Author Topic: BE-4 Reverse Engineered  (Read 12979 times)

Offline MikeM8891

BE-4 Reverse Engineered
« on: 04/20/2018 05:26 pm »
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 Performance
PropertyMetricImperialUncertainty
Chamber Pressure134 bar1950 psi
Thrust at sea level2,447 kN550,000 lb
Thrust in vacuum2,713 kN609,924 lb+/-0.8%
Specific Impusle at sea level312 sec312 sec+/-1 sec
Specific Impusle in vacuum346 sec346 sec+/-3 sec

Dimensional Uncertainty
DimensionUncertainty
Nozzle Exit Diameter+/- 4.2%
Nozzle Throat Diameter+/- 0.9%
Chamber Diameter+/- 4.7%
Expansion Nozzle Length+/- 5.5%
Chamber Length+/- 32.6%
« Last Edit: 04/29/2018 12:45 am by MikeM8891 »

Offline HMXHMX

  • Full Member
  • ****
  • Posts: 1690
  • Liked: 2099
  • Likes Given: 634
Re: BE-4 Reverse Engineered
« Reply #1 on: 04/20/2018 09:49 pm »
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 Performance
PropertyMetricImperialUncertainty
Chamber Pressure134 bar1950 psi
Thrust at sea level2,447 kN550,000 lb
Thrust in vacuum2,713 kN609,924 lb+/-0.8%
Specific Impusle at sea level320 sec320 sec+/-5 sec
Specific Impusle in vacuum355 sec355 sec+/-3 sec

Dimensional Uncertainty
DimensionUncertainty
Nozzle 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.

Offline MikeM8891

Re: BE-4 Reverse Engineered
« Reply #2 on: 04/20/2018 11:00 pm »
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 Performance
PropertyMetricImperialUncertainty
Chamber Pressure134 bar1950 psi
Thrust at sea level2,447 kN550,000 lb
Thrust in vacuum2,713 kN609,924 lb+/-0.8%
Specific Impusle at sea level320 sec320 sec+/-5 sec
Specific Impusle in vacuum355 sec355 sec+/-3 sec

Dimensional Uncertainty
DimensionUncertainty
Nozzle 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.

I agree the contraction ratio seems high. I have a textbook that suggests it should be around 1.8-2.7. There is actually a lot of uncertainty in my calculation. Based on the photo of the combustion chamber I get a contraction ratio of 3.0 but since this is based on the outer dimensions of the throat and chamber liner I believe the actual contraction ratio is higher. The the outer dimensions of the chamber based on the rendering posted to twitter is ~28.13 inches.  I figured this would be the largest the chamber could be since it is based on the outer dimension.  A 28.13-inch chamber results in a contraction ratio of ~3.55. So I figure the contraction ratio could be 3.0-3.5.
« Last Edit: 04/20/2018 11:06 pm by MikeM8891 »

Offline MikeM8891

Re: BE-4 Reverse Engineered
« Reply #3 on: 04/21/2018 11:53 pm »
To supplement my calculations, the throat diameter is based on solving for the vacuum thrust coefficient. The vacuum thrust coefficient can be calculated two ways: as a function of vacuum thrust, chamber pressure, and throat area; or as a function of pressure ratio, heat capacity ratio, and expansion ratio, where vac thrust = SL thrust + exit nozzle area x 1 atm. I set these functions equal to each other and solved for the unknowns. The max vacuum thrust coefficient and expansion ratio corresponds to the max exit nozzle area and min heat capacity ratio. From here the throat diameter is easily calculated from the expansion ratio and exit nozzle diameter.

Inputsminmaxunits
Exit Nozzle Area2.412.85sq m
Vacuum Thrust2,6912,735kN
Chamber Pressure134.4134.4bar
Heat Capacity Ratio1.211.31
Outputs
Expansion Ratio21.025.7
Vacuum Thrust Coefficient1.7421.835
Throat Diameter0.3760.383m

Offline Rocket Surgeon

  • Full Member
  • ***
  • Posts: 370
  • Berlin, Germany
  • Liked: 229
  • Likes Given: 78
Re: BE-4 Reverse Engineered
« Reply #4 on: 04/23/2018 06:56 am »
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 Performance
PropertyMetricImperialUncertainty
Chamber Pressure134 bar1950 psi
Thrust at sea level2,447 kN550,000 lb
Thrust in vacuum2,713 kN609,924 lb+/-0.8%
Specific Impusle at sea level320 sec320 sec+/-5 sec
Specific Impusle in vacuum355 sec355 sec+/-3 sec

Dimensional Uncertainty
DimensionUncertainty
Nozzle Exit Diameter+/- 4.2%
Nozzle Throat Diameter+/- 0.9%
Chamber Diameter+/- 4.7%
Expansion Nozzle Length+/- 5.5%
Chamber Length+/- 32.6%

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.

