Combustion Characteristics of H2-CO-CO2 Mixture in an IC Engine

Reformed fuel from hydrocarbons or alcohol mainly consists of hydrogen, carbon monoxide and carbon dioxide. The composition of the reformed fuel can be varied to some extent with a combination of a thermal decomposition reaction and a water gas shift reaction. Methanol is known to decompose at a relatively low temperature. An application of the methanol reforming system to an internal combustion engine enables an exhaust heat recovery to increase the heating value of the reformed fuel. This research analyzed characteristics of combustion, exhaust emissions and cooling loss in an internal combustion engine fueled with several composition of model gases for methanol reformed fuels which consist of hydrogen, carbon monoxide and carbon dioxide. Experiments were made with both a bottom view type optical access single cylinder research engine and a constant volume combustion chamber.

The thermal decomposition reaction produces 1mol of carbon monoxide and 2mol of hydrogen from 1mol of methanol, and the water gas shift reaction produces the same amount of hydrogen and carbon dioxide from carbon monoxide and water. Therefore, an increase in hydrogen means an increase in carbon dioxide, an inert gas with large heat capacity, and a decrease in the heating value of the fuel. This research cleared a balance of the combustion promotion by the increased hydrogen and the demerit by the increased heat capacity of mixture due to the increased carbon dioxide. The highest overall thermal efficiency including the exhaust heat recovery is obtained in the combustion of the methanol-reformed fuel with just the thermal decomposition reaction, which consists of 33% of hydrogen and 67% of carbon monoxide.