The problem of environmental degradation in megapolises, particularly because of the toxicity of the exhaust gases of transport engines, requires an integrated solution. The peculiarity of the processes of mixture formation and combustion in diesel engines is the presence of local areas, rich in fuel or air. This results in in-complete diesel fuel combustion and contributes to the formation of toxic and mutagenic-carcinogenic compounds. Exhaust gases from diesel engines contain solid particles (SPs) that, due to their developed surface, are carriers of mutagenic-carcinogenic compounds. A very important factor affecting the com-pleteness of fuel combustion in the cylinder of an internal combustion engine (ICE) is the intensive heat exchange between the walls of the combustion chamber and the working fluid. As a result, a relatively cold gas wall layer occurs. In this layer, the unburned hydrocarbons CnHm reside, and SPs are formed. The mi-croaddition of hydrogen to the incoming charge makes it possible to significantly reduce the thickness of the “cold” layer due to the intensification of the combus-tion process in the ICE cylinder and near-wall areas. The generation and use of hydrogen, on board a vehicle, as a microaddition to normal engine fuel is justified as follows. First, the activation of combustion processes in the engine cylinder and, accordingly, fuel combustion completeness increase, which helps reduce the level of mass emissions of SPs and unburned hydrocarbons with the exhaust gases from ICEs. Secondly, such an approach makes it possible to reduce the level of load on the regular exhaust gas neutralization systems of modern vehicle engines, and increase the reliability of their work and their resource. The design of the on-board small-size electrolyzer and its control algorithm are developed. Compre-hensive motor studies of the influence of hydrogen microadditions to diesel fuel on the effective 1H 8.5 / 11 diesel engine performance and the toxicity of its exhaust gases were carried out. Experimental studies show that with hydrogen microaddi-tions, owing to an increase in fuel reactivity and combustion completeness, carbon monoxide emissions and smoking at the exhaust are reduced by 5–6% and 20%, respectively, with practically no unburned hydrocarbons present. The use of the proposed design and algorithm of the on-board electrolyzer operation will signifi-cantly reduce the level of toxicity of the exhaust gases from vehicle ICEs with minimal energy consumption for the functioning of the system.