Increasing EGR flow for better mileage

[Daox]

Alright, I've been thinking and I am going to change the EGR control around a little bit. As it is currently I'm just adjusting the duty cycle to the EGR valve to control its position. However, when in use, there will be pressure pulling/pushing the valve and its position will be unknown. However, the engineers in their ultimate wisdom added a position sensor to the EGR valve so they can tell the position of the EGR valve. I will now be modifying my circuit and programming to get feedback from that position sensor and adjust the PWM accordingly to maintain the set position.

Here is the pinout/circuit for the EGR valve:

[Leadfoot]

Just some random words:

Daox, nice EGR system.

I have experimented with my stock EGR setup and have found a decrease in mpg and power when increasing EGR levels over their stock value. On the opposite side, my engine started missing badly under high load @ 1500 - 2000 rpm. I thought that too much EGR flow was to blame so I disabled it completely. I did not notice any change in performance of mileage. The actual culprit was weak spark. I installed a hotter coil pack and gapped the plugs to 0.065" which solved the problem until the hot coil pack fried the stock plug wires.

My belief is that in an old 2 valve motor such as mine, the exhaust gas is not getting mixed enough with the fuel and air. On top of that the ignition system is far from optimal. I believe that to have a lot of egr flow and avoid missing, you would need 2 wide gapped spark plugs per cylinder and 2 hot coil packs. Having two spark plugs would decrease burn time and help with flame propagation.

[Daox]

A power loss with increased EGR flow is definitely to be expected. Thats kind of what we're after actually.

When you experimented, how did you control the EGR valve? Did you have it running long at all before you had ignition problems? Do you have any data/testing to share?

Definitely getting too much EGR will decrease mileage as it causes misfires and incomplete burning just as running too lean would do. A high swirl head and strong ignition system will definitely help you run higher mixes of EGR.

[Leadfoot]

I controlled the EGR flow by changing the ECU tune with a programmer which I custom tune from my laptop. I first doubled the EGR flow with no problems, just a loss of power and mileage. When I tripled the EGR flow some missing was noticeable. Scangauge does not work with this truck so the gas mileage was recorded over a few tanks of 93 octane. I record the mileage onto index cards but I never marked the info for this test so I cannot give you an actual figure, I just remember that doubling or tripling the EGR flow resulted in less gas mileage. The stock EGR flow values seem to be optimal. With no EGR flow I did not notice any change in mileage or power but I set the EGR flow back to stock for the chance that id did improve fuel mileage 1%.

My theory to this matter is that it robbed too much power. I think trying to move a 4000lb vehicle that is 20% down on power actually eats up more fuel. Like how some trucks with modular V8's get better gas mileage in the city than modular V6's. That or some of the fuel is not being burned.

One thing to watch out for is the EGR gumming up your intake, after 80,000miles it will rob power and fuel economy if not cleaned. The throttle body getting gummed up is the biggest thing to worry about.

[EdKiefer]

Originally Posted by Leadfoot

I controlled the EGR flow by changing the ECU tune with a programmer which I custom tune from my laptop. I first doubled the EGR flow with no problems, just a loss of power and mileage. When I tripled the EGR flow some missing was noticeable. Scangauge does not work with this truck so the gas mileage was recorded over a few tanks of 93 octane. I record the mileage onto index cards but I never marked the info for this test so I cannot give you an actual figure, I just remember that doubling or tripling the EGR flow resulted in less gas mileage. The stock EGR flow values seem to be optimal. With no EGR flow I did not notice any change in mileage or power but I set the EGR flow back to stock for the chance that id did improve fuel mileage 1%.

My theory to this matter is that it robbed too much power. I think trying to move a 4000lb vehicle that is 20% down on power actually eats up more fuel. Like how some trucks with modular V8's get better gas mileage in the city than modular V6's. That or some of the fuel is not being burned.

One thing to watch out for is the EGR gumming up your intake, after 80,000miles it will rob power and fuel economy if not cleaned. The throttle body getting gummed up is the biggest thing to worry about.

Extra EGR flow should only affect low rpm/part throttle conditions, it should not affect WOT (EGR should be closed)

If your able to tweek ECU , I would try raising spark timing in part throttle/cruising area (when EGR is on). The stock ECU probably does this also so some testing would be needed .
For sure adding extra EGR will make the car less responsive and need more throttle (thats what you want, and if all goes right some extra MPG might happen) .
2x increase sounds a little extreme , I would start lower % and test, work your way up .

[Leadfoot]

EGR is shut off at WOT but then you have a preheated intake manifold stealing some initial power. I am not too concerned about this but at part throttle when the EGR is on there is less torque to lug the gears so downshifts happen sooner.

