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Present paper discusses the advantages and disadvantages of fuel injection rate shaping for a medium-duty diesel engine using computational analysis. The analysis was performed using three-dimensional (3D) Computational Fluid Dynamics (CFD) code KIVA-3V. Fuel injection rate-shape is parameterized and a Design of Experiments (DoE) is constructed. CFD simulations are performed at discrete DoE points to construct a statistical model, which is then used to predict the engine response for variation in injection shape parameters. Trends of NOx, soot, noise and Indicated Mean Effective Pressure (IMEP) are investigated to understand the impact and potential of injection rate-shaping on engine performance. It is found that slow increase in injection rate leads to reduction in NOx and IMEP, but has almost no effect on soot emissions. Effect of rate shaping during fall of injection rate does not show strong influence on emissions and performance.

The nitrogen dioxide (NO₂) emissions of compression ignition diesel engines are usually relatively small, especially when operated at medium and high loads. Recent experimental investigations have suggested that adding hydrogen (H₂) into the intake air of a diesel engine leads to a substantial increase in NO₂ emissions. The increase in NO₂ fraction in the total NOx is more pronounced at lower engine load than at medium- and high-load operation, especially when a small amount of H₂ is added. However, the chemistry causing the increased NO₂ formation in H₂-diesel dual-fuel engines has not been fully explored. In the present work, kinetics of NO and NO₂ formation in a H₂-diesel dual-fuel engine are investigated using a CFD model integrated with a reduced hydrocarbon oxidation chemistry and an oxides of nitrogen (NOx) formation mechanism. A low-load and a medium-load operating condition are selected for numerical simulations.

Three different approaches for modeling diesel engine combustion are compared against cylinder pressure, NOx emissions, high-speed soot luminosity imaging, and 2-color thermometry data from a heavy-duty DI diesel engine. A characteristic time combustion (KIVA-CTC) model, a representative interactive flamelet (KIVA-RIF) model, and direct integration using detailed chemistry (KIVA-CHEMKIN) were integrated into the same version of the KIVA-3v computer code. In this way, the computer code provides a common platform for comparing various combustion models. Five different engine operating strategies that are representative of several different combustion regimes were explored in the experiments and model simulations. Two of the strategies produce high-temperature combustion with different ignition delays, while the other three use dilution to achieve low-temperature combustion (LTC), with early, late, or multiple injections.