Poppet Inlet Valve Characteristics and Their Influence on the Induction Process

In view of the wide use made of the poppet valve in internal combustion engines it seems strange that, comparatively, so little has been published on its flow characteristics since these are so important in determining the breathing capacity of an engine. Indeed, the main sources of detailed information on inlet valves are still the papers of Tanaka (1)§ and of Dennison, Kuchler, and Smith (2), both of which represent work done a considerable time ago. It is perhaps more remarkable, if the published information is taken as a guide, that so-called ‘static’ tests, in which the air flow through a stationary valve is measured, seem very rarely, if ever, to have been supplemented by experiments in which the kinetics of the valve motion and of the air column have been taken into account. In the present investigation, a series of static tests was followed by a series in which the valve was reciprocated whilst the overall pressure drop across valve and port was kept constant. The apparatus used permitted high rates of reciprocation, similar to those which would occur in high-speed engines, and enabled the flow characteristics at various rates of reciprocation, and with different cams, to be measured. As a third stage in the investigation, more elaborate equipment enabled valves which had previously been tested in the ‘static’ and ‘kinetic’ rigs to be used in conjunction with a piston and cylinder apparatus of a special type. This allowed valve-and-port performance to be evaluated under conditions closely similar to those which apply in a real engine, and measurements to be made of the effects of alterations in the inlet arrangements on the volumetric efficiency of the cylinder. An analytical technique was developed for calculating pressure–time and temperature–time variations in the cylinder during the induction process. The rather complex calculations were carried out with the help of a digital computer and in those instances where the results could be compared with values obtained experimentally, a fair agreement was achieved.