Optical test devices and methods for internal combustion engines and optical studies on spray combustion characteristics for three different alternative fuels: A review

Due to the increasingly stringent emission regulations and the rising call for energy saving and emission reduction, efficient and clean combustion in internal combustion engines have become a research priority. However, the in-cylinder spray combustion process is complex and variable due to a variety of factors. Spray combustion, as a key segment of combustion in internal combustion engines, plays a key role in the efficient and clean combustion of internal combustion engines. The optical test device can truly observe the spray combustion in the cylinder of an internal combustion engine by equipping with an optical window. This paper focuses on the study of internal combustion engine optics, and reviews the current major optical test devices, optical detection methods, and spray combustion characteristics of three different alternative fuels. Firstly, the paper reviews three commonly used optical test devices, namely, CVCB, RCM and optical engine, and their studies on laminar flame, ignition delay and flash spray. Subsequently, the paper summarizes the spray combustion characteristic parameters and nine commonly used optical test methods that are well suited to determine spray morphology, concentration field, velocity field, combustion characteristics and intermediate composition. Finally, the paper summarizes the spray combustion characteristics of three alternative fuels.