The global objective of the proposed research is to elucidate the diffusion flame stabilizing and lifting mechanisms. The specific aims include: (1) analyze thoroughly the SLICE liftoff velocity limit data to extract general trends, (2) conduct ground-based liftoff experiments using C1 – C4 hydrocarbons to study fuel effects, (3) perform computation with full chemistry to reveal the flame structure and flame-flow interactions, leading to the liftoff conditions. The overall merit of the proposed research is fundamental contributions to combustion science and NASA’s microgravity combustion research, through the effective use of underutilized SLICE data on the liftoff limits and the rigorous validation of the numerical methods, including reaction mechanisms, soot formation, and radiation models.

The Principal Investigator (PI) has more than 20 years of experience and knowledge in microgravity combustion research and has served as a co-Investigator for the SLICE project. Case Western Reserve University has recently expanded the Fire and Combustion Laboratories, equipped with various fire testing instruments, and the computation will be performed using the Case High Performance Computing Cluster. If successful, the proposed research will give a significant impact on the research area of flame stabilization, which has been one of major subjects of interest since the early days of modern combustion research, started several decades ago. As a result of recent advances in flame diagnostic techniques and numerical predictive capabilities, including comprehensive chemical kinetics, it is now feasible to elucidate complex flame-flow interacting phenomena such as flame stabilization.

During the reporting period, we have performed the following tasks.

(1) Measured the stability limits of laminar coflow jet diffusion flames of propene in 1g for the fuel tubes with inner diameters of 0.8 and 1.6 mm, in addition to the fuels investigated previously (i.e., methane, ethane, ethylene, acetylene, propane, butane, butene).

(2) Performed the computation using the in-house numerical code (UNICORN) with a newly incorporated chemical reaction mechanism applicable to C1 to C4 hydrocarbons. Successfully revealed the structure of a butane jet diffusion flame, for the first time, as the flame base lifted off the burner rim gradually until blowout, in response to incremental increases in the coflowing air velocity. The predicted flame stability limit was in good agreement with the measurement.

The global objective of the proposed research is to elucidate the diffusion flame stabilizing and lifting mechanisms. The specific aims include: (1) analyze thoroughly the SLICE liftoff velocity limit data to extract general trends, (2) conduct ground-based liftoff experiments using C1 – C4 hydrocarbons to study fuel effects, (3) perform computation with full chemistry to reveal the flame structure and flame-flow interactions, leading to the liftoff conditions. The overall merit of the proposed research is fundamental contributions to combustion science and NASA’s microgravity combustion research, through the effective use of underutilized SLICE data on the liftoff limits and the rigorous validation of the numerical methods, including reaction mechanisms, soot formation, and radiation models.

The Principal Investigator (PI) has more than 20 years of experience and knowledge in microgravity combustion research and has served as a co-Investigator for the SLICE project. Case Western Reserve University has recently expanded the Fire and Combustion Laboratories, equipped with various fire testing instruments, and the computation will be performed using the Case High Performance Computing Cluster. If successful, the proposed research will give a significant impact on the research area of flame stabilization, which has been one of major subjects of interest since the early days of modern combustion research, started several decades ago. As a result of recent advances in flame diagnostic techniques and numerical predictive capabilities, including comprehensive chemical kinetics, it is now feasible to elucidate complex flame-flow interacting phenomena such as flame stabilization. A federal financial assistance is needed to accomplish such an important scientific goal.

During the reporting period 12/13/2018 to 12/12/2019, we have performed the following tasks:

(1) By using the engineering model of the Smoke Point in Co-flow Experiment (SPICE) experiment assembly, loaned from the NASA Glenn Research Center (GRC), the stability limits (lift-off and blow-off) of laminar diffusion flames have been measured in 1g [2, 3]. The fuels are methane, ethane, ethene, propane, butane, 1-butene, 70% methane in nitrogen, and 20% ethane in nitrogen. The fuel tube inner diameters are 0.4 mm and 0.8 mm. In general, the critical fuel jet velocities at the flame stability limits are larger for a larger fuel tube diameter, for alkenes than alkanes (due to the higher reactivity), and for a lower number of carbon atoms (due to the lower fuel density).

(2) Furthermore, by using a newly fabricated experimental apparatus, the stability limits have been measured over much larger ranges of the fuel and air velocities as well as the fuel tube diameter than those of the SPICE rig. The apparatus consists of a stainless-steel fuel tube (0.4 – 3.2 mm i.d.) coaxially installed in a glass chimney (95 mm i.d.). In addition to the pure C1 – C4 hydrocarbons mentioned above, acetylene is also used as the fuel.

(3) The computation with detailed chemistry to reveal the diffusion flame structure and flame-flow interactions leading to the flame stability-limit conditions has been initiated. A chemical reaction mechanism for butane has newly been incorporated in the in-house numerical code, especially capable of simulating unsteady flame-flow interaction phenomena such as the flame stabilizing process.

REFERENCES

1. Takahashi, F., Kulakhmetov, R., Stocker, D.P., Ma, B., and Long, M.B., Microgravity Enhances the Stability of Gas-Jet Diffusion Flames, 28th Annual Meeting of the American Society for Gravitational and Space Research, New Orleans, LA, November 28-December 2, 2012.

2. Smith, L., Souza, D., and Takahashi, F., Stabilization of Laminar Jet Diffusion Flames, 34th Annual Meeting of the American Society for Gravitational and Space Research, Bethesda, Rockville, MD, October 31-November 3, 2018.

3. Smith, L., Souza, D., and Takahashi, F., Stabilization of Laminar Hydrocarbon Jet Diffusion Flames in Earth Gravity and Microgravity, 27th International Colloquium on the Dynamics of Explosions and Reactive Systems, Beijing, China, July 28th - August 2nd, 2019.

