A THEORETICAL-STUDY OF A VARIABLE COMPRESSION RATIO TURBOCHARGED DIESEL-ENGINE

A variable compression ratio concept that can give a different expansi on ratio to the compression ratio has been evaluated by means of a sim ulation of a turbocharged diesel engine. The compression ratio is cont rolled by varying the ratio of the connecting rod length to the crank throw, hence the name variable crank radius/connecting rod length engi ne (VR/LE). The VR/LE mechanism kinematics have been defined and descr ibed, and the compression ratio and expansion ratio have been presente d as a function of the eccentric phase angle (alpha(o)). A zero-dimens ional engine simulation that has been the subject of comprehensive val idation has been used as the basis of the VR/LE study. The effect of t he compression ratio on the engine performance at fixed loads is prese nted. The principal benefits are a reduction in fuel consumption at pa rt load of about 2 per cent and a reduction in ignition delay that lea ds to an estimated 6 dB reduction in combustion noise. The study has b een conducted within the assumption of a maximum cylinder pressure of 160 bar.