Renewable energy should be used instead of fossil fuels owing to the negative impact of fossil fuels on both humans and the environment, as well as the toxic emissions of carbon dioxide, unburned hydrocarbons, and nitrogen oxide. Studies investigated the consideration of using alternative fuel that is renewable, sustainable, and eco-friendly, especially because of the huge demand for energy, the decline, and the environmental initiatives to decrease the usage of petroleum sources. The addition of oxyhydrogen [HHO] to biodiesel and diesel blends can enhance characteristics; however, there is a concern about raising nitrogen oxide levels, which can have negative impacts on human lives and the environment, contributing to the increase of chronic respiratory conditions, acid rain occurrences, and global warming. Hence, it has been proposed that these issues can potentially be resolved by employing a homogeneous charge compression ignition engine fueled by a mixture of oxyhydrogen gas and biodiesel/diesel fuel to reduce nitrogen oxide until it is negligible. Recent research efforts have discussed the combination of oxyhydrogen gas with biodiesel and diesel blends in an HCCI engine. These studies were performed to obtain the characteristics that result in an improvement in the values of performance parameters like brake thermal efficiency [BTE], brake specific fuel consumption [BSFC], exhaust gas temperature [EGT or Texh.], and volumetric efficiency [ηvol.]. Furthermore, combustion parameters that include peak cylinder pressure [PCP], heat release rate [HRR], mean gas temperature [MGT], ignition delay [ID], and combustion duration [CD] were observed. In addition, exhaust emissions parameters such as nitrogen oxide [NOx], carbon monoxide [CO], unburned hydrocarbon [UHC or HC], carbon dioxide [CO2], exhaust oxygen [EO] or oxygen rate [O2], and smoke opacity [soot] were measured
