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Natural Gas (NG) is currently a cost effective substitute for diesel fuel in the Heavy-Duty (HD) diesel transportation sector. Dual-Fuel engines substitute NG in place of diesel for decreased NOx and soot emissions, but suffer from high engine-out methane (CH4) emissions. Premixed Dual-Fuel Combustion (PDFC) is one method of decreasing methane emissions and simultaneously improving engine efficiency while maintaining low NOx and soot levels. PDFC utilizes an early diesel injection to adjust the flammability of the premixed charge, promoting more uniform burning of methane. Engine experiments were carried out using a NG and diesel HD single cylinder research engine. Key speeds and loads were explored in order to determine where PDFC is effective at reducing engine-out methane emissions over Conventional Dual-Fuel which uses a single diesel injection for ignition.

Over recent years, in order to develop more efficient and cleaner gasoline engines, a number of new engine operating strategies have been proposed and many of them have been studied on different engines but there is a lack of different comparison between various operating strategies. In this work, a single cylinder direct injection gasoline engine equipped with an electro-hydraulic valvetrain system has been commissioned and used to achieve seven different operation modes, which are 4-stroke throttle-controlled SI, 4-stroke intake valve throttled SI, 4-stroke positive valve overlap SI, 4-stroke negative valve overlap CAI, 4-stroke exhaust rebreathing CAI, 2-stroke CAI and 2-stroke SI. Their performance and emission characteristics are presented and discussed.

Controlled Auto Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), is one of the most promising combustion technologies to reduce the fuel consumption and NOx emissions. Currently, CAI combustion is constrained at part load operation conditions because of misfire at low load and knocking combustion at high load, and the lack of effective means to control the combustion process. Extending its operating range including high load boundary towards full load and low load boundary towards idle in order to allow the CAI engine to meet the demand of whole vehicle driving cycles, has become one of the key issues facing the industrialisation of CAI/HCCI technology. Furthermore, this combustion mode should be compatible with different fuels, and can switch back to conventional spark ignition operation when necessary. In this paper, the CAI operation is demonstrated on a 2-stroke gasoline direct injection (GDI) engine equipped with a poppet valve train.

This work was concerned with increasing the attainable load during gasoline controlled auto-ignition combustion in a multi-cylinder direct fuel injection research engine. To extend the peak output under naturally aspirated conditions it proved favourable to combine internal and external exhaust gas recirculation under stoichiometric fuelled conditions. During turbocharged high load operation it was beneficial in terms of fuel economy to dilute the charge with a combination of internally re-circulated exhaust gases and excess air. Replacing a proportion of these diluents with externally re-circulated burned gases appeared to facilitate lower emissions of HC and CO. The highest load generated via boost was limited by increasing peak in-cylinder pressure and falling gas exchange efficiency. Regardless, the use of boost increased the load at which CAI could be invoked without lean NOx after-treatment.