Simulation Study on Lifted Hydrogen and Methane Jet Flames in Hot Vitiated Coflow

Combustion of fossil fuels is the most important energy source today. Burning fossil fuel is however expensive and bad for the enviroment. Improving the combustion technology to reduce fuel consumption, and to be able to burn renewable fuels is therefore of great importance. Analysing the flames in gas turbine engine-like burners can give knowledge about the burning process, which can be used to improve the design of such engines, and to optimize their operating conditions. Simulations of a closed burner, used at Tongji University, have been conducted, where different operating conditions have been tested when burning hydrogen and methane. For burning methane, different velocities of the jet and coflow have been simulated. For methane, the flame’s liftoff height increased both when the jet- and the coflow velocity increased. The increase due to changes in coflow velocity was however smaller than the results from previous research on similar cases. When the jet velocity was between 25 to 75 m/s, the flame’s liftoff height was very dependent on the coflow velocity. At speeds ranging from 75 to 200 m/s, the liftoff height was less dependent of coflow velocity. The jet’s reduced influence was due to a recirculating zone that appeared at high jet velocities. A jet velocity of 50-100 m/s gives a liftoff height that is neither too low, nor too high, and no recirculating zone is formed in those jet velocities. For hydrogen, different jet velocities and background pressures have been simulated. For the hydrogen case, the flame was blown out at fairly low pressures. The flame was blown out as early as 1.2 bar when the jet velocity was set to 107 m/s. The pressure limit rose as the jet velocity declined, and with a jet velocity of 25 m/s, the limit was logged to 1.4 bar. There is no clear trend for the liftoff behaviour from 1.0 to 1.1 bar, but the liftoff height increase rapidly when the pressure increase beyond 1.1 bar. When using hydrogen as a fuel, the pressure must be controlled very precisely to be able to run it efficiently, due to the flames sensibility to pressure differences