Jeffrey Scott Goldmeer

System-Level Performance Estimation of a Pulse Detonation Based Hybrid Engine

A key application for a Pulse detonation engine concept is envisioned as a hybrid engine, which replaces the combustor in a conventional gas turbine with a pulse detonation combustor (PDC). A limit-cycle model, based on quasi-unsteady computational fluid dynamics simulations, was developed to estimate the performance of a pressare-rise PDC in a hybrid engine to power a subsonic engine core. The parametric space considered for simulations of the PDC operation includes the mechanical compression or the flight conditions that determine the inlet pressure and the inlet temperature conditions, fill fraction, and purge fraction. The PDC cycle process time scales, including the overall operating frequency, were determined via limit-cycle simulations. The methodology for the estimation of the performance of the PDC considers the unsteady effects of PDC operation. These metrics include a ratio of time-averaged exit total pressure to inlet total pressure and a ratio of mass-averaged exit total enthalpy to inlet total enthalpy. This information can be presented as a performance map for the PDC, which was then integrated into a system-level cycle analysis model, using GATECYCLE, to estimate the propulsive performance of the hybrid engine. Three different analyses were performed. The first was a validation of the model against published data for a specific impulse. The second examined the performance of a PDC versus a traditional Brayton cycle for a fixed combustor exit temperature; the results show an increased efficiency of the PDC relative to the Brayton cycle. The third analysis performed was a detailed parametric study of varying engine conditions to examine the performance of the hybrid engine. The analysis has shown that increasing the purge fraction, which can reduce the overall PDC exit temperature, can simultaneously provide small increases in the overall system efficiency.

The Effect of Fuel Density on Mixing Profiles in a DACRS Type Premixer: Experiments and Simulation

A combined experimental and computational study was conducted to investigate the effect of fuel density variations on mixing from a double annular counter-rotating swirl (DACRS) nozzle operated at atmospheric pressure under non-reacting conditions using either helium (He) or a mixture of He and CO2 as fuel simulants. A small probe traversed through the flow collecting gas samples that were sent to gas analyzers measuring the concentration profiles. The resulting measurements are then used to validate the computational fluid dynamics (CFD) model. A commercial CFD code (CFX 10) with a Reynolds averaged Navier-Stokes (RANS) formulation was used to simulate the experiment. Multiple turbulence closures, such as standard and realizable k-e and SSG Reynolds stress model were evaluated. Additionally, several geometrical considerations, such as modeling a 72° sector versus a full 360°, were tested. While at high fuel-to-air momentum flux ratios (J) the fuel simulant concentration profiles were outward-peaked, and at low J the profiles were center-peaked. An analysis of the experimental results clearly indicate the momentum flux ratio is the most influential parameter controlling mixing in a DACRS nozzle. The simulations produced quantitative agreement with the experimental measurements using the realizable k-e turbulence closure and only modeling a 72° sector of the nozzle. The complexity of the studied problem required a considerable refinement of the grid to produce an accurate and grid independent solution. The validated model may now be used to explore the design space for optimization of a nozzle for utilization in a syngas application.© 2007 ASME

Systems-Level Performance Estimation of a Pulse Detonation Based Hybrid Engine

A key application for a Pulse Detonation Engine concept is envisioned as a hybrid engine, which replaces the combustor in a conventional gas turbine with a Pulse Detonation Combustor (PDC). A limit cycle model, based on quasi 1-D, unsteady Computational Fluid Dynamics (CFD) simulations, was developed to estimate the performance of a pressure-rise PDC in a hybrid engine to power a subsonic engine core. The parametric space considered for simulations of the PDC operation includes the mechanical compression or the flight conditions that determine the inlet pressure and the inlet temperature conditions, fill fraction and purge fraction. The PDC cycle process time scales including overall operating frequency were determined via limit-cycle simulations. The methodology for estimation of performance of the PDC considers the unsteady effects of PDC operation. These metrics include a ratio of time-averaged exit total pressure to inlet total pressure and a ratio of mass-averaged exit total enthalpy to inlet total enthalpy. This information can be presented as a performance map for the PDC, which was then integrated into a systems-level cycle analysis model, using Gate-Cycle, to estimate the propulsive performance of the hybrid engine. Three different analyses were performed. The first was a validation of the model against published data for specific impulse. The second examined the performance of a PDC versus a traditional Brayton cycle for a fixed combustor exit temperature; the results show an increased efficiency of the PDC relative to the Brayton cycle. The third analysis performed was a detailed parametric study varying engine conditions to examine the performance of the hybrid engine. The analysis has shown that increasing the purge fraction, which can reduce the overall PDC exit temperature, can simultaneously provide small increases in overall system efficiency.Copyright

Passive Control of Dynamic Pressures in a Dry, Low NOx Combustion System Using Fuel Gas Circuit Impedance Optimization

Dry, Low NOx (DLN) gas turbine combustion systems that use the lean, premixed combustion technique for emissions control are susceptible to dynamic pressure oscillations. During the initial full-load prototype testing of the MS5002E, excessive dynamic pressures were encountered when attempting fully premixed combustor operation, preventing the gas turbine from meeting a 15 ppm NOx emissions target. A series of experiments were performed to examine potential acoustic differences between the original laboratory fuel injection system and the prototype hardware used in the field test. The experimental results were used to validate an analytical model that was used to optimize the fuel circuit geometry for dynamics reduction. The resulting revised design demonstrated a ten-fold reduction in dynamic pressure amplitudes. As a result, the system was able to operate over the premixed mode operating range and provides the desired NOx levels with acceptable dynamic pressures and operability.Copyright