Study on Combustion Detection of a Spark-Ignition Engine with Fuel Variation Using Various Sensors

The use of alternative fuels, such as biofuels and synthetic fuels in automotive engines has been more common these days. Although these fuels contribute to the carbon neutral society, it is known that changes in the composition of these fuels significantly affect the combustion characteristics of an engine, such as knocking and combustion duration. Therefore, it is necessary to develop engine systems that are highly robust to variations in fuel composition. To achieve this goal, detecting changes in fuel using various sensors is required. Although in-cylinder piezoelectric pressure sensor is useful for research in the laboratory, it is not suitable for the use in commercial engines because of its high cost. Therefore, the use of other sensors should be considered. The purpose of this study is to experimentally analyze what information related to combustion and fuel can be obtained from multiple cost-effective sensors mounted on an engine. Experiments were conducted on a 4-cylinder SI engine, and combustion characteristics of multiple fuels were investigated by varying engine operating conditions, such as engine speed and ignition timing. In addition to gasoline, CH4, CO2, and N2 gases were introduced into cylinders to simulate the change in fuel composition. Sensors used in this study included intake and exhaust pressure sensors, thermocouples, and in-cylinder ion current sensors. These sensors are already used in commercial engines or can be implemented at a relatively lower cost compared to in-cylinder pressure sensors. It was clarified that exhaust port temperatures and ion-current values can be used to predict lower heating value of fuels and combustion duration.