Glow Plug Integrated Cylinder Pressure Sensor for Closed Loop Engine Control

The PressureSense Glow Plug combines a miniature fiber optic-based cylinder pressure sensor with the automotive glow plug. The 1.7mm diameter sensor is sealed inside a glow plug heater and the sensor signal conditioner is encapsulated into a “smart connector”. The sensor operates on the proven principle of light intensity changes, transmitted by two optical fibers, upon reflection from a deflecting metal diaphragm. The sensor materials, dimensions, and the assembly technique are optimized to compensate for diaphragm deflection dependence on temperature associated with engine load changes. The device is compensated for all major environmental factors encountered under the hood of an automobile including LED and photodiode temperature dependence and aging, fiber-to-opto-electronics coupling fluctuations, and vibration and humidity effects. Under combustion conditions the sensor offers the total accuracy of +/-1.5% over the projected sensor life of 10 thousand hours. Such high sensor accuracy allows advanced closed loop control strategies for diesel and HCCI engines based on real time computations of Indicated Mean Effective Pressure (IMEP) and mass fraction burned. These control strategies have been shown to result in as much as 12% reduction in NOx emissions and 15% of particulate emissions in a closed loop controlled diesel engine versus its conventional counterpart.