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This study measures transient torque, smoke opacity and pumping-losses derived from in-cylinder pressure, as a function of Variable Geometry Turbocharger (VGT) vane position (derived through Engine Control Unit, ECU). Tests were conducted using a typical passenger car/light duty truck application turbo-charged common-rail diesel engine, of 14 configuration. The aim was to seek potential improvements in engine pumping-losses (and thus fuel economy) during full-load transients and at low engine speeds, due to opening of VGT vanes. The objective was to record engine performance (e.g. engine transient-torque, smoke opacity, fuel-demand, engine pressure-ratio etc.), under full-load operation, and at engine speeds of 900-1600 rpm. The effects of “slow” and “fast” transient manoeuvres were established (in a transient test facility) by performing four different acceleration rates (i.e. 2s, 5s, 10s and 20s).

An optically accessed, single-cylinder engine capable of operating at both spark ignition and Homogeneous Charge Compression Ignition (HCCI) combustion was used to investigate the difference in the initiation and development of HCCI combustion due to charge stratification, internal Exhaust Gas Recirculation (iEGR) or spark discharge. Natural-light images were acquired to visualise the differences in chemiluminescent structure (i.e. reaction structures) at the early and late stages of formation during HCCI combustion in an attempt to find better ways of controlling HCCI combustion at low and high loads. Regardless of charge stratification, the cycle-to-cycle deviation of autoignition from temporal and spatial repeatability was comparatively small. Flame initiation appeared initially at single or spatially adjacent sites and we did not observe the growth of any new, (i.e. “secondary” in time) reacting ‘islands’ separate from the original sites.

A high-swirl, low Compression Ratio (CR), optically accessed engine that was able to produce a stratified charge was used to investigate the differences in HCCI combustion and in the propagation of the autoignition front between a non-stratified and a stratified charge. Furthermore the relevance of charge stratifying an engine using variable injection timing with large temperature inhomogeneities was investigated. The CHEMKIN code and a detailed reaction mechanism were used to simulate the fuel chemistry of ignition and combustion in a low CR engine. The aim of the simulation was to quantify the effect of initial mixture temperature, Ti and A/F ratio on cool flame and main ignition timing and to evaluate the possibility of charge stratifying our engine.