Chatter on Gasoline as a rocket fuel

[MrZayas1]

Okay, so I know that it is not a widespread topic, maybe it has been beaten to death on these forums, and I don't know anything, but what are the reasons why we don't use gasoline as a rocket fuel? If you can elaborate that is nice. Maybe the MJ/L isn't as high as some other fuels or some other reason, but I think that it is somewhere upon those lines. Also, Gasoline is probably pretty dense for a rocket fuel. Again, not sure, but if you could clear that up for me, I would appreciate it.

[Ethanadams]

diesel can work not sure about gasoline

[Kryten]

With the kind of temperatures you get in a rocket engine, various components in standard gasoline will polymerise together. Polymerise partially blocks fuel channels used for cooling, blockage leads to further heating, heating leads to further polymerisation-the end result is destruction of the engine. Hydrocarbon rockets make use of highly refined fuel blends, with compounds that promote polymerisation removed.

[Sillychris]

Gasoline burns slowly, which is why we use it in conventional engines. A slowly expanding fireball that the steel container can survive.

[magnemoe]

With the kind of temperatures you get in a rocket engine, various components in standard gasoline will polymerise together. Polymerise partially blocks fuel channels used for cooling, blockage leads to further heating, heating leads to further polymerisation-the end result is destruction of the engine. Hydrocarbon rockets make use of highly refined fuel blends, with compounds that promote polymerisation removed.

This sounds more like an jet engine issue than rocket engine issue I doubt you get much build up in the engine bell, however the turbopump is an jet engine.

On the other hand rocket engines are fussy with the mix of various compounds in kerosene so they have RP1 who have an more exact mix.

[Kryten]

That's the thing, you don't need much build up to destroy a rocket engine. It's a very sensitive system.

[Iskierka]

Gasoline burns slowly, which is why we use it in conventional engines. A slowly expanding fireball that the steel container can survive.

Gasoline/petrol actually detonates near-instantly in regular engines, diesel is the one that burns and expands. RP-1 is actually extremely similar to petrol, as is Jet A1 and its local variations - but all of them are, as mentioned, extremely refined to remove some problematic compounds that will tend to gunk up in these engines. Rockets are actually the more sensitive to this issue though, as they use their fuel for cooling where jet engines do not - fuel's first interaction with significant heat and air in a jet engine is combustion, and modern engines consistently have near-total combustion leaving very little residue. Jets can, entirely feasibly, run on petrol, and quite often will be demonstrated doing so - rockets are too sensitive to risk to a problematic fuel, and so performance-driven that you'd rather have something you can be absolutely sure of the performance and behaviour of.

[zxczxczbfg]

Hypothetically you could make a liquid-fueled rocket fueled by gasoline. But with all the malarkey about greenhouse emissions, you're MUCH better off with hydrogen; it's more practical, doesn't generate (significant) greenhouse gases, and is astronomically more common (literally).

Edited April 27, 2015 by zxczxczbfg

[Bill Phil]

Isn't gasoline defined as a mixture of many hydrocarbons? So if you want to refine it you get many different ones.

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Hypothetically you could make a liquid-fueled rocket fueled by gasoline. But with all the malarkey about greenhouse emissions, you're MUCH better off with hydrogen; it's more practical, doesn't generate greenhouse gases, and is astronomically more common (literally).

H2O is a greenhouse gas. But there's already so much of it in the atmosphere it hardly matters.

[PB666]

The reason gasoline is not used is that it has a rather high level of aromatics, the stabilization energy of aromatics takes away from the final energy released from the chemical reaction. In addition these compounds have a high carbon to hydrogen ratio, which takes away from the bond energy/gram of fuel. Its not much worse the kerosene, but still.

[mrfox]

Specific energy (MJ/kg)

Kerosene 46

Gasoline (petrol) 44.4

Energy density (MJ/L)

Kerosene 37.4

Gasoline (petrol) 32.4

Its inferior to RP1 on both counts of weight and volume.

Edited March 18, 2015 by mrfox

[kerbiloid]

Robert Goddard was testing such rockets in 1920-30s, also Soviet engineers in 1930s.

[Drunken Hobo]

Hypothetically you could make a liquid-fueled rocket fueled by gasoline. But with all the malarkey about greenhouse emissions, you're MUCH better off with hydrogen; it's more practical, doesn't generate greenhouse gases, and is astronomically more common (literally).

You've got to get the hydrogen from somewhere, and at present that's either electrolysis of water or cracking methane. Both of which are energy-intensive processes, so unless you're on 100% nuclear or renewables, then you're pumping out CO₂. The most common method of cracking methane also releases carbon dioxide. So in terms of being environmentally friendly, hydrogen is pretty rubbish.

[Acemcbean]

Using Gasoline in a rocket would be similar to buying Sushi from a Gas Station. Yeah, you could PROBABLY do it, but you should probably be getting your Sushi elsewhere.

[henryrasia]

On a different note, if I were to construct a rocket, what fuel should I choose? Sugar and KNO3 is pretty common suggestion on the internet, but what other could work? Or even be better?

And unrelated to space: what fuel should I use if I want to build a functional internal combustion engine? I've seen gasoline, methane, and even steam. Any suggestions?

Edited March 22, 2015 by henryrasia

[Ethanadams]

Gunpowder

[miracmert]

AFAIK, gasoline has difficulty burning completely into H20 and CO2 thus giving less energy then kerosene. And there are probably operating difficulties of gasoline since it has much lower boiling point (difficult to stabilize I suppose). But looking at density and CO2 emmission, kerosene looks like a heavy and polluting option. But, again, it gives much more energy and contains less impurities, gasoline is less efficient compared to kerosene. Some smart guy correct me if I'm wrong But also I should add that even though kerosene gives a lot energy I don't think it's very efficient too. Liquid hydrogen is environment friendly when burned with pure oxygen and gives a lot more energy per kg. liquified propane would be a nice choice too if it wasn't too unstable for a rocket engine. But I also think maybe they should give a try to ethanol for more lightweight rockets:)

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On a different note, if I were to construct a rocket, what fuel should I choose? Sugar and KNO3 is pretty common suggestion on the internet, but what other could work? Or even be better?

And unrelated to space: what fuel should I use if I want to build a functional internal combustion engine? I've seen gasoline, methane, and even steam. Any suggestions?

I think gas fuel for ground vehicles are dangerous no matter how safe the system is. If you are living in a country where gasoline price is very high like I do, I would say ethanol is good choice