The performance of an in-cylinder optical combustion intensity sensor is presented. The sensor and associated processing electronics are described. The ability of the sensor to detect defining combustion events is examined by evaluating test results against mass fraction burned and heat release models. The optical sensor is shown to effectively detect start of combustion (SOC) and 50% mass burned angles, and give excellent correlation to heat release profiles.The sensor is also shown to be able to determine optimum ignition angles for maximum brake torque (MBT) timing, using features of the optical intensity response. A control scheme which implements these features to enable MBT control of ignition is outlined.