The global objective of the proposed research is to elucidate the diffusion flame stabilizing and lifting mechanisms. The specific aims include: (1) analyze thoroughly the SLICE liftoff velocity limit data to extract general trends, (2) conduct ground-based liftoff experiments using C1 – C4 hydrocarbons to study fuel effects, (3) perform computation with full chemistry to reveal the flame structure and flame-flow interactions, leading to the liftoff conditions. The overall merit of the proposed research is fundamental contributions to combustion science and NASA’s microgravity combustion research, through the effective use of underutilized SLICE data on the liftoff limits and the rigorous validation of the numerical methods, including reaction mechanisms, soot formation, and radiation models.

The Principal Investigator (PI) has more than 20 years of experience and knowledge in microgravity combustion research and has served as a co-Investigator for the SLICE project. Case Western Reserve University has recently expanded the Fire and Combustion Laboratories, equipped with various fire testing instruments, and the computation will be performed using the Case High Performance Computing Cluster. If successful, the proposed research will give a significant impact on the research area of flame stabilization, which has been one of major subjects of interest since the early days of modern combustion research, started several decades ago. As a result of recent advances in flame diagnostic techniques and numerical predictive capabilities, including comprehensive chemical kinetics, it is now feasible to elucidate complex flame-flow interacting phenomena such as flame stabilization. A federal financial assistance is needed to accomplish such an important scientific goal.

(1) Hand-carried an engineering model of the Smoke Point in Co-flow Experiment (SPICE) experimental assembly from the NASA Glenn Research Center (GRC) to the Case Western Reserve University (CWRU) on 3/23/18. After setting up and running the experiment over the spring/summer, the apparatus was returned to the GRC on 8/31/18, in response to a request by NASA. Additional experiments are needed.

(2) Measured the stability limits (lift-off and blow-off) of laminar diffusion flames in the Earth gravity (1g) in the SPICE apparatus for various fuels using various burner tube diameters. The fuels tested thus far include ethane, propane, butane, and 1-butene and the burner tube diameters used are 0.4 mm and 0.8 mm. In general, the critical fuel jet velocity at the flame lifting is larger for a larger fuel tube diameter, for alkenes than alkanes (due to the higher reactivity), and for a lower number of fuel carbon atoms (due to the lower fuel density). The critical fuel jet velocity for ethane with 0.8 mm dia. fuel tube in the present experiment is approximately 21% higher than that obtained in the SLICE’s 1g test in 2012 [Takahashi et al., 2012]. The calibration of the fuel mass flow controller and the air fan need to be completed. Other fuels planned to be tested include methane, ethylene, acetylene, and propene. However, because of the SPICE apparatus’s upper limits of the mass flow controller for fuel (500 sccm in N2) and the coflowing air speed (~65 cm/s), the lifting limit could barely be reached for the fuel with a high reactivity such as ethylene even using the smallest burner tube diameter (0.4 mm). For a highly reactive fuel such as acetylene and/or for a larger diameter will require an experimental apparatus capable of wider fuel and air flow rate ranges.

(3) Initiated the fabrication of a new burner system for studying the structure and stabilization of laminar diffusion flames in 1g at the CWRU campus. The burner consists of a stainless-steel fuel tube (0.4 – 2.1 mm i.d.) and a coaxially installed contour nozzle (~25 mm i.d. exit) for the coflow air. Four mass flow meters (Hastings, HFM-200 and HFM-201) have been purchased for the flow ranges of 500 sccm N2 for the fuel, 200 sccm N2 for an additive to the fuel, 50 slpm for the coflow air, and 15 slpm for an additive to the air. The burner assembly will be installed on a 3D translational stage for the diagnostic measurements.

(4) Made an oral presentation of the results of the stability limits, obtained using the SPICE experimental apparatus, at the 34th Annual Meeting of the American Society for Gravitational and Space Research, Bethesda, Rockville, MD, October 31-November 3, 2018.

Reference: Takahashi, F., Kulakhmetov, R., Stocker, D.P., Ma, B., and Long, M.B., Microgravity Enhances the Stability of Gas-Jet Diffusion Flames, 28th Annual Meeting of the American Society for Gravitational and Space Research, New Orleans, LA, November 28-December 2, 2012.

The global objective of the proposed research is to elucidate the diffusion flame stabilizing and lifting mechanisms. The specific aims include: (1) analyze thoroughly the SLICE liftoff velocity limit data to extract general trends, (2) conduct ground-based liftoff experiments using C1 – C4 hydrocarbons to study fuel effects, (3) perform computation with full chemistry to reveal the flame structure and flame-flow interactions, leading to the liftoff conditions. The overall merit of the proposed research is fundamental contributions to combustion science and NASA’s microgravity combustion research, through the effective use of underutilized SLICE data on the liftoff limits and the rigorous validation of the numerical methods, including reaction mechanisms, soot formation, and radiation models.

The Principal Investigator (PI) has more than 20 years of experience and knowledge in microgravity combustion research and has served as a co-Investigator for the SLICE project. Case Western Reserve University has recently expanded the Fire and Combustion Laboratories, equipped with various fire testing instruments, and the computation will be performed using the Case High Performance Computing Cluster. If successful, the proposed research will give a significant impact on the research area of flame stabilization, which has been one of major subjects of interest since the early days of modern combustion research, started several decades ago. As a result of recent advances in flame diagnostic techniques and numerical predictive capabilities, including comprehensive chemical kinetics, it is now feasible to elucidate complex flame-flow interacting phenomena such as flame stabilization. A federal financial assistance is needed to accomplish such an important scientific goal.