“…It is important to realize that mixing and combustion in the enclosure of the engine cylinder will be significantly affected by the physical boundaries and therefore, since early on in the development of internal combustion engines, researchers have thought of ways to study internal combustion engine phenomena through the use of optical engines (Rassweiler and Withrow, 1938;Withrow and Boyd, 1931;Bowditch, 1960). The direct observation of flame initiation, growth and extinction, and correlation of these data with, e.g., pressure measurements, quickly gained in importance.…”