INFLUENCE OF WATER SPRAYS AND HEAT LOSS ON NEGATIVELY AND POSITIVELY STRETCHED CURVED PREMIXED FLAMES

摘要

In the present study,the structure of normal (or inverted) Bunsenflame tips under the influence of a monodisperse dilute water spray and external heat loss is investigated using large activation energy asymptotics.We consider two flame structures: normal and inverted Bunsenflames,and two spray modes: completely and' partially prevaporized burnings.In this way,a complete parametric study of flame tip intensification or extinction (opening) can be conducted.Five parameters are used in the analysis.Three are the droplet size,amount of liquid-water loading (which indicates internal heat loss for inert spray),and the external heat loss.The other two are the stretch and Lewis number (Le).Stretch is negative for a normal Bunsen flame but positive for an inverted Bunsen flame.Stretch strengthens (or weakens) the burning intensity of the Le> 1 (orLe < 1) normal Bunsen flame but decreases (or increases) the burning intensity of the Le > 1 (or Le < 1) inverted Bunsen flame.Burning intensity of the flame tip weakens when the water spray has a smaller droplet size or a larger amount of liquid loading,or when the curved flame experiences a larger amount external heat loss.For a rich methane-air normal Bunsen flame with Le > 1 or a lean methane-air inverted Bunsen flame with Le< 1,closed-tip solutions are obtained Conversely,stretch weakens the burning intensity of a rich methane-air inverted Bunsen flame with Le> l,ora lean methane-air normal Bunsen flame with Le < 1,eventually leading to tip opening.Moreover,the opening becomes wider when the droplet size decreases,liquid loading increases,or external heat loss enlarges.