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A conceptual approach to help understand and simulate droplet induced pre-ignition is presented. The complex phenomenon of oil-fuel droplet induced pre-ignition has been decomposed to its elementary processes. This approach helps identify the key fluid properties and engine parameters that affect the pre-ignition phenomenon, and could be used to control LSPI. Based on the conceptual model, a 3D CFD engine simulation has been developed which is able to realistically model all of the elementary processes involved in droplet induced pre-ignition. The simulation was successfully able to predict droplet induced pre-ignition at conditions where the phenomenon has been experimentally observed. The simulation has been able to help explain the observation of pre-ignition advancement relative to injection timing as experimentally observed in a previous study [6].

Natural gas is one of the promising alternative fuels due to the low cost, worldwide availability, high knock resistance and low carbon content. Ignition quality is a key factor influencing the combustion performance in natural gas engines. In this study, the effect of pre-chamber geometry on the ignition process and flame propagation was studied under varied initial mixture temperatures and equivalence ratios. The pre-chambers with orifices in different shapes (circular and slit) were investigated. Schlieren method was adopted to acquire the flame propagation. The results show that under the same cross-section area, the slit pre-chamber can accelerate the flame propagation in the early stages. In the most of the cases, the penetration length of the flame jet and flame area development are higher in the early stages of combustion.

An experiment was carried out to investigate the effect of single and double-deck pre-chamber on the combustion characteristics of premixed CH4/air in a constant volume vessel using schlieren method. A special design was proposed for the visualization of the pre-chamber. Combustion with different initial temperatures (300 K, 400 K, 500 K) were observed at stoichiometric ratio to lean-burn limit. Although single-deck pre-chamber has advantages over double-deck pre-chamber in both initial flame development duration and main combustion duration, the latter could extend the lean-burn limit by up to 0.3 and promote the stability of ignition. It is also found that extensive distribution of active species in main chamber before ignition can accelerate speed of flame propagation enormously.

Urea selective catalytic reduction (SCR) is a key technology for heavy-duty diesel engines to meet the increasingly stringent nitric oxides (NOx) emission limits of regulations. The urea water solution injection control is critical for urea SCR systems to achieve high NOx conversion efficiency while keeping the ammonia (NH3) slip at a required level. In general, an open loop control strategy is sufficient for SCR systems to satisfy Euro IV and Euro V NOx emission limits. However, for Euro VI emission regulation, advanced control strategy is essential for SCR systems due to its more tightened NOx emission limit and more severe test procedure compared to Euro IV and Euro V. This work proposed an approach to achieve model based closed loop control for SCR systems to meet the Euro VI NOx emission limits. A chemical kinetic model of the SCR catalyst was established and validated to estimate the ammonia storage in the SCR catalyst.

Polyoxymethylene dimethyl ethers (PODEn) have high cetane number, high oxygen content and high volatility, therefore can be added to gasoline to optimize the performance and soot emission of Gasoline Compression Ignition (GCI) combustion. High speed imaging was used to investigate the spray and combustion process of gasoline/PODEn blends (PODEn volume fraction 0%-30%) under various ambient conditions and injection strategies in a constant volume vessel. Results showed that with an increase of PODEn proportion from 10% to 30%, liquid-phase penetration of the spray increased slightly, ignition delay decreased from 3.8 ms to 2.0 ms and flame lift off length decreased 29.4%, causing a significant increase of the flame luminance. For blends with 20% PODEn, when ambient temperature decreased from 893 K to 823 K, the ignition delay increased 1.3 ms and the flame luminance got lower.