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University of Arkansas: Investigation of hybrid rocket motors

dSPACE DS1104 controls mass flow

March 14, 2011: Hybrid rocket motors contain a solid, inert fuel element and an oxidant that is pumped into contact with the fuel. This configuration is distinct from a liquid rocket where both the fuel (hydrogen) and the oxidant (oxygen) are mixed or a solid rocket where the fuel and oxidant are combined in the propellant grain. The research group at the University of Arkansas at Little Rock investigates fundamental aspects of combustion in hybrid rocket motors, for example thrust oscillations, pressure, plume flicker and acoustical output. The chamber pressure is controlled by modulating the oxygen mass flow. The mass flow is measured by a laminar flow heater element, and a control circuit opens or closes a valve until the measured mass flow equals the desired mass flow. This setup is based on a dSPACE DS1104 R&D Controller Board. The board has 12-bit ADCs to measure the pressure and oxygen mass flow and a 16-bit DAC to regulate the oxygen mass flow. The DAC signal is amplified by a transistor amplifier to provide the current necessary to power the mass flow controller circuit. Computer-controlled solenoid valves turn the gases on and off. These valves are located in the gas distribution panel, and are activated by digital outputs on the DS1104. The digital outputs modulate transistor amplifiers to provide the necessary current to power the solenoid driver circuits.
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