Feasibility Study of Using Matrix-Stabilized Combustion Technologies to Enable Ultra-low Emission Combustion in Aviation Gas Turbines
Leading Edge Aeronautics Research for NASA (LEARN)
Principal Investigator: Matthias Ihme (Stanford University)
Co-Investigators: Waldo Hinshaw (Stanford University), John Sullivan (ALZETA Corporation)
Sadaf Sobhani, Danyal Mohaddes, Emeric Boigne, Priyanka Muhunthan (Stanford)
David Bartz, Bret Haley (ALZETA Corporation)
Article in Stanford Engineering:
The objective of this multidisciplinary research program is to enable the utilization of matrix stabilized combustion as a low-emission fuel-flexible combustion strategy for gas turbines by developing predictive simulation techniques for the combustion analysis and design optimization, by establishing advanced diagnostics techniques using X-Ray Computed Tomography (CT) for non-intrusive 3D measurements of combustion processes inside the porous matrix, and by conducting experiments to evaluate the durability, stability, and performance at gas-turbine relevant conditions. Matrix-stabilized combustion is an advanced combustion technology, in which combustion is facilitated inside a porous heat-conducting matrix. The internal heat-recirculation is used for preheating the unburned reactants to achieve superadiabatic combustion, thereby providing enormous opportunities for improving emissions, combustion stability, and fuel-flexible operation. The proposed research program directly addresses the research needs on developing innovative concepts for low-carbon and ultra-efficient propulsion systems. To achieve the stated objectives, a closely coordinated research effort will be undertaken, addressing the most critical research issues.
The computational research effort addresses the development of a multi-resolution high-fidelity simulation capability that provides a detailed description of the unsteady heterogeneous combustion and gas/solid interaction inside the porous structure. To this end, a simulation method is developed to accurately model the fluid dynamics and heterogeneous combustion processes inside the porous structure, and heat-exchange processes between gas-phase and solid structure are represented using a conjugate heat-transfer model.
Advanced non-intrusive X-Ray CT diagnostics techniques will be developed to obtain quantitative measurements for examining the 3D flame-structure and temperature field inside the porous structure. Such detailed and volumetric measurements are unprecedented, and will provide quantitative information for model validation and for obtaining fundamental insight about the flame topology in porous media, solid/gas coupling effects, and the construction of regime diagrams for heterogeneous combustion processes.
These computational and diagnostics efforts are complemented by a comprehensive measurement campaign to demonstrate the feasibility of matrix-stabilized combustion at gas-turbine relevant operating conditions. Measurements will be conducted to characterize performance, emissions, and durability for different porous materials.
To accomplish this research plan, a research team is assembled that combines unique expertise on the high-fidelity combustion modeling, numerical methods, and optimization techniques (Ihme, Stanford), the development of advanced X-Ray CT diagnostics techniques (Hinshaw, Stanford), and our industrial partner Alzeta Corporation (Sullivan) brings over 30 years of experience on the development and commercialization of porous burner technologies to this research.
The objective of this research program is to extend the feasibility assessment of matrix-stabilized combustion as low-emission and fuel-flexible combustion strategy for gas turbines (GTs). Essential proof-of-concept of this technology was established in phase I. The proposed phase-II research directly addresses critical research aspects that were identified as outcome of the phase-I effort and through feedback from NASA and industry by
- experimentally demonstrating the performance of the newly developed burner concept with variable porosity
- extending the performance tests to liquid fuels at elevated pressures;
- performing pore-resolved simulations of matrix-stabilized combustion;
- further improving the accuracy and spatial resolution of the XCT-diagnostics.
The goal of the proposed measurement campaign is to characterize the performance (stability, emissions, pressure drop, and durability) of PMBs using Jet-A and alternative liquid fuels at pressures up to 20 bar. For this, our existing burner setup will be modified for liquid-fuel delivery, and we will access the SE-5 facility at the NASA Glenn Research Center for performance testing at elevated temperature and pressure conditions. The newly proposed burner concept with continuous flame stabilization will be implemented and benchmarked to experimentally confirm predicted performance gains for reduced pressure losses, emissions, and enhanced flame stability.
