# KSP inspired me to design a liquid-fueled rocket engine

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Hard to say. It looks like tests 2-3 were very under expanded and test 4 was a over expanded, which seems counterintuitive because 2-3 were conducted at lower pressure. Maybe for tests 2-3 the throat size was too large to properly choke the flow so the exhaust exited at higher than ambient pressure, but for test 4 the pressure was high enough to choke the flow and drop the pressure. Seems like there's a sweet spot somewhere inbetween 7-8 bar for the fuel pressure and 8-9 bar for the oxygen for ideal performance. Have you considered building some sort of thrust measuring rig? Might be easier to compare performances that way.

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Yes I have to design thrust measuring system. Then I know better.

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Great day today! I test fired my homemade rocket engine four times and it is still alive.

My goal is to have total 10 seconds thrust without melting.

Last run no. 8 was very good. Tank wasn't full becouse I ran out fuel mixture but still I got a record 7 seconds.

After test the engine wasn't too hot, I think cooling works well (sure, it doesn't melt...)

Here are videos:

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I installed a thrust measurement system and did two test run with bigger fuel tank.

Thrust is 29 N (3 kg). I expected more but this engine may have low isp or there is not enough pressure in combustion chamber.

11 seconds burning time with 190 grams of fuel. Engine weight is 180 grams (without any fittings) so TWR=16,7.

Fuel is alcohol 70 % water 30 %.

Videos here (RUD-10 test 9 and RUD-10 test10).

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That would give you an isp of 173 seconds, not too bad for something that you build yourself.

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Posted (edited)

Not quite.

Isp=F/W total. If I assume O/F ratio was 1 then W total=2*0,038 lb/s=0,076 lb/s

So Isp=6,61/0,076=87.

That is bad. I try to raise combustion chamber pressure next time.

Edited by totalitor

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New test today. More pressure - more thrust?

Look what happened. Same engine, same test platform. Thrust in earlier test 29 N (3 kg)

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New engine: RUD-11 with regenerative AND film cooling. How much film cooling eats thrust? Answer: a lot.

Videos here:

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I wonder how your engine would handle diesel fuel. Of course it is much harder to atomize so probably would require a different engine entirely. Just a thought though.

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New engine RUD-12, new test.

Better injector, does it increase thrust?

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