Low NO_X Combustion of DME by Exhaust Gas Recirculation Under the High Pressure

This study focuses on the fundamental characteristics of DME (Dimethyl ether) combustion with exhaust gas recirculation EGR, aiming at development of the low NOx combustion technology of DME under the high pressure. EGR reduces the NOx emission by recirculating the exhaust gas into the combustion chamber to control the oxygen concentration and the combustion gas temperature. EGR at the high mixing ratio, however, may lead to unstable combustion of conventional fuels, methane or city gas. On the other hand, DME has high potential of applicability of EGR even at the high mixing ratio because of its high burning velocity and low ignition temperature. In this experiment, the oxygen concentration and the combustion air temperature were systematically regulated, so that the exhaust gas recirculation was simulated. The combustion test was conducted with laboratory-scale 8kW combustor. Initial air ratio λ was 1.5. At the atmospheric pressure, the exhaust gas recirculation can be applied to 54% of the EGR ratio. The NOx concentration reduces to 10ppm at 0%-O₂, which corresponds to about 22% of NOx emission without EGR. However, the flame became unstable at 54% of the EGR ratio. By increasing the pressure in the combustion chamber, the NOx concentration increased the 84ppm at 0.3MPa-without EGR. The maximum EGR ratio can be applied to 59% under the pressure of 0.3MPa, wihch is almost the same with that at atmospheric pressure. The NOx emission in the exhaust gas decreases to 17ppm. The exhaust gas recirculation is effective to the low NOx combustion of DME at the high pressure.