The Flammability Limits of Hydrogen and Methane in Air at Moderately Elevated Temperatures

1997 ◽  
Author(s):  
B. B. Ale ◽  
I. Wierzba
Keyword(s):  
Residence Time ◽  
Initial Temperature ◽  
Elevated Temperatures ◽  
Hydrogen Oxidation ◽  
Initial Mixture ◽  
Spark Ignition ◽  
Stainless Steel Surface ◽  
Flammability Limits ◽  
Simple Method ◽  
The Rich

The flammability limits of hydrogen and methane in air were determined experimentally at elevated initial mixture temperatures up to 350°C at atmospheric pressure for upward flame propagation in a conventional steel test tube apparatus. Additionally the extent to which a prolonged exposure (i.e., residence time) of the mixture to elevated temperatures before spark ignition and, consequently, the existence of pre-ignition reactions that may influence the value of the lean and rich flammability limits was also investigated. It was shown that the flammability limits for methane widened approximately linearly with an increase in the initial mixture temperature over the whole range of temperatures tested. These limits were not affected by the length of the residence time before spark ignition. Different behaviour was observed for flammability limits of hydrogen. They were also widened with an increase in the initial temperature but only up to 200°C. In this initial temperature range the limits were not affected by the length of the residence time. However, at initial temperature exceeding 200°C the flammability limits, especially, the rich limits narrowed with an increase in the temperature and were significantly affected by the residence time before spark ignition. The results of detailed chemical kinetic simulation showed that the gas phase reactions of hydrogen oxidation could not be responsible for the substantial drop in the value of the rich limit. It was therefore, suggested that this drop in the value of the rich limit with the increase in the residence time was caused by the relatively low temperature catalytic reactions on the stainless steel surface of the flame tube. Simple method for calculating the hydrogen conversion to water was proposed. The results of calculations are in fair agreement with the experimental evidence.

scholarly journals The Effect of Time of Exposure to Elevated Temperatures on the Flammability Limits of Some Common Gaseous Fuels in Air

1998 ◽  
Author(s):  
B. B. Ale ◽  
L. Wierzba
Keyword(s):  
Exposure Time ◽  
Atmospheric Pressure ◽  
Entire Range ◽  
Elevated Temperatures ◽  
Initial Mixture ◽  
Spark Ignition ◽  
Test Tube ◽  
The Other ◽  
Flammability Limits ◽  
Gaseous Fuels

The flammability limits of methane, ethylene, propane and hydrogen were determined experimentally at elevated initial mixture temperatures up to 350°C at atmospheric pressure for upward flame propagation in a steel test tube apparatus. The existence of preignition reactions at these levels of temperatures that may influence the value of the flammability limits was also investigated. The fuel-air mixtures were exposed to elevated temperatures over different periods of time before spark ignition (up to 2 hours). It was shown that the flammability limits for methane widened approximately linearly with an increase in the initial mixture temperature over the entire range of temperatures tested and were not affected by the length of the exposure time to these temperatures before spark ignition. However, different behaviour was observed for the flammability limits of the other tested fuels — ethylene, propane and hydrogen. At higher temperatures the flammability limits narrowed and were very significantly affected by the exposure time. The longer was the exposure time of fuel-air mixtures to the elevated temperatures, the narrower were their flammability limits.

The Effect of Time of Exposure to Elevated Temperatures on the Flammability Limits of Some Common Gaseous Fuels in Air

1999 ◽  
Vol 121 (1) ◽  
pp. 74-79 ◽  
Author(s):  
I. Wierzba ◽  
B. B. Ale
Keyword(s):  
Exposure Time ◽  
Atmospheric Pressure ◽  
Entire Range ◽  
Elevated Temperatures ◽  
Initial Mixture ◽  
Spark Ignition ◽  
Test Tube ◽  
The Other ◽  
Flammability Limits ◽  
Gaseous Fuels

The flammability limits of methane, ethylene, propane, and hydrogen were experimentally determined at elevated initial mixture temperatures up to 350°C at atmospheric pressure for upward flame propagation in a steel test tube apparatus. The existence of preignition reactions at these levels of temperatures that may influence the value of the flammability limits was also investigated. The fuel-air mixtures were exposed to elevated temperatures over different periods of time before spark ignition (up to 2 h). It was shown that the flammability limits for methane widened approximately linearly with an increase in the initial mixture temperature over the entire range of temperatures tested and were not affected by the length of the exposure time to these temperatures before spark ignition. However, different behaviour was observed for the flammability limits of the other tested fuels—ethylene, propane, and hydrogen. At higher temperatures the flammability limits narrowed and were very significantly affected by the exposure time. The longer was the exposure time of fuel-air mixtures to the elevated temperatures, the narrower were their flammability limits.

scholarly journals The Temperature and Pressure Dependencies of Propagation Characteris-tics for Premixed Laminar Ethanol-Air Flames

