Long term durability testing of combustion sensors

The performance and reliability of engine control systems can be improved with closed loop ionisation feedback. This measures the time for combustion and compares the corresponding crankshaft rotational angle to a preset value in a computer look-up table. The spark timing or fuelling is then adjusted to maintain the optimum position of heat release. This is important in the interests of exhaust emissions, engine noise and vibration, fuel economy, knock and preignition. In the closed loop mode of operation, the control system will correct deviations from the open loop calibration. These deviations may occur under the following conditions: changes in fuel quality; changes in ambient conditions (altitude or humidity); engine wear and deterioration; and variation in production build tolerances. The author discusses the reliability of the closed loop system and describes an engine test cycle which examines the durability of the sensor