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Oxyfuel combustion and nitrogen-free combustion coupled with Carbon Capture and Storage (CCS) techniques have been recently proposed as an efficient method to achieve carbon free emissions and to improve the combustion efficiency in diesel engines. In this study, a 3-D computational fluid dynamics model has been used to evaluate the influence of oxyfuel-HCCI combustion on engine operating conditions and combustion characteristics in a HSDI diesel engine. Investigations have conducted using four different diluent strategies based on the volume fraction of pure oxygen and a diluent gas (carbon dioxide). The first series of investigations has performed at a constant fuel injection rating at which 4.4 mg of fuel has injected per cycle. In the second part of analysis, the engine speed was maintained at 1500 rev/min while the engine loads were varied by changing the fuel injection rates in the range of 2.8 to 5.2 mg/cycle.

A three-dimensional simulation was carried out for investigating effects of negative valve overlap (NVO) on gas exchange and fuel-air mixing processes in a diesel homogeneous charge compression ignition (HCCI) engine with early fuel injection. It was found that the case with longer NVO produced a stronger swirl motion and a more significant vortex below the intake valve due to the high annular jet flow through the valve curtain area during the intake stroke. However, there was not much difference in the values of swirl ratio, tumble ratio and turbulence intensity between different NVOs at the end of compression stroke. It was also seen that enlarged NVO not just increased in-cylinder temperature but also improved the temperature homogeneity. With increased NVO, there is a bigger spray shape and more droplets exist in gaps of sprays. This demonstrates that stronger turbulence intensity and higher temperature homogeneity with higher NVO improve fuel vaporization and air-fuel mixing.

Effects of split injection with different EGR rate on combustion process and pollutant emissions in a DI diesel engine have been evaluated with CFD modeling. The model was validated with experimental data achieved from a Caterpillar 3401 DI diesel engine and 3D CFD simulation was carried out from intake valve closing (IVC) to exhaust valve opening (EVO). Totally 12 different injection strategies for which two injection pulses with different fuel amount for each pulse (up to 30% for the second pulse) and different separation between two pulses (up to 30° CA) were evaluated. Results show that adequate injection separation and enough fuel amount of the second pulse could form a separate 2nd stage of heat release which could reduce the peak combustion temperature and improve the oxidation of soot formed in the first heat release stage.

Owing to the potentials for low NOx and soot emissions, diesel PCCI combustion has been widely studied over last 10 years. However, its control is still the main barrier to constrain it to be applied on production engines. As there are a number of variables which affect the mixing and combustion process, it is difficult to develop control strategies with adequate functions but simple control order for implementing them. In the current research, a reformed Homogeneity Factor (HF) of in-cylinder charge has been explored as a control medium for simplifying the control model structure. Based on multi-pulse injection, the effects of operating parameters on the Homogeneity Factor and the relationship between Homogeneity Factor and mixing, combustion processes, emissions were investigated in a four-valve, direct-injection diesel engine by CFD simulation using KIVA-3V code coupled with detailed chemistry.

An advanced turbulence modeling using Large Eddy Simulation (LES) has been employed for studying diesel engine flow and its effects on combustion process and amount of pollutant emissions in a DI Diesel engine. An improved version of the Extended Coherent Flame Model combustion model (ECFM-3Z) coupled with advanced models for NOx and soot formation has been applied for CFD simulation. The model performance was assessed by comparison of the calculation results with corresponding experimental data. Very good agreement of calculated and measured in-cylinder pressure, heat release rate as well as pollutant formation trends were obtained. The simulation results was further compared with those obtained by traditional Reynolds-averaged Navier-Stokes model (RANS) at three different mesh resolutions. It was concluded that sensivity of LES approach to geometric details is affected by increasing resolution as compared to existing RANS.

Carbon Capture and Storage (CCS) techniques in combination with oxy-fuel combustion have been applied as an effective way to achieve nitrogen-free combustion and zero-carbon emissions. The present study has been carried out computationally in the framework of a European project (RIVER) (funded by Interreg North-West Europe) to explore the effect of intake charge temperature on oxy-fuel combustion in an HSDI diesel engine under HCCI combustion mode. Experimental data obtained from a Ford Puma common-rail diesel engine for a conventional part-load condition at 1500 rev/min and 6.8 bar IMEP have been used to validate the CFD model. To simulate the combustion process of HCCI, a reduced chemical n-heptane-n-butanol-PAH model has been adopted. The model has 349 elementary reactions and 76 species. The simulation has been carried out at five different intake charge temperatures (140°C, 160°C, 180°C, 200°C, and 220°C) and five different intake oxygen percentages (15%, 17%, 19%, and 21% v/v).