MICROPHONES AND KNOCK SENSORS FOR FEEDBACK CONTROL OF HCCI ENGINES

Homogeneous charge compression ignition (HCCI) engines lack direct in-cylinder mechanisms, such as spark plugs or direct fuel injection, for controlling the combustion timing. Many in- direct methods have been used to control the combustion timing in an HCCI engine. With any indirect method, it is important to have a measure of the combustion timing so the control inputs can be adjusted for the next cycle. In this paper, it is shown that microphones and knock sen- sors can be used to detect combustion in HCCI engines. The out- put from various microphones and a knock sensor on an HCCI engine are measured at light and high loads. The combustion timing data obtained from the sensors are compared to the com- bustion timing data obtained from a piezoelectric cylinder pres- sure transducer. One of these sensors is selected and used for closed-loop control of the combustion timing in a single cylinder HCCI engine.