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Post by nerd1000 on Apr 23, 2017 9:02:22 GMT
I've been trying to model a real rocket engine in CoaDE, namely the Rocketdyne J-2 seen on the Saturn V. The real-life J-2 attained an exhaust velocity of 4.13 km/s using a nozzle ratio of 27.5 and oxygen:hydrogen ratio of 5.5:1 by mass. Putting these numbers into CoaDE gives rather different results: I can only get 3.08 km/s using a nozzle expansion angle of 20 degrees (which looks like the real engine). So what could be causing this discrepancy? Well the game tells me that the combustion temperature is only 2073K. This document: www.nasa.gov/centers/marshall/pdf/499245main_J2_Engine_fs.pdf claims that the chamber temperature of the real engine is 3450K. It seems that CoaDE's calculations of combustion temperatures are wrong... But I don't know how this problem might have come about. |
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Post by ash19256 on Apr 23, 2017 12:13:25 GMT
Really, I suspect that all of the combustion setups are bugged to some extent, because IIRC methalox engines can't achieve performance on the level of what the Raptor is purported to be capable of, even though the Raptor engine really should be something that is recreated to make certain that the calculations are accurate, along with engines like the RS-25, RL-10, J-2, and F-1.
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Post by newageofpower on Apr 23, 2017 15:53:19 GMT
Really, I suspect that all of the combustion setups are bugged to some extent, because IIRC methalox engines can't achieve performance on the level of what the Raptor is purported to be capable of, even though the Raptor engine really should be something that is recreated to make certain that the calculations are accurate, along with engines like the RS-25, RL-10, J-2, and F-1. IIRC Rocket Witch recreated the Raptor awhile back... |
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Post by Rocket Witch on Apr 23, 2017 16:43:30 GMT
I did post it before, but it was made by someone called DecidedlyNinja: steamcommunity.com/sharedfiles/filedetails/?id=789741049Also uses a rather suspect diamond chamber. I also made replicas of the F-1 and unflown J-2S engines myself, but the former was done before RP-1 was reworked and I deleted it, while neither of the two achieved the real versions' exhaust velociies. There may not be a problem with the reaction as such, it might be in how the stoichiometric ratio math affects the reaction. |
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Post by ash19256 on Apr 24, 2017 17:38:45 GMT
I did post it before, but it was made by someone called DecidedlyNinja: steamcommunity.com/sharedfiles/filedetails/?id=789741049Also uses a rather suspect diamond chamber. I also made replicas of the F-1 and unflown J-2S engines myself, but the former was done before RP-1 was reworked and I deleted it, while neither of the two achieved the real versions' exhaust velociies. There may not be a problem with the reaction as such, it might be in how the stoichiometric ratio math affects the reaction. Actually, that Raptor isn't a perfect recreation. It achieves the same sea-level thrust, but not only is the Raptor engine supposed to achieve much higher thrust in a vacuum (which is what CoaDE would be simulating for all of the engines), it doesn't achieve even the sea-level specific impulse of the Raptor engine. And I also suspect that the fuel ratios are all wrong, and it's achieving at most 331-332 Isp. |
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