Tumbling flow in a pentroof-type combustion chamber of an internal combustion engine (2nd report, breakdown of tumble near TDC of compression stroke).

In a four-valve spark-ignition engine with pentroof combustion chamber, the tumbling flow and its turbulence in compression stroke were measured with a laser Doppler velocimeter in two kinds of compression ratios under the condition of motoring. The main results are as follows. In the latter stage of the compression stroke under the condition of higher compression ratio, the tumbling flow is broken down to several small-size eddies because of narrow top clearance, and the turbulence intensity increases. Then the power spectrum of the turbulence is increased in the higher frequency region at the top dead center of the compression stroke. In the early stage of the compression stroke, the effect of the compression ratio on the power spectrum of the turbulence does not appear due to use of the same intake system.