Multi-location laser ignition using a spatial light modulator towards improving automotive gasoline engine performance

• Published in: Optics and lasers in engineering Vol. 90; pp. 275 - 283
• Main Authors: Kuang, Zheng, Lyon, Elliott, Cheng, Hua, Page, Vincent, Shenton, Tom, Dearden, Geoff
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2017
• Subjects: Automotive gasoline engine; Computer generated hologram; Laser ignition; Multi-location laser-induced spark; Spatial light modulator; Computer generated hologram; Automotive gasoline engine; Multi-location laser-induced spark; Laser ignition; Spatial light modulator
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2016.10.024

We report on a study into multi-location laser ignition (LI) with a Spatial Light Modulator (SLM), to improve the performance of a single cylinder automotive gasoline engine. Three questions are addressed: i/ How to deliver a multi-beam diffracted pattern into an engine cylinder, through a small opening, while avoiding clipping? ii/ How much incident energy can a SLM handle (optical damage threshold) and how many simultaneous beam foci could thus be created? ; iii/ Would the multi-location sparks created be sufficiently intense and stable to ignite an engine and, if so, what would be their effect on engine performance compared to single-location LI? Answers to these questions were determined as follows. Multi-beam diffracted patterns were created by applying computer generated holograms (CGHs) to the SLM. An optical system for the SLM was developed via modelling in ZEMAX, to cleanly deliver the multi-beam patterns into the combustion chamber without clipping. Optical damage experiments were carried out on Liquid Crystal on Silicon (LCoS) samples provided by the SLM manufacturer and the maximum safe pulse energy to avoid SLM damage found to be 60mJ. Working within this limit, analysis of the multi-location laser induced sparks showed that diffracting into three identical beams gave slightly insufficient energy to guarantee 100% sparking, so subsequent engine experiments used 2 equal energy beams laterally spaced by 4mm. The results showed that dual-location LI gave more stable combustion and higher engine power output than single-location LI, for increasingly lean air-fuel mixtures. The paper concludes by a discussion of how these results may be exploited. •A gasoline engine was tested using multi-location laser ignition.•Multi-beam diffracted patterns were delivered to the engine cylinder without clipping.•Multi-location ignition gave more stable combustion and higher engine power output.