Thread: Engine Braking
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Old 10-02-2012, 08:18 AM   #7 (permalink)
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13% of all the fuel used is wasted in idling engines in the US vehicle fleet.

Manifold restrictions in gasoline engines restrict the flow of air into the cylinders. The lower mass of air means lower compression in the cylinder which means much less power produced for the same amount of fuel consumed. This is because higher compression is a better "lever" to produce power. An engine produces power by compressing air and fuel then igniting the fuel, which expands the combustive mixture which produces pressure to push the piston and make power. If you reduce the in cylinder compression then you have much less power produced.

As was previously posted, in this thread, a diesel always has maximum compression. The diesel can run at air fuel mixtures as high as 50 to 1, so it will idle while using much less fuel than a gasoline engine becasue it can run at much leaner mixtures than a gas engine.

P&G utilises the peak BSFC of any engine by reducing to a minimum any partial compression operation. In a diesel P&G utilises the highest range of efficiency of that particular engine.

The most efficient hypermiler will eliminate all idling and acceleration will always be at peak efficiency. Measured by fuel consumption this means you are producing much more motive power for the same amount of fuel consumed.

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