Cycle Resolved LDV Measurements in a Motored IC Engine

Abstract

LDV measurements have been made in an IC engine motored at 1200 rpm. The data rates were sufficiently high to allow the bulk velocity to be characterized in individual cycles. The relative cyclic fluctuation of the bulk velocity was found to be as large as 200 percent. The turbulence intensity was calculated using both the velocity fluctuation with respect to the ensemble average velocity and the velocity fluctuation with respect to the cycle resolved bulk velocity. The former includes both the cyclic fluctuation of the bulk velocity and the turbulence, and therefore gave estimates of the ensemble averaged turbulence intensity which were from 50 to 100 percent greater than that obtained using the in-cycle fluctuation with respect to the bulk velocity. The relative cyclic fluctuation of the time averaged turbulence intensity, calculated over a 64-degree interval in each cycle, was found to be small, i.e., less than 20 percent. The high data rates also made it possible to determine the ensemble averaged temporal autocorrelation function from which the spectral energy distribution and the integral time scale were calculated.