Although diesel after-treatment techniques demonstrate a substantial decrease in tailpipe emissions, the primary goal continues to be attaining nearly zero emissions to comply with current regulatory requirements and foreseeable imminent rigorous regulations. To achieve this objective, engine combustion systems and fuel formulations require fine-tuning. Taking insights from the recent literature, this review examines various processes, including homogeneous in situ methods, the incorporation of fuel-borne catalysts, and the use of biofuels. Despite progress in in-cylinder pollution mitigation techniques like low-temperature combustion, which exhibits substantial reductions in oxides of nitrogen (NO x ) and soot emissions, it is crucial to consistently advance technology to conform to evolving emission regulations and environmental concerns. A discussion is presented regarding the advantages and disadvantages of the homogeneous charge compression ignition (HCCI) mode and their potential for the future, focusing on biodiesel-fueled HCCI engines. The review assesses the effectiveness of thermal management strategies and engine design modifications that extend the operational range of HCCI engines powered by biodiesel in light of the inherent limitation of a restricted engine operating range. The review critically examines the merits and demerits of biofuels and HCCI systems and provides an essential analysis of current after-treatment approaches. With an imperative focus, the primary aim of this review is to ascertain modern catalysts designed explicitly for use in contemporary combustion systems. An exhaustive examination of the progress made in diesel oxidation catalysts, selective catalytic reduction techniques, lean NO x traps, diesel particulate filters, and catalyst regeneration is presented. The concluding remarks analyze the catalytic characteristics necessary for smooth incorporation with modern technological developments in various combustion systems.
