| Summary: | A new concept is presented to enhance the combustion performance and to reduce the combustible species gas emission of a combustion engine. Exhaust gases are still rich in typical combustible species whose chemical energy can be harvested to increase efficiency. The idea is to provide extra time to the combustion reactions by the addition of two-post-expansion-strokes to the Otto cycle. The chemical energy of the working-gas residual combustible species is converted into an additional heat-input. The new thermodynamic cycle, called the MUB-2 cycle, is similar to an Otto cycle but has two isochoric heat-inputs instead of one. The cycle has been experimentally tested and analytically evaluated. It is found that even though the engine’s thermal-conversion efficiency is not changed, however, the average values of combustion efficiency, fuel-conversion efficiency, heat-input per cycle, and indicated work per cycle are increased by 6.42 (%), while average levels of HC, CO, and H2 are reduced by 43.86 (%), 38.58 (%), and 38.58 (%), respectively. Other advantages of the MUB-2 cycle are higher heat input per cycle and more robustly work to the changes of air-fuel mixture homogeneity over the Otto cycle, the Atkinson-Miller cycle, and other cycles that only incorporate a single combustion process.
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