Temperature affects fuel economy-how much?
Ridiculously Active Enthusiast
Joined: Aug 2006
Posts: 859
From: Waterloo, ON
Re: Temperature affects fuel economy-how much?
gpsman1 — Those energy numbers you quoted from Wikipedia are confusing (to me at least), because they are per fuel-air ratio. That is, thay are the equivalent numbers obtained by dividing the actual energy numbers by the fuel-air ratio used. For gasoline, for example, the fuel-air ratio is around 15, and the gasoline number you quoted would need to be multiplied by that ratio to obtain the (to my mind) more meaningful and more commonly quoted energy numbers for gasoline:
43.8 MJ/kg = 32 MJ/L = 121 MJ/gal US = 115 000 BTU/gal US
[gasoline has a density of ~730 g/L; 1 BTU = 1.055 kJ; 1 gal US = 3.79 L].
Stan
43.8 MJ/kg = 32 MJ/L = 121 MJ/gal US = 115 000 BTU/gal US
[gasoline has a density of ~730 g/L; 1 BTU = 1.055 kJ; 1 gal US = 3.79 L].
Stan
Joined: May 2005
Posts: 2,468
From: Jupiter, FL
Re: Temperature affects fuel economy-how much?
Ok, what if I said it doesnt matter what temp the air is coming into the motor. 
The Atkinson motor has a two stage compression cycle, the first stage is a low compression, the 2nd stage is a high compression, after the first stage the air has probably already warmed well above the engines ambient temperature. Then as the 2nd stage compresses the air probably reaches what 1000 degrees before ignition? This really makes the temperature of the air not matter. Its all about the flow.
Just something else to consider.
http://peswiki.com/index.php/Directory:Atkinson-Cycle_Rotary_Engine:Libralato
_Ruggero
The Atkinson motor has a two stage compression cycle, the first stage is a low compression, the 2nd stage is a high compression, after the first stage the air has probably already warmed well above the engines ambient temperature. Then as the 2nd stage compresses the air probably reaches what 1000 degrees before ignition? This really makes the temperature of the air not matter. Its all about the flow. Just something else to consider.
http://peswiki.com/index.php/Directory:Atkinson-Cycle_Rotary_Engine:Libralato
_Ruggero
Pat, I really don't understand what your saying here. The Atkinson we have is not a rotary engine. On the compression stroke, the intake valve stays open for a short bit which allows some fuel mixture back in the intake manifold. This reduces the final compression ratio for combustion. This does allow a small portion of warmer mixture to blend with the colder air before combustion again.
As far as the gas your using, looks like your best choice is 87 octane and if you can only get it with ethanol, that has to be it. If I could get gas without ethanol, I'd do it. I'm lucky here in South Florida as I get straight 87 octane year round. I have gotten Citgo gas with ethanol by mistake and it cause a 5mpg drop in MPG for about 1500 miles. After you use 10% ethanol for a while, your fuel maps will adjust to it and your mileage should improve though.
GaryG
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