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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.

Considering the generalized diversification of the energy mix, the use of alcohols as gasoline replacement is proposed as a viable option. Also, alternative control strategies for spark ignition engines (SI) such as lean operation and exhaust gas recirculation (EGR) are used on an ever wider scale for improving fuel economy and reducing the environmental impact of automotive engines. In order to increase the stability of these operating points, alternative ignition systems are currently investigated. Within this context, the present work deals about the use of plasma assisted ignition (PAI) in a direct injection (DI) SI engine under lean conditions and cooled EGR, with gasoline and n-butanol fueling. The PAI system was tested in an optically accessible single-cylinder DISI engine equipped with the head of a commercial turbocharged power unit with similar geometrical specifications (bore, stroke, compression ratio).

A plasma ignition system was tested in a GDI engine with the target of combustion efficiency improvement without modifying engine configuration. The plasma was generated by spark discharge and successively sustained to enhance its duration up to 4 ms. The innovative ignition system was tested in an optically accessible single-cylinder DISI engine to investigate the effects of plasma on kernel stability and flame front propagation under low loads and lean mixture (λ≅1.3). The engine was equipped with the head of a commercial turbocharged engine with similar geometrical specifications (bore, stroke, compression ratio). All experiments were performed at 2000 rpm and 100 bar injection pressure. UV-visible 2D chemiluminescence was applied in order to study the flame front inception and propagation with particular interest in the early combustion stages. A bandpass filter allowed selecting luminous signal due to OH radicals.