Motorcycle usage continues to expand globally. Motorcycles use various fuels in different countries and regions, and it is required that they comply with emissions and fuel consumption regulations as specified in UN-GTR No.2 (WMTC). In general, a motorcycle engine has a large bore diameter and a high compression ratio due to demands of high performance. Poor fuel quality may cause damage to the engine, mainly by knocking.
Knock control systems utilizing high-frequency vibration detection strategies like knock sensors, which are equipped on several sport-touring motorcycles, are not used widely for reasons of complex construction and high cost.
This research aims to develop a new concept of combustion control for common motorcycle as an alternative. The new combustion control focuses on the effect of engine combustion-chamber surface temperature, because a proportional relationship exists between the combustion chamber surface temperature and the pressure peak within the cylinder, and the combustion chamber temperature shows a sharp increase when knocking occurs. The difference between the combustion chamber surface temperature and the engine reference temperature was used as an indicator of the combustion state, and it was compared with that of an ideal state calculated from the generated torque. The ignition timing is adjusted so that, if the actual temperature is lower than the ideal temperature, the cylinder internal pressure is increased in order to raise the temperature, and if the actual temperature is higher than the ideal temperature, the cylinder internal pressure is reduced in order to lower the temperature.
When we applied this control algorithm to actual motorcycles, we obtained results showing its effectiveness in preventing engine damage from knocking and improving transient torque in the transition of acceleration from low-load to high-load.