This paper investigates the concept of using piston engines as chemical reactors to convert CO2 to more useful substances. Conditions are presented under which significant conversions of CO2 and CH4 to synthesis gas (CO and H-2) can be achieved in internal combustion engines (ICE). Numerical optimization of the process based on detailed chemistry is employed to identify initial values of temperature, pressure and gas composition which theoretically yield maximal CO2 conversions. The optimization results are used to guide experiments in a rapid compression machine (RCM) setup that is used in place of a real ICE. The optimization predicts that the addition of molecular oxygen enables the endothermal dry reforming reaction (CO2 + CH4, reversible arrow 2 H-2 + 2 CO) to proceed by delivering the required energy from burning a part of the fuel. Despite combustion taking place, experiments show that over 50% of the CO2 contained in mixtures of Ar, O-2, CH4, DME (dimethylether) and CO2 can be converted to syngas with H2O as a by-product. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.