| Summary: | Diesel engines are extensively used across automotive, agricultural, and industrial sectors due to their high thermal efficiency and robust performance. However, their operation is associated with significant levels of noise and vibration, in addition to the depletion of fossil fuel resources. Biodiesel has emerged as a promising alternative fuel due to its renewability, compatibility with existing diesel engines, and potential to reduce environmental and acoustic impacts. This review critically examines the influence of biodiesel and its blends on noise, vibration, and harshness (NVH) characteristics in diesel engines. Emphasis is placed on how biodiesel's physicochemical properties—such as cetane number, viscosity, density, and oxygen content—affect combustion behavior and subsequent NVH outcomes. While many studies report reductions in noise and vibration with low biodiesel blend ratios (e.g., B20), higher blends often introduce trade-offs related to combustion irregularity and fuel atomization. Key challenges, such as cold flow limitations and variability among feedstocks, are also discussed. This paper identifies methodological gaps in NVH assessment, highlights inconsistencies across existing literature, and proposes future directions for research, including standardization of testing protocols and the application of advanced analytical techniques. The review contributes a structured synthesis of findings across biodiesel generations and feedstocks, supporting more informed development and deployment of biodiesel in compression-ignition engines.
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