Abhijit Kushari

The effect of heat content and composition of fuel on pulse combustor performance

This paper reports partial results of an investigation into the use of pulse combustors to provide the heat required for the pyrolysis of organic wastes, such as black liquor, in fluidized beds. This process is economical only if the pyrolysis products, which are low in heat content but high in hydrogen concentration, can be used to fire the pulse combustor. This lead to a study of the effect of low heat content fuels with high hydrogen content on the operation of pulse combustors, the results of which are reported here. The performance of the pulse combustor was monitored by measuring sound pressure levels, heat release oscillations, frequencies of pulsations and the phase angle by which the heat release oscillations lead those of pressure. Sound pressure levels were found to be largely insensitive to heat content in fuels consisting only of methane and inert diluents. However, if the fuel contains hydrogen, the amplitude of the pulsations decreases as the heat content in the fuel is increased. This occurs because addition of hydrogen to the fuel accelerates the heat release during the cycle. In order to determine whether this early heat release is due to changes in the fluid mechanics, i.e., the mixing of reactants and ignition source in the combustor, or to the different kinetics of the combustion processes without and with hydrogen, a series of experiments was devised in which the composition of the fuel could be varied without changing the fluid mechanics in the pulse combustor. These tests clearly showed that the earlier heat release in the cycle, responsible for lower sound pressure levels in the pulse combustor, is caused by the faster burning rate of hydrogen.

Weighted Sum of Gray Gas Modeling for Nongray Radiation in Combusting Environment Using the Hybrid Solution Methodology

A hybrid solution approach is proposed to solve the radiation transfer equation (RTE) in combusting environment using the weighted sum of gray gases model for modeling the absorption coefficient. The hybrid approach uses a selective combination of the finite-volume method (FVM) and P1 approximation to solve the RTE for different gray gases. A comprehensive study with a wide range of test cases with homogenous and nonhomogenous media is carried out to study the accuracy, speed, and convergence rate of the hybrid solution approach. The differences between hybrid and FVM results are described, and the sources of errors are discussed.

Effects of Geometric and Structural Parameters on Coupled Bending Torsion Flutter in Turbo Machinery Blades

The development of propulsion system technology over the last few decades has encountered and overcome several technological barriers. A large number of problems were resolved resulting in considerably higher component efficiencies and reduced fuel consumption. These advances led to lighter overall designs and higher power densities compared to earlier designs. The accomplishment of lighter designs for the turbomachinery components also led to some drawbacks due to the reduced margins on the design factor-of-safety. Consequently, aeroelastic stability has become a major concern, and is often the limiting design constraint. So a careful and systematic study of coupled bending-torsion flutter of a cascade in incompressible flow was carried out which requires estimation of unsteady aerodynamic loads, and a structural model of the cascade. Unsteady aerodynamic loads were evaluated using Whiteheads solution for incompressible flow through a cascade of arbitrary geometry and interblade phase angle. The lift and moment coefficients calculated were found to match within the four decimal place accuracy with the results given by Whitehead and other literature. The blades were modeled as an equivalent 2-D section at 75% of span, and structural and inertia! couplings were lumped into an effective CG-EA offset. Structural damping was included in the equations of motion. The resulting complex eigenvalue problem was solved recognizing the fact that there are two parameters in the eigenvalue problem, namely the reduced frequency k and the interblade phase angle β. The critical flutter speed was determined by minimizing it with respect to β, keeping the constraint on β as suggested by Lane. The solution provided the critical flutter speed with respect to both the torsion and the bending modes as a function of the interblade phase angle as well as dominant vibration frequencies at flutter. Various structural and aerodynamic parameters of the cascade were varied and the effect of the variations on the coupled bending torsion flutter was studied. A jump was observed in the flutter boundary near frequency ratio of 1, which was explained by the change iri the mode shape of the vibration, which is represented by interblade phase angle. The developed technique can be used as a preliminary design tool for the aeroelastic flutter analysis of turbo-machinery blades.

Macroscopic Flow Behavior in a Low Aspect Ratio Dump Combustor with Tapered Exit

11 point bold, left) This paper describes an experimental study of the re-circulating flow of air inside a dump combustor having a low length/diameter ratio and a tapered exit section. The length of the combustor studied was less than the «attachment length for the separated flow after the dump. The re-circulation was driven by the fluid dynamics of the onedimensional flow from a smaller area to a larger area. The re-circulation was not forced either by a swirler or by acoustic oscillations due to cavity effects. It was observed that the jet penetration increases with in increase in the flow Reynolds number. However, a distinct thickening of the recirculating flow was observed inside the combustor, which can be attributed to the flow reversal from the exit section, causing flow adjustment to fill the whole combustor with a recirculating flow. The findings of the visual study were corroborated by measuring the axial velocity field and the wall pressure distribution and the results were found to be in very good qualitative agreement with each other. The findings of this study can have applications in the design of better combustors with proper alignment of the fuel injectors with respect to the flow for better evaporation and mixing of the fuel.

Aerodynamic Influence of Oscillating Adjacent Airfoils in a Linear Compressor Cascade

Turbomachinery aeroelasticity is gaining renewed interest in the light of current trends, which tend toward thinner blade designs that are not only highly loaded, but also have minimal weight. This...

