Paper 14: Discharge from a Cylinder through a Poppet Valve to an Exhaust Pipe

Abstract

This paper is concerned with the gas exchange processes which occur in an engine. Previous work has been concerned with unsteady flow within the exhaust pipework; the present investigation provides a link between the cylinder and the pipe.

The modifications to the pulse generator machine which was used to simulate an engine are described, and an account is given of the tests carried out with the machine. The previous steady flow tests are briefly summarized and the unsteady flow tests which were carried out are summarized with the aid of a table.

The paper also presents a discussion of the test results and of calculations carried out to compare with the experiments.

The main conclusion from the results is that a very satisfactory method has been devised for calculating the gas exchange processes occurring in an engine model.

The main detailed conclusions are:

1. (1)

The dependence upon pressure ratio of the effective area of a poppet valve need not be taken into account for the analysis of unsteady flow tests.

(2)

Calculations on unsteady flow and gas exchange should be made on a theoretical model which has an exhaust pipe equal in length to the actual external exhaust pipe plus the length of the ‘exhaust bend’.

(3)

The method of calculation using the cylinder boundary conditions is an improvement on the previous type of calculations, which used a ‘pressure input’ as a boundary condition.

Finally, the present work on a pulse generator with fixed piston using cold air, has provided a means of calculating the gas exchange processes from a knowledge of the release and supercharge pressures and the engine geometry. It has, therefore, provided an important link between the engine cylinder and the exhaust pipe system.