Like an EGR valve??? It might lower egt's in a gasser to lower nox emissions, but not real sure how it works in a diesel. I know they use EGR's in newer diesels but dont know if it works the same way in gassers.

 

THE question was brought on by a quote a guy told me that diesels only burn about 30% of the fuel the rest goes out the exaust, ,,,,all righty then,,lets recirculate????

 

If thats the case, i bet some trucks more than 30% goes out the tail pipe lol. Just got to thinkin, an egr is mainly to lower combustion temps, dont think it would be benificial to actualy re-burn exhaust for power since such little exhaust would be recirculated. If you dump too much exhaust through it, it would smother its self and cause lower power and mpg's. I think anyways lol.

 

There is a reason the too-many-valvers with the schmancy new comp-ute-ters for them em-mission moters take the EGR off.

 

The EGR is used to artificially enrich the mixture. You could do it with fuel, but then your efficiency drops way off and EGT rises. By putting some exhaust back in, you enrich it by lowering the amount of oxygen in the cylinder.

In a gas motor it may help with economy, because you need X gas for Y oxygen, or you run the chance of burning valves. So you put some exhaust back into it to lower the amount of oxygen in the cylinder. In a diesel you don't burn valves because if it's too lean, it just won't run.

 

Ya, the diesel egrs get plugged up with soot I guess then trouble starts. Just one more gadget to mess up.

 

Yeah, my boss asked me about the newer Cummins, as he has a 96 and a 94 or 95, and wants to replace one next year. I told him that the 6 speed auto is supposed to be a lot tougher than the 4 speed, and if he gets one with EGR and DPF, spend the cash and get rid of them, and he'll have a good truck and not burn fuel as fast as the 470 Detroit in the freightshaker when pulling a gooseneck.

 

I think that DPF is what really kills the mpg's, literaly wasting fuel out the exhaust pipe lol.

(sorry to get off subject)

 

SORRY DIDN'T MEAN TO GET OFF THE IC POST . I'm having trouble understanding , the ic is to kool the engine for better mpg.,yet it seems some want the intake air hoter to help atomize the fuel, again sorry about the interuption.

 

The cooler the air at a given pressure, the more oxygen you get into the motor. That allows more fuel to be burned, making more power. Too much fuel for the amount of oxygen available makes for high EGT's, though, which melts things down because of the increased amount of heat that they absorb. The fuel is atomized inside the cylinder, by being injected under pressure.

In a carbeurator, the fuel being atomized sucks the heat out of the carb housing. So a warmer intake charge can be a benefit in cold weather, with a carb'd engine. Most other times, it's not.

 

BC, can you explain this further?

I understand that density increases across the intercooler, but why does this necessarily result in pressure drop? Density will increase with decrease in temperature, even at constant pressure. And while mass flow is constant, volume flow certainly isn't.

Perhaps I'll have to dig out my thermo book again...

 

Think of density as a highway. When the air is hot, the molecules (cars) are on a 4 lane highway, very separated. Now the highway goes from 4 lanes to 2 when the air gets cooled. Same amount of molecules, just tightly packed.

 

Hey scott, thanks.

 

Actually, temperature would relate more to the cars' speeds. The highway should be the same width, the cars' speeds change as does the spacing between cars. Pressure would be the frequency and energy of collisions between cars and the guardrails.

Density, mass per unit volume, or molar density, number of molecules per unit volume, is a function of pressure and temperature (molar density = P/RT). Mass flowing into the intercooler = mass flowing out. Mass flow is density times volumetric flow. If density increases, volumetric flow decreases to keep mass flow constant. The air definitely contracts/shrinks and increases density, but does that necessarily reduce the pressure or does the higher volumetric flow before the change in density "fill in" that pressure difference?

 

In a static setting I would say yes easily to the latter. With a running engine, I imagine the barometric differences between the cylinder and the turbo's outlet (the given circuit) would further compel it.

So say the voices in my head.

In my mind, with the OP's question about better MPGs. I keep going back to the thought that the infernal combustion engine works by expanding air with the addition of heat. To me, getting all the best quality of air in the engine should be a primary focus. The key words there are best quality air. Not just a lot of it.