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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.