Ford Trucks to Get 62 MPG?

[slowzuki]

Egon I like how you made a statement in the form of a question! Why yes, yes compression matters in a way.

The efficiency is a function of the mean effective pressure delivered to the piston face for a given amount of fuel.

You can raise this by compression ratio, turbo/supercharging, injection strategies, timing advance etc etc but the main problems are:

-high pressure requires high temperature as per ideal gas law.
-high temps melt pistons, erode ceramic coatings, change nice tight clearances in the engine parts
-high temps make lots of NOx pollution.

So regardless of what some people in this thread think, you can't just magically increase the efficiency because that means hotter combustion at higher temps.

I've discounted the throttling/pumping loses because they are minimal in modern engines and certainly not a key factor. Only a problem for people looking for high hp.

 

[slowzuki]

The old lead added Sunocco super grades with high octane levels where the only way old muscle cars could get their engines to run at 10:1 when everything else could only get to 8 to 1 or so. High octane gasoline resists ignition.

High compression ratios lead to knock which is basically an explosion in the cylinder. Normal combustion is a uniform process starting at the spark plug and the flame front burning and spreading through the cylinder volume via the turbulence in the cylinder. This gives a nice smooth pressure increase.

OK, if high compression is good one would think the gasoline from the olden days may not be as good as todays gasoline?

 

[Egon]

Egon I like how you made a statement in the form of a question!/QUOTE]

But it's nice to get a competent explanation.:thumbsup:

 

[Renze]

What we today know as a turbocharger, was described by Rudolf Diesel in his patent in an abstract manner: "the compression may also be done in two stages" what he effectively was describing is turbocharging.
The turbocharger compresses, then it enters the actual engine where it is compressed to ignition conditions. These both compression actions require energy.
Then ignition stroke, which is decompression while converting energy into motion. Then the gases are still under the compression: with a turbocharger, this last bit of energy is regained by the exhaust turbine.
In a supercharger, the energy which the supercharger put in, is released at once when the exhaust valve opens at bottom dead point of the piston stroke.This very same thing happens when using an exhaust brake: energy is put into compressing air, but this energy is converted into heat and let loose into the exhaust.