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Propulsion

Overview

Engine cycle analysis uses the DLR developed code LRP (Liquid Rocket Propulsion). The core of the code is the solver for a system of nonlinear equations, which are defined by the cycle's general framework as given by the user. The modular structure of the program allows for a quick rearrangement of the engine components, specifically the turbine and pumps assembly. The program will calculate the fluid properties sequentially, according to the respective components, through which the fluid flows. To obtain consistent conditions at each internal station of the engine, a system of nonlinear equations is solved. To calculate the change of fluid properties within the engine's components, the program LRP relies on a variety of different subroutines. All fluid properties calculations assume equilibrium compositions.

Engines

Numerous different engines have been analysed by SART in different levels of detail. The following table, showing a selections of engines gives a general overview.

Engine	Propellant Combination	Cycle
RD-180	LOX/RP	Staged Combustion
SSME	LOX/LH2	Staged Combustion
Vinci	LOX/LH2	Expander
Vulcain	LOX/LH2	Gas Generator
Vulcain 2	LOX/LH2	Gas Generator
SE-11	LOX/RP	Gas Generator
SE-12	LOX/CH4	Staged Combustion
SE-21	LOX/LH2	Expander-Bleed
SE-22	LOX/LH2	Gas Generator (transpiration cooled)
SE-23	LOX/LH2	Staged Combustion (transpiration cooled)

Ceramic Combustion Chamber

The DLR Ceramic Combustion Chamber utilises transpiration cooling at elevated wall temperatures. Depending on the position and the design of the combustion chamber, the transpiration coolant mass flow influences the chamber's performance. However, since the bulk of the hydrogen flow does not pass through the cooling channels (as in a regeneratively cooled engine), the necessary pump exit pressure to maintain the chamber pressure is reduced. To demonstrate the engine's possible performance gain, a study has been made. The basis for the comparison is a regeneratively cooled engine. Performance increases with decreasing pressure loss in the cooling channels. Different possibilities exist to augment an engines performance.

• It is possible to make use of the decreasing necessary LH2 pump pressure rise. Since the pump's power demand decreases, the turbines pressure ratio can also be increased, which means the turbine's exhaust gas increases in pressure. This leads to a higher specific impulse for the TEG and thereby slightly increases the engine's specific impulse.
• It is possible to use the reduced power demand of the LH2 pump to decrease the gas generator mass flow accordingly. The excess hydrogen (at constant engine mass flow and mixture ratio) is injected in the main chamber. The higher chamber mass flow and lower chamber mixture ratio lead to a higher specific impulse.
• It is possible to use the excess turbine power to increase the combustion chamber pressure. Using a constant gas generator mass flow, the power generated by the turbines can thus be used to increase the specific vacuum impulse, assuming the gases are expanded to the same nozzle exit pressure (i.e. at a higher expansion ratio).

Publications