Anthony John Dean

Experimental Investigations of the Performance of a Multitube Pulse Detonation Turbine System

A multitube pulse detonation combustor consisting of eight unvalved tubes arranged in a can-annular configuration was integrated with a single-stage axial turbine nominally rated for 10 lbm=s, 25,000 rpm and 1000 hp. The multitube pulse-detonation-combustor-turbine hybrid was operated using ethylene-air mixtures for runs of 5 min to achieve thermal steady state in order to quantify performance at two operating conditions using simultaneous and sequential firing patterns. Analysis of these data reveal that turbine efficiency under pulsedetonation-combustor-fired operation was indistinguishable from steady performance within the 8 points measurement uncertainty. Furthermore, the pulse-detonation-combustor-turbine hybrid system demonstrated a potential 25% improvement in efficiency once corrections were made for the suboptimal fueling design, which resulted in lower-than-anticipated combustion efficiency. The present work is promising as it suggests that a pulsedetonation-combustor-turbine hybrid engine performance benefit can be realized with further development.

Rig and Engine Testing of Melt Infiltrated Ceramic Composites for Combustor and Shroud Applications

General Electric has developed SiC fiber-reinforced SiC-Si matrix composites produced by silicon melt infiltration for use in gas turbine engine applications. High temperature, high-pressure combustion rig testing, and engine testing has been performed on combustor liners and turbine shrouds made from such MI composites. Frame 5 sized combustor liners were rig tested under lean head end diffusion flame conditions for 150 hours, including 20 thermal trip cycles, with no observed damage to the ceramic liners. Similarly, 46-cm diameter single-piece turbine shroud rings were fabricated and tested in a GE-2 gas turbine engine. The fabrication and testing of both components are described.

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.

PULSED DETONATION ENGINE PROCESSES: EXPERIMENTS AND SIMULATIONS

Computational and experimental investigations of a pulsed detonation engine (PDE) operating in a cycle using ethylene/air mixtures are reported. Simulations are performed for two geometry configurations, namely, an ideal tube PDE with a smooth wall fueled with premixed C2H4/O2 and a benchmark tube PDE with internal geometry and a valveless air supply fueled with C2H4. Performance estimates of fuel-specific impulse (Ispf) of an ideal tube PDE, obtained using a two-step reduced mechanism for a C2H4/O2 mixture, are in good agreement with existing test measurements from the literature. Realistic simulations of all processes of the PDE cycle (fill, deflagration-to-detonation transition (DDT), detonation propagation, blowdown, and purge) of a benchmark tube PDE yielded important insights into continuous cycle operation. Experimental measurements include DDT visualizations and dynamic pressure measurements. Comparisons of experimental and computational visualizations show good agreement in cycle process timescales. However, run-up distance is underpredicted, indicating a need to improve the flame propagation mechanism. The predicted decrease in the fuel-specific impulse (Ispf) for the benchmark tube when compared to the I spf of an ideal tube may be attributed to nonuniformities in the mixture composition, the pressure drop resulting from internal geometry, and backflow in the benchmark tube due to a compression wave propagating into the upstream geometry.

Experimental Investigation of a Pulse Detonation Engine with a Two-Dimensional Ejector

A parametric study into the integration of a pulse detonation engine (PDE) with an ejector was performed. High-speed shadowgraph visualizations of the flow inside the two-dimensional ejector provided a qualitative method of determining the performance of the integrated system. The performance was observed to be sensitive to the inlet geometry of the ejector as well as its axial position relative to the exhaust plane of the PDE. Significant levels of entrainment were obtained when the ejectors inlet was contoured, whereas flow separation reduced entrainment efficiency in the ejector with a straight thin inlet lip

Performance Estimations of a Pulse Detonation Engine with Exit Nozzle

The PDE exit nozzle maintains operating pressure and also controls operating frequency. Two parametric studies were performed for two flight Mach number (Minf) conditions of 0.8 and 3.0 and an altitude of 30 kft, in which the exit nozzle contraction ratio Rnc, was systematically varied from 1.6 to 6.4. For the supersonic flight Mach number of 3.0, fuel-specific impulse, Ispf, increases with increasing values of Rnc and attains a constant value of 1950 s for Rnc > 5.0. For the subsonic flight conditions of Minf = 0.8, Ispf increases with increasing values of the exit nozzle contraction ratio and attains a constant value of 1600 for an exit nozzle contraction ratio of 3.0. These parametric studies also quantified PDE operation parameters such as mass flowrates of air and fuel, frequency, and fill velocity. Two additional parametric studies were performed in which purge fraction and fill fraction were systematically varied and they show opposite effect on Ispf and thrust generated. The estimated Ispf was found to have a maximum of 1980 s at a flight Mach number of 3.0, and a minimum value of 1580 s, at a flight Mach number of 0.8 and an altitude of 30 kft.

