Experimental study on the effects of gas additives on uncatalyzed partial oxidation of methane in a spark-ignition engine

This study investigated the effects of gas additives (H 2 , CO, N 2 , H 2 O, and CO 2 ) on the uncatalyzed partial oxidation of methane in a spark-ignition engine. The combustion phases, exhaust compositions, and performance outcomes of each additive were compared. The dilution components (N 2 , H 2 O, and CO 2 ) impeded methane combustion owing to their thermal effects, with CO 2 exhibiting the most pronounced delay in combustion. The addition of CO 2 and H 2 O led to increased CO and H 2 yields, respectively, owing to shifts in the water gas shift reaction equilibrium. In contrast, fuel additives (H 2 and CO) enhanced combustion by increasing the flame initiation and propagation speed, resulting in reduced unburned CH 4 and increased work. Negligible soot emissions were detected for all the experimental cases, whereas NO x emissions increased significantly in the CO additive experiments, which was attributed to accelerated NO x formation reactions. This comprehensive analysis provides insights into the combustion and reforming characteristics of methane-based mixed gases, such as natural gas and biogas, during partial oxidation using internal combustion engines.