Abstract
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.
Highlights
In response to the environmental problems related to oil consumption and the associated emissions of CO2 and other pollutants, many politicians, researchers and others advocated for the use of alternative fuels to replace conventional fossil fuels
Compared to the data of Bradley et al [13] (2009), Konnov et al [14] (2011) and Eisazadeh-Far et al [15] (2011), it was obvious that our measurements were comparable, and the best agreements appeared in the comparison with the experiment made by Bradley et al Compared to the results of Bradley et al and Konnov et al, some apparent deviations were displayed for flames of equivalence ratio bigger than 1.3
It is possible due to the small dimensions of the vessel used. These discrepancies were within an acceptable zone against those measured by Gülder and Egolfopoulos et al We can see that, for ethanol-air flame, at normal pressure of 0.1 MPa and temperature of 358K, the maximum burning velocity was approximately between 58 cm/s and 61cm/s
Summary
In response to the environmental problems related to oil consumption and the associated emissions of CO2 and other pollutants, many politicians, researchers and others advocated for the use of alternative fuels to replace conventional fossil fuels. Ethanol is a renewable energy since it can be commonly produced from bio-mass [1], such as softwoods, sugar cane and maize. It has been identified as offering an attractive potential to improve air quality when used to replace conventional gasoline or diesel in engines because of its good anti-knock characteristics and the reduction of CO and unburned hydrocarbon (HC) emissions [2]. The tested fuels have covered most of hydrocarbon fuels, The bursting attentions on ethanol laminar flames occurred in the beginning of the 21st century, because of the approved attraction of ethanol to improve engine performances.
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