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Experimentally Derived Scaling Laws from Spatiotemporally Resolved Measurements in High-Pressure Combustors

Description:

TECHNOLOGY AREA(S): Air Platform

OBJECTIVE: Develop spectroscopic test platforms for quantitative, interference-free, spatiotemporally resolved measurements of temperature and species concentrations in turbulent combustors at pressures and temperatures relevant to Air Force propulsion systems.

DESCRIPTION: An understanding of fundamental combustion processes at elevated pressures relevant to Air Force propulsion systems is critical for the validation of predictive models and the development of advanced propulsion systems. Combustion proceeds through a multitude of elementary reaction steps, each of which involves various time and length scales ranging from atomic excitation to turbulent transport. Since most technologies of interest to Air Force applications operate at Reynolds numbers that are inaccessible to direct numerical simulation (DNS), even with petascale computational power, the kinetic and transport models of combustion remain critical. However, many models are not well validated and have large discrepancies due to incomplete and inaccurate reaction mechanisms. Many reaction rates are estimated using scaling laws that are not experimental validated under realistic turbulence and high-pressure conditions; as such, in many cases only a lower or upper bound can be estimated.

From an experimental point of view, most atomic and radical intermediate species (OH, CH, CO, H, and O) are transient, highly temperature dependent, and persist at low concentrations in the flame. These conditions pose significant challenges for quantitative measurements. Although there has been significant progress in the development of kinetic and transport models, experimental data on local temperatures and key rate-controlling (atomic, radical, and intermediate) species measured in laminar and turbulent flames at pressures relevant to Air Force applications (10-30 atm) are rare and qualitative, leading to large uncertainties in the models. Measurements that may be quantitative at atmospheric pressures may fail to provide quantitative data at elevated pressures because of interferences from a range of incoherent and laser-dependent processes, including collisional quenching, photoionization, stimulated emission, saturation and Stark shifting, photolytic production of atomic species, and broadband fluorescence interferences from other flame species[1-2]. Other techniques based on line-of-sight absorption or emission measurements may provide limited spatiotemporal resolution but the path integrated nature of these diagnostics can preclude detailed validation of locally varying physicochemical processes under turbulent conditions[3].

Novel, robust, quantitative, interference-free, spatially resolved, high-speed diagnostic methods are highly desired for benchmark measurements of temperature and key rate-controlling species in gas and liquid fueled combustion processes at elevated pressures (10-30 atm) to extend the current state-of-the-art capabilities[4-5] to conditions of relevance to Air Force applications. Such measurements require well-defined boundary conditions and well characterized uncertainties for model validation, necessitating close coordination between experimental diagnostics and reactor design. It is anticipated that a spectroscopic test platform integrating advanced diagnostics will be required to achieve the desired measurements at elevated pressures. By demonstrating and utilizing novel diagnostic tools, researchers are expected to build a benchmark database that can be used to verify predictive turbulent combustion models at elevated pressures.

PHASE I: Demonstrate and document quantitative, spatiotemporally resolved interference-free experimental measurements of temperature and key rate-controlling species (OH, CH, CO, H, and O) concentrations in flames at elevated pressures relevant to Air Force propulsion systems (up to 30 atm).

PHASE II: Demonstrate and document quantitative, interference-free measurements of temperature and key rate-controlling intermediate species in standard laboratory-scale turbulent burners that can be used to build a benchmark database for combustion model validation at elevated pressures. Discover and document scaling laws for temperature and these intermediate species in canonical turbulent gas and liquid-fueled combustors at elevated pressures (10-30 atm).

PHASE III DUAL USE APPLICATIONS: Availability of the quantitative measurements of high-pressure combustion will be used for engineering design and development of gas-turbine engines, hypersonic propulsion systems, industrial burners, and combustion test facilities.

REFERENCES:

    • P.M. Allison, Y. Chen, M. Ihme, and J.F. Driscoll, “Coupling of flame geometry and combustion instabilities based on kilohertz formaldehyde PLIF measurements,” Proceedings of the Combustion Institute, Vol. 35, Issue 3, (2015)

 

    • C.S. Cooper and N.M. Laurendeau, “Quantitative measurements of nitric oxide in high-pressure (2–5 atm), swirl-stabilized spray flames via laser-induced fluorescence,” Combust. Flame, Vol. 123, p.175, (2000).

 

    • C.S. Goldenstein, R.M. Spearrin, J.B. Jeffries, and R.K. Hanson, “Scanned-wavelength-modulation spectroscopy near 2.5 µm for H2O and temperature in a hydrocarbon-fueled scramjet combustor,” Applied Physics B, Vol. 116, Issue 3, (2014).

 

    • J.R. Gord, T.R. Meyer, and S. Roy, “Applications of Ultrafast Lasers for Optical Measurements in Combusting Flows,” Annual Review Analytical Chemistry, Vol. 1, p. 663, (2008).

 

  • M.P. Thariyan, A.H. Bhuiyan, S.E. Meyer, S.V. Naik, J.P. Gore and R.P. Lucht, “Dual-pump coherent anti-Stokes Raman scattering system for temperature and species measurements in an optically accessible high-pressure gas turbine combustor facility,” Measurement Science and Technology, Vol. 22, Num. 1, (2011).

KEYWORDS: laser diagnostics, high-pressure combustion, interference-free measurements, high-speed measurements, temperature, rate-controlling species

  • TPOC-1: Andrew Caswell
  • Phone: 937-255-7098
  • Email: andrew.caswell.4@us.af.mil
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