Hello!
I decided to start this new thread to share my experiments with cooled Exhaust Gas Recirculation on spark ignition engine.
To make it clear this thread is about EGR on GASOLINE (also known as "petrol" or just "spark ignition") engine. NO DIESEL please, this is completely different story.
One previous thread about the EGR topic (little out of hand by now, too many replies and no conclusion):
Increasing EGR flow for better mileage
The theory:
Gasoline engine running at part throttle is equivalent to running it with very low compression. But compression is main factor in Otto cycle efficiency calculation. So in theory Otto cycle engine runs with maximum efficiency at full throttle only. Adding some inert gasses to intake from exhaust should reduce throttling therefore increase efficiency. Although there are definetly some other factors to consider with this.
Other way to say it is that we need to minimize the intake manifold vacuum to keep the efficiency high at low loads.
Test car:
VW Passat 1990, 2.0l doch, 100kW. Engine code 9A. Original Bosh mechanical fuel injection.
First test:
Last week I added EGR pipe to my car:
Drilled 12mm diameter hole to the exhaust pipe 30cm from the end (at the back of the car. Welded threaded pipe joint to the hole. Connected rubber hose to the joint. Run the hose to the engine room from below the car (actually used some plastic aluminium pipe in the middle).
In the engine room I connected the hose to the idle air intake, so that the full vacuum applies to the pipe.
Experience:
I took the test drive this weekend 2x70 km. Quiet country road, no city driving. I feel that I certanly did not use more fuel than usual. Unfortunatly I do not have exact way to measure the fuel consumption of such a short trips. But based on experience fuel consumption dropped about 0-20%.
I did not have any particularly bad effects. I was afraid of EGR hose overheating, but that was absolutely not the case. The hose felt only slightly warm when touched after driving 70km.
Of course such a simple system is not without drawbacks. Less manifold vacuum upsets the idle stabilization system, and at my case it became
"hunting" when engine warm. Also I noticed slight hesitation at some point. Apart from that the car was completely driveable.
Outside temperature below 0C. No noticeable difference in engine heating up time.
Conclusion:
The increased cooled EGR seems promising for reducing fuel consumption. Despite the idle hunting and that I was scared to use the engine's deceleration fuel shutoff, overall fuel consumption was less than usual, so most of the time it must have been running more efficiently.
To do:
-Add means to adjust EGR amount from inside the cabin.
-Build electronic(or mechanical) regulator to adjust egr automatically, and to disable at idle to make idle stabilisation work as normal.
-Electronic regulator to disable EGR while deceleration fuel shutdown and slightly after that.
-Find the way to measure instant fuel consumption.
-add temperature meter to EGR pipe.
Worries:
-What happens to the catalytic converter?
-Is there possibility for some other engine damage?
-possible condensation inside EGR pipe and freezing in winter.
Thats it for now.
Best Regards.