I am able to tweak the EGR flow through the ECU. There is also a parameter to advance timing with EGR flow which I did. However since this motor has no knock sensor I did not want to be overly ambitious.

Another thing to note:
During extended coasts the ECU enters "coasting fuel shut off" mode. I don't know if all the injectors are shut off or if fuel is just reduced but The EGR flow during this time is jurastically increased. The stock values had the ECU enter "C.F.S." after 15 seconds of coasting. I changed it to enter "C.F.S." after three seconds of coasting. One thing I really noticed was a huge increase in drive line drag to the point where you would slow down going down hill. To improve the driveability, I totally disabled coasting fuel shutoff.

2x EGR flow might be a bit excessive as a first step.

Originally Posted by EdKiefer

Extra EGR flow should only affect low rpm/part throttle conditions, it should not affect WOT (EGR should be closed)

If your able to tweek ECU , I would try raising spark timing in part throttle/cruising area (when EGR is on). The stock ECU probably does this also so some testing would be needed .
For sure adding extra EGR will make the car less responsive and need more throttle (thats what you want, and if all goes right some extra MPG might happen) .
2x increase sounds a little extreme , I would start lower % and test, work your way up .

[EdKiefer]

Originally Posted by Leadfoot

EGR is shut off at WOT but then you have a preheated intake manifold stealing some initial power. I am not too concerned about this but at part throttle when the EGR is on there is less torque to lug the gears so downshifts happen sooner.

I am able to tweak the EGR flow through the ECU. There is also a parameter to advance timing with EGR flow which I did. However since this motor has no knock sensor I did not want to be overly ambitious.

Another thing to note:
During extended coasts the ECU enters "coasting fuel shut off" mode. I don't know if all the injectors are shut off or if fuel is just reduced but The EGR flow during this time is jurastically increased. The stock values had the ECU enter "C.F.S." after 15 seconds of coasting. I changed it to enter "C.F.S." after three seconds of coasting. One thing I really noticed was a huge increase in drive line drag to the point where you would slow down going down hill. To improve the driveability, I totally disabled coasting fuel shutoff.

2x EGR flow might be a bit excessive as a first step.

normally all injectors get shut down in 0 throttle coast modes . Seems like there using EGR to reduce pumping losses by enabling it there .

It will feel slower and you have to add more throttle to get same power but would have to see how it affects mpg .
To bad no knock sensor you could use that to monitor advanced timing conditions .

[Daox]

No new progress on this, nothing really planned for the immediate future either. However, I did stumble across some interesting info. Apparently Toyota is looking to use cooled EGR in combination with a long stroke engine design to drastically increase the thermal efficiency of their next generation of hybrid engines.

I find it very interesting that turbocharging plus lean burn give very little efficiency increase compared to EGR + long stroke.


Toyota targets 45% thermal efficiency for engines in next-gen hybrids - Autoblog Green

In early April, at the SAE 2011 High Efficiency IC Engines Symposium in Detroit, MI, Toyota's Koichi Nakata declared that the Japanese automaker is exploring ways to further reduce the fuel consumption of its upcoming hybrid models. According to Nakata, Toyota aims to develop a gasoline engine that operates at more than 45 percent thermal efficiency for use in future hybrid vehicles.

To put that number into perspective, the engine in the first- and second-generation Toyota Prius had a thermal efficiency of approximately 37 percent and the 1.8-liter mill in the third-gen Prius boasts a thermal efficiency of 38 percent.

Toyota is focusing on two concepts to reach its thermal efficiency goal. Concept 1 is a cooled EGR stoichiometric spark-ignited direct-injection engine that features a long stroke design. The long-stroke setup, according to Toyota, reduces heat loss, increases piston speed and creates more chamber turbulence, which improves combustion. Concept 2 is a turbocharged, lean-burning engine that incorporates the same basic design of Concept 1.

So far, Nakata claims that the engine development team has achieved a 42.4 percent thermal efficiency with Concept 1 and 43.7 percent thermal efficiency using the turbocharged, lean-burning Concept 2 design. Does this mean that a turbo'd Prius may be coming soon?

[ConnClark]

Originally Posted by Daox

I find it very interesting that turbocharging plus lean burn give very little efficiency increase compared to EGR + long stroke.

You need to keep in mind that it gets much much harder to get that extra 1% as you increase in efficiency.

The real gain is going with the direct injection.

I also wouldn't give the long stroke too much credit. Only when its paired with the direct injection that it gains you something due to the better turbulence. Otherwise the long stroke just increases the surface area for the combustion gases to loose heat/energy to the cooling system. Of course the cooled EGR compensates for that to some degree.

[cleanspeed1]

This all sounds like applying modern diesel technology to gasoline engines. Undersquare design, direct injection, cooled egr, etc.