Two-Component Laser Velocimeter Measurements in a Spark Ignition Engine

Abstract

Simultaneous two-component laser Doppler velocimeter measurements for homogeneous charge combustion in a spark ignition engine are used to calculate ensemble-averaged turbulence stresses. Cyclic variation hias in the data is reduced by conditional sampling. 011 the flame arrival time at the probe volume. Results are presented for engine speeds of 300. 600. and 1200 rpm. The lower speed is believed to be transitional because the general character of the fluid motion is found to he unique. For the two higher engine speeds. the following conclusions can he made: (1) The precombustion turbulence is highly anisotropic. with the component parallel to the piston surface nearly double the component in the direction of piston motion; (2) both the norrnul and shear turbulence stresses scale with mean piston speed; (3) combustion does not have an appreciable effect on either the preflame or postflame normal turbulence stresses. hut compression in front of the flame docs appear to reduce the degree of correlation of the velocity fluctuations: (4) combustion creates strong secondary velocity patterns that persist well after combustion is complete.