The application of thick-film piezoresistive technology for combustion pressure sensing
This thesis identifies the benefits offered by combustion pressure measurement in petrol engines to real-time engine control. Benefits include reduced exhaust emissions and better engine performance. The various techniques used for combustion pressure measurement are reviewed, and thick-film piezoresistive technology is identified as a technology capable of producing a low cost sensor. Two possible locations for. the thick-film pressure sensor are experimentally investigated, both on the spark plug. The piezoresistive material chosen is Heraeus 8241, a widely used material based on jt ruthenium dioxide particles in a glass matrix. Properties relevant to the construction of a combustion pressure sensor are evaluated; the elastic modulus is measured for the first time between 173 and 573K, and piezoresistivity is measured for the first time between 77 and 533K. The response of thick-film piezoresistors to hydrostatic pressure is investigated. A spark plug sensor is constructed, calibrated and engine tested. The detection of the angle of peak pressure, magnitude of peak pressure and knock is demonstrated.