Hypersonic Ground Testing Combustion Air Heater Ignition Optimization via Design of Experiments

Abstract

This paper describes the ignition optimization of the Aerodynamic and Propulsion TestUnit's (APTU) combustion air heater (CAH) with a fixed-area ratio (AR) nozzle installed. During a recent facility upgrade to a new Basic Process Control System (BPCS), the facility incorporated an improved capability to set parameters for ignition at various levels. However, CAH ignition reliability with a fixed-AR nozzle used during checkout was significantly lower than that demonstrated with the previous control system. A project was established to study, improve, and demonstrate reliability with the new control system. As a part of the study, key factors were identified for the ignition process. The CAH owner's manual described high and low settings for two parameters, delta pressure (DP) across the fuel injectors and CAH chamber pressure (psia). With the new BPCS the facility could easily and repeatably set these parameters at various levels within the high and low ranges for ignition. The historical data from the previous control system ignition process were reviewed, analyses were completed for the process with the new control system, and control measures for noise that may affect ignition were identified and implemented. From the results of the study, a design of experiment (DOE) checkout matrix was created and executed. During execution the results were analyzed and the matrix was modified to narrow in on the high probability for ignition region. Post-DOE testing, the results were analyzed and optimized, and parameter settings were selected. Ignition reliability of the CAH with the fixed-AR nozzle was verified to be greater than 90% with 80% confidence through the execution of consecutive successful ignition sequences at those settings. NomenclatureAEDC = Arnold Engineering Development Center APTU = Aerodynamic Propulsion Test Unit BPCS = Basic Process Control System BUT = Isobutane CAH = Combustion Air Heater CCD = Central Composite Design DOE = Design of Experiments DP = Delta Pressure FAN = Fixed-Area Ratio Nozzle FCV = Flow Control Valve FCD = Face-Centered Design FINJ = Fuel Injectors GH2 = Gaseous Hydrogen