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In an effort to improve the trade-off between fuel economy and emissions in the rotary combustion engine, research was undertaken to provide a better understanding of the sources of unburned hydrocarbons in the exhaust. Flame photography was used in conjunction with extensive time-resolved exhaust gas sampling. Examinations were made of the effects of air-fuel ratio, engine load, residual gas, and engine speed on combustion and hydrocarbon emissions using the two experimental techniques. These studies identified two major sources of hydrocarbon emissions: flame extinction and, not surprisingly, apex seal leakage. Conclusions were the following: (1) at lean air-fuel ratios (i.e., ≥18.0 to 1), flame extinction in the trailing portion of the chamber was a major source of exhaust hydrocarbons, and (2) at richer air-fuel ratios (i.e., ≤16.5 to 1), apex seal leakage was a major source of exhaust hydrocarbons.