ENHANCED POWER OUTPUT FROM A GASEOUS FUEL BURNER INVOLVING PULSED SPARK DISCHARGE

摘要

The thermal output of a burner comprising concentric methane/air mixtures was increased upon using a modulated frequency, pulsed electric discharge via spark plugs. The computations predicted that the density/velocity gradients introduced by the spark pulsating temperature field increased the local peak acceleration to 251 m/s(2). At 40 Hz, a velocity difference as high as 3.5 times the mixture local velocity was provided ahead of the flame lift-off position. By displacing the two electrodes along the combustor centerline, the favorable turbulence effects on combustion were maximized at 120 Hz. The burner firing capacity with inner fuel-rich and outer fuel-lean mixtures was thus extended to 14.9 m/s, where 0.28% of the burner output was required for the dielectric breakdown of gases across a 2-mm gap between the two electrodes thus providing plasma-assisted combustion. Although the peak temperature around the spark increased at least by 1200 K, the correspondingly reduced residence time across the flame zones by 93.3% reduced the NOx specific emissions by 76%. While the flame was shifted downstream from the burner face along the first half of the combustor, the HC and CO emissions, respectively, reached magnitudes as low as 0.09% and 730 ppm. As the mixture fraction gradient was reduced to 0.01 cm(-1) with inner fuel-lean and outer fuel-rich mixtures, there was a flame speed increase of 16.4 m/s, which provided a maximum firing intensity of 28.6 MW/m(3), while the heat flux increased with the flame stabilization height. As the peak rate of radiation heat transfer preceded the convection one, the combustor efficiency as a heater was maintained above 29%. Increasing the mixtures' velocity difference to 3.0 m/s increased the turbulent kinetic energy to a maximum of 9.8 m2/s(2) such that enlarging the gap distance to 4 mm increased the temperature fluctuations at least by 32%.