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A new hydraulic cam follower with variable valve timing (VVT) properties is described. Experimental results show that the point of closure of the valve may be delayed as a linear function of engine speed without external control. No other parameter of the valve event is modified by the device. An obvious application is the control of intake valve timing for engines with a wide speed range, where the point of valve closure could be scheduled with engine speed in order to maximise the trapped mass, hence improving the torque curve at low and high speeds. The device is considered for application to the Ford 2.5 litre DI diesel engine, where it may be used to retard inlet valve closure from close to bottom dead centre (BDC) at cranking speed to 50-60 deg after BDC at rated speed.

A variable compression ratio concept that can give a different expansion ratio to the compression ratio has been evaluated by means of a simulation of a turbocharged diesel engine. The VR/LE mechanism kinematics have been defined and described, and the compression ratio and expansion ratio have been presented as a function of the eccentric phase angle (αo). A zero-dimensional engine simulation that has been the subject of comprehensive validation, has been used as the basis of the VR/LE study. The effect of the compression ratio on the engine performance at fixed loads is presented. The principal benefits are a reduction in fuel consumption at part load of about 2%, and a reduction in ignition delay that leads to an estimated 6 dB reduction in combustion noise. The study has been conducted within the assumption of a maximum cylinder pressure of 160 bar.

This paper explains the reasons for applying variable valve timing to a diesel engine, in order to reduce the likelihood of inlet port fouling at part load. The results from a cycle simulation are compared with experimental results, from an engine tested with three different valve timings. Good agreement between the model and the engine is demonstrated by comparisons of experimental and simulation results for both global parameters, and cycle resolved pressure measurements (cylinder and manifolds). The cycle simulation has thus been used to predict the benefits that accrue from the application of variable valve timing to a turbocharged diesel engine. Reducing the valve overlap was found to be beneficial at part load. The greatest reduction in the reverse flow of exhaust residuals into the inlet manifold, was obtained if the inlet valve opening was delayed by phasing the inlet valve events.

The paper describes the development of a hydraulic variable valve motion system which has been used successfully to study the relationship between rate of exhaust valve opening and exhaust pulse energy with reference to exhaust turbocharging. The device may be configured to provide variation of timing, rate of opening or closing, or lift. Each of these variations could be achieved independently, for example, the start of valve opening could be varied without altering either the rate of opening or the full lift. The device is described in detail and preliminary experimental results are given. An alternative configuration in which the variation of motion may be achieved digitally is described.