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Misfires in SI engines are one of the major causes for increase in vehicle exhaust emissions beyond the regulatory limit. Misfires have a great potential to destroy catalytic converters due to increased exhaust temperatures caused by unburned fuel from the misfired cylinders. It also leads to decrease in engine efficiency and high fuel consumption. Misfires are majorly caused due to unfavorable spark plug temperatures, low ignition energy, fuel system malfunction, improper air-fuel mixture ratio, flame propagation speed, etc. Monitoring of misfire detection in SI engines is an essential requirement of On-Board Diagnostic (OBD) regulations in many countries. This paper compares the conventional and advanced misfire detection technologies in spark-ignition engines, available and under development for meeting the OBD regulations worldwide. It describes the misfire detection principle.

In the recent years, due to rising fuel costs, transportation technologies that provide better fuel economy than conventional vehicle are gaining in popularity with masses. Also, tighter emission norms by various governments have prompted OEMs to look at alternate solutions such as hybrid vehicles. Hybrid vehicles employ an internal combustion engine as well as an alternate energy source to power road vehicles. Various types of hybrid vehicles are available such as mild hybrid, full hybrid, series, parallel and series-parallel hybrids. The level of hybridization (mild or full) and the different powertrain combination (series or parallel) result that on the same route, the engine in a hybrid vehicle operates very different to that of conventional vehicle. The fuel consumed and emissions are also significantly lower in hybrid vehicle. To certify hybrid vehicles, regulators in many countries have modified existing procedures applicable to conventional vehicles.