Ion Based High-Temperature Pressure Sensor
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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A high speed, durable, ion probe based pressure sensor is being investigated for use in pulse detonation engines. The environment encountered in such engines necessitates high temperature and durable vibration resistant devices. Traditional pressure sensors can be used, however thermal insulating materials must be used to protect the diaphragm. These materials dampen and reduce the pressure wave allowing for qualitative results only. An alternative pressure sensing method is investigated for pressures behind a hydrocarbon flame in the pulse detonation engine. Hydrocarbon flames generate ions that are quenched by collisions with other species and walls. As the collision rate is a function of pressure, so too is the ion quench rate. The ion decay rate is measured using an ion probe well suited for the high temperature flow, inexpensive, and has no moving parts. Similar systems have been used to determine equivalence ratio in automobile engines. Further, wave speed may be determined through the use of multiple sensors. This investigation builds upon these capabilities to examine the quantitative pressures. In the current design, the ion probe acts as a charged capacitor. When an ionized field nears the probe, the electrical circuit is connected. The electrode on the probe discharges through the ionized field to a grounded plate. The rate of discharge indicates the strength of the ionized field which decays according to pressure. The experimental setup for this investigation and preliminary findings are presented here. Correlations between the decay rate and pressure are to be determined and compared to theory.
- Electric and Ion Propulsion