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The PressureSense Glow Plug combines a miniature cylinder pressure sensor with the automotive glow plug. The 1.7mm diameter fiber optic-based sensor is welded into the glow plug heater and the signal conditioner is encapsulated into a “smart connector” located on the top of the glow plug body. The sensor offers accuracy better than +/-2% of reading between 220 bar and 5 bar and +/-0.2 to +/-0.5 bar error for pressures below 5 bar. The performance of “dummy” as well as glowing and pressure sensing devices was evaluated on various engines and over a wide range of engine operating conditions.

A high-accuracy and low-cost cylinder pressure sensor reported in this paper compensates for all major temperature errors encountered in internal combustion engines. The auto-referencing technique maintains sensor calibration compensating for temperature effects on the sensor signal conditioner over the range of -40 to +135°C. In an inexpensive design sensor head materials and dimensions are optimized to compensate for the mid-term thermal errors associated with engine load changes over a temperature range of -40 and 300°C, resulting in the thermal coefficient of sensitivity as low as 0.005%/°C. A miniature, specially shaped diaphragm results in less than 0.5% error associated with rapidly changing combustion gas temperatures. Under non-combustion conditions the sensor offers +/-0.25 - 0.5% accuracy while under combustion conditions the accuracy is typically in the 1- 2% range.

We report a low-cost fiber-optic combustion pressure sensor integrated with an ignition system of a passenger car. A miniature sensor is attached to a shaft extending from the spark plug boot. Simultaneously with the boot mounting on the spark plug the sensor shaft is pressed into a cylindrical hole of a modified production spark plug. The sensor cable is combined either with the boot, or boot and high voltage cable, depending whether a coil-at-plug or a Distributed Ignition System is used, respectively. The sensor optical and Application Specific Integrated Circuit (ASIC) components are packaged inside a miniature module, embedded either in a coil-at-plug package or a Distribute Ignition System module. Engine test results are reported for a single-cylinder, gasoline fueled stationary gen-set engine.

An eight-channel fiber-optic combustion pressure system is described intended for continuous monitoring and control applications in diesel- and natural gas-engines. The portable control/monitoring unit of the system offers capabilities of real-time data acquisition and triggering from a shaft position or TDC sensors. Several processing functions are offered including calculations of peak pressure (PP), Indicative Mean Pressure (IMEP), and location of peak pressure (LPP). The system allows for 50 kHz, burst mode transfer of multi-sensor data to a PC. OPTRAND's commercially available combustion sensors for 1000 and 3000 psi maximum pressure ranges can interface to the unit with optical patch cables available up to 100 meters in length. The system offers 0.1Hz to 15 kHz frequency response, 1% accuracy at constant temperature, and maximum uncooled sensor housing temperature of 300°C.

We present design considerations of a diaphragm-type spark-plug-integrated fiber-optic combustion pressure sensor employing low-cost sensor and optoelectronic components suitable for large-scale production. Sensor system evaluation data are presented for high-engine-load and high-combustion-temperature conditions, and for knock detection. The fiber-optic sensor output closely resembles that of a heat-sunk, flame-shielded instrumentation-grade piezoelectric reference transducer, and demonstrates a high degree of temperature stability. Better than 4% accuracy is demonstrated over a full-scale pressure range.