Velocity and Turbulence Measurements in a Combustion Chamber of S. I. Engine under Motored and Firing Operations by L. D. A. with Fiber-Optic Pick-Up

In order to improve adaptability of the laser Doppler anemometer (LDA) to measurement of gas flow velocities in an internal combustion engine, an optical fiber system composed of a couple of single mode, polarization-preserving optical fibers has been developed to transmit the incident beams. The overall light transmission efficiency of the system is 24 % and not so high, but the system enables real-time measurements of gas flow velocity in the combustion chamber of a small two-cycle engine during firing operation.

The velocity data measured are processed with cycle by cycle analysis by stationary time-averaged method to obtain bulk velocity Ū, turbulence intensity u′ and integral time scale of turbulence Lt. The results indicate that Ū varies very much depending on motored and firing operations due to the expansion flow of combustion, accompanying a new flow field formation, and that u′ is about twice and Lt is 40 - 50 % higher during combustion period than the respective values during the same period of motored operation.