Visualisation and Modelling of In-Cylinder Phenomena Using Optical Engines

Modern-day IC engines face an ever-increasing challenge of reducing fuel consumption and tail-pipe emissions to mitigate environmental concerns and to increase engine performance in terms of higher torque and power output with a lower fluctuation to improve driveability. This has resulted in a renewed interest in further investigations into spark-ignition (SI) engines. Newer variants of SI engines like gasoline direct injection (GDI) and pre-chamber combustion engines have emerged over the years and have become quite popular due to their better emission and fuel economy performance than the traditional port fuel injection (PFI) counterparts. Lately, the emergence of optical engines has provided valuable optical access inside the combustion chamber resulting in the development of several laser-based in-situ measurement techniques. These laser diagnostic methodologies have resulted in the direct imaging of in-cylinder flow-field, fuel spray, mixture distribution and combustion flame fronts providing highly accurate data sets that have proved to be extremely crucial for the development of valid CFD models. These CFD studies have then provided valuable insights into several in-cylinder phenomena that have a direct impact on augmenting combustion. This chapter discusses the evolution of optical engines and compares them with the corresponding metal engines. Some very popular laser diagnostic methodologies are then discussed like particle image velocimetry (PIV) for flow field visualisation, planar laser-induced fluorescence (PLIF) for fuel distribution imaging, diffused backlight imaging (DBI) for spray morphology studies and finally combustion flame front imaging. The chapter concludes with a detailed discussion of several studies that have used these visualisation tools to develop CFD models and have provided various interesting results.