Again, many different chemicals have been proposed, investigated, and tested. Only a few have been used in production rocket engines. Liquid fuels other than those listed below have been used in experimental rocket engines, in older experimental designs, and in some older production engines. These include aniline, furfuryl alcohcol, xylidine, gasoline, hydrazine hydrate, borohydrides,-methyl and/or ethyl alcohol, ammonia, and mixtures of some of these with one or more other fuels.
Petroleum derivatives encompass a large variety of different hydrocarbon chemicals, most of which can be used as a rocket fuel. Most common are those types that are in use with other applications and engines, such as gasoline, kerosene, diesel oil, and turbojet fuel. Their physical properties and chemical composition vary widely with the type of crude oil from which they were refined, with the chemical process used in their production, and with the accuracy of control exercised in their manufacture. Typical values are listed in Table 7-2.
In general, these petroleum fuels form yellow-white, brilliantly radiating flames and give good preformance. They are relatively easy to handle, and there is an ample supply of these fuels available at low cost. A specifically refined petroleum product particularly suitable as a rocket propellant has been designated RP-1. It is basically a kerosene-like mixture of saturated and unsaturated hydrocarbons with a somewhat narrow range of densities and vapor pressure. Several hydrocarbon fuels can form carbon deposits on the inside of cooling passages, impeding the heat transfer and raising wall temperatures. Ref. 7-7 indicates that this carbon formation depends on fuel temperature in the cooling jacket, the particular fuel, the heat transfer, and the chamber wall material. RP-1 is low in olefins and aromatics, which can cause carbonaceous deposits inside fuel cooling passages. RP-1 has been used with liquid oxygen in the Atlas, Thor, Delta, Titan I, and Saturn rocket engines (see Figs. 5-1 to 5-6).
Methane (CH4) is a cryogenic hydrocarbon fuel. It is denser than liquid hydrogen and relatively low in cost. Compared to petroleum refined hydro-
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