Introduction to the optically accessible engine for investigation of in-cylinder phenomena

To improve the performance of an internal combustion engine, three types of engines were developed that allows direct observation of the in-cylinder phenomena. Called the opticaly accessible engines, they are capable of maintenance-free operation exceeding 100 hours in total, under a partial load of 1500 rpm. They can also be used for more than an hour of continuous observation at a time. To prevent contamination of the optical components, the piston sliding area was non-lubricated and oil loss was prevented by sealing the piston ring and valve guide. Laser Doppler velocimeters were used to measure the velocity of flow.