But why did von B stick with alcohol for the Redstone? Surely there was not much technical difficulty in switching from alcohol to kerosene, unless perhaps the purity issues that later led to the formulation of RP-1 dissuaded him?
RP-1 is most commonly burned with LOX (liquid oxygen) as the oxidizer, though other oxidizers have also been used. RP-1 is a fuel in the first-stage boosters of the Delta I-III and Atlas rockets. It also powered the first stages of the Titan I, Saturn I and IB, and Saturn V.During and immediately after World War II, alcohols (primarily ethyl alcohol, occasionally methyl alcohol) were the single most common fuel for large liquid-fueled rockets. Its high heat of vaporization kept regeneratively-cooled engines from melting, especially considering that alcohols would typically contain several percent water. However, it was recognized that hydrocarbon fuels would increase engine efficiency, due to a slightly higher density, the lack of an oxygen atom in the fuel molecule, and negligible water content. Whatever hydrocarbon was chosen, though, would have to replicate alcohol's coolant ability.Many early rockets had burned kerosene, but as burn times, combustion efficiencies, and combustion-chamber pressures grew, and engine masses shrank, the engine temperatures became unmanageable. Raw kerosene used as coolant would dissociate and polymerize. Lightweight products in the form of gas bubbles, and heavy ones in the form of engine deposits, then blocked the narrow cooling passages. The coolant starvation raised temperatures further, accelerating breakdown. This cycle would escalate rapidly until an engine wall ruptured.This occurred even with the entire flow of kerosene used as coolant. Rocket designers turned to the fuel chemists to formulate a heat-resistant hydrocarbon. The specification was completed in the mid-50s.
Quote from: Proponent on 11/27/2008 08:28 amBut why did von B stick with alcohol for the Redstone? Surely there was not much technical difficulty in switching from alcohol to kerosene, unless perhaps the purity issues that later led to the formulation of RP-1 dissuaded him?That wasn't "purity". The jet fuels had too wide of specifications for use as rocket propellant, density being among the critical ones. It wasn't viable until RP-1 came along, much later than Redstone
What about propane? If as of 1950 people were well aware that hydrocarbons would perform better than alcohol, wouldn't propane have been an obvious candidate, one which would not have suffered from coking? Of course, it's either mildly cryogenic or needs pressurization, but if you're using lox anyway, then the cryogenics shouldn't be much of an issue, and pressurization might even be an advantage for a balloon design like the Atlas. Or does propane have poor cooling properties?
With regards to propane (and other possible candidate fuels), I came across this interesting post on the subject: http://yarchive.net/space/rocket/fuels/fuel_table.htmlIn short, propane is very similar to RP-1 both in terms of density and Isp, it has to be liquefied, but on the plus side it doesn't freeze in contact with LOX. You could construct a tank with a common bulkhead which doesn't insulate and would be perfectly fine for propane storage. Propane's otherwise higher vapor pressure might imply cavitation problems unless pressurized more heavily than RP-1.