Laminar burning velocities and Markstein numbers of hydrocarbon/air flames
- Univ. of Michigan, Ann-Arbor, MI (United States). Dept. of Aerospace Engineering
Effects of positive flame stretch on the laminar burning velocities of hydrocarbon/air mixtures were studied experimentally using outwardly propagating spherical flames. The test conditions included propane, methane, ethane, and ethylene -- air flames at various fuel-equivalence ratios and normal temperature and pressure. Karlovitz numbers generally were less than 0.3 so that the flames were remote from quenching conditions. Within this range, the ratio of the unstretched (plane flames) to stretched laminar burning velocities varied linearly with Karlovitz numbers, yielding Markstein numbers that were independent of Karlovitz numbers for a particular reactant mixture. In addition, Markstein numbers varied in a roughly linear manner with fuel-equivalence ratios over the range of the measurements, which were somewhat removed from flammability limits where behavior might differ. Effects of stretch were substantial: Markstein numbers varied from [minus]2.5 to 7.2 yielding corresponding laminar burning velocity variations of 0.4--2.7 times the value for an unstretched (plane) flame over the test range. The ranges of fuel-equivalence ratios for unstable preferential-diffusion conditions (negative Markstein numbers) were as follows: propane, greater than 1.44; methane, less than 0.74; ethane, greater than 1.68; and ethylene, greater than 1.95. Fuel-equivalence ratios for maximum flame temperatures and laminar burning velocities are near unity for the present flames; therefore, neutral preferential-diffusion conditions are shifted toward fuel-equivalence ratios on the unstable side of unity, in qualitative agreement with recent approximate theories treating the effects of stretch on laminar premixed flames.
- OSTI ID:
- 5524967
- Journal Information:
- Combustion and Flame; (United States), Vol. 95:4; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
02 PETROLEUM
03 NATURAL GAS
ETHANE
COMBUSTION KINETICS
ETHYLENE
FLAMES
MORPHOLOGY
METHANE
PROPANE
AIR
DIFFUSION
FLOW RATE
LAMINAR FLOW
MIXTURES
ALKANES
ALKENES
CHEMICAL REACTION KINETICS
DISPERSIONS
FLUID FLOW
FLUIDS
GASES
HYDROCARBONS
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400800* - Combustion
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025000 - Petroleum- Combustion
034000 - Natural Gas- Combustion