Abstract
Diesel engine injection strategy plays a crucial role in fuel–air mixing and consequent soot formation, requiring optimisation. Fuel properties affect the combustion characteristics of the engine significantly. In this study, the fundamental mechanisms of pilot-main injection interactions and the effects of fuel properties have been investigated using a combined approach of optical diagnostics in an optical engine and computational fluid dynamics (CFD) tools. A single-cylinder optical research engine (SCORE) with a cylindrical piston bowl was used for the optical engine investigations. Simulations were carried out using a re-entrant piston geometry model. Reynolds-Averaged Navier-Stokes (RANS) based Re-Normalization Group (RNG) k-ε model was adopted and solved using CONVERGE CFD solver. SAGE detailed chemistry solver was used for the calculations of combustion kinetics. The adaptive mesh refinement (AMR) strategy was used for improved grid resolution. The investigation results highlighted a striking difference between the combustion mechanisms of the pilot injection and the main injection. The pilot-main injection interactions became crucial for igniting the main fuel spray. The swirl intensity was dominant in the pilot-main injection interactions and the combustion initiation. The impinging spray jet and swirl interactions improved the radial mixing and reduced the soot in the up-swirl direction. Dieseline (a blend of diesel and gasoline) and diesohol (a blend of diesel and alcohol) resulted in lower soot formation than baseline diesel. This study demonstrated that in-cylinder swirl and oxygen concentration could be optimised to simultaneously reduce oxides of nitrogen (NOx) and soot emissions using oxygenated fuels.
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