With the available data on the BE-4 sea level engine, I have reverse engineered some other likely performance numbers. The performance numbers are based on the published chamber pressure of 1950 psi (ArsTechnica.com), sea level thrust of 550,000 lb (BlueOrigin.com), and an estimated exit nozzle diameter of 72 in (+/- 3 in) from a rendering by Blue Origin (Twitter.com/blueorigin). I also attached some estimated thrust chamber dimensions based on the above data and an image of the thrust chamber (which is also attached). I included some uncertainties of the dimensions because some aspects of thrust chamber design are more art than engineering. Specifically, the thrust chamber upstream of the throat can be all sorts of proportions and my predicted chamber is surprisingly short and stout so I am pretty uncertain about its length.Predicted BE-4 Sea Level Engine PerformancePropertyMetricImperialUncertaintyChamber Pressure134 bar1950 psiThrust at sea level2,447 kN550,000 lbThrust in vacuum2,713 kN609,924 lb+/-0.8%Specific Impusle at sea level320 sec320 sec+/-5 secSpecific Impusle in vacuum355 sec355 sec+/-3 secDimensional UncertaintyDimensionUncertaintyNozzle Exit Diameter+/- 4.2%Nozzle Throat Diameter+/- 0.9%Chamber Diameter+/- 4.7%Expansion Nozzle Length+/- 5.5%Chamber Length+/- 32.6%

Quote from: MikeM8891 on 04/20/2018 05:26 pmWith the available data on the BE-4 sea level engine, I have reverse engineered some other likely performance numbers. The performance numbers are based on the published chamber pressure of 1950 psi (ArsTechnica.com), sea level thrust of 550,000 lb (BlueOrigin.com), and an estimated exit nozzle diameter of 72 in (+/- 3 in) from a rendering by Blue Origin (Twitter.com/blueorigin). I also attached some estimated thrust chamber dimensions based on the above data and an image of the thrust chamber (which is also attached). I included some uncertainties of the dimensions because some aspects of thrust chamber design are more art than engineering. Specifically, the thrust chamber upstream of the throat can be all sorts of proportions and my predicted chamber is surprisingly short and stout so I am pretty uncertain about its length.Predicted BE-4 Sea Level Engine PerformancePropertyMetricImperialUncertaintyChamber Pressure134 bar1950 psiThrust at sea level2,447 kN550,000 lbThrust in vacuum2,713 kN609,924 lb+/-0.8%Specific Impusle at sea level320 sec320 sec+/-5 secSpecific Impusle in vacuum355 sec355 sec+/-3 secDimensional UncertaintyDimensionUncertaintyNozzle Exit Diameter+/- 4.2%Nozzle Throat Diameter+/- 0.9%Chamber Diameter+/- 4.7%Expansion Nozzle Length+/- 5.5%Chamber Length+/- 32.6%Your analysis suggests a contraction ratio ~3.25 (exactly 3.247:1, so design point must be 3.25:1). That's fairly high but consistent with trying to get very high combustion efficiency. I tend to design between 3-4 typically.

This is fascinating, informative and very useful!Which of the above variables could you realistically alter without having to completely redesign the engine to squeeze more performance out of it? see Merlin.

Predicted BE-4 Sea Level Engine PerformancePropertyMetricImperialUncertaintyChamber Pressure134 bar1950 psiThrust at sea level2,447 kN550,000 lbThrust in vacuum2,713 kN609,924 lb+/-0.8%Specific Impusle at sea level320 sec320 sec+/-5 sec316+/-9 secSpecific Impusle in vacuum355 sec355 sec+/-3 sec351+/-7 sec

Quote from: MikeM8891 on 04/20/2018 05:26 pmPredicted BE-4 Sea Level Engine PerformancePropertyMetricImperialUncertaintyChamber Pressure134 bar1950 psiThrust at sea level2,447 kN550,000 lbThrust in vacuum2,713 kN609,924 lb+/-0.8%Specific Impusle at sea level320 sec320 sec+/-5 sec316+/-9 secSpecific Impusle in vacuum355 sec355 sec+/-3 sec351+/-7 secI am adjusting my specific impulse prediction because the prediction was based on analyzing the SpaceX Raptor performance, specifically the characteristic exhaust velocity (c*). Based on the published design performance of the Raptor, I expect c* to be between 1879-2015 m/s. However the Raptor is likely to have more efficient combustion than the BE-4 because both propellants are expected to enter the combustion chamber as gases. Available data published in textbooks puts the c* of LOX/CH4 at 1838-1857 m/s. This puts the expected lower end of the BE-4 Isp at 308 sec @ SL and 344 sec @ vac.

Quote from: MikeM8891 on 04/24/2018 11:35 pmQuote from: MikeM8891 on 04/20/2018 05:26 pmPredicted BE-4 Sea Level Engine PerformancePropertyMetricImperialUncertaintyChamber Pressure134 bar1950 psiThrust at sea level2,447 kN550,000 lbThrust in vacuum2,713 kN609,924 lb+/-0.8%Specific Impusle at sea level320 sec320 sec+/-5 sec316+/-9 secSpecific Impusle in vacuum355 sec355 sec+/-3 sec351+/-7 secI am adjusting my specific impulse prediction because the prediction was based on analyzing the SpaceX Raptor performance, specifically the characteristic exhaust velocity (c*). Based on the published design performance of the Raptor, I expect c* to be between 1879-2015 m/s. However the Raptor is likely to have more efficient combustion than the BE-4 because both propellants are expected to enter the combustion chamber as gases. Available data published in textbooks puts the c* of LOX/CH4 at 1838-1857 m/s. This puts the expected lower end of the BE-4 Isp at 308 sec @ SL and 344 sec @ vac.What text books are you using to help guide your analysis?

Quote from: Rocket Surgeon on 04/25/2018 11:05 pmQuote from: MikeM8891 on 04/24/2018 11:35 pmQuote from: MikeM8891 on 04/20/2018 05:26 pmPredicted BE-4 Sea Level Engine PerformancePropertyMetricImperialUncertaintyChamber Pressure134 bar1950 psiThrust at sea level2,447 kN550,000 lbThrust in vacuum2,713 kN609,924 lb+/-0.8%Specific Impusle at sea level320 sec320 sec+/-5 sec316+/-9 secSpecific Impusle in vacuum355 sec355 sec+/-3 sec351+/-7 secI am adjusting my specific impulse prediction because the prediction was based on analyzing the SpaceX Raptor performance, specifically the characteristic exhaust velocity (c*). Based on the published design performance of the Raptor, I expect c* to be between 1879-2015 m/s. However the Raptor is likely to have more efficient combustion than the BE-4 because both propellants are expected to enter the combustion chamber as gases. Available data published in textbooks puts the c* of LOX/CH4 at 1838-1857 m/s. This puts the expected lower end of the BE-4 Isp at 308 sec @ SL and 344 sec @ vac.What text books are you using to help guide your analysis?Mostly Modern Engineering for Design of Liquid-Propellant Rocket Engines, by Huzel and Huang.