This work is aimed at solving the problem of converting diesel power drives to diesel−hydrogen fuels, which are more environmentally friendly and less expensive alternatives to diesel fuel. The method of increasing the energy efficiency of diesel fuels has been improved. The thermochemical essence of using methanol as an alternative fuel to increase energy efficiency based on the provisions of thermotechnics is considered. Alternative methanol fuel has been chosen as the initial product for the hydrogen conversion process, and its energy value, cost, and temperature conditions have been taken into account. Calculations showed that the caloric effect from the combustion of the converted mixture of hydrogen H2 and carbon monoxide CO exceeds the effect from the combustion of the same amount of methanol fuel. Engine power and fuel energy were increased due to the thermochemical regeneration of engine exhaust gas heat. An experimental setup was created to study the operation of a converted diesel engine on diesel−hydrogen products. Experimental studies of power and environmental parameters of a diesel engine converted for diesel−hydrogen products were performed. The studies showed that the conversion of diesel engines to operate using diesel−hydrogen products is technically feasible. A reduction in energy consumption was accompanied by an improvement in the environmental performance of the diesel−hydrogen engine working together with a chemical methanol conversion thermoreactor. The formation of carbon monoxide occurred in the range of 52−62%; nitrogen oxides in the exhaust gases decreased by 53−60% according to the crankshaft speed and loading on the experimental engine. In addition, soot emissions were reduced by 17% for the engine fueled with the diesel−hydrogen fuel. The conversion of diesel engines for diesel−hydrogen products is very profitable because the price of methanol is, on average, 10−20% of the cost of petroleum fuel.