A unique design for a mobile system that reforms flare gas or natural gas, using air without steam, to directly produce dimethyl ether (DME), a diesel substitute, is disclosed. The system first reforms the air-methane mixture at ambient atmospheric pressures, and then compresses the resulting CO-hydrogen-nitrogen gas mixture to up to 600 psi, and feeds it through a combined reactor which reacts the gas mixture directly into dimethyl ether. The nitrogen is returned by the system back to the atmosphere. DME is an excellent diesel fuel, and can be used to displace significantly costlier and dirtier petroleum-based diesel fuel, while solving a critical problem with flaring. For example, the over 120 billion cubic feet per year that is currently flared in North Dakota could be converted into over 3 million tons of DME.