The Hydrogen Revolution in Diesel Engines: A Comprehensive Review of Performance, Combustion, and Emissions

Fossil fuels have been the conventional source of energy that has driven economic growth and industrial development for a long time. However, their extensive use has led to immense environmental problems, especially concerning the emission of greenhouse gases. These problems have stimulated researchers to turn their attention to renewable alternative fuels. Hydrogen has risen in recent years as a prospective energy carrier because it is possible to produce it in an environmentally friendly manner and because it is the most common element. Hydrogen may be used in diesel engines in a dual-fuel mode. Hydrogen has a higher heating value, flame speed, and diffusivity in air. These superior fuel properties can enhance performance and combustion efficiency. Hydrogen can decrease carbon monoxide, unburned hydrocarbons, and soot emissions due to the absence of carbon in hydrogen. However, hydrogen-fuelled diesel engines have problems such as engine knocking and high nitrogen oxide emission. This paper presents a comprehensive review of the recent literature on the performance, combustion, and emission characteristics of hydrogen-fuelled diesel engines. Moreover, this paper discusses the long-term sustainability of hydrogen production methods, nitrogen oxide emission reduction techniques, challenges to the large-scale use of hydrogen, economic implications of hydrogen use, safety issues in hydrogen applications, regulations on hydrogen safety, conflicting NOx emission results in the literature, and material incompatibility issues in hydrogen applications. This study highlights state-of-the-art developments along with critical knowledge gaps that will be useful in guiding future research. These findings can support researchers and industry professionals in the integration of hydrogen into both existing and future diesel engine technologies. According to the literature, the use of hydrogen up to 46% decreased smoke emissions by over 75%, while CO2 and CO emissions significantly decreased. Moreover, hydrogen addition improved thermal efficiency up to 7.01% and decreased specific fuel consumption up to 7.19%.