Re: Bioethanol water mix (e.g. overproof Rum or vodka e.g. Stroh 80) as an engine fuel?

Paul Ryan wrote:


Robert Reynolds wrote:


Paul Ryan wrote:

Well, I'm a Bonanza pilot, and mixture does affect CHT, but no, it doesn't control it. The speed you're going, the position of the cowl flaps, and power setting - throttle position all have as much or more effect on CHT than mixture.


Sorry for the misunderstanding, but this appears to be one of those discussions where one person makes a true statement, and then another person claims that there are other more important factors even though that's not what the original conversation was about.

Considering airplanes in general, a lot of factors affect cylinder head temperature. Considering the function of fuel in a piston engine, at least half of the fuel is used for cooling. Use something else to cool the engine and you can avoid throwing the wasted fuel out the exhaust pipe. Then we could save the money we spend now on catalytic converters.



The original statement was that mixture controls cylinder head temp, and that is not true.... and neither is it true that half the fuel is used for cooling... (?) What gives you that idea?
You're an engineer, right? you should easily understand this. In thermodynamic terms-
The function of gasoline in an internal combustion engine is to provide a nearly instantaneous increase of temperature to the gases compressed in the cylinder, hence an increase in pressure in the cyl. With gas you also get about 26% more volume combustion product gasesthan you started with. Work is done as this pushes the piston down. The more heat the better.
That heat is exactly what gives you power.
[Glow engines generate much more volume of combustion product gases since they carry some of their own oxygen, and a lot less heat.]
You want to avoid operation right at peak EGT because the ideal mixture (stochiometric) tends to erode the exhaust valve surfaces. Operation either on the lean or rich side of peak is okay, just not at peak EGT. Most people prefer to operate on the rich side since the power drops off much more gradually on this side.
Incomplete combustion is another issue, and is usually due to either misfiring or an excessively rich mixture...
Personally, I prefer to use the cooling system to cool the engine... yeah, it has its limits, like I said in my last post, but within these limits, it does a pretty good job; it also doesn't cost $5 a gallon.
-Paul

Inlet charge cooling happens, which does cool the inflow to the cylinder. Adiabatic expansion also removes heat, and is roughly how that heat is converted to work. The rest goes out the exhaust, and may indeed add a few pounds of thrust as it does so.

I guess you can say that its the fuel air burn mixture that is responsible for cooling the thing, as thats what comes out hot. OTOH its the fuel air mixture that generates the heat too.

The difference is accounted for by the work produced, and the cooling system the engine employs.

Which probably just shows how dangerous a little knowledge is.




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