Effect of Leading-Edge Tubercles on Compressor Cascade Performance

Tubercles are modifications to the leading edge of an airfoil in the form of blunt wave-like serrations. Several studies on the effect of tubercles on isolated airfoils have shown a beneficial effect in the poststall regime as reduced drag and increased lift, leading to a delay of stall. The prospect of delaying stall is particularly attractive to designers of axial compressors in gas turbines, because this leads to designs with higher loading and therefore higher pressure rise with fewer number of stages. In the present study, experiments were performed on a cascade of airfoils with a NACA 65209 profile with different tubercle geometries. The measurements were made over an exit plane using a five-hole probe to compare the cascade performance parameters. Additionally, hot-wire measurements were taken near the blade surface to understand the nature of the flow in the region close to the tubercles. Oil-flow visualization on the cascade end wall reveals the flow through the passage of blades with and without...

Behavior of Spray in a Twin-Fluid Atomizer

This paper describes an experimental study of the behaviour of spray structure in an internally mixed, twin–fluid atomizer in which air was introduced tangentially into the liquid stream inside the atomizer. The atomization in such atomizers is perceived to be strongly influenced by the mass flow ratio of atomizing gas (air) and the liquid (water). The order of magnitude of the ALR (Air-liquid mass flow ratio), for which the study was conducted, ranged from 0.0277 to 0.623. A PDPA (Phase Doppler Particle Analyzer) was used to study the spray formation process. The behaviour of the spray was studied by velocity and Sauter Mean Diameter (SMD) variations at a plane normal to the spray axis as well as along the flow direction of the atomizer. It was observed that the mass flow rate of the liquid deceases with an increase in air pressure while it increases with liquid pressure. The droplet diameter decreases with an increase in ALR for a given liquid supply pressure but sprays having droplet SMD of less than 60 μm at the centerline of the spray was produced at relatively lower ALR (i.e., 0.1). The variation demonstrated by the atomizer in this study makes it flexible to be used for various commercial applications, as the atomizer is capable of providing a wide range of spray patterns depending upon the application requirement.Copyright

Computational Investigation of Cold Flow in a Dump Combustor With Tapered Exit

This paper reports the results of a numerical study of the cold flow field in a dump combustor with a tapered exit. The numerical model was benchmarked against the data available in the literature. The flow field inside the combustor was investigated by numerical visualization of different regions in the flow field, and the effect of the combustor length was studied. It was seen that the presence of shear layer between the potential core and the recirculation region, as well as the pressure and velocity variation inside the combustor, alters the recirculation region and hence the flow field. It was also observed that the extent of the recirculation region increases, while the shear layer becomes thinner as the length of the chamber decreases. The effect of the variation in the flow Reynolds number and the inlet turbulence intensity on the flow.field of a low aspect ratio (2.3) dump combustor was studied in detail. It was observed that the extent of recirculating flow increases with a decrease in the Reynolds number, and the increase in turbulence intensity results in higher turbulence energy generation in the shear layer. The pressure recovery was found less, but the recirculation was stronger in the low aspect ratio combustor. The results of this study can help optimize the combustor chamber to achieve better mixing of fuel with air and stabilization of the flame.

Operation of an auto‐initiated pulsed plasma thruster

Purpose – The purpose of this paper is to develop and characterize a pulsed plasma thruster (PPT) that does not need a spark plug to initiate the plasma discharge.Design/methodology/approach – Two parallel rail thrusters were built and their performances were characterized inside a vacuum chamber to elucidate the effect of vacuum level and thruster geometry on the performance. The thruster electrical performance was quantified by measuring the voltage output from a Rogowski coil connected to the power supply. The thrust produced by the developed thruster was estimated by measuring the force exerted by the plume on a light weight pendulum, whose deflection was measured using a laser displacement sensor.Findings – The thruster can operate without a spark plug. In general, the performance parameters such as thrust, mass ablation, impulse bit, and specific impulse per discharge, would increase with increasing pressure levels up to an optimum level due to the increase in discharge energy as well as the decreas...

Auto-initiating Solid Propellant Pulsed Plasma Microthruster

*† ‡ Research results have inferred that the electromagnetic pulsed plasma thruster can attain competitive efficiency and specific impulse levels. The pulsed plasma thruster’s unique characteristics can be used to provide propulsive attitude control, orbit raising, translation, and precision positioning. Besides pulsed plasma thrusters are attractive for small satellite applications because they are essentially stand alone devices which eliminate the need for toxic and/or distributed propellant systems. They can also operate at low power and over a wide power range without loss of performance. The present work dealt with designing a better Pulsed Plasma Thruster (PPT) that has lower mass and power requirements and better longevity. Teflon is used as the propellant in this work. An attempt is made to design an auto-initiating pulsed plasma thruster that can be used without an igniter plug. The performance of the auto-initiating pulsed plasma thruster is assessed in the light of the data collected through the experiments conducted on the model and from the experiments conducted elsewhere. The possibility of using the capacitor and the supply voltage for manipulating the discharge frequency is also discussed. The results of the study are important for the application of Pulsed Plasma Thruster in satellite and interplanetary classes of missions where restrictions in terms of mass and power requirements are very critical.