Fuel-air mixing enhancement by synthetic microjets

Next-generation combustors must maintain combustion efficiency while considerably reducing emissions, such as CO, NOx, and unburned hydrocarbons. A viable methodology is to enhance the fuel-air mixing process so that the initial dense spray regime is minimized and the subsequent mixing between the vaporized fuel and air is maximized. Current investigations of mixing methods using microelectromechanical systems (MEMS)-based microjet injectors have demonstrated a possible active control technique for rapidly increasing the mixing process. However, detailed understanding of the coupling between the MEMS device and the fuel injector is not yet available. Here, a Lattice Boltzmann Equation method (which is computationally much more efficient than the conventional finite-volume approach) is employed to simulate the flow both inside and outside a synthetic jet actuator. The effects of varying the forcing amplitude and frequencies and different configurations of the synthetic actuators are examined in order to evaluate sensitivity of the actuation to design parameters. Subsequently, the synthetic jets are integrated within a typical fuel injector, and the efficiency of the microactuation on fuel-air mixing is addressed. It is shown that synthetic microjets embedded inside the fuel injector can provide a mechanism for significantly enhancing fuel-air mixing. Implications for practical applications are also discussed.