DYNAMIC MODELING OF STARTING CAPABILITIES OF LIQUID PROPELLANT ROCKETENGINES

An analytical technique is developed for predicting the mass flow rate and heat addition in a liquid propellant rocket engine fuel system du ring the initial portion of an engine start. The analysis emphasizes n ozzle jacket heat exchange; specifically, flow and heat transfer chara cteristic influence on power availability. The outstanding feature of this model is the accurate representation of fluid properties during p hase change, and the subsequent affect on mass flow rates. The model a lso considers conduction and energy storage within the nozzle walls an d makes use of extensive hydrogen heat convection data. The analytical technique is applied to a proposed 20,000-lb thrust expander engine f or the determination of the minimum initial nozzle jacket metal temper ature that will promote starting at various operating conditions. The energy content of engine fuel flow during the initial portion of start up is compared to predicted turbomachinery torque requirements to dete rmine start capability. Starting capability is determined for various initial nozzle metal temperatures at fuel inlet pressures of 50 and 70 psi at sea level. The minimum initial jacket metal temperature that w ill produce enough energy to overcome predicted turbine breakaway torq ue is determined to be 135 degrees R for 70-psi and 385 degrees R for 50-psi inlet pressures.