A huge part of today was spent deliberating between what type of propellant to use in this engine. It's been a back and forth battle between performance, propellant cost and suitability. At first I had envisioned this engine to be LOX/Methanol but after some research into propellant chemistry, I stumbled upon the fact that Methanol is not the best fuel to use in regenerative cooling as it has a lower specific heat than ethyl alcohol (ethanol). At first it was, "Oh, well that's easy, I'll just use ethyl alcohol then". However, a quick Google search demonstrated that my wallet was going to be hurting if I went that route. In fact, it would be hurting if I choose methanol or ethanol. A gallon of both can run up a hefty price tag. Like $75+ per gallon hefty depending on the supplier. Next up for deliberation was isopropyl alcohol (IPA) which looks to have a decent specific heat capacity and very low price tag. There has been some good work done in the past with IPA and LOX, particularly at XCOR Aerospace, so that's a good sign. I'm still going to look for more resources, but I'm warming up to the performance characteristics of IPA coupled with LOX. This engine is meant to be a test bed, so it might not be a bad idea to design the engine around the better of the propellant options and then be able to test with similar fuels (methanol, ethanol if using IPA). In the end, I'm looking for a fuel that will end up working well. I don't want to have to go through a (re)design review after designing all of the hardware, but sometimes that's how propulsion system engineering is...
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