- #1
GPracer2500
- 16
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I'm trying to learn about how differing distillation curves affect gasoline's performance. I'm coming at this from the perspective of a performance engine enthusiast who uses racing fuels. My research thus far indicates typical pump fuels have a 90% distillation temp in excess of 300 degrees F. 100LL avgas has a 90% figure of 262 deg F. Many racing fuels have a corresponding dist temp below 230 deg F.
In trying to understand how these values change the deflagration process of the fuel in an operating gasoline engine I realized I don't know exactly when fuel vaporizes within the engine. I suspect that some components of the fuel (lighter molecules) vaporize shortly after the carburetor atomizes the fuel and if begins to enter the hot engine. Heavier molecules may not vaporize until combustion has actually started--the heavy molecules need more heat to vaporize.
I understand that the heavy hydrocarbons vaporize at higher temps and the lighter hydrocarbons vaporize at lower temps? Is that right? Do fuels with more light hydrocarbons have faster flame speeds because they vaporize at lower temps (and therefore more quickly--not having to wait to be heated up)??
I found one engine builder who says this about fuel (in reference to the use of avgas):
"...Normal ground level race fuels are made up of gas molecules that have a "light end" and a "heavy end". The light end of the molecule ignites easily and burns quickly with a low temperature flame (as a piece of thin newspaper would burn). The heavy end of the molecule is not so easily ignited, but it burns with a much more intense heat (as an oak log would). This heavy end of the gasoline molecule is responsible for the hotter, more powerful part of the combustion process..."
Is that right? By light end and heavy end is he talking about heavy and light hydrocarbons? If he is, then why do many racing fuels have dist curves indicating far fewer heavy molecules that 100LL avgas?
Sorry for all the questions...I'll appreciate any insight into these matters you may be able to provide...
In trying to understand how these values change the deflagration process of the fuel in an operating gasoline engine I realized I don't know exactly when fuel vaporizes within the engine. I suspect that some components of the fuel (lighter molecules) vaporize shortly after the carburetor atomizes the fuel and if begins to enter the hot engine. Heavier molecules may not vaporize until combustion has actually started--the heavy molecules need more heat to vaporize.
I understand that the heavy hydrocarbons vaporize at higher temps and the lighter hydrocarbons vaporize at lower temps? Is that right? Do fuels with more light hydrocarbons have faster flame speeds because they vaporize at lower temps (and therefore more quickly--not having to wait to be heated up)??
I found one engine builder who says this about fuel (in reference to the use of avgas):
"...Normal ground level race fuels are made up of gas molecules that have a "light end" and a "heavy end". The light end of the molecule ignites easily and burns quickly with a low temperature flame (as a piece of thin newspaper would burn). The heavy end of the molecule is not so easily ignited, but it burns with a much more intense heat (as an oak log would). This heavy end of the gasoline molecule is responsible for the hotter, more powerful part of the combustion process..."
Is that right? By light end and heavy end is he talking about heavy and light hydrocarbons? If he is, then why do many racing fuels have dist curves indicating far fewer heavy molecules that 100LL avgas?
Sorry for all the questions...I'll appreciate any insight into these matters you may be able to provide...