Thermal Efficiency Discussion

[RobertISaar]

had some thoughts lately that have me coming back to this thread.

some more thoughts on a current topic: catalyzing the fuel before it gets oxidized: won't fuel constantly being in contact with the catalyst cause the issue of the catalyst "melting down" like it does in the cat converter?

and new thought: EGR does a lot more than what i had previously thought... we all know it's original purpose is to reduce NoX emissions and while it's nice and all to have cleaner air, i'm more curious about the other benefits it can have, specifically on fuel economy, since burning less fuel means there are less potential polutants to deal with. sometimes it can hurt emissions, but i'm curious to see some interesting results.

but here is where some recently new thoughts came in: EGR is literally using the vacuum of the engine to draw exhaust gasses out of the exhaust, which lowers exhaust backpressure. obviously, the amount of pressure reduced will depend on a lot of factors, such as orifice size, manifold vacuum, exhaust backpressure and probably some other small factors.

but, applying a vacuum to the exhaust SHOULD actually help the VE of the engine, since now it has to work less to push the exhaust gasses out of the head. and of course, the gasses flowing into the intake should also reduce pumping/throttling losses since now there is a higher manifold pressure present.



actually accounting for all of this in the calibration? not a lot of masks seem to do that. they appear to do a pretty simplified calculation. i'm curious to see how the "linear" EGR valves effect all of this, compared to the older EVRV or 3 tower digital setups.

[EagleMark]

Plus there is heat in the EGR entering intake cold charge, so how does that effect things?

[RobertISaar]

well, as we've seen, heat helps the vaporization of fuel, which if significant enough, CAN hurt VE due to expanding fuel vapor pushing air back into the plenum rather than sitting in the runner. it will also likely contain SOME unburned fuel.

a hotter mass also experiences less friction when it moves since it is less dense(so less molecules to scrub up against port walls and even other air molecules).

i haven't thought too much about it, but i think some of the OBD1 stuff does have a correction to the intake runner temp due to EGR being active. how complex GM's code engineers got here, i have no idea.



it would be interesting if the equivalent of the carbon cannister used for evaporative emissions could somehow be used in the exhaust to capture any unburned fuel and have it get sucked up through the EGR system. i'm not sure how much raw fuel could be collected though. i would think one would want to position a device immediately before the catalytic converter since the exhaust stream will be the coolest there(and most dense) before the cat uses the unburned fuel and does it's job as a catalyst.

[delcowizzid]

egr is meant to help by reducing pumping losses by lowering vacuam in the inlet ive played around a lot with egr and it doesnt really help at all for saving fuel mostly emissions.ive turboed a lot of non turbo cars and they get better MPG at cruise even without boost.the gain in torque at 100kpa is huge on turbo conversions but the whole cruise map is up in torque and you use less TPS to move the car at the same speed

[Fast355]

egr is meant to help by reducing pumping losses by lowering vacuam in the inlet ive played around a lot with egr and it doesnt really help at all for saving fuel mostly emissions.ive turboed a lot of non turbo cars and they get better MPG at cruise even without boost.the gain in torque at 100kpa is huge on turbo conversions but the whole cruise map is up in torque and you use less TPS to move the car at the same speed

I have had luck getting MPG gains by tuning the EGR to come on at specific times. From the factory the EGR is open during heavy loads at part-throttle and minimal EGR at low load cruising speeds. This is exactly opposite of what you need for fuel economy but works well to control NOx.

[34blazer]

I finally noticed MPG gains after removing the orifice washer on the gasket and turned up the DC 100%.

[RobertISaar]

perhaps i'm not used to EGR systems other than the 2 and 3 tower digi setup, but orifice washer on/in the gasket? as in, an attempt to reduce EGR flow?



also, the puttmaster(92 ranger 2.3/5 speed) has had a check engine lamp on forever, just never saw it due to the instrument cluster being of a crap design(it's a copper foil sandwhiched between two sheets of plastic, i soldered everything on it rather than it relying on friction, now it all works correctly), pulled codes on it and got an EGR position code and an O2 lean code. an O2 code i was expecting based on behavior when ambient temps drop and the ECM wants to drop into closed loop but goes so lean as to cause significant misfiring until foot is on the floor or idling. the EGR position code combined with the O2.... may explain why fuel economy has been less than expected. 27MPG in the summer is about 4-5MPG lower than what i was expecting based on what i see with the other vehicles.