N15A-T021 TITLE: Time-resolved Measurements of Temperature and Product Mass Fractions within Detonation-based Combustion Devices at Elevated Pressures and Temperatures

TECHNOLOGY AREAS: Air Platform, Sensors, Weapons

OBJECTIVE: Develop spectroscopic tools for the time-resolved measurement of combustion product mass fractions and temperatures within detonation channels, along the combustor axis, and across the nozzle exit plane of Rotating Detonation Engine (RDE) systems to characterize flow field features, support combustion efficiency calculations, and determine the combustor exit enthalpy conditions.

DESCRIPTION: Temporally-resolved measurements of the mass fractions and temperature of major combustion species in detonation-based combustion devices are necessary to complement and ensure accurate modeling of flow physics and chemistry. The predicted thermodynamic advantages of rotating detonation engines provide motivation for the continued development of diagnostic tools to experimentally validate such predictions and also provide insight into performance deficits that may occur during system development. The operation of pressure-gain combustion systems, such as rotating detonation engines, generates specific challenges due to the high pressure oscillations and stratified flow fields associated with various architectures. To investigate the characteristics and structure of the reacting flow fields through mass fraction and temperature measurements, 0.1 to 1 Megahertz (MHz) resolution rates are required. In situ measurements of mole or mass fractions of major combustion species (water (H2O), carbon monoxide (CO), carbon dioxide (CO2)) will allow temporal characterization of the widely varying flow field behavior under highly transient conditions. Such measurements must be made at regions along a combustor axis with sufficient temporal resolution (< 10 microseconds (�s)) to achieve discrete information of the flow condition; furthermore, such measurements should not require flow seeding.

The ability to effectively and practically measure major combustion species can be based upon various spectroscopic techniques such as spontaneous Raman and absorption spectroscopy. However, more complicated and less portable techniques such as coherent anti-Stokes Raman scattering (CARS), Raman-excited laser-induced electronic fluorescence, and laser-induced fluorescence can be considered if a practical approach could be determined. Accessibility and vibration would likely limit the broad use of such systems due to the challenges associated with their practical integration.

The objective of this effort is to develop high-speed, temporally resolved spectroscopic tools based on the spectroscopy of major species inherent to hydrocarbon fuel combustion, but at significantly higher combustion pressures (10-50 atmospheres (atm)) and temperatures (approximately equal to 3000 Kelvin (K)) than past techniques. This is due to the widely varying conditions associated with detonation events, especially near the detonation event itself. The techniques developed should be able to be applied to experimental combustors and engines with transmission paths ranging from 0.5 centimeters (cm) up to 5 cm and run time durations of several seconds. Vibration, large pressure and temperature variations, broadband attention (soot), and bandwidth requirements will generate significant challenges.

PHASE I: Determine enabling spectroscopic features and demonstrate a viable, proof-of-concept, non-intrusive combustion diagnostic tool (instrumentation, database, analysis method(s)) to arrive at H2O, CO, and CO2 mass fractions and temperatures at frequencies above 100kHz within combustors possessing narrow combustion channels (approximately 1 cm) and pressures up to 50 atm.

PHASE II: Develop and demonstrate a prototype diagnostic system (hardware and software) for the characterization of combustion phenomena associated with Rotating Detonation Engines. The demonstration(s) shall occur at engine-relevant conditions and durations. Results shall be post-processed such that they can be readily utilized for control strategies or for stand-alone performance assessments. At the completion of Phase II, the prototype hardware and software shall be delivered to the Government Point of Contact.

PHASE III: Further develop the prototype hardware for applications in full-scale military engines as well as for laboratory-scale use. Further develop the software to enable relevant output parameters applicable to any control strategy and to conduct engine health monitoring. At the completion of Phase III, the fully functional prototype hardware developed in Phase III for laboratory-scale use and the associated software for both control strategies and engine health monitoring shall be delivered to the Government Point of Contact.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: These spectroscopic techniques will produce the experimental capability to measure combustion dynamics near the injector plate of a rotating detonation engine and also provide insight on the combustion efficiency for such engines. The measurement approach will also be applicable for determining the performance and combustion characteristics associated with gas-turbines, power plants, IC engines, and turbine engines.

REFERENCES:
1. V. Nagali, and R.K. Hanson, "Design of a diode-laser sensor to monitor water vapor in high-pressure combustion gases," Applied Optics, Vol. 36, No 36, pp. 9518-9527, Dec. 1997.

2. X. Ouyang and P. L. Varghese, "Selection of spectral lines for combustion diagnostics," Applied Optics, Vol. 29, No. 33 pp 4884-4890, 20 November 1990.

3. X. Ouyang and P. L. Varghese, "Line-of-sight absorption measurements of high temperature gases with thermal and concentration boundary layers," Applied Optics, Vol. 28, No. 18, pp. 3979-3984, 15 September 1989.

4. J. A. Silver, "Frequency-modulation spectroscopy for trace species detection: theory and comparison among experimental methods," Applied Optics, Vol. 31, pp. 707-717, 1992.

5. D. S. Bomse, A. C. Stanton, and J. A. Silver, "Frequency-modulation and wavelength modulation spectroscopies: Comparison of experimental methods using a lead-salt diode laser," Applied Optics, Vol. 31, pp. 718-731, 1992.

6. X. Zhou, X. Liu, J. Jeffries, and R. K. Hanson, "Development of a sensor for temperature and water concentration in combustion gases using a single tunable diode laser," Measurement Science Technology, Vol. 14, pp. 1459-1468, 2003.

7. J. M. Seitzman, R. Tamma, R. Vijayan, "Infrared absorption based sensor approaches for high Pressure combustion," AIAA Paper 97-0318, Los Angeles, January 1997.

8. A. Farooq, J. Jeffries, and R. K. Hanson, "In situ combustion measurements of H2O and temperature near 2.5 �m using tunable diode laser absorption," Measurement Science Technology, Vol. 19, 2008.

9. Sanders S T, Baldwin J A, Jenkins T P, Baer D S and Hanson R K 2000 Diode-laser sensor for monitoring multiple combustion parameters in pulse detonation engines Proc. Combust. Inst. 28 587�94.

KEYWORDS: Combustion, High-Bandwidth Measurements, Laser Spectroscopy, Detonation, Combustion Efficiency, Energy Efficiency

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