Detailed and Reduced Mechanisms of Jet a Combustion at High Temperatures

For the Computational Fluid Dynamics (CFD) modeling of combustion and detonation of Jet A aviation fuel it is necessary to use the simplest kinetic mechanism that accurately describes the essential relevant phenomena. A surrogate that demonstrated good agreement with the parent fuel in the detonation process was chosen. A detailed kinetic mechanism was elaborated using a multilevel approach. A reduced mechanism was derived from the detailed mechanism for use in the CFD simulation of real detonation processes in combustors.

Operation and Noise Transmission of an Axial Turbine Driven by a Pulse Detonation Combustor

Pulse Detonation Combustors (PDC’s), as part of a hybrid PDC-turbine engine, have potential thermodynamic benefits over existing Brayton-cycle gas turbines. The form of combustion is a cyclic, controlled series of detonations. These systems apply a near or quasi-constant volume combustion process that provides both heat addition and pressure. In a hybrid PDC-turbine engine, the goal of incorporating a pulsed detonation chamber upstream of a turbine is to extract more mechanical energy in a turbine that receives the products of a repeating, pressure-rise detonation process versus the constant pressure, steady-flows available in conventional gas turbines. A rig was built to investigate PDC-turbine interactions and was operated to gather data on performance, operability, and noise levels. The rig consists of a single pulsed detonation combustor firing into a partial-admission, two-stage axial turbine. This paper reports findings of critical risk areas including turbine response to PDC operation, mechanical robustness, noise and system control. At a PDC operating frequency of 5 Hz, the acoustic level near the rig was approximately 3 dB higher than from the turbine operating at the same speed with steady flow input. The noise level is 28 dB lower than a PDC with no turbine downstream operating at the same frequency and discharging directly into the room. Insights into the mechanism for noise reduction were gained via imaging experiments and CFD simulation. High speed video imaging in a 2D PDC-turbine cascade configuration showed significant shock reflection from the cascade. An unsteady, reacting flow computational study showed similar shock reflection as well as a shock system that forms downstream of the cascade. Together, these results show that shock waves are both transmitted and reflected by the turbine stages in proportions that are dependent upon turbine stage design.Copyright

Rig and Gas Turbine Engine Testing of MI-CMC Combustor and Shroud Components

GE is continuing work on the development of Melt-Infiltrated Ceramic Matrix Composites (MI-CMC) for use in industrial gas turbine engine components. Long-term environmental degradation of test samples under realistic engine conditions is being determined using a unique high-pressure combustion rig apparatus. Rig testing is also being used to evaluate an F-class 1st stage shroud system incorporating an MI-CMC inner shroud component. While large, advanced engines, such as the F and H classes, offer the greatest benefits for using MI-CMC components, initial engine tests have been done using a GE-2 (2MW) machine to reduce costs and risk. Long term (1000 hours) engine testing results for single piece GE-2 shrouds are also described.Copyright

Performance of a Pulse Detonation Combustor-Based Hybrid Engine

A key concept envisioned for Pulse Detonation Engine (PDE) technology is a hybrid engine, where a Pulse Detonation Combustor (PDC) replaces the combustor in a conventional gas turbine. A systems level performance estimation model for a PDC-based hybrid engine cycle was presented. A variable property formulation was used to estimate the cycle performance parameters namely the thermal efficiency (ηth ) and the net specific work (Wnet ). Performance estimations were obtained using a one-step finite-rate chemistry to simulate reactions, and the frozen reactions assumption to model the products of combustion. Two specific parametric studies are performed in which the compression ratio (CR) and the purge fraction (pf) were systematically varied. The predicted variations of ηth and Wnet with varying compression ratio and purge fraction are in agreement with the trends reported in the literature. For a range of values of CR (1-40), performance (ηth ) advantage of a PDC-based hybrid engine is predicted, when compared to a conventional gas turbine engine. The present calculations show that the assumed unsteady turbine component efficiency (ηT ) for the case of a PDC-based hybrid engine has a large effect on ηth . An experimental study investigating the operation of a multi-tube PDC-turbine hybrid system was performed to understand the effect of unsteady flows entering the turbine on the turbine component performance (ηT ). An eight-tube PDC can-annular configuration was integrated with a single-stage axial turbine nominally rated for 10 lbm/s, 25000 RPM and 1000 hp. The system accumulated a total of 144 minutes of operation with long duration runs of approximately 5 minutes, in order for the rig to achieve thermal steady state and for the turbine to attain constant speed. The turbine component efficiency was found to be similar under PDC-fired operation and steady flow operation within the uncertainty of the measurement.Copyright