Role of Biofuels in Reducing Diesel Engine Emissions: A Systematic Review

Diesel engines are widely used due to their high thermal efficiency
and reliability, but they contribute significantly to environmental
pollution, especially nitrogen oxides (NOx), particulate matter (PM),
carbon monoxide (CO), and unburned hydrocarbons (UHC). Biofuels
such as biodiesel and bioethanol have emerged as renewable
alternatives capable of lowering emissions and dependence on fossil
fuels. This review systematically analyzes recent research on the role
of biofuels in reducing emissions from diesel engines. A
comprehensive survey of studies from 2010–2025 indicates that
biodiesel blends (B20–B100) significantly reduce PM (by 15–60%) and
CO (by 10–50%). However, biodiesel can increase NOx by 2–15%
depending on blend ratio and engine conditions. The review also
discusses fuel properties, combustion characteristics, environmental
impacts, and challenges, presenting both quantitative and qualitative
data.