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Discussion Starter #1
First, gasoline is a mix of the first 20, more or less, alkanes, some alkenes and alkynes but mostly alkanes. each one of them is going to have, at a given temperature, a pressure and for the lightest compounds (methane, ethane) that's one atmosphere or more at room temperature. Liquids will evaporate until the partial pressure of the vapor above the liquid equals the vapor pressure of the compound in liquid form. That is, if methane has a vapor pressure of 1 atm at, oh, 22C, then that gas will just keep evaporting until the air above the liquid is 100% methane (assuming that gas is at 1atm pressure). Likewise, if ethane has a vp of 0.5 atm at 22C, it will evaporate until the air above that liquid is 50% ethane.

And then it gets tricky. Because we're talking about multiple components of the gasoline evaporating into the air above the liquid gasoline, the lightest components, the most volatile, cannot ever really comprise 100% of the gas above the liquid. there will always be something else (slightly heavier components). But, I'm not sure you really need to consider this part because I'd probably leave the answer like this:

at temperatures above the boiling point for methane, all the methane will eventually evaporate from solution to displace any air in the atmosphere. At higher temperatures, heavier components will follow (only above the bp of c20-anes will that last component evaporate but that's probably pretty high). In essence, there will be saturation of air at any temperature above bp of CH4. Below that temperature the vapor pressure of "gasoline" components in the air will drop off.

Diesel and Jet fuels are heavier so the starting molecular weight of the alkanes might be about octane or nonane - and the computation is the same. Below the bp of octane, you'll have a mix of air and octane (octane is C8H18), above that temperature you can pretty much saturate whatever volume of air you have.

Thanks for letting me play with some of that chemistry.

Edit: everything evaporates at or above the bp of the heaviest component. For gasoline that might be C20-ane - and that would be...hard to guess without a good CRC. Okay, here, check wikipedia, they have a good article on alkanes and it has a graph of mp/bp of alkanes up to 14 (only)...the bp line looks quadratic so you could fit a curve or eyeball it. Bear in mind too, the composition of gasoline is approximate and I only have that statement ("the first 20 alkanes") because somebody told me that's what it is - they neve gave me a real spec, nor the equivalent spec on diesel. Just eyeballing it, it looks like at about 300C all the first 20 alkanes would be vaporized at 1atm.

http://www.hotrod.com/techarticles/engine/hrdp_1009_what_ever_happened_to_smokeys_hot_vapor_engine/viewall.html

250 hp from 1984 2.5 litre carb engine that was only good for 130 hp stock, this guy heated up the air to 400 to 450 and got double horsepower and double MPG...this is crazy stuff, but I found it is very true. The big oil companies shut him down so we don't have the tech today/.
 

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Discussion Starter #6
A warm air intake or WAI is a system to decrease the amount of the air going into a car for the purpose of increasing the fuel economy of the internal-combustion engine. This term may also be used to describe a short ram air intake, a totally different intake modification.
All warm air intakes operate on the principle of decreasing the amount of oxygen available for combustion with fuel. Warm air from inside the engine bay is used opposed to air taken from the generally more restrictive stock intake. Warmer air is less dense, and thus contains less oxygen to burn fuel in. The car's ECU compensates by opening the throttle wider to admit more air. This, in turn, decreases the resistance the engine must overcome to suck air in. The net effect is for the engine to intake the same amount of oxygen (and thus burn the same amount of fuel, producing the same power) but with less friction losses, allowing for a gain in fuel economy, at the expense of top-end power.
Opposite principle of a cold air intake (CAI) which significantly differs by collecting air from a colder source outside of the engine.
In the extreme, a warm air intake can eliminate the need for a conventional throttle and thus eliminate throttle losses
throttleless premixed-charge engines
Since the TPCE concept requires the use of lean mixtures and preheating of the intake air, TPCE engines are in general limited by lean-limit fuel performance and engine knock (sometimes called “autoignition,” “detonation” or “pinging”) which is more prevalent at elevated intake temperatures [2]. For these reasons conventional fuels such as gasoline, which have relatively poor lean-limit performance and knock characteristics, do not perform well in TPCE engines [1]. However, by using natural gas fuel, which has excellent lean-limit performance and anti-knock properties even at elevated temperatures, the required range of torque adjustment was demonstrated [1]. Somewhat unexpectedly, lean mixtures exhibited excellent resistance to engine knock compared to stoichiometric mixtures. This is significant because the intake charge preheating used in the TPCE concept might have worsened knock problems, but for lean mixtures our research has shown that this is not the case. An important implication of these results is that optimal fuels for TPCE engines may be different from those of conventional stoichiometric-burning throttled engines.

http://carambola.usc.edu/Research/TPCE/TPCE.html

http://ronney.usc.edu/Research/TPCE/JAEThrottlelessEngine.pdf
 
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