Pore-resolved simulations will be performed to gain fundamental physical understanding about flame structure and coupling processes between heat-release distribution, solid/gas heat exchange, and hydrodynamics. Using methods that were established in phase I, the matrix topology will be directly extracted from PMB- experiments using micro-CT and surface reconstruction. This enables the direct comparison against XCT- temperature measurements, and the pore-resolved simulations will be analyzed to reconcile deficiencies of low- order models.
Research efforts to further advance the XCT-diagnostics for quantitative 3D-temperature measurements will focus on increasing the spatial resolution and improving the signal strength for measurements at elevated pressures. For this, iterative reconstruction techniques will be utilized to introduce constraints on the physical realizability. Together with the installation of an ultra-high resolution detector and dual-energy XCT, we target to achieve temperature measurements with standard deviation below 50 K at spatial resolution of 25 micrometer.
Experimental Research Effort
Experimental Investigation of Flame Stability in a Variable Porous Media Burner
Ambient pressure experiments are performed to demonstrate the new concept of a variable Porous Media Burner (PMB) design. Stable operating characteristics are determined for methane / air premixed flames over various equivalence ratios and flow rates up to 2 kg/(m²s). Pressure drop across the burner as well as inner gas temperatures are examined.
The PMB used are made of Silicon carbide (SiC) and silicon infiltrated silicon carbide (SiSiC) from different manufacturers. Their topology is characterized using X-ray microtomography and correlations between stability results and geometrical parameters are investigated.
PMB-operation with liquid Fuel and High-pressure conditions
A liquid-fuel Porous Media Burner setup is being tested under elevated temperature and pressure conditions at the SE-5 facility at the NASA Glenn Research Center. The goal of the proposed measurement campaign is to characterize the performance (stability, emissions, pressure drop, and durability) of PMBs using Jet-A and alternative liquid fuels at pressures up to 20 bar.
Porous Media Combustion diagnosis using X-ray Computed Tomography
X-ray Computed Tomography (XCT) measurements are performed to characterize the internal volumetric flame structure within a Porous Media Burner (PMB). X-ray attenuation measurements are obtained using a radiodense Kr/O2/N2/CH4 mixture designed to enhance X-Ray contrast. Several key internal physical phenomena are observed, including heat recirculation within the combustion region, spatial inhomogeneity within the reaction zone, and preheating of gas in the upstream porous section. The theory of XCT measurements applied to combustion systems is developed and implemented to arrive at 3D implied temperature field measurements at high spatial resolution. Implied temperature results are compared quantitatively with those of a known 1D volume-averaged model for porous media combustion as well as with standard thermocouple measurements.
Further diagnosis using Synchrotron light source is currently being performed at the Advanced Light Source (ALS) research facility at Lawrence Berkeley National Laboratory. Resolution up to several microns would improve further our understanding of the pore-scale physics.
Computational Research Effort
Analyzing trends in flame stability, pressure drop and emissions
The aim of this work is to determine the accuracy of volume-averaged models for predicting the temperature distribution and pressure drop in PMBs. Two materials of different thermal conductivities, namely Yttria-stabilized Zirconia Alumina (YZA) and Silicon Carbide (SiC), are tested in different configurations and across a range of equivalence ratios and mass flow rates. The temperature predictions of a 1D volume-averaged model with detailed chemistry are assessed against thermocouple measurements from the experimental burner. Pressure drop is computed with the Darcy-Forchheimer equation, using Ergun’s relations for the drag and permeability coefficients, and compared to experimental measurements.
Detailed Pore-Resolved Simulations
Current efforts aim at simulating the combustion process at the pore scale inside the PMB using reconstructed geometry from XCT. An unstructured flow solver resolving the chemistry coupled with the solid heat transfer occurring inside the solid matrix is being developed. Alternative work investigates the use of pore network models to simulate the combustion inside the PMB.