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Nowadays, emission regulations and the requirement to reduce greenhouse gas emissions have escalated engine development efforts. In the present work, the effect of compression ratio on the performance, combustion and emission characteristics of a spark-ignition engine is evaluated at different operating conditions. A single-cylinder, water-cooled, spark-ignition engine (modified from a compression-ignition version) was used, with combustion chamber geometry consisted of flat cylinder head and a hemispherical bowl in the piston. Results showed that the brake thermal efficiency was increased from 9.8% to 12.9% when compression ratio was increased from 6.7:1 to 9.4:1 at low operating load of 5 N-m. Carbon monoxide emission was decreased when compression ratio was increased at all operating loads. However, as expected, nitric oxide emission was increased with the increase in compression ratio, with lower difference at low loads compared to medium and high loads.

A single-cylinder gasoline direct-injection engine was used for fuel spray and combustion visualizations with optical access to the combustion chamber. Experiments were conducted to investigate the effect of fuel injection pressure on spray and combustion characteristics inside the engine cylinder. A multi-hole high-pressure production injector was used with fuel pressures of 5 and 10 MPa. A Mie scattering technique was used to image the liquid phase of the fuel dispersion. The obtained spray images were then used to study the macroscopic spray characteristics such as spray structure, spray tip penetration and spray angle. Combustion visualization tests were performed to evaluate the effect of fuel injection pressure on combustion characteristics. In-cylinder pressure signals were recorded for the combustion analyses and synchronized with the high-speed combustion imaging recording.

The aim of this work is to study the combustion and gaseous emissions characteristics of a diesel engine dual-fueled with natural gas at different operating conditions (light to full load) for generator application. The electromechanical system was composed of a commercially available 18 liter, 6-cylinder diesel engine, coupled with the generator rated at 600 kWe at full-load. The flow of natural gas was electronically controlled using a throttle valve, and was inducted in the intake manifold before being introduced into the combustion chambers. Gaseous emissions of carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) were measured under both diesel and dual fuel operations at different loads. This work also presents the effects of diesel oxidation catalyst to reduce HC and CO emissions under dual fuel operation. At each operating load, gas percentage was increased with corresponding decrease in diesel pilot while maintaining the same power output.