In-Cylinder Flow Measurement in Diesel Engine by Laser Velocimeter

In order to measure in-cylinder flow of direct injection diesel engine accurately by laser doppler velocimeter (LDV) with frequency tracker, a new data acquisition technique was developed. In this method, only available velocity data are obtained and all of them are related to crank angle. The results of the measurements can be monitored by an online and real time system with a personal computer. Velocity measurements in circumferential direction were made at the position apart from the inside of the cylinder head by 13mm near the center of the cylinder. Test engine has a cylinder bore of 102mm and a stoke of 106mm. Mean velocity and velocity fluctuation were derived from statistical analysis of LDV data and the reliability was investigated by calculating the confidence interval. The experimental results are as follows. (1) Velocity distribution histogram within a crank angle interval of 5 degrees can be approximated to gaussian distribution. (2) Even if the number of sampling data varies with crank angle, mean velocity and velocity fluctuation can be acquired accurately during intake and compression stroke by obtaining 10000 velocity data in many engine cycles. Lack of data in a certain crank angle interval can be indicated in confidence interval distribution. (3) Velocity fluctuation is about a half of the maximum mean velocity in intake stroke. but in compression stroke it is low and varies little. (4) Moving average over a crank angle interval of 5 degrees decreases the confidence interval of both mean velocity and velocity fluctuation to 20 % of mean piston speed