2012 ◽  
Vol 6 (1) ◽  
pp. 55-64 ◽  
Author(s):  
S. Y. Liao ◽  
D. L. Zhong ◽  
C. Yang ◽  
X. B. Pan ◽  
C. Yuan ◽  
...  
Keyword(s):  
Equivalence Ratio ◽  
Initial Temperature ◽  
Burning Velocity ◽  
Initial Mixture ◽  
Spark Ignition ◽  
Laminar Burning Velocity ◽  
Propagation Characteristics ◽  
Activation Temperature ◽  
Temperature And Pressure ◽  
Premixed Laminar

Laminar burning velocity is strongly dependent on mixture characteristics, e.g. initial temperature, pressure and equivalence ratio. In this work, spherically expanding laminar premixed flames, freely propagating from a spark ignition source in initially quiescent ethanol-air mixtures, have been imaged and then the laminar burning velocities were obtained at initial temperatures of 358 K to 500K, pressure of 0.1 to 0.2 MPa and equivalence ratio of 0.7 to 1.4. The measured re-sults and literature data on ethanol laminar burning velocities were accumulated, to analyze the effects of initial tempera-ture and pressure on the propagation characteristics of laminar ethanol-air flames. A correlation in the form of ul=ulo(Tu/Tu0)αT (Pu/Pu0)βP , and validated over much wide temperature, pressure and equivalence ratio ranges. The global activation temperatures were determined in terms of the laminar burning mass flux for ethanol-air flames. And the Zel’dovich numbers were estimated as well. The dependencies of global activation temperature and Zel’dovich number on initial mixture pressure, temperature and equivalence ratio were explored. Additionally, an alterna-tive correlation of laminar burning velocities, from the view of theoretical arguments, was proposed on the basis of the de-termined ethanol-air laminar mass burning flux. Good agreements were obtained in its comparison with the literature data.

scholarly journals Combustion and Deposition, Erosion, and Corrosion Tests of Coal Turbine Fuels

1985 ◽  
Author(s):  
C. Wilkes ◽  
R. Wenglarz ◽  
D. W. Clark
Keyword(s):  
Residence Time ◽  
Combustion Efficiency ◽  
Water Slurry ◽  
Lean Combustion ◽  
Coal Water Slurry ◽  
Unburned Hydrocarbons ◽  
Alternative Approaches ◽  
The Rich ◽  
Burning Coal ◽  
Distillate Fuel

This paper discusses the results obtained from the rich-quench-lean (RQL) combustion system running on distillate fuel and coal water slurry (CWS). Estimates of fuel bound nitrogen (FBN) yield indicate that rich lean combustion is successful in reducing the yield from coal water slurry fuel to between 8% and 12%. Some improvements in combustion efficiency are required when burning coal water slurry to reduce carbon monoxide and unburned hydrocarbons to acceptable levels. These improvements are achievable by increasing the lean zone residence time. Further testing is planned to investigate the effects of residence time in more detail. The planned deposition, erosion, and corrosion (DEC) testing will evaluate alternative approaches for protection from deposition, erosion, and corrosion of turbines operating with coal derived fuels.

scholarly journals Flow Characteristics of a Rich-Quench-Lean Combustor-Combined Low-Emission and High-Temperature Rise Combustion

2019 ◽  
Vol 2019 ◽  
pp. 1-22
Author(s):  
Jianzhong Li ◽  
Jian Chen ◽  
Li Yuan ◽  
Ge Hu ◽  
Jianhan Feng
Keyword(s):  
High Temperature ◽  
Flow Field ◽  
Residence Time ◽  
Temperature Rise ◽  
Recirculation Zone ◽  
Flow Characteristics ◽  
Field Structure ◽  
Low Emission ◽  
The Rich ◽  
High Temperature Rise

To determine the flow field structure and flow characteristics of a rich-quench-lean (RQL) combustor-combined low-emission and high-temperature rise combustion, a two-dimensional PIV technology was used to evaluate the effect of aerodynamic and structural parameters on the flow field and flow characteristics of the combustor. The variation in the total pressure loss of the combustor has little effect on the flow field structure of the combustor. However, the variation in the parameters of primary holes significantly affects the structure of the central recirculation zone, the distribution of local recirculation zones in the rich-burn zone and quenching zone, and the average residence time in the quenching zone. On the plane that passes through the center of the primary hole, the variations in the array mode and diameter of primary holes would form entrainment vortexes with different characteristics, thus affecting the position and flow state of local recirculation in the rich-burn zone and the local structure of the central recirculation zone. As the rotational direction of local recirculation coincides with that of the main air flow in the primary zone, the local center recirculation is intensified. In contrast, it is weakened. As the primary holes are located at half height (H/2) of the combustor, the residence time of air flow at the quenching zone can be shortened by 65% through using the staggered structure of primary holes and increasing the momentum of the partial single-hole jet. The quick-mixing process in the quenching zone is not beneficial to increase the number of primary holes and decrease the momentum of the single-hole jet.

