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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.

In the paper the design of the single-cylinder research engine equipped with the mechanism which make it possible to adjust the compression ratio continuously and currently during the engine operation is introduced. The concept of that engine, called VR/LE (Variable R/L Engine), and its theory was presented elsewhere before, but so far the concept has not been brought into practice. By that the feasibility of constructing the real variable compression ratio engine according to the VR/LE principle has been proved. The presented results of the preliminary investigations confirm the advantages of that concept.

A theoretical analysis of the stoichiometry of the mixture produced in a main fuel system of the engine carburetor is presented. The analysis made it possible to develop a computer code which was applied to the particular Weber type carburetor from a small, two-cylinder car engine. The operation of the carburetor in the regimes of the steady and unsteady flow, including the influence of back flows, was investigated. It is concluded that the air pressure pulsations and, in particular, the existence of the back flows cause the significant enrichment of the mixture produced in the carburetor.