Experimental apparatus for studying the ignition of a fuel spray by a hot surface

Graves, Christopher; Tang, Yupai; Skifstad, J. G.

doi:10.2514/6.1985-1317

Cited by 1 publication

(3 citation statements)

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“…As noted in Ref. 4, the nickel surface exhibited serious oxidation under fuel-rich conditions and it was accordingly difficult to obtain data representative of a clean nickel surface. The oxide coating generally tended to increase the wall temperature at ignition and also tended to render erratic results for similar run conditions.…”

Section: Apparatus and Proceduresmentioning

confidence: 99%

“…(1) (2) If y*/d t denotes the nondimensional distance from the wall corresponding to the isotherm r ign , then the wall temperature at ignition can be expressed as (3) Now, making use of an expression for d t corresponding to the growth of a thermal boundary layer on a length of heated wall subject to a (laminar) momentum boundary layer starting a distance x 0 upstream from the start of the heated surface, 6 6, -4.52 Re x ~ 1/2 Pr~I /3 x [ 1 -(x 0 /x) 3/4 (4) Taking the case where both the thermal and momentum boundary layers start at the beginning of the length of heated surface and where the length of the surface is L, then (5) where u* is a characteristic velocity defined in terms of the properties of the gas, the length of the heated wall, and y* t the distance from the wall to the r ign isotherm at the ignition site. The slope dT w /du QO for a given composition (given r ign ) and inlet temperature depends on the variation of y*/d t with MO,.…”

Section: =(T W -T)/(t W -T 00 )mentioning

confidence: 99%

“…The experimental apparatus designed for the study 4 had provisions for creating suitable flow conditions and for making measurements in the boundary layer under conditions approaching ignition. The ranges of flow conditions under which ignition was investigated were: freestream velocity, 1-5 m/s; momentum thickness of the boundary layer, 3-20 mm; freestream air temperature, 40-250°C; fuel concentration, ignitability limits; and droplet size (SMD), 20-200 /mi.…”

Section: Apparatus and Proceduresmentioning

confidence: 99%

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Ignition of a fuel spray by a hot surface

1986

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An experimental study of the ignition of Jet-A fuel sprays by an isothermal hot surface was conducted in a vertical axisymmetric duct. The ranges of flow conditions under which ignition was investigated were: 1) freestream velocity, 1-5 m/s; 2) boundary-layer momentum thickness, 3-20 mm; 3) freestream air temperature, 40-250°C; 4) fuel concentration, ignitability limits; and 5) droplet size (SMD), 20-200 /im. In addition to measurements of the wall temperature necessary for ignition under the above conditions, local measurements of velocity, "turbulence" intensity, fuel concentration, and the fraction of fuel vaporized were measured in the boundary layer at surface temperatures just below that required for ignition. The results exhibited vapor ignition trends for most of the flow conditions, with some exceptions where single-droplet ignition appeared to be present. The experimental data are compared with existing vapor ignition theory. A PHIPr Re x SMD T ign y y* Nomenclature = [(4PrkL c p 00 c 00 )/U QO ] (c^hr/CpT^), parameter used by Toong = specific heat at constant pressure = c p associated with the freestream flow = enthalpy of combustion per unit mass = rate constant in an Arrhenius expression for the global reaction rate = length of heated surface = characteristic length in Toong's A parameter = bulk equivalence ratio in the flow = Prandtl number = freestream Reynolds number based on x -Sauter mean diameter of the droplets in the spray = temperature = spontaneous ignition temperature of the mixture = wall temperature at ignition = freestream temperature = gas velocity in the boundary layer = freestream velocity = 20.45 Lv/y* 2 Pr 2A = streamwise distance from the start of the momentum boundary layer = streamwise distance from the start of the momentum boundary layer to the start of the heated section = distance normal to the wall = distance from the wall to the isotherm corresponding to the spontaneous ignition temperature = thermal boundary-layer thickness = kinematic viscosity = mass density in the freestream flow

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Section: Apparatus and Proceduresmentioning

confidence: 99%