Paper 3: An Experimental Study of Flow through Poppet Valves

Abstract

This report gives an account of steady flow tests carried out on poppet valves. The object of the investigation was to determine the boundary conditions for exhaust and inlet valves for subsequent use in the general programme of unsteady flow research. The exhaust valve was tested with and without pipes over a much wider range of pressure ratio and valve lift than has been carried out before and the boundary conditions have been found to be independent of the pipe and also almost independent of the position of the pressure tapping in the exhaust pipe. This result is very important and it will simplify subsequent boundary curve tests. Comprehensive tests have also been performed on the inlet valve and for reverse flow through each valve. The two usual mathematical flow models, namely, the constant pressure and the sudden enlargement, are discussed in detail and the concept of an effective area for a poppet valve is clearly explained. The effective areas for the exhaust and inlet valves for normal and reverse flow have been computed on the basis of the constant pressure flow model. The pressure ratio has been found to have little effect on the effective areas at low valve lifts but has considerable effects at high valve lifts. The results are presented graphically on a complete set of charts. It is illustrated in Appendix 3.II that the effective area of an exhaust poppet valve may be predicted for low valve lifts.