What commercially available fuel, such as kerosene or diesel, has the least variation in different hydrocarbon chains and thus the most uniform boiling point? I ask this because I'm searching for a fuel to use in a rocket engine, but unrefined fuels such as regular petroleum, which have a lot of variation in its constituents, will start to coke the engine plumbing when exposed to high temperatures. I understand that most commercially available fuels will do this, but are there any fuels which at the very least minimize this.

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    $\begingroup$ If I understand your question, you are looking for a pure hydrocarbon. Pure substances can be characterized by your requirements : 1) most uniform boiling point, and 2) least variation in hydrocarbon chain. So any pure hydrocarbon will meet your requirement. $\endgroup$
    – Maurice
    Sep 2 '20 at 9:56
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    $\begingroup$ Doesn't even have to be a hydrocarbon. Just any pure liquid that's got high energy content. Hydrazine is a classic one. There is. however, a specific grade of refined kerosene called RP-1 that has a narrower bp and is intended for rockets, though the bp range is still not what you'd get with a pure compound. $\endgroup$
    – Andrew
    Sep 2 '20 at 11:13
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    $\begingroup$ Compulsory reference to Ignition: an informal history of liquid rocket propellants by John D Clark. On Amazon here. he specifically talks about special grades of kerosine with these properties. $\endgroup$
    – matt_black
    Sep 2 '20 at 13:08

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