Low-Cost Spark Plug-Integrated Fiber Optic Sensor for Combustion Pressure Monitoring

A fiber optic in-cylinder combustion pressure sensor system design is presented that exhibits the necessary operation and cost characteristics required for combustion pressure-based engine control applications. The sensor system consists of a small, spark plug-integrated, rugged, and high temperature operable sensor head; a low cost optoelectronic transceiver including LEDs, photodiodes, and simple optical couplers; and a DSP-based signal processing circuitry intended for future ASIC integration. A theoretical approach is developed to predict sensor response and signal-to-noise performance. The agreement between theoretical analysis and experimental results demonstrates that the present low cost system design results in required signal-to-noise performance and provides pressure measurement accuracies better than 5%. Engine tests performed with the fiber optic sensors demonstrate signal-to-noise performance comparable to instrumentation grade piezoelectric combustion pressure transducers as well as better temperature stability. The fiber optic pressure sensor can readily detect engine misfire and mis-timing of spark advance.