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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

Quote:

The present paper is focused on the application of the Low Temperature Combustion (LTC) systems to modern diesel engines.

Aim of the work was to assess the possibility to optimize LTC systems performances in terms of both engine efficiency and pollutant emissions.

In particular, the results of a study of the effects of highly cooled Exhaust Gas Recirculation (EGR) on a diesel engine running at LTC condition, will be presented and discussed.

The engine employed for the experimental activity was a FIAT JTD 4-cylinder CR diesel engine, EURO 4 version. The EGR layout was modified with respect to the production one, in order to obtain lower temperatures of the recirculated exhaust gases.

The performed tests evidence the advantages offered by the strong EGR cooling (and so the lower intake air temperature) in reducing NOx emissions, leaving very low soot emissions, typical of premixed low temperature combustion.

The results suggest the possibility to improve the EGR cooling system of the production engines or to arrange a "long route" EGR system in order to improve the engine emission performance.

Living with Cooled-EGR Engines

Quote:

EGR cooler design differs
among engine manufacturers,
but all use engine coolant to reduce
exhaust temperature from around 1,100F
to 300F. Corrosion-resistant alloys help protect coolers
from acidic exhaust gases and poorly maintained coolant.
Cooled exhaust gases are channeled to a mixer, which
ensures that intake air and exhaust gases are thoroughly
blended before reaching the engine’s cylinders.

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).

Quote:

Originally Posted by vtec-e (Post 200685)

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.

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.

Quote:

Originally Posted by vtec-e (Post 200685)

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!

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.