In conclusion More EGR in a diesel is not better. The optimum percentage used for efficiency will be determined by injector pop pressure, atomization of the fuel, droplet velocity, etc.... Even if you were to tune all your injectors to be exactly the same then you will be limited by the ability of your emissions control system's ability to control it accurately. Unless you really have studied, weighed and measured all factors involved and the trade offs, increasing your EGR flow is more likely to drop your mileage on a modern direct injection diesel.

Edit: I should add that I think changing your EGR system to a cooled EGR system will probably be beneficial to mileage.

I'm picking on your words, but overall more heat is transfered to the cooling system with EGR than without. Not from the cylinders walls, but the EGR cooler itself. Quicker warmup times are becoming quite handy for some people this time of year.

The following is for a fairly typical diesel engine with rotary pump type injection system. It's possible to increase efficiency with EGR, it's just tough and it's not a panacea.

http://ecomodder.com/forum/emgarage-...ab12759775.JPG

EGR will contribute to clog your intake manifold because it introduces soot back in the intake charge. This soot combines with crankcase vapors to form a thick paste in your intake manifold over the miles. Also, EGR should not be cooled below the condensation point as this would aggravate the clogging .

ConnClark, thanks for the comprehensive (not to say exhaustive;)) write up. The main reason I decided to go ahead with the EGR cooler is because later versions of my engine have it, so it is a no-fuss direct swap. Yes, I take into account that the newer engine's ECU compensates for cooled EGR and may keep the valve open for a shorter time. I'll see if I notice a difference in fuel economy and in power. If something goes wrong I can still tweek the EGR valve to open less.

NOx hardly qualifies as secondary pollution, it's about the most harmfull thing to come out of the exhaust !

Biodiesel generates around 10% more NOx than regular diesel, so disabling the EGR while on biodiesel is not the best of options.


If your car has EGR, please keep it operational !
Better mileage at the expense of polluting MORE is not my idea of driving more environmentally friendly.

I picked up the car today. The EGR cooler is fitted, cam belt and pulleys replaced, coolant heater installed. It's hard to tell if there is any difference, since I only drove 8km, and the engine was warm when I got the car back. It did feel like it had more power, but this may only be a feeling - I spent half the day driving my Grandma's Corsa (1.0 liter engine), plus I had biking shoes on. My brother-in-law said that maybe the cam timing was (unintentionally) adjusted while replacing the cam belt and pulleys.

"EGR will contribute to clog your intake manifold because it introduces soot back in the intake charge. This soot combines with crankcase vapors to form a thick paste in your intake manifold over the miles". ---I have read that this should not be as much of a problem since low sulpher diesel has been adopted in the U.S. Does anyone have any experience with this?

So EGR reduces Nox and may help with faster warmup but what would make more power on say, an off-road racing diesel engine, EGR or no EGR?

Maybe you can support that claim. All that I've read about NOx is it requires hydrocarbons and UV to create smog. Modern pollution controls have reduced vehicle HC output to the point that additional NOx control is pointless.

Even so, if I net 10% better mileage with the disabled EGR, my total pollution output with biodiesel is WAY ahead. Additionally, I don't have to clean out my intakes anymore. Bonus.

That's easy. No EGR will allow more air. More air allows more fuel. More fuel equals more power. If EGT is an issue, use water injection.

I did read somewhere that water mist injection would lower combustion temps and therefore NOx.

probably and it is true. Water injection has been successfully used on car ferries and large stationary diesel generators as a NOx pollution control. As a side effect maximum power and fuel efficiency goes up slightly. Note usually when used for pollution control water injection is not tuned to to improve power or fuel economy but is tuned for the maximum practical NOx control.

It's not only about smog. From What is Acid Rain and What Causes It?:

On gas engines.
On diesels, NOx (and PM) remains a serious problem.

Using biodiesel in non-EGR engines, NOx output is further increased over regular diesel.
(EPA test on non-EGR vehicles)

Biodiesel has serious advantages over regular diesel, being renewable and having lower HC, particulate, sulphates and PAH emissions.

