A statistical model for determining firevalve controller settings to regulate gaseous rocket propellant mass flow

Testing throttleable rocket engines at simulated altitude requires controllable firevalves to adjust propellant mass flows for desired O/F's and chamber pressures (P_c’s) Obtaining accurate mass flows is essential for determining the operational O/F's and chamber pressures for the engine during test. The ability to predict mass flows, when the O/F and chamber pressure changes, is crucial. How so? Because, if the predictions aren't accurate, the engine operating parameters do not match the desired engine performance during a test. This results in another test run. Another test run increases costs, shortens the engine's life, and possibly results in not meeting all of the test objectives. Also, because the engine run times are so short, the firevalves must be set prior to the test run. The controller settings must accurately reflect the proper mass flow rates for the desired O/F and P_c. If throttling is involved, the initial set point for the controller needs to be accurate. Obviously, the best solution is to provide a feedback mechanism between the valve and the controller to automatically adjust the mass flow. However, during my tour at NASA Lewis Research Center (1986-1988), the computers weren't fast enough to maintain a constant O/F and P_c. It was estimated that a sampling rate of 50 Hz was required. Also, digital technology wasn't cost effective at that time. Today, there is a strong interest in implementing a feedback, controller system, but none has been installed. Another possible method to vary propellant mass flow rate would be to change the propellant supply pressures during a run. Unfortunately, it makes throttling the engine very difficult and could possibly lead to undesirable rocket engine and propellant feed line dynamics. If throttling is not part of the test matrix, and the regulated pressures are preset prior to engine test firing, then this method will work. However, it complicates the process the test engineer uses to determine correct controller settings. Therefore, in a research environment with declining budgets, the need to accurately predict firevalve plug positions during test firings, without controller to valve feedback systems, demands a simple and inexpensive methodology for doing so. The purpose of this thesis is to design a technique for predicting firevalve controller settings to regulate propellant mass flow based on rocket engine P_c and O/F.