Extending diluent limits in methane/air combustion by adding simulated reformer gases

The laminar burning velocities (Su) of methane (CH4)-air, CH4-air-diluent and CH4-air-diluent-reformer gas (CO + H2) mixtures have been measured using a constant volume cubical combustion chamber. The burning velocities have been measured from the pressure rise inside a cubical combustion chamber with the help of a multi-zone thermodynamic equilibrium model. The initial pressure was always maintained at either 1 atm or 2 atm. The gases were mixed in proper proportion using the method of partial pressures. A mixture containing 81.5% N2 and 18.5% CO2 was used to simulate the exhaust gases. The mixture was chosen by matching its specific heat capacity with that of the products of combustion of stoichiometric CH4-air combustion. The S u of the stoichiometric CH4-air mixture was found to be 34.9 cm/s. The Su gradually decreased as simulated exhaust gas was added to the mixture. The variation of volumetric percentage of reformer gas-air required to raise the Su back to undiluted levels was measured. The Su of hydrogen-carbon monoxide-air over a range of hydrogen and carbon monoxide volume fractions were also measured.