Review: Multipoint laser ignition system and its applications to IC engines

•The various techniques used for creating multi-point laser ignition has been reviewed.•Multi-point laser ignition shows better performance over single-point laser and multi-point spark ignition.•Effect of laser energy and ignition locations on combustion characteristics has been studied.•An increase in laser energy shows improvement in combustion characteristics.•Realization of the laser spark plug with multiple-beam output for IC engines has been reviewed. The stringent emission norms, increasing demands for higher efficient and reliable engine operation and rapid depletion of petroleum resources, motivated researchers to explore on advanced combustion and ignition technologies as well as the use of alternative fuels for internal combustion (IC) engines. Lean burn combustion with high spark energy is an advanced combustion approach that improves thermal efficiency, reduces knocking tendency, exhaust emissions, especially NOx (Nitrogen oxides), and heat transfer. However, there are many difficulties in current operating engines with lean mixtures like slower flame initiation, incomplete combustion, increased cyclic variation and potential misfiring, etc. which causes decreased efficiency, power output, and excessive emission. The exhaust gas recirculation (EGR) can reduce nitrogen oxide (NOx) emissions but increases particulate matter (PM) and have ignition problem during engine idle operation. The conventional electric discharge ignition system performs well at normal operating conditions; however, for igniting lean mixtures require significantly higher spark energy with multi-point ignitions. The higher spark energy will increase the ignitibility but decrease the life of spark plug due to electrode erosion, and electrodes act as a thermal energy sink. However, multi-location ignitions with conventional electric discharge systems will require several electrodes. Therefore to overcome these difficulties, the multi-point laser-induced ignition is an innovative alternative approach to burn lean mixtures compared to the conventional electric discharge ignition system. A laser is a high energy electrode less ignition source with the easy possibility of multi-location ignitions. Therefore, this article aims is to review various techniques used for multi-point laser ignition and its impact on combustion characteristics and engine performance. The effect of laser energy and ignition locations on combustion characteristics has also been reviewed. Also, demonstrat