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Most people know that when you add oil to a fire, it grows rapidly and becomes more powerful. So, why isn't added into the propellant just before it comes out of the engine?

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    $\begingroup$ When you add oil (or gasoline) to a fire it burns rapidly because of air. Rockets carry the oxidizer. The oxidizer to fuel ratio is very carefully controlled. Adding extra oil would destroy that ratio -- and would destroy the engine. $\endgroup$ May 5 at 12:16
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    $\begingroup$ @user47149 The oxidizer to fuel ratio in a rocket engine is rarely stoichiometric. Rocket engines usually run rich -- more fuel than the stoichiometric ratio would suggest. There have been multiple questions here regarding why rockets do not use oxidizer / fuel in a stoichiometric ratio. $\endgroup$ May 5 at 12:19
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    $\begingroup$ I am not sure whether you are questioning the use of "oil" (as implied by the title) or the potental to add oil " just before it comes out of the engine". Others have informed that RP!, one of the most common rocket fuels, is essential a refined crude oil. In the latter case, that would be to add fuel essentially as an afterburner. There is merit to the idea of a rocket afterburner. For information, aerojet general, has patented a rocket engine afterburner concept. contest.techbriefs.com/2013/entries/aerospace-and-defense/3364. Afterburner gave up to 77% more thrust. Tom Kosvic $\endgroup$
    – tckosvic
    May 5 at 13:09
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    $\begingroup$ Do you actually know how a rocket works? I'm not being jokey, it's just that what you describe is essentially the operation of a rocket, i.e. to mix a fuel with a concentrated oxygen source just before ignition. In fact, it's how just about any fuel based engine works, be it a jet or an internal combustion engine. $\endgroup$
    – GdD
    May 5 at 13:14
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    $\begingroup$ I’m voting to close this question because it is based on a false premise and shows a lack of research. $\endgroup$ May 5 at 16:50

2 Answers 2

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Because 'oil' is basically what most rockets already use for fuel.

To be a useful fuel you want a high energy density so your rocket is not lifting 'stuff' that does not burn, ideally both in terms of volume and mass (light fuel weight AND low tank weight). In the middle of this table from the Wikipedia page enter image description here

you see most of the things we think of as 'oil' in the middle with a trend for less useful densities going for longer (oiler?) chains with Kerosene, pretty close to the canonical rocket fuel as RP1 bang in the middle.

Natural Gas and Hydrogen are 'better' but depend on very good tank design to not end up with big and/or massive tanks eating the performance advantage.

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Oil, whether vegetable or petroleum based, does not burn nearly as cleanly as other types of fuel used for rockets. One of the types of rocket fuel are those based on hydrazine and its derivatives; these types of fuel do not contain any carbon chains, and thus easily and cleanly burn completely to volatile products. Meanwhile, oil is composed of compounds which contain relatively long carbon chains (about 12 atoms). In circumstances where such fuel cannot be burnt completely, like during the engine shutdown, it could polymerize or carbonize, leaving non-volatile deposits which build up in the engine and the nozzle, and rockets are extremely sensitive to such contamination.

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    $\begingroup$ Hydrazines are just one group of fuels. There's also RP-1 and friends (which is refined oil), as well as Hydrogene and Methane, for example. $\endgroup$
    – DarkDust
    May 5 at 11:55
  • $\begingroup$ Dimethylhydrazine has as much carbon as nitrogen, and only a couple rockets still use hydrazine fuel. The most common booster fuel is RP-1, which is a highly refined grade of kerosene...in other words, "oil". $\endgroup$ May 5 at 11:58
  • $\begingroup$ @DarkDust Nowhere does my answer contradict any facts mentioned in your comment. RP-1 is oil-based and suffers from the disadvantaged mentioned in my answer. $\endgroup$
    – user47149
    May 5 at 12:01
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    $\begingroup$ In an earlier version your answer had "Common types of rocket fuel are based on hydrazine and its derivatives" which suggests other fuels are rare, which is not the case. That's what my comment was about. $\endgroup$
    – DarkDust
    May 5 at 13:39

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