So why ruin its NOx emissions by disabling EGR :confused:

CO2 is not the issue as biodiesel is renewable.


If we all throw the emissions control gear out of our cars, motoring would be a lot cheaper for all ... Bonus.
Or not ?
We'd also be going back to the pollution levels of the 50's-60's-70's.

So you and some others claim.
I accept that, but it's not a particularly large amount.
Because the engine functions better and lasts longer. And it gets better mileage. Yes there are tradeoffs, but I am not convinced NOx is a serious problem. Acid rain is not an issue in the front range of Colorado, smog was much worse than it is now. My understanding of acid rain is it's caused mostly the sulfur from coal plants.

I never advocated "throwing out all the emissions control gear from our cars", so please don't put words in my mouth. I am not ripping out the catalytic converters from my vehicles, and certainly not disabling EGR or evaporative controls on my gasser. I also never advocated making modifications solely on the basis of cost savings either.

If you are reasonable I think you will find my actions are proper enough, regardless of whether you agree with me specifically. If you want to be a purist, I'm not interested in your judgment. You will only invite the same on yourself.

So if the NOx you produce doesn't effect you locally, then it's not a problem?

I knew this was coming. :rolleyes:

I already stated my position that the small amount of NOx is not a big problem compared to the gain in fuel efficiency, and the marginal amount extra from burning biodiesel is balanced by using renewable, lower carbon fuel.

Maybe I should go back to burning fossil fuels? If you are not happy with my compromises, I can tell you emphatically I'm not happy with yours either. So let's agree to disagree, OK?

Seeing as how you live in Denver, you have to pass emmisions tests, correct? Or is it exempt due to being a diesel?

I lived in CO Springs a few years ago for a year, and have a ton of family in Auroura and surrounding area. I do miss seeing those mountains. I had Pikes Peak as my front door vista during that time, and its beauty is something I miss greatly.

We do have emissions testing specifically for diesels. It's twice as expensive as gassers, and annual instead of biannual. However the only measurable is soot output as opacity, and the standard is quite low. You've got to be smoking pretty heavily to fail. And biodiesel helps with less soot output.

Diesel EGR FAQ
 

I just found this article today. It may be useful for this discussion. It is written specifically for the VW TDI engine (pumpe duese is the injectors driven by the cam as in my car).

TDI EGR system FAQ

"Removal of the EGR will turn on the check engine light which will results in automatic failure during emissions testing and can prevent you from registering the vehicle in many states. Disabling the light or taping over it won't work since they plug in an obd2 scanner which reads your car's computer. There are ways to trick the computer into not showing a check engine light like through a chip tune but tampering with emissions devices is illegal in most places.

The biggest gain is reduced cleaning of the intake manifold. However, ultra low sulfur fuel used in all US and Canadian diesel fuel has greatly reduced major clogging. Biodiesel users report no excess intake buildup although there'll always be a small film. There are only small mileage or power gains from disabling the EGR system since it only operates at partial throttle and idle. Generally speaking, at full throttle, the EGR system is closed by the computer so it makes no noticeable difference in peak power. If you are removing the EGR for reduced pumping losses and the small power or economy gains, bigger and better gains can be made elsewhere. See 1000q: basic performance upgrades for a list of starting performance modifications. Also, the pumpe duse cars use an O2 sensor to regulate the EGR system much more efficiently than non pumpe duse cars. Even newer technologies on the common rail system cars allow more precise fuel delivery and burn, resulting in less intake clogging."

^^^

I've tried that, just pulling the EGR control, and it results in drivability issues and in the short time I tolerated it, no discernable mileage change. Probably because the MIL is set (malfunction indication lamp.) But I am running something else in my Jeep, a circuit that electronically emulates the presence of the EGR system so the engine computer does not trip the MIL. I intend to do the same on my ALH TDI.

