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Dual-fuel engines represent a simple and flexible approach to employing gaseous fuels including hydrogen in conventional diesel engines. This paper reports on the investigation into the effects on performance, emissions and combustion characteristics of introducing low volumetric concentrations of hydrogen into the intake air of a multi-cylinder IDI diesel engine. It is shown that increasing the admission of hydrogen up to a certain low concentration increased power output, whereas further increases in hydrogen admission began to decrease power output. For the same total fuel energy input, the engine brake power and thermal efficiency were less with hydrogen admission as compared to the corresponding pure diesel operation. The exhaust gas opacity and the emissions of oxides of nitrogen and carbon monoxide showed correspondingly relatively significant reductions.

Results of an experimental investigation into the extent of methane conversion when introduced in extremely small concentrations down to around a fraction of one percent by volume into the intake of a swirl chamber diesel engine are presented. Such an approach represents effectively an unconventional dual fuel engine operation with exceptionally lean gaseous fuel mixtures but combined with unusually very large diesel fuel pilot quantities. It is to be shown that for wide ranges of gas admission concentrations, diesel fuel quantity injected, load and speed that much of the methane added did get oxidized in the indirect injection engine to an extent from 53% to 80%, to appear in the form of carbon dioxide while contributing at the same time to the power output. Such methane admission tended to increase carbon monoxide exhaust emissions slightly, indicating that part of the methane may not have been fully oxidized.

The paper examines the rapid compression process of methane-air mixtures while using a zero-dimensional simulation and a detailed chemical kinetic scheme involving 137 reaction steps for methane-air combustion with an account made for heat transfer. The results of this simulation are compared with the corresponding values obtained when using multi-dimensional CFD simulation of the temporal and spatial evolution of the physical properties inside the cylinder while using KIVA-3 code both for reactive and non-reactive “methane”-air mixtures. The reaction rate data used in the code were overall rates of varyingly fitted data based on results of the full detailed kinetic scheme under the same local conditions. The effects of the non-uniformity in the charge physical properties due to heat transfer and compression effects on the evolution of the chemical processes leading to autoignition are presented and discussed.

The dual fuel engine is a means for utilizing gaseous fuel resources efficiently in diesel engines after appropriate conversion. These converted engines can provide an effective method for producing power while reducing exhaust emissions, especially exhaust particulates and oxides of nitrogen. More efficient and increased power output relative to the corresponding diesel operation can be achieved with dual fuel engines at relatively high load. The light load performance, especially with high gas to diesel fuel ratios, remains relatively inferior. Poor fuel utilization efficiencies and high unburnt hydrocarbons and carbon monoxide exhaust concentrations are readily encountered at light loads. This trend has necessitated usually the resorting back to diesel operation at idling and very light load conditions. The paper describes the combustion phenomena that bring about these limitations at light load.

The preignition processes in a dual fuel engine are described and the roles of the formation and consumption of formaldehyde in these and subsequent processes are discussed. Reference is made to the results of detailed chemical kinetic modelling of the oxidation reactions of the gaseous fuel component during the compression stage. This is supported by experimental evidence of the kinetic role of formaldehyde through its deliberate induction with the intake charge of a dual fuel engine over a range of operating conditions and fuels. It is suggested that the preignition reaction activity of the gaseous fuel-air charge during compression contributes significantly to the observed extension of the ignition delay in dual fuel engines at very low load conditions when relatively small gaseous fuel concentrations are being used.

The paper describes the successful operation of a research single cylinder direct injection dual fuel engine on excessively rich mixtures of methane and oxygen enriched air. This is done with the view that the partial oxidation of methane would produce significant concentrations of hydrogen in the exhaust gas while producing simultaneously mechanical power. Various features of engine performance and exhaust hydrogen production under such unconventional operation are presented and discussed.

The results of an experimental investigation into the performance of a single cylinder direct injection dual fuel engine fuelled with methane when very rich intake mixtures were employed are presented and discussed.