Tumbling flow in a pentroof-type combustion chamber of an internal combustion engine

In a four-valve spark-ignition engine, the turbulence produced by tumbling gas motion plays an important role in promoting the combustion. In this study, the tumbling flow and its turbulence in cylinder were measured with LDV under the condition of no firing in changing with the parameters of piston stroke, compression ratio, configuration of the intake port and engine speed. Furthermore, the oil spot method was applied to observe the flow pattern on the piston surface near the top dead center (TDC) of the compression stroke. The main results are as follows : (1) The tumbling air motion is converted into several smaller eddies before the TDC, and this phenomenon contributes to the increase in the intensity and the degree of isotropy of turbulence near the TDC. (2) The experiments in changing the engine speed and stroke express clearly that the turbulence intensity increases linearly with increasing mean piston speed.