Investigation of the Fuel Distribution in a Shockless Explosion Combustor

Shockless explosion combustor (SEC) is a promising concept for implementing pressure gain combustion into a conventional gas turbine cycle. This concept aims for a quasi-homogeneous auto-ignition that induces a moderate rise in pressure. Since the ignition is not triggered by an external source but driven primarily by chemical kinetics, the homogeneity of the auto-ignition is very sensitive to local perturbations in equivalence ratio, temperature, and pressure that produce undesired local premature ignition. Therefore, the precise injection of a well-defined fuel profile into a convecting air flow is crucial to ensure a quasi-homogeneous ignition of the entire mixture. The objective of this work is to demonstrate that the injected fuel profile is preserved throughout the entire measurement section. For this, two different control trajectories are investigated. Optical measurement techniques are used to illustrate the effect of turbulent transport and dispersion caused by boundary layer effects on the fuel concentration profile. Results from line-of-sight measurements by tunable diode laser absorption spectroscopy indicate that the transport of the fuel-air mixture is dominated by turbulent diffusion. However, comparisons to numerical calculations reveal the effect of dispersion toward the bounds of the fuel concentration profile. The spatially resolved distributions of the fuel concentration inside the combustor gained from acetone planar laser induced fluorescence (PLIF) replicates a typical velocity distribution of turbulent pipe flow in radial direction visualizing boundary layer effects. Comparing both methods provides deep insights into the transport processes that have an impact on the operation of the SEC.

Investigation of the Fuel Distribution in a Shockless Explosion Combustor

Shockless explosion combustion is a promising concept for implementing pressure gain combustion into a conventional gas turbine cycle. This concept aims for a quasi-homogeneous autoignition that induces a moderate rise in pressure. By this, considerable losses due to entropy generation by inherent shock waves of detonation-based concepts can be avoided. Since the ignition is not triggered by an external source but driven by chemical kinetics only, the homogeneity of the autoignition is very sensitive to local perturbations in equivalence ratio, temperature, and pressure that produce undesired local premature ignition. Therefore, the precise injection of a well-defined fuel profile into an convecting air flow is crucial to ensure a quasi-homogeneous ignition of the entire flammable mixture. The objective of this work is to demonstrate that the injected fuel profile is preserved throughout the entire measurement section. For this, two different control trajectories are investigated. Optical measurement techniques are used to illustrate the effect of turbulent transport and dispersion caused by boundary layer effects on the fuel concentration profile inside the combustor. Results from line-of-sight measurements by tunable diode laser absorption spectroscopy indicate that the transport of the fuel-air mixture is dominated by turbulent diffusion. However, comparisons to numerical calculations reveal the effect of dispersion towards the bounds of the fuel concentration profile. The spatially resolved distributions of the fuel concentration inside the combustor gained from acetone planar laser induced fluorescence replicates a typical velocity distribution of turbulent pipe flow in radial direction visualizing boundary layer effects. Comparing both methods provide deep insights into the transport processes that have an impact on the operation of the shockless explosion combustor.

Combustion Stability and Emissions in a Lean Premixed Industrial Gas Turbine Burner Due to Changes in the Fuel Profile

This paper deals with an experimental investigation of dry low emission (DLE) burners for industrial gas turbines. Changes in the fuel profile, pressure drop over the burner and external pilot flame stabilization have been investigated regarding combustion stability and emissions. This has been achieved by parallel experimental work in a water rig and a newly commissioned atmospheric combustion test rig. Some verifying tests in a high pressure rig were also conducted. The work in the water rig has been directed towards evaluating different fuel profiles at the burner exit due to changes in the fuel outlet geometry. Variations of the fuel outlet geometry were achieved by altering the effective area of the hardware configuration of the fuel outlet ports or by moving or adding fuel outlet ports. A few of the tested configurations in the water rig was chosen for further evaluation by atmospheric combustion tests with respect to combustion stability and emissions. A more general study on combustion stability and emissions was also performed for different burners, burner configurations and variations in pressure drop over the burner. The pressure drop over the burner in the test corresponds very well to the pressure drop measured over a single burner in an annular combustion chamber of an industrial gas turbine at different loads. The combustion was monitored by a high speed video camera equipped with an image intensifier. Simultaneously the dynamic pressure was measured by a piezoelectric pressure transducer, making it possible to know when each image was taken relative to the pressure. Results for different hardware configurations will be shown considering the frequency response from the flame and the dynamic pressure as well as the characteristic combustion instability close to lean blowout.

Assessing mitigation of wildfire severity by fuel treatments - an example from the Coastal Plain of Mississippi

Fuel treatments such as prescribed fire are a controversial tenet of wildfire management. Despite a well-established theoretical basis for their use, scant empirical evidence currently exists on fuel treatment effectiveness for mitigating the behaviour and effects of extreme wildfire events. We report the results of a fire severity evaluation of an escaped prescribed fire that burned into an area previously treated with repeated prescribed fires. We observed significantly lower scorch heights, crown damage, and ground char in the treated area. We attribute the moderated fire severity in the treated area to a significantly altered fuel profile created by the repeated prescribed fires. Though our results represent just one treatment area in a single wildfire, they add to a depauperate database and bring us a step closer to defining the conditions under which fuel treatments are an effective pre-suppression strategy.