Improvement in part-load performance of a manifold injected spark ignition engine - an experimental investigation

This paper deals with the experimental investigations carried out on a single-cylinder, four-stroke, manifold injected spark ignition engine to improve the part-load performance and emission characteristics by modulating the inlet valve closure timing (IVCT) and clearance volume (CV). The IVCT is delayed in order to reduce the volumetric efficiency of the engine with full throttle operation which in turn reduces the brake power output so that engine can be operated at part-load. In addition, the CV is also reduced with respect to IVCT to maintain the effective compression ratio (ECR) of the engine. These things change the geometric expansion ratio (GER) and ECR of the engine along with reduced pumping losses to increase the brake thermal efficiency and reduce the exhaust emissions at part-loads. In order to vary the part-load brake power output, a suitable combination of the IVCT and CV is used which in turn vary the GER/ECR ratio of the engine. In this study, experiments are carried out for the different GER/ECR ratios varying from 1.25 to 2 with two ECRs of 7 and 8 at a constant engine speed of 1500 rev/min. From the results, it is found that for GER/ECR ratio of 1.5 with ECR of 8 and 7, the improvement in brake thermal efficiency is about 3.5 and 6.6%, the reduction in unburned hydrocarbon emissions is about 25 and 22.5% and the reduction in nitric oxides emissions is about 51 and 52% respectively compared to conventional engine at the corresponding brake power outputs.