Kinetics Modeling on NOx Emissions of a Syngas Turbine Combustor Using RQL Combustion Method

2019 ◽  
Author(s):  
Haoyang Liu ◽  
Wenkai Qian ◽  
Min Zhu ◽  
Suhui Li
Keyword(s):  
Gas Turbine ◽  
Residence Time ◽  
Air Flow ◽  
Nox Reduction ◽  
Outlet Temperature ◽  
Nox Emissions ◽  
Gas Turbine Combustor ◽  
Kinetics Modeling ◽  
The Rich ◽  
Nox Control

Abstract To avoid flashback issues of the high-H2 syngas fuel, current syngas turbines usually use non-premixed combustors, which have high NOx emissions. A promising solution to this dilemma is RQL (rich-burn, quick-mix, lean-burn) combustion, which not only reduces NOx emissions, but also mitigates flashback. This paper presents a kinetics modeling study on NOx emissions of a syngas-fueled gas turbine combustor using RQL architecture. The combustor was simulated with a chemical reactor network model in CHEMKIN-PRO software. The combustion and NOx formation reactions were modeled using a detailed kinetics mechanism that was developed for syngas. Impacts of combustor design/operating parameters on NOx emissions were systematically investigated, including combustor outlet temperature, rich/lean air flow split and residence time split. The mixing effects in both the rich-burn zone and the quick-mix zone were also investigated. Results show that for an RQL combustor, the NOx emissions initially decrease and then increase with combustor outlet temperature. The leading parameters for NOx control are temperature-dependent. At typical modern gas turbine combustor operating temperatures (e.g., < 1890 K), the air flow split is the most effective parameter for NOx control, followed by the mixing at the rich-burn zone. However, as the combustor outlet temperature increases, the impacts of air flow split and mixing in the rich-burn zone on NOx reduction become less pronounced, whereas both the residence time split and the mixing in the quick-mix zone become important.

Experimental determination of flame speed and flame stretch using an optically accessible, spark-ignition engine

2019 ◽  
pp. 146808741987771 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A Miers ◽  
Jeffrey D Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
Engine Speed ◽  
Spark Ignition ◽  
Flame Speed ◽  
Dominant Factor ◽  
Lean Mixture ◽  
Flame Stretch ◽  
Flame Development ◽  
The Rich

The current research experimentally studied flame speed and stretch under engine in-cylinder conditions. A direct-injection, spark-ignition, and optically accessible engine was utilized to image the flame propagation, and E10 was selected as the fuel. Also, three fuel–air mixtures (stoichiometric, lean, and rich) were examined. The flame front was located by processing high-speed images. This study introduces a novel approach for calculation of equivalent spherical flame radius for analysis of flame speed and stretch. Flame front propagation analysis showed that during the flame propagation period, the stretch decreased until the flame front touched the piston surface. This was a common trend for stoichiometric, lean, and rich mixtures, which occurred because the flame radius was the dominant factor in the stretch calculation. In addition, the rich fuel–air mixture showed a lower flame stretch compared to stoichiometric or lean mixture. This was the result of a lower Markstein number for the rich fuel–air mixture. To study the sensitivity of different fuel–air mixtures to the flame stretch, the trajectory of the flame centroid was tracked until the flame front touched the piston surface. The results showed that the end centroid for the lean mixture deviated from the start point more than those of the rich and stoichiometric mixtures because the lean mixture had a higher flame stretch and lower flame speed. Furthermore, comparing the flame stretch at three different engine speeds revealed that increasing the engine speed increased the flame stretch, especially during the early flame development period. According to previous studies which discussed flame stretch as a flame extinguishment mechanism, the probability of flame extinction is higher when the engine speed is higher. Also, uncertainty analysis was conducted to determine the effect of camera setting on the flame stretch. Results showed that a maximum relative uncertainty of 4.5% occurred during the early flame development.

scholarly journals Thermal delay of drop coalescence

2017 ◽  
Vol 833 ◽  
Author(s):  
Michela Geri ◽  
Bavand Keshavarz ◽  
Gareth H. McKinley ◽  
John W. M. Bush
Keyword(s):  
Critical Temperature ◽  
Residence Time ◽  
Temperature Difference ◽  
Initial Temperature ◽  
Theoretical Study ◽  
Fluid Viscosity ◽  
Drop Coalescence ◽  
Thermocapillary Flows ◽  
Silicone Oils ◽  
Thermal Delay

We present the results of a combined experimental and theoretical study of drop coalescence in the presence of an initial temperature difference $\unicode[STIX]{x0394}T_{0}$ between a drop and a bath of the same liquid. We characterize experimentally the dependence of the residence time before coalescence on $\unicode[STIX]{x0394}T_{0}$ for silicone oils with different viscosities. Delayed coalescence arises above a critical temperature difference $\unicode[STIX]{x0394}T_{c}$ that depends on the fluid viscosity: for $\unicode[STIX]{x0394}T_{0}>\unicode[STIX]{x0394}T_{c}$, the delay time increases as $\unicode[STIX]{x0394}T_{0}^{2/3}$ for all liquids examined. This observed dependence is rationalized theoretically through consideration of the thermocapillary flows generated within the drop, the bath and the intervening air layer.

Sign in / Sign up

Export Citation Format

Share Document