A Novel Design of Engine Misfire Detection System Suitable for Small Capacity S.I. Engine for Two Wheeled Vehicle 2020-01-0267

As per the OBD II regulations, it is essential to detect and monitor the misfire event in an I.C. engine. Misfiring of an I.C. engine affects the quality of combustion and degrades the performance of catalyst convertor which can lead to an increase of emissions. Misfire event can be categorized as partial or complete, based on amount of combustion occurred during that particular engine cycle. Most of the production engine for non-two wheeler vehicle identifies misfire by monitoring angular acceleration of the engine crank-shaft. However, single cylinder engine with lower capacity (less than 300 cubic centimeter) provides challenges to identify misfire due to low mechanical inertia of the I.C. engine using the same approach. The problem of misfire identification for this category of I.C. engine turn out to be more challenging due to presence of various load disturbances on the powertrain. Ion current sensing is one of the alternate method to detect misfire, which received good attention during the last decade of the previous century. When the air-fuel mixture ignites inside the I.C. engine cylinder, air particles get ionize. By applying a suitable high-voltage on spark plug, it is possible to measure the ion current as the amount of ion current reflects the level of ionization of air fuel mixture.

The ion current measurement system presented in this paper is implemented in a production vehicle ignition system for two wheeled vehicles. The vehicle ignition system is unique due to the shorted terminals of high & low voltage sides. Due to the shorted primary and secondary connection, it is challenging to implement ion current measurement system using available research work. The proposed novel design of ion current measurement system accommodates the above constraint. The ion current signal is captured during normal combustion event as well as by creating misfire in the combustion. There are significant changes observed in the ion current signal with and without misfire. The information extracted from the ion current signal is utilized to detect the misfire. The proposed design is analyzed with suitable 1D theoretical model of the ignition system.