Buoyant Unstable Behavior of Initially Spherical Lean Hydrogen-Air Premixed Flames
Open Access
- 30 July 2014
- Vol. 7 (8), 4938-4956
- https://doi.org/10.3390/en7084938
Abstract
Buoyant unstable behavior in initially spherical lean hydrogen-air premixed flames within a center-ignited combustion vessel have been studied experimentally under a wide range of pressures (including reduced, normal, and elevated pressures). The experimental observations show that the flame front of lean hydrogen-air premixed flames will not give rise to the phenomenon of cellular instability when the equivalence ratio has been reduced to a certain value, which is totally different from the traditional understanding of the instability characteristics of lean hydrogen premixed flames. Accompanied by the smoothened flame front, the propagation mode of lean hydrogen premixed flames transitions from initially spherical outwardly towards upwardly when the flames expand to certain sizes. To quantitatively investigate such buoyant instability behaviors, two parameters, “float rate (ψ)” and “critical flame radius (Rcr)”, have been proposed in the present article. The quantitative results demonstrate that the influences of initial pressure (Pint) on buoyant unstable behaviors are different. Based on the effects of variation of density difference and stretch rate on the flame front, the mechanism of such buoyant unstable behaviors has been explained by the competition between the stretch force and the results of gravity and buoyancy, and lean hydrogen premixed flames will display buoyant unstable behavior when the stretch effects on the flame front are weaker than the effects of gravity and buoyancy.Keywords
This publication has 30 references indexed in Scilit:
- Renewable hydrogen economy in Asia – Opportunities and challenges: An overviewRenewable and Sustainable Energy Reviews, 2014
- Recent progress in the use of hydrogen as a fuel for internal combustion enginesInternational Journal of Hydrogen Energy, 2014
- An overview of hydrogen as a vehicle fuelRenewable and Sustainable Energy Reviews, 2012
- Research on cellular instabilities in outwardly propagating spherical hydrogen-air flamesInternational Journal of Hydrogen Energy, 2012
- Research and development of hydrogen fuelled engines in ChinaInternational Journal of Hydrogen Energy, 2012
- Burning Speed and Entropy Production Calculation of a Transient Expanding Spherical Laminar Flame Using a Thermodynamic ModelEntropy, 2010
- Experimental study on combustion characteristics of a spark-ignition engine fueled with natural gas–hydrogen blends combining with EGRInternational Journal of Hydrogen Energy, 2008
- Intrinsic Flame Instabilities in Premixed and Nonpremixed CombustionAnnual Review of Fluid Mechanics, 2007
- Hydrogen as a spark ignition engine fuelInternational Journal of Hydrogen Energy, 2003
- Studies of cellular flames in hydrogenoxygennitrogen mixturesCombustion and Flame, 1980