Investigation into fuel pre-treatments for combustion improvement on a compression ignition engine

Abstract

This project aims to improve the combustion performance of a compression ignition engine using three novel fuel pre-treatments, the employment of renewable fuels, nano additive modified fuels and supercritical (SC) fuel combustion, from the perspective of spray characteristics and engine performance. In this project, HVO and GTL are selected as the renewable fuels, whilst CeO2 nanopowder and CNT are the nano additives. A CVV system is fabricated to investigate macroscopic spray characteristics of test fuels at various conditions. A 2D CFD model coupled with the DoE method is developed to correlate experimental conditions to macroscopic spray characteristics. A Cummins ISB4.5 diesel engine test rig is employed to obtain the in-cylinder behaviour and pollutant emissions. A 3D CFD model is built to study the advantages of SC fuel combustion. GTL shows the smallest spray tip penetration during both the injection and post-injection periods, whilst DF has the largest penetration, but the average cone angles are almost the same. Nano additives have no impact on the average cone angle and spray tip penetration, except that CNT can increase the spray tip penetration slightly in the post-injection period. Empirical models are formulated and indicates different impacts of each experimental condition during injection and post-injection. HVO and GTL have lower fuel consumption and NOx, HC and PN emissions than DF. CeO2 nanopowder can significantly reduce NOx, HC and PN emissions, whilst CO can only be reduced in a certain engine load and speed range. CNT lowers down all emissions when blending with most test fuels except GTL. Compared with conventional spray combustion, SC fuel combustion illustrates significantly higher in-cylinder peak pressure and thus improved engine output power. Moreover, the fuel concentration and temperature field during the SC combustion are more evenly distributed, which enables more sufficient combustion and reduction of NOx and soot generation.