For me, using less fuel is part of how I try to pollute less. If I had the option to reduce fuel consumption and certain pollutants while increasing certain others, I would research the matter and make an educated choice. I believe this is what you did in good faith and I respect that. If you are not indifferent to NOx pollution on a global scale and your post cited above was only worded unfortunately, then I take back my comment.

How a certain engine reacts to adding/removing EGR seems to be a highly individual thing. Some report milage going up, others down. I read recently that in newer cars the ECU has so much control over the engine that EGR operation is almost unnoticible, so we have cleaner cars without sacrificing performance.

I would also like to ask everyone to keep the focus on the differences between cooled and non-cooled EGR. There many threads on EGR in general, so please move any off-topic discussions there.

Despite higher traffic and all that, acid rain is now less of a problem, but that didn't come magically - it is because of better fuels, pollution control systems in cars, and in the industry.

They can / should wash their gases before emitting them into the atmosphere.
We have to do so at work to get rid of gasses containing sulphur.

But you are knowingly disabling a pollution control system - and unfortunately enough, you're not the only one on this forum to do so.

It's a good thing you're running on B100 as it has great advantages over regular diesel - I wish I could - but why negate a good part of that effort by putting out more NOx :confused:

I'm not one of those greenies in sheepwool socks and sandals ;)

I have not researched the differences in diesel EGR in the US vs. Europe, but I hear the US has stricter standards for NOx and thus flows more EGR. That causes definite problems with intakes, reduces mileage, and makes it necessary to have EGR coolers on the newer diesels.

The US Jeep Liberty (Cherokee in Europe) CRD will develop serious issues with the manifold sensors, the EGR valve and FCV (flow control valve) if left alone from the factory, not to mention intake cleaning is prohibitively expensive due to the labor involved in removing the manifold. Just do a search in the CRD section of lostjeeps.com if you want data on EGR related failures. Green Diesel Engineering has adopted this orphan vehicle, and is doing excellent work in optimizing the EGR flow to the point where it stops causing problems. An ECO tune is out of my reach at the moment; soon, but not yet.

I answered that in a previous post, and in my last post.

I have disabled my EGR. My justification is my car with was the first production car to have a Diesel Particulate Filter. This was before cars had a regeneration mode and in fact was why it was discovered one was needed. Anything that produces soot plugs up the filter which makes the engine work harder and that makes more NOx on its own.

These filters had a problem with plugging up so bad that four possible bad things could happen. The best case is your mileage sucks and you have no power. the next best case was the car would quit running. The next best case is the pressure would cause the filter to break up and throw chunks of itself into the turbo (it was located between the exhaust manifold and the turbo). The worst case is the back pressure was enough to crack the head.

Eventually the EPA mandated a recall to refit the cars with a newer Catalytic Diesel Particulate Filter that didn't filter as much. Unfortunately the cars still don't have a regeneration mode so the filters still get plugged to the point that it doesn't flow well. The only way to clean it out is to drive at sustained high speed (90mph+) for a couple of minutes or to drive it up a long steep hill a few times.

Since it was designed for California Emissions the engineers assumed a different driving profile and warmer climate conditions. IF you spend two hours a day on the highway and don't drive in cold climates it will stay relatively clear. If not you must "regenerate" it as mentioned above. Since I live in a colder climate and only get on the highway twice a week for less than fifteen minutes, I can't keep it clean even if I disable the EGR.

ConnClark, you need something like this in your exhaust:http://www.breathepureair.com/trion/...clone-diag.gif
:thumbup:
Now theres an ecomod that could change things!

Hmmm, you come back home, shovel that soot into the furnace, and you've got free heat;)

Stricter NOx standards will become the norm for diesels everywhere.
It's only a matter of time.

http://ecomodder.com/forum/attachmen...8&d=1260189842
(Click on image for discussion.)

There are far better ways of dealing with NOx than EGR. Catalysts for example. Water injection as another. No need to sacrifice fuel efficiency to the NOx bogeyman.

...my thoughts exactly, because EGR is simply automotive "...fart sniffing..." in my mind.