Experimental investigation of the near field in sooting turbulent nonpremixed flames at elevated pressures

A recently commissioned high-pressure combustion duct is used to investigate a family of ten, piloted, sooting, turbulent nonpremixed flames over a range of pressures and Reynolds numbers. For all conditions, the central jet is composed of 35% ethylene and 65% nitrogen by volume. In one series of flames, the Reynolds number is kept constant while the pressure is increased, whereas in the other series, the bulk jet velocity is maintained. The maximum pressure, p, is 5 bar and the maximum Reynolds number, Re, is 50,000. A DSLR camera and 10-kHz OH-PLIF are used to characterized the near field. DSLR camera images show that the length of the blue region immediately downstream of the nozzle decreases as the pressure increases, rapidly in the constant Reynolds number series, and gradually in the constant velocity series. Analysis of OH-PLIF images in the near field show that corrugation of the flame front is fairly insensitive to changes in pressure if the Reynolds number is held constant. As the Reynolds number (and pressure) is increased, the flame front becomes more corrugated and the frequency of OH layer extinction increases. This leads to smaller “islands” of OH that are separated by shorter distances. However, despite increased local extinction, the flames remain attached even as the Reynolds number is increased to more than twice the maximum Reynolds number that is possible at atmospheric pressure.