The History and Evolution of Optically Accessible Research Engines and Their Impact on Our Understanding of Engine Combustion

The development and application of optically accessible engines to further our understanding of in-cylinder combustion processes is reviewed, spanning early efforts in simplified engines to the more recent development of high-pressure, high-speed engines that retain the geometric complexities of modern production engines. Limitations of these engines with respect to the reproduction of realistic metal test engine characteristics and performance are identified, as well as methods that have been used to overcome these limitations. Lastly, the role of the work performed in these engines on clarifying the fundamental physical processes governing the combustion process and on laying the foundation for predictive engine simulation is summarized.