Plasma Assisted Ignition Effects on a DISI Engine Fueled with Gasoline and Butanol under Lean Conditions and with EGR

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). All experiments were performed at 2000 rpm and 100 bar injection pressure. Optical accessibility through the piston crown allowed the application of two different techniques, UV-visible 2D chemiluminescence and natural emission spectroscopy. The first one gave information on the flame morphology and the second investigative method ensured insight into the specific processes related to the active chemical species. With the alternative ignition system, an increase in engine stability was obtained and the effects of butanol were related to its different chemical properties compared to gasoline. The differences among in-cylinder pressure data were correlated to the characteristics of flame shape and displacement, especially during the first stages of kernel formation and propagation.