Design Features of Optically Accessible Engines for Flow and Combustion Studies - A Review

For long time, the measurement of spatially and temporally varying quantities like in-cylinder flow, mixing, and burning in an internal combustion engine remained impossible due to the lack of access to the engine cylinder. Hence, for quite some time, in-cylinder pressure remained the only quantity that could be temporally measured during an engine cycle, and the variations of quantities like temperature, heat release deduced from it. However, to guide modern engine developments for improved fuel economy and reduced emissions, understanding the intricacies of in-cylinder processes are essential. The advent of optical engine in conjunction with laser-based diagnostic techniques enabled measurement of various in-cylinder processes and study their influences on the combustion process. This paper highlights some key design features of optically accessible engines for flow and combustion studies.