Experimental visualization of the gas-liquid two-phase flow inside the multi-cavity during reciprocating motion

The piston cooling of engines are usually controlled by the “cocktail shake” mechanism inside the single cooling cavity, according to most studies of piston cooling published before. This paper researched on flow in multiple cooling cavities which are extensively used on pistons of low-speed engines, revealing that the flow in multi-cavity is quite different from that in a single cooling cavity. In this work, complete reciprocating cycles are captured to study the gas-liquid two-phase flow behavior of each cavity inside the multi-cavity piston, by conducting synchronous experiments using benchmarked high-speed camera and a real size piston. The effects of different engine speeds (40–64 rpm) and different inlet pressures (0.1–0.3 MPa) were investigated. Both the inner and annular cavities are cooled mainly by cocktail shaking, but two cooling mechanisms are observed in the outer cavity, the oscillatory effect and cyclonic effect, providing further development on piston cooling studies. The cyclonic effect enhances the heat transfer capacity of the sidewall surfaces. The coupling effect between multiple cavities produces a secondary mixing effect of the liquid and improves the overall turbulence. In this paper, a comprehensive analysis of the flow mechanism within a typical multi-cavity piston is presented.