Modern automotive engines almost exclusively operate on the 4-stroke Otto cycle and utilize poppet valves for gas exchange. This state of affairs has not always been the case, however, and one unusual and relatively successful technology that was once in mass production (albeit in piston aero engines) was the Burt-McCollum single sleeve valve. This paper investigates the timing and angle-area of a Bristol Centaurus engine cylinder, which utilized such a single sleeve valve for gas exchange, using some modern tools. A comparison with poppet valve angle-areas is made. Finally, the results are also used to study the potential of variable valve timing and the interaction with variable compression ratio of a single sleeve mechanism. An opportunity for the sleeve valve is provided by the fact that direct injector placement in the cylinder junk head is effectively completely free, and furthermore multiple ignition sites can be incorporated to increase the delivered ignition energy for dilute mixtures, for example. Furthermore, as there are no mechanical impact loads (as arise from poppet valves hitting their seats, for instance), theoretically ceramics or temperature-swing materials could be more simply applied when using the technology as well, and over a larger proportion of the total combustion chamber surface area than is possible with poppet valves. The motivation for studying the interaction of timing and compression ratio was driven by the observation that it would be relatively simple to incorporate a wide-range continuously-variable compression ratio mechanism without the spatial limitations enforced by the presence of poppet valves and their timing and drive mechanisms in the cylinder head of a conventional 4-stroke engine. The potential range of compression ratio variation is also significantly larger than for poppet-valve engines because the piston does not have to incorporate valve pockets for valve-to-piston clearance at high compression ratio settings. As a result the surface-area-to-volume ratio of the combustion chamber would be expected to be less effected over any given ratio range as well. The results of this study show a very favourable trade-off between port timing, compression and expansion ratios with a simple variable compression ratio mechanism being employed. Furthermore, the system is found to provide a large potential to yield increased Miller cycle operation automatically.
ASJC Scopus subject areas
- Safety, Risk, Reliability and Quality
- Automotive Engineering
- Industrial and Manufacturing Engineering