The usage of a methane-fueled homogeneously charged compression ignition (HCCI) engine process for producing base chemicals like ethylene and synthesis gas together with some work output is investigated. This polygeneration process is studied by numerical modeling, accompanied by rapid compression machine experiments. Studies include the seeding of dimethyl ether (DME) as a reaction enhancer which allows methane conversion already at moderate, technically easily accessible compression ratios and precompression temperatures. The concept is promising for equivalence ratios above 2, predicting product gas mole fractions of up to 25 mol % H-2, 20 mol % CO, and 2 mol % C2H4. These simulation results are largely consistent with the outcome of rapid compression machine (RCM) experiments, in which production of up to 20 mol % H-2, 16 mol % CO, and 1 mol % C2H4 was detected. In addition to studying the product composition, thermodynamic aspects of the approach were investigated by comparing the exergetic efficiency of fuel-rich and fuel-lean combustion. These calculations also confirmed the advantages of fuel-rich combustion.