Power and mileage 1

[1]

Hi,<br>
I am a mech eng. stud..I was wondering about what sort of relation existsbetween power and mileage and how do we get both the benefits from 1 engine<br>
Could anyone possibly help me out<br>

 

I don't know exactly how this forum works, I'm just trying to find my way around. I know a little about natural gas as a fuel. Heating value of that fuel should relate to mileage. I would think that octane rating would be analagous in the gase of gasoline.

 

[shortee]

This has always been an engine design issue. One of the things I've always liked about diesel engines is that there is no intake manifold vacuum holding them back. Just about any size diesel engine consumes the same amount of fuel for the same power out. That's one of the reasons a diesel engine gets the same or better fuel economy in the city. In the generator business, the simalarly designed engines of different sizes have nearly identical G/kW (Gallons per kilowatt) ratings.<br>
<br>
Gas engines are theoretically the most efficient at full throttle. At full throttle there is little or no vacuum holding them back. All of the power goes out the crankshaft. This is why a small gas engine at full throttle will always have better economy than a big engine at half or quarter throttle.<br>
<br>
There is other power dissipation at bearings, cylinders and assesories, but I believe this is negligible compared to the vacuum affect.

 

How does a modern fuel injection engine analyze fuel quality (including combustion air). Does the amount metered depend on quality?

 

[shortee]

modern fuel injection engines do not analyze fuel quality... In fact all they analyze is the combustion result for oxygen content. When a factory new engine is turned on, it has a best

 

[Nigel]

Just a note for rethand.&nbsp;&nbsp;The octane rating of a fuel, in this case gasoline has nothing to do with calorific values, or as you put it the heating value.&nbsp;&nbsp;The octane rating of a fuel is also known as it's anti-knock value.&nbsp;&nbsp;It is a messure of the fuels resistance to detonation under high pressure.&nbsp;&nbsp;This is why you need high octain fuels in high performance engines.&nbsp;&nbsp;The pressures (and therefore temps) in the cylinders are so high that regular low octain fuel would detonate before the spark, causing knocking, loss of power and possible engine damage.<br><br>The octane rating of a fuel is derived from a test engine running on a mix of isoheptane and isooctain.&nbsp;&nbsp;Isoheptane will detonate as soon as you look at it!&nbsp;&nbsp;Isooctain is added untill the engine runs without detonation.&nbsp;&nbsp;A gasoline with the same anti knock qualities is given the octain rating with is the ratio of isoheptane and isooctain of the comparison test fuel.<br><br>For your information... <p>Nigel Waterhouse<br><a href=mailto:n_a_waterhouse@hotmail.com>n_a_waterhouse@hotmail.com</a><br><a href= > </a><br>A licensed aircraft mechanic and graduate engineer. Attended university in England and graduated in 1996. Currenty,living in British Columbia,Canada, working as a design engineer responsible for aircraft mods and STC's.

 

[surge]

Calarific value of gasoline = Q <br>Average consumption = m<br>Engine thermal efficiency = Te<br>Engine Mechanical Efficiency = Tm<br><br>Power available at the transmission = Q.m.Te.Tm<br><br>Transmission efficiency = Tt<br>Distance traveled to burn m mass of gasoline = d<br>Average mass of the car + Passengers = M<br><br>On a flat road energy required = M.d = Q.m.Te.Tm.Tt<br>Therefore m = (M.d)/Q.Te.Tm.Tt<br>