Study of Ion Current Based Misfire Detection in Motorcycle Applications 2017-32-0011

Concerning internal combustion engines (ICEs), the analysis and evaluation of combustion quality and pollutant agents has drawn the attention of public opinion and worldwide authorities. Moreover, combustion quality in ICEs affects the drivability of motorbikes/cars, a most important quality for the customers’ point of view. The possibility to monitor engine behavior is a target that every car/motorcycle OEM is seeking, so as to comply with legislated pollutant limits. As the EURO V OBD Stage II regulations state, starting from the year 2020 all the emission related components will need to be monitored. In particular, the legislator requests to monitor the frequency of misfires, due to possible damage to the catalytic converter; in fact, the malfunction of this component can dramatically affect exhaust gas pollutant emissions. This article introduces a method for combustion quality and misfire monitoring, aimed at motorcycle engine applications, based on ion current flowing in an electronic circuit in which the sensing element is the common spark plug. It is well known that motorcycle engine characteristics, such as increased speed, low inertia and chain transmission, represent limits and challenges for conventional misfire monitoring methods based on readings from the crankshaft speed sensor. The scope of the paper is to demonstrate that the use of ion current sensing for combustion analysis is suitable and reliable for motorcycle applications. The study is developed using a production Eldor electronic control unit (ECU), with an integrated ion acquisition circuit and installed on a production series sport motorcycle, compliant with the Euro 4 emissions legislation. Moreover, the ECU software (SW) is modified to stimulate misfiring caused by both ignition and injection failures. A phase of system calibration was needed in order to identify the proper misfire detection thresholds, as a function of engine speed/load. After calibration, the overall test has been carried out by means of a chassis dynamometer test bench, with the vehicle following a WLTC emission cycle. The analysis of results shows that ion current based misfire monitoring is worthwhile and can be used as a feedback for cycle-by-cycle improvement of combustion in small engines for motorcycle applications.