Simulations of laminar flame propagation in droplet mists
- Department of Engineering, University of Cambridge (United Kingdom)
In order to clarify the conditions conducive to propagation of premixed flames in quiescent sprays, a one-dimensional code with detailed chemistry and transport was used. n-Heptane and n-decane, distinguished by their volatility, were studied under atmospheric and low temperature, low pressure conditions. The effects of initial droplet diameter, overall equivalence ratio {phi}{sub 0} and droplet residence time before reaching the flame front were examined. Increasing the residence time had an effect only for n-heptane, with virtually no evaporation occurring before the flame front for n-decane. The trends were only marginally correlated with the local gaseous equivalence ratio {phi}{sub eff} at the location of maximum heat release rate. {phi}{sub eff} could be as low as 0.4 (beyond the lean flammability limit), but the flame speed could still be 40% of the gaseous stoichiometric flame speed S{sub L,0}. For n-heptane, {phi}{sub eff} increased towards {phi}{sub 0} with smaller droplets while high flame speeds occurred when {phi}{sub eff} was near 1. This implied that the highest flame speed was achieved with small droplets for {phi}{sub 0} {<=} 1 and with relatively large droplets for {phi}{sub 0} > 1. In the latter case, the oxidiser was completely consumed in the reaction zone and droplets finished evaporating behind the flame where the fuel was pyrolysed. The resulting small species, mainly C{sub 2}H{sub 2}, C{sub 2}H{sub 4} and H{sub 2}, diffused back to the oxidation zone and enhanced the reaction rate there. Ultimately, this could result in flame speeds higher than S{sub L,0} even with {phi}{sub 0} = 4. For n-decane, the same trends were followed but smaller droplets were needed to reach the same {phi}{sub eff} due to the slow evaporation rate. Under low pressure and low temperature, the effects of pressure and temperature on {phi}{sub eff} and the flame speed were competitive and resulted in values close to the ones at atmospheric conditions. (author)
- OSTI ID:
- 21212919
- Journal Information:
- Combustion and Flame, Vol. 156, Issue 8; Other Information: Elsevier Ltd. All rights reserved; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
33 ADVANCED PROPULSION SYSTEMS
ETHYLENE
LAMINAR FLAMES
DECANE
HEPTANE
DROPLETS
VELOCITY
TEMPERATURE RANGE 0065-0273 K
EVAPORATION
HYDROGEN
COMBUSTION KINETICS
OXIDATION
SIMULATION
SPRAYS
FLAME PROPAGATION
ONE-DIMENSIONAL CALCULATIONS
STOICHIOMETRY
VOLATILITY
SIZE
AMBIENT TEMPERATURE
PRESSURE RANGE KILO PA
Flame structure
relight