NOVELTY - Proposed method is carried out in plant including multi-cylinder four-stroke or two-piston air-injection internal combustion engine working in mode of chemical compression reactor.    USE - Technology of processing hydrocarbon materials, production of synthesis-gas in particular.    ADVANTAGE - Enhanced efficiency of production of methanol and synthetic motor fuels.2 cl, 1 dwg, 1 tbl    DETAILED DESCRIPTION - Proposed method consists in preparation of mixture containing hydrocarbon material, water vapor and oxygen-enriched air -fuel charge at excess-air-oxidizer coefficient of 0.3-0.58 for methane followed by preheating of fuel charge and delivery of it to engine cylinders; then additional heating is performed in compression stroke followed by ignition in top dead center due to self-ignition of additives introduced into fuel charge in form of liquid or gaseous agents whose ignition temperature is below that of fuel charge; as a result, engine is started as chemical compression reactor and partial oxidation of fuel in volume of internal combustion cylinders is performed; then, products formed during reverse stroke of piston are expanded and cooled and products of this process containing synthesis-gas are discharged to bottom dead center, after which they are cooled and cleaned from soot and are subjected to final cooling and conversion into methanol or dimethyl ether. Process of partial oxidation at attaining the working mode of operation by chemical reactor is maintained due to availability of residual gases in cylinders whose amount is controlled by re-adjusting of the valve gear, additional heating due to warming-up of engine and external control of fuel charge heating temperature. Proposed plant includes multi-cylinder four-stroke or two-piston two-stroke air-injection internal combustion engine working as chemical compression reactor; engine is provided with intake and exhaust valves and system for delivery of air, hydrocarbon material and additives, as well as heating and preheating systems including air heaters, heat exchangers and mixer; engine is also provided with synthesis-gas cooling system which also consists of heat exchanger and cooler; engine is provided with reversible motor-generator set generating the electric power for multi-stage synthesis-gas compressor and high-temperature filter rigidly connected with engine and used for cleaning the synthesis-gas from soot; engine is provided with cooler and drip pan. Working of engine in mode of chemical compression reactor and composition of synthesis-gas are controlled through control of oxidizer-excess coefficient and preheating temperature in heat exchanger at steady state conditions or temperature at starting air heater outlet. Invention makes it possible to increase specified productivity by 2.5-3 times at volume ratio of H2/CO of 1.4:2.