A Theoretical Study of a Variable Compression Ratio Turbocharged Diesel Engine

Abstract

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 compression ratio is controlled by varying the ratio of the connecting rod length to the crank throw, hence the name variable crank radius/connecting rod length engine (VR/LE). 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 per cent 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.

The Szymkowiak’s over-expanded cycle in the rocker engine with the variable compression ratio – kinematics

“…Additionally, the mechanism provides possibility of change in both the compression and expansion ratio. This concept refers to the solution presented by Rychter and Teodorczyk [4,5]. The mechanism VR/VL, which they proposed, applies a variable ratio of the length of the crank to the connecting rod in order to change the compression ratio.…”

Estimation of effective compression ratio for engines utilizing flexible intake valve actuation

“…Using conventional engine hardware and actuators, the compression ratio is generally fixed or has limited variability, however the work of Shaik et al 16 motivates a need for variable compression ratios in automobile engines for improved performance through implementation of advanced combustion strategies, such as homogeneous charge compression ignition. Rychter et al 17 detail a theoretical study in which variation of the compression ratio allows a reduction in both fuel consumption and combustion noise. Experimental studies by Gerard et al 18 and Pesic et al 19 also show the benefits of varying the compression ratio to reduce emissions and improve fuel economy.…”