Energy in chemical rocket fuels compared to car fuels

  • Thread starter JT Blue
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  • #1
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Summary:
I want to know they compare to each other.
I am no expert, so forgive me if I sound rather ignorant, but I'm curious about this: are typical automobile fuels like gasoline, diesel and ethanol more energetic than, specifically, *chemical* rocket fuels [like perhaps the types used in missiles, space-bound rockets and such] if measured by volume? And how much more so? I'm not talking about theoretical devices or ones still in the testing phase, but rockets that are actually already commonly built and used frequently in their fields of technology [be it space-related, military, model rocketry of whatever] - how does the volume taken up by their chemical fuels, including the oxidizer [be they liquid, solid or hybrid] compare to common automobile fuels? How much more or less energy do they have?
 

Answers and Replies

  • #3
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I unfortunately do not know enough about the subject to tell which of those listed at wikipedia are rocket fuels, and I don't know if they are listing the rocket fuels specifically, or the fuel combined with the oxdidizer.
 
  • #4
berkeman
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I unfortunately do not know enough about the subject to tell which of those listed at wikipedia are rocket fuels, and I don't know if they are listing the rocket fuels specifically, or the fuel combined with the oxdidizer.
Just compare Hydrogen to Gasoline in that table. What is the approximate ratio in the first column? :smile:
 
  • #5
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Ummm, berkman...yer' spozeda' gimme an a, b, c, or d list of answers. My answers gonna c, of course: 😅
 
  • #6
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I unfortunately do not know enough about the subject to tell which of those listed at wikipedia are rocket fuels, and I don't know if they are listing the rocket fuels specifically, or the fuel combined with the oxdidizer.
It says "not counting oxidizer mass or volume " at the top of the graph. This

You'll want
https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Bipropellants
to compare rocket fuels and oxidizers. You need to Look at the Ve column. (exhaust velocity).
The density can be important too. Liquid hydrogen has a low density, so RP-1 (kerosine) is often uses in first stages, because the fuel tanks would get very large when using hydrogen, so that isn't much better in practice.
 
  • #7
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are typical automobile fuels like gasoline, diesel and ethanol more energetic than, specifically, *chemical* rocket fuels [like perhaps the types used in missiles, space-bound rockets and such] if measured by volume?

No. The Saturn V used kerosene and liquid oxygen. Kerosene is quite similar to the fuels usually used for cars. But as cars are using gaseous oxygen the energetic densinty including the oxidiser is much higher in case of rockets.
 
  • #8
phinds
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@JT Blue just think about your question this way for a second: if car gasoline WERE more fuel efficient than what is used it rockets, why wouldn't they just USE gasoline?
 
  • #9
Drakkith
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@JT Blue just think about your question this way for a second: if car gasoline WERE more fuel efficient than what is used it rockets, why wouldn't they just USE gasoline?

Gasoline has a greater energy density than kerosene (46.4 vs 43.28 MJ/kg) according to my sources. The reason it isn't used much is because it has a far greater tendency to clog up the injectors and plumbing, is much more *volatile than RP-1, which is the highly refined form of kerosene that is used as a rocket fuel, and gasoline typically has more contaminants than RP-1.

Basically, gasoline offers practically no advantages over RP-1 except a very slight increase in energy density, which isn't enough to offset the other factors I've mentioned.

*volatile as in a measure of the tendency of a substance to vaporize.
 
  • #10
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Anyone interested in the chemistry of rocket fuels should read "Ignition - An Informal History of Liquid Rocket Propellants" bu John Clark. It is finally back in print again but is also still available as a free PDF. It covers the development of liquid rocket propellants and some of the science behind it from the start up until the early 70s. Not that much have happened since except for the recent development of green mono-propellants.
 
  • #11
Drakkith
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Anyone interested in the chemistry of rocket fuels should read "Ignition - An Informal History of Liquid Rocket Propellants" bu John Clark.

Yes, I have that book msyself. Very interesting read. Especially about all the things that they blew up during testing!
 

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