Combination Of Swirl Research Articles

Study on flame structures and emission characteristics according to various swirl combinations and fuel compositions in a CH4/H2/CO syngas swirl-stabilized combustor

In an integrated gasification combined cycle (IGCC) power plant, the initial operating procedure is driven by natural gas first, and then by H2/CO syngas. This study attempted to find the optimal operating procedure in the fuel changeover section, such as from natural gas to syngas. Therefore, the influences of various swirl combinations and syngas compositions on flame structures and NOx and CO emissions characteristics were investigated through experimental and numerical analyses in a partially premixed dual swirl combustor. To observe the various flame structures, such as lifted, tubular, and attached flames, the two-dimensional particle image velocimetry (PIV) technique was applied and compared with the results obtained by computational fluid dynamics (CFD). The combustion characteristics of co– and counter-swirling flames were observed, and the optimal swirl combination was subsequently confirmed by using the parameter of modified unmixedness. When the flame shape and fuel and air mixing efficiency are considered, Sco, 1.3/1.46 condition is the optimal swirl combination for stable conversion of the syngas fuel. In addition, the operating parts with a methane content of 25% and a hydrogen content of 75% are considered to be avoided in the operating part of fuel changeover. The operating part of fuel changeover can be divided into 10 paths for stable syngas operation. The optimal operating procedure to control the content of hydrogen and carbon monoxide after the syngas operation with the Path No. 2, such as H2 = 25% and CO = 75%.

High-speed PIV, spray, combustion luminosity, and infrared fuel-vapor imaging for probing tumble-flow-induced asymmetry of gasoline distribution in a spray-guided stratified-charge DISI engine

In this study, the influence of intake-generated swirl and tumble flow on fuel–air mixing and combustion is investigated in a spray-guided stratified-charge direct-injection spark-ignited engine. Previously, it was demonstrated that the introduction of a combined swirl–tumble flow recovered combustion stability, which was otherwise lost when increasing the engine speed from 1000 to 2000rpm. However, the improved combustion came at the expense of elevated engine-out soot emissions. Here, high-speed combustion luminosity and PIV measurements at 2000rpm confirm that soot incandescence is more prevalent with high swirl and tumble. The application of high-speed infrared (IR) gasoline-vapor imaging introduced here provides unique insights, revealing that operation with a combination of swirl and tumble generates an asymmetric fuel distribution that spatially correlates with highly luminous sooting combustion. The IR fuel-vapor imaging technique collects line-of-sight mid-infrared thermal emission from the CH stretch band of the heated fuel near a wavelength of 3.4µm. The IR images resolve the penetrating vapor plumes distinctly, demonstrating that the 3.4µm band is suitable for quantitative measurements of vapor penetration during injection. After injection, the IR images provide a qualitative description of fuel-vapor spread without combustion. It is found that the no-swirl case has a symmetric fuel-vapor development during the latter part of the compression stroke. In contrast, for operation with strong swirl and tumble, vapor rotation and the development of an asymmetric and non-uniform fuel-vapor distribution is observed. PIV measurements reveal that the swirl flow dominates the vapor rotation, while the tumble flow appears to be a major reason for the asymmetric fuel-vapor distribution.

Experimental study of novel passive control methods to improve combustor exit temperature uniformity

The effect of non-uniform temperature flow which comes in contact with the turbine blades is of paramount importance since the thermal damage that occur to the blade during its operation, is governed by the non-uniformities present in the oncoming flow. This thermal damage leads to increased maintenance cost and reduced life-span of the turbine blades. This paper investigates the effectiveness of some novel passive control techniques to improve the temperature uniformity of the combustor exit flow to address the need to reduce the thermal damage and hence decrease the overall maintenance cost of the gas turbine system. The novel passive control techniques tested in this study include the use of streamlined body or guide vanes in the dilution zone of the combustor. For the guide vanes four different orientations were tested—0°, 30°, 60°, 90°. Extensive experimentation was conducted under different flow conditions. The deviation of the exit temperature from the equilibrium mixing temperature was used to compare the effectiveness of different passive control techniques. It was found that the 30o guide vanes gave the most uniform temperature flow under majority of cases considered. On an average, the flow with 30o guide vanes was about 15 % more uniform in temperature as compared to the staggered holes geometry with only 1 % higher pressure loss. The possible reason for this improvement is the combination of swirl and depth to which the dilution flow can enter the dilution zone and mix with the primary hot flow. The streamlined body came second with an improvement in pressure losses. Based on these experimental findings, the use of these guide vanes and streamlined body has potential in the gas turbine industry to deal with the high maintenance cost involved in these systems.

Internal Flow Dynamics and Regression Rate in Hybrid Rocket Combustion

The present study is the analyses of what has been attempted and what was understood in terms of improving the regression rate and enlarging the basic understanding of internal flow dynamics. The first part is mainly intended to assess the role of helical grain configuration in the regression rate inside the hybrid rocket motor. To improve the regression rate, a combination of swirl (which is an active method) and helical grain (which is a passive method) was adopted. The second part is devoted to the internal flow dynamics of hybrid rocket combustion. A large eddy simulation was also performed with an objective of understanding the origin of isolated surface roughness patterns seen in several recent experiments. Several turbulent statistics and correlations indicate that the wall injection drastically changes the characteristics of the near-wall turbulence. Contours of instantaneous streamwise velocity in the plane close to the wall clearly show that the structural feature has been significantly altered by the application of wall injection, which is reminiscent of the isolated roughness patterns found in several experiments.