A non-thermal plasma reactor (NTPR) using two 2.45 GHz Microwave (MW) generators for the abatement of Nitrogen Oxides (NOx) and Sulphur (SOx) contained in the exhaust gas of a 200 kW marine diesel engine was built and tested. Numerical analysis based on a non-thermal plasma kinetics model for the abatement of NOx and SOx from marine diesel engine exhaust gas was performed. A generic kinetic model that implements electron collisions and plasma chemistry has been developed for applications involving low temperature (50K-100K) non-thermal plasma. Abatement efficiencies of NOx and SOx were investigated for a range of mean electron energies which directly impact on the rate constants of electron collisions. The simulation was conducted using the expected composition of exhaust gas from a typical two-stroke slow speed marine diesel engine. The simulation results predict that mean electron energy of 0.25eV-3.2eV gives abatement efficiency of 99% for NOx and SOx. The minimum residence time required was found to be 80ns for the mean electron energy was 1eV. Multi-mode cavity was designed using COMSOL multi-physics. The NTPR performance in terms of NOx and SOx removal was experimentally tested using the exhaust from a 2 kW lab scale two stroke diesel engine. The experimental results also show that complete removal of NO is possible with the microwave plasma (yellow in color) generated. However it was found that generating right Microwave plasma is a challenging task and requires further investigation.

It is commonly reported in the literature that NO x emissions from a diesel engine increase when fuelling with biodiesel. However, some studies report varying or opposite results. This work scrutinized operating conditions known to yield both increases and decreases in NO x emissions when running on biodiesel. This involved sweeping the injection timing of an instrumented 2 L diesel engine from 14 BTDC (before top-dead-center) to 3 ATDC (after top-dead-center), under loads of 40 Nm and 80 Nm (equating to BMEP (brake mean effective pressure) of 2.5 bar and 5 bar, respectively), using ultralow sulfur diesel (ULSD) and rapeseed methyl ester (RME). Under a 40 Nm load, RME consistently generated lower NO x emissions than ULSD, whereas, under an 80 Nm load, RME generated higher NO x emissions at all but the most advanced/retarded injection timings. This behavior was linked to differences in combustion duration, ignition delay (ID), and the relative size of the premixed burn fraction (PMBF). Combustion tended to progress more quickly overall for the fuel that generated highest NO x emissions at most operating conditions. ID was always reduced when fuelling with RME, and hence PMBF was also reduced. Thus, reduced ID exerted conflicting influences over relative RME NO x emissions; a tendency to increase NO x , due to advanced start of combustion (SOC), and a tendency to decrease NO x , due to reduced PMBF. Additionally, calculations indicated that for the same SOC and PMBF RME would normally be expected to generate higher NO x emissions than ULSD. However, as the level of premixing increased, the magnitude of the ceteris paribus RME NO x increase appeared to decline. That is, as PMBF increases, the impact of the inherent factors beyond advanced SOCthat lead to higher NO x emissions when fuelling with biodiesel appear to be reduced. This may be related to variations in soot radiative heat losses. Changes in operating PMBF may therefore explain some of the variety that exists in the literature relating to the effects of biodiesel fuelling on NO x emissions.

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This chapter presents a concise treatment of diesel engine exhaust emissions and its mitigations. The working principle of the diesel engine is first given to establish the background and further to describe the influence of various parameters that affect the formation of engine exhaust emissions. The factors that influence exhaust emissions are linked to the engine design and the operating factors that promote good fuel-air mixing and combustion. These factors are air induction, fuel injection equipment, fuel injection schemes, in-cylinder gas exchange process and heat transfer. Thermochemistry essentially gives insight to the global reaction kinetics and how this is applied in practical engine combustion determinations in terms of equivalence ratios. Based on these, the fuel spray structure, atomization, penetration and the spray combustion model are described. The formation of exhaust emissions such as carbon monoxide, unburnt hydrocarbon and its intermediates, oxides of nitrogen and soot in diesel engines has been discussed. The techniques of their mitigation from the view of internal factors that deals with the optimization of engine design and it performance, as well as various exhaust after-treatment techniques used for NO x and soot reduction have been briefly discussed.

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