Offline MikeM8891

Re: BE-4 Reverse Engineered
« Reply #5 on: 04/24/2018 11:09 pm »
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.

Raising the chamber pressure and enlarging the expansion nozzle would be the simplest way to increase both thrust and specific impulse.

Offline MikeM8891

Re: BE-4 Reverse Engineered
« Reply #6 on: 04/24/2018 11:35 pm »

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


I 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.
« Last Edit: 04/25/2018 09:11 pm by MikeM8891 »

Offline Rocket Surgeon

  • Full Member
  • ***
  • Posts: 370
  • Berlin, Germany
  • Liked: 229
  • Likes Given: 78
Re: BE-4 Reverse Engineered
« Reply #7 on: 04/25/2018 11:05 pm »

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


I 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?

Offline MikeM8891

Re: BE-4 Reverse Engineered
« Reply #8 on: 04/25/2018 11:28 pm »

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


I 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.

Online Davidthefat

  • Full Member
  • ****
  • Posts: 463
  • Rockets are life.
  • Greater Los Angeles Area, California
  • Liked: 287
  • Likes Given: 71
Re: BE-4 Reverse Engineered
« Reply #9 on: 04/25/2018 11:31 pm »

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


I 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.

Liquid Rocket Thrust Chambers: Aspects of Modeling, Analysis, and Design is a good text I recommend.

Offline MikeM8891

Re: BE-4 Reverse Engineered
« Reply #10 on: 04/29/2018 12:39 am »

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


I 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.

I realized I needed better c* data to predict the BE-4 Isp. I am going to trash the data based on Raptor because Raptor will be a gas-gas engine and the BE-4 definitely will not.  I am surprised by how efficient SpaceX expects the Raptor to be (c* = ~1950 m/s for Raptor vs ~1850 m/s textbook value) however this is inline with the expected efficiency increase between gas-gas and liq-liq hydrolox (c* = 2550 m/s vs 2416 m/s). Since the rocket engine power cycle has a great influence on the c*, I think the most accurate way to estimate the BE-4 c* may be to calculate the c* of oxygen-rich staged combustion kerosene rocket engines and adding 3.2% expected performance increase for using methane. I get 3.2% from comparing the textbook c* values of RP-1 and methane for SL engines.  As you can see from the below data this results in an average c* identical to the textbook value.  This data also revealed a trend of decreasing c* with increasing coefficient of thrust (Cf), see the attached graph. Using this trend and adding 3.2% performance increase for using methane, the Isp is 312+/-1 and 346+/-3 sec for SL an vac, respectively. The original post has been updated accordingly.

Textbook LOX/CH4 c* (also available on Wikipedia: Liquid rocket propellant)
1857 m/s for a SL optimized engine
1838 m/s for a vacuum optimized engine

Oxygen-rich stage combustion rocket performance
Rocket EngineCfc* (m/s)c* +3.2% (m/s)
YF-1001.8917431799
RD-1701.8617751832
RD-1801.8118251883
RD-1901.7918521912
Average-17991857

Offline ZachF

  • Full Member
  • ****
  • Posts: 1389
  • Immensely complex & high risk
  • NH, USA, Earth
  • Liked: 2226
  • Likes Given: 444
Re: BE-4 Reverse Engineered
« Reply #11 on: 09/27/2018 12:00 am »
Cool exercise. What mixture ratio are you assuming for this?
artist, so take opinions expressed above with a well-rendered grain of salt...
https://www.instagram.com/artzf/

Tags: BE-4 Blue Origin 
 

Advertisement NovaTech
Advertisement SkyTale Software GmbH
Advertisement Northrop Grumman
Advertisement
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
0