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This paper describes an investigation of a method of implementing VVT with the use of a secondary valve in series with the conventional intake valve of the engine. The secondary valve is not required to withstand the temperatures and pressures of combustion, and therefore can be of relatively lightweight design, so that it is easier to adjust the timing of the secondary valve than that of the main valve. Experiments with such a valve installed in a production engine indicate that benefits of variable valve timing such as overlap optimisation and throttleless load control (4% Fuel benefits at 980 rpm and 1.5 bar IMEP) are attainable with this system.

This paper describes an investigation of implementing variable valve timing with the use of a secondary valve in the intake tract The secondary valve acts in series with the conventional poppet valve of the engine, which is actuated in the conventional manner and with fixed timing It is significantly easier to adjust the timing of the secondary valve than that of the main valve There are two possible modes of operation of this device One is to control valve overlap, improving low speed low load performance The other is to use it as a load control mechanism, replacing the conventional throttle and therefore reducing the ‘pumping losses’ associated with conventional throttling We have implemented such a system on a motored single-cylinder research engine using pneumatic actuation Our experiments have demonstrated successful load control, significant pumping loss reduction, and control of backflow from the exhaust to the intake manifold

Pressure waves in the inlet manifold of internal combustion engines have a significant effect on volumetric efficiency. This paper considers the possibility of generating further pressure waves as a method of increasing volumetric efficiency. A theoretical and experimental investigation, the former based on a novel linear model for supercharging, has revealed that actuators driven by the waves present in the waves, “passive” actuators, are able to significantly alter the volumetric efficiency; with ±15% changes demonstrated experimentally. Further improvement with energising or “active” actuators, however, requires more potent actuators than are in general use at present: to provide significant benefit, the power introduced by the actuator must be comparable to that of the natural excitation of the manifold by the induction stroke. A few possible classes of active actuators are discussed.

The measurement of volumetric efficiency is discussed, with particular attention given to the design of surge tanks to smooth the inlet flow pulsations. It is shown that smoothing the inlet flow can be impractical for single-cylinder research engines. A simple and convenient method of characterising volumetric efficiency, based on in-cylinder pressure variation, is discussed, and practical implementations for both motored and firing engines are described. The method is extremely useful for the comparison of different manifold configurations or the assessment of other factors affecting volumetric efficiency.