Thermal Efficiency Discussion

[1project2many]

They're typically used after combustion, yes. But that's not the only place they work. All the converter is doing is "burning" unused fuel... reacting oxygen with hydrocarbons and carbon monoxide. And really, if you think about it, what are hydrocarbons? They're just unburned fuel. The catalytic converter actually decreases the total fuel efficiency of our vehicle by making even more heat while burning the last of the fuel we didn't use in the engine. It's always seemed like such a huge waste to me. One way to save that heat, though. Put a turbo on the end of the cat. The exhaust can be thousands of degrees leaving the converter... why not use it? I actually think that's how some of the remote turbos are able to function so well. In the old days, pre converters, it seemed well proven that the turbo didn't work well that far away from an engine.

[Fast355]

Easiest way to help thermal efficiency at part-throttle cruising is to heat the incoming air/fuel mixture. I saw 1-2 mpg increase by simply using a solenoid off my EBL ecm to operate the vacuum operated switching valve on the front of the air cleaner on my 83 G20 with the TBI swap. I saw IAT readings of 160-170*F cruising down the highway and MAT temps (open cage sensor in vacuum fitting) of 130-140*F. Unheated on a 100*F day, I saw 120-130*F IAT and 70-80*F MAT readings. Heating the intake air really helped me with being able to lean the engine out in lean cruise and keep it running smoothly.

[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.

[34blazer]

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?

Im assuming that was the intention of the orifice in the gasket, this is on the Fiero BTW.

Now that im thinking about it, there is also an orifice gasket on my mustang(5.slow).

[ericjon262]

we all know the fuel vapor is what's really powerful, so here's an idea, draw a vacuum on a fuel canister to lower the saturation temperature, and heat it up a bit, much like how a distilling unit would boil water, the trick will be getting the vaporized fuel delivered to the engine, because when you pressurize it, saturation temperature will raise, and you'll be back to a liquid. how about a carburetor? (please don't shoot me yet!) a venturi could easily deliver the vapor at a low pressure so that you don't have to worry about raising saturation pressure.

want to stick with fuel injection?

how about heating the pressurized fuel in the lines, where the pressure keeps the saturation temperature very high, that way when the fuel goes from the high pressure injector to the low pressure atmosphere, and saturation temperature drops, the fuel requires less latent heat to be absorbed from the atmosphere to flash to vapor.

the big thing though, will be to use exhaust heat to heat the fuel, much like an economizer in a steam plant. that way the heat is doing useful work, not just going off into atmosphere. the only real problem I see there, is the exhaust might be too hot to use for the heat source. if you used a turbo, the turbo compressor outlet would probably be a better heat source as it's not silly hot, and some of the heat is being used by the turbine blades to do useful work. but then you're also lowering air charge temps by effectively creating an air/fuel intercooler.

problems:

electronics don't like heat, how long will fuel injectors last with 250F fuel running through them? do we need to add a heat sink and liquid cooling to keep them happy?

the biggest problem I see is oil, most oil doesn't like being hot. roller bearings would reduce oil requirements, but add more complexity, and more points of failure.

Safety: will the hot fuel sit an the rail safely without problems when the engine is shut down?

[pmkls1]

I just noticed this thread so I read through the posts to get caught up. I definitely have a lot to add, but I don't have the time right this minute. I just wanted to say that as soon as I have a minute (or more like an hour lol) to put together a response I'll add a little bit of info to the thread and address some of the ideas that I have seen some experimentation with.

[RobertISaar]

i've seen the heated fuel idea work before on a carb.... the biggest issue i've seen with it is that due to the fuel being at such a wide range of temperatures, the density of the fuel changes enough to cause some interesting effects on the actual AFR.

at least with fuel injection, we could track fuel temp and get the fueling back in-line after some trial/error.

oil..... i don't think this would introduce that much more heat into the oil?

hot fuel that isn't moving would likely vaporize at the pressures a MPFI system runs at..... i imagine the simple solution behind that would be either a microcontroller that turns the fuel pump on and runs it for a few seconds at a time and repeats that a few times(either a set number of times or until fuel temp drops below x *F) or perhaps going really simple and setting up some 555 timers to just run it for a while after the ignition is off.

[ericjon262]

i've seen the heated fuel idea work before on a carb.... the biggest issue i've seen with it is that due to the fuel being at such a wide range of temperatures, the density of the fuel changes enough to cause some interesting effects on the actual AFR.

at least with fuel injection, we could track fuel temp and get the fueling back in-line after some trial/error.

oil..... i don't think this would introduce that much more heat into the oil?

hot fuel that isn't moving would likely vaporize at the pressures a MPFI system runs at..... i imagine the simple solution behind that would be either a microcontroller that turns the fuel pump on and runs it for a few seconds at a time and repeats that a few times(either a set number of times or until fuel temp drops below x *F) or perhaps going really simple and setting up some 555 timers to just run it for a while after the ignition is off.

I was meaning that if the engine were running hot (to reduce heat losses) oil would take a beating.

IIRC, the Smokey Yunick Fiero didn't have a cooling system at all, just an oil cooler.

I see a small problem with the microcontroller idea, if you send the more or less superheated fuel back to the low pressure tank, it'll flash to vapor, you'd need to bring the temp back down to a more reasonable level before sending it back to the tank. A check valve could hold the pressure on the rail, but would the fuel start breaking down in the rail?

the thing I like best about the idea of doing an adiabatic engine fuel injected, is that you can make it idle until it's hot. whereas a carb you have way less control.

additional sensors I would think are necessary on top of the usual compliment:

fuel pressure sensor
fuel temperature sensor
fuel composition sensor
wide band a/f
MAT instead of IAT

egt probe may prove useful as well.

another "problem" gasoline is a mix of several different petroleum distillates, which will all vaporize at different temperatures and pressures, but this is easy enough to overcome by cranking the fuel pressure higher, thus raising the saturation temp of the lowest distillate higher then the fuel temp. which would improve total vaporization as a plus. Now for the next bit of science fun we would have to look at, what pressures will be necessary to prevent the vaporization at the higher temps?

then, there's the valves and valve seats, I see the heat being a bit of a bear on them, I'm sure there's some exotic material we could use.

damnit! you guys are making me want to start another project!

[gregs78cam]

The easiest way is just like Smokey did heat the fuel and air in the intake tract, and heat it to a temp where all of the different distillates have vaporized, then mix the them REALLY well with a rotary vane type of compressor to also act as a check valve. And using TBI would still give a much more precise control as opposed to carb'ed, especially during warm-up.