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Emissions of unburned methane are the Achilles heel of premixed gas engines whether they are spark ignited or diesel pilot ignited. If the engine is operated lean, lower temperatures prevail in the combustion chamber and several of the mechanisms behind the hydrocarbon emissions are aggravated. This paper presents an experimental investigation of the contribution from combustion chamber crevices and quenching to the total hydrocarbon emissions from a diesel-methane dual fuel engine at different operating conditions and air excess ratios. It is shown that the sensitivity to a change in topland crevice volume is greater at lean conditions than at stoichiometry. More than 70% of hydrocarbon emissions at air excess ratios relevant to operation of lean burn engines can be attributed to crevices.

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. Attention has recently been drawn to the fact that the tip of the diesel injector may reach intolerable temperatures. The high injector tip temperatures in the DDF engine are caused by the reduction in diesel flow through the injector. For dual fuel operation, as opposed to diesel, high load does not necessarily imply a high flow of diesel through the injector nozzle. This research investigated the factors causing high injector tip temperatures in a DDF engine and the underlying mechanisms which transfer heat to and from the injector tip. Parameter sweeps of each influential parameter were carried out and evaluated. In addition to this, a simple and useful model was constructed based on the heat balance of the injector tip.

Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with diesel combustion. A series of tests has been carried out on a single-cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. One feature of port-injected Dual Fuel is that full diesel functionality is maintained, which is of great importance when bringing the dual fuel technology to market. The objective of the study was to characterize and investigate the potential for dual fuel combustion utilizing all degrees of freedom available in a modern diesel engine. Increased diesel pilot proved efficient at reducing NOx emissions at low λ.

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. One benefit of having two fuels on board the vehicle is the additional degree of freedom provided by the ratio between the fuels. This additional degree of freedom enables control of combustion phasing for combustion modes such as Homogenous Charge Compression Ignition, HCCI, and Partly Premixed Compression Ignition, PPCI. These unconventional combustion modes have great potential to limit emissions at light load while maintaining the low pumping losses of the base diesel engine. A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners.

An effective way of meeting future emission legislation with a heavy-duty diesel engine is to equip the engine with an EGR-system combined with a particulate trap. In this study the work was concentrated on the EGR-system. The goal of the investigation was to find an EGR-system that could deliver enough air and exhaust gases to the engine to meet the Euro IV emission levels with minimum penalty on engine performance and fuel consumption, starting from a Euro 0 engine. The tests showed that it was possible to significantly improve emissions with all the tested EGR-systems in combination with a particulate trap, but notable differences with respect to fuel consumption were found. For all EGR systems under study, the main factors influencing engine performance and fuel consumption were found to be. Pumping losses. Residual gases. Temperature of the recirculated exhaust gases. Distribution of the recirculated exhaust gases between the cylinders