Jet Diffusion Flame: Visualization of a Turbulent Flame Impinging on a Wall | Papers Mechanical Engineering

MCEN 5228 Jet Diffusion Flame Joshua Grages

Flow Visualization 12/5/04

University of Colorado at Boulder

Jet Diffusion Flame

The purpose of this image is to photograph the complex phenomena of a turbulent

jet flame. An aerosol can of WD-40 was used as the fuel for the jet diffusion flame. The

source of oxidizer for this combustion process is just the oxygen contained in the ambient

air. The flame is impinging on a wall as seen below in Figure 1. The fuel jet was shot

through a match to ignite the fuel and begin combustion. The only source of light for this

image is the small amount of moonlight coming in through the open garage door. The

very dark garage enhances the image because of the drastic contrast. For safety reasons,

the flame is impinging on a cool cement wall in the garage. Furthermore, the image was

taken at night so the garage door could be open to allow for proper ventilation.

Figure 1. Jet Diffusion Flame, Re = 8323.

The general flow set up is shown below in Figure 2. This is a top view of the

experimental set-up. The WD-40 aerosol can was approximately two and a half to three

feet away from the wall. Initially, the fuel jet was shot through a match to initiate

combustion, after which the flame was stabilized near the wall. The camera was

approximately two and a half feet away from the flame, next to the wall, as seen in Figure

2. Since WD-40 is proprietary, there is little to no chemical or physical properties that are

published. The Material Safety Data Sheet lists two of the constituents in WD-40 as 2-

Butoxyethanol and Liquefied Petroleum Gas [1]. The MSDS states that 2-Butoxyethanol

and Liquefied Petroleum Gas make up approximately 25% and 10% of the weight of

WD-40 respectively. Since the fuel is mainly composed of 2-Butoxyethanol, and its

chemical and physical properties are published, the fuel will now be assumed to be

composed completely of this chemical. 2-Butoxyethanol is a hydrocarbon that is often in

the liquid state, and has the chemical formula C8H16O2. The viscosity of this fuel was

found on the web to be 2.9 cP at 25oC [2]. Likewise, the density was found online to be

0.9019 g/mL [3]. The velocity for this flow was found experimentally. The velocity was

approximately 2.3 ft/s. Similarly, the diameter of the jet, seen in Figure 1, is

approximated to be 1.5 inches. Using these parameters, and the proper unit conversions,

the Reynold’s number turns out to be 8323. The equation for Reynold’s number, and the

converted parameter values are below in Equation 1.

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Flow Visualization 12/5/

Jet Diffusion Flame

The purpose of this image is to photograph the complex phenomena of a turbulent jet flame. An aerosol can of WD-40 was used as the fuel for the jet diffusion flame. The source of oxidizer for this combustion process is just the oxygen contained in the ambient air. The flame is impinging on a wall as seen below in Figure 1. The fuel jet was shot through a match to ignite the fuel and begin combustion. The only source of light for this image is the small amount of moonlight coming in through the open garage door. The very dark garage enhances the image because of the drastic contrast. For safety reasons, the flame is impinging on a cool cement wall in the garage. Furthermore, the image was taken at night so the garage door could be open to allow for proper ventilation.

Figure 1. Jet Diffusion Flame, Re = 8323.

The general flow set up is shown below in Figure 2. This is a top view of the experimental set-up. The WD-40 aerosol can was approximately two and a half to three feet away from the wall. Initially, the fuel jet was shot through a match to initiate combustion, after which the flame was stabilized near the wall. The camera was approximately two and a half feet away from the flame, next to the wall, as seen in Figure

Since WD-40 is proprietary, there is little to no chemical or physical properties that are published. The Material Safety Data Sheet lists two of the constituents in WD-40 as 2- Butoxyethanol and Liquefied Petroleum Gas [1]. The MSDS states that 2-Butoxyethanol and Liquefied Petroleum Gas make up approximately 25% and 10% of the weight of WD-40 respectively. Since the fuel is mainly composed of 2-Butoxyethanol, and its chemical and physical properties are published, the fuel will now be assumed to be composed completely of this chemical. 2-Butoxyethanol is a hydrocarbon that is often in the liquid state, and has the chemical formula C 8 H 16 O 2. The viscosity of this fuel was found on the web to be 2.9 cP at 25 oC [2]. Likewise, the density was found online to be 0.9019 g/mL [3]. The velocity for this flow was found experimentally. The velocity was approximately 2.3 ft/s. Similarly, the diameter of the jet, seen in Figure 1, is approximated to be 1.5 inches. Using these parameters, and the proper unit conversions, the Reynold’s number turns out to be 8323. The equation for Reynold’s number, and the converted parameter values are below in Equation 1.

Flow Visualization 12/5/

μ Re =ρ^ ⋅ v^ ⋅ D Equation 1. Reynold's Number

Where ρ is the density, and after a unit conversion the value for the density of 2- Butoxyethanol is 901.9 kg/m^3. Similarly, after unit conversion, the value for velocity v , characteristic dimension D , and the viscosity μ come out to be 0.703 m/s, 0.0381 m, and 0.0029 kg/m*s respectively. The turbulent jet diffusion flame in Figure 1 was able to be stabilized against a cement wall. Flame stabilization is a very important parameter in combustion, and the design of a combustor. Some examples of common everyday devices that rely on flame stabilization include a furnace, natural gas stove, and a jet aircraft engine. Furthermore, flame stabilization is paramount in the new NASA SCRAMJET engine that traveled at nearly Mach 9.8. Basically, “the attachment of a diffusion flame to a solid or liquid surface is of both fundamental and practical importance because of their relation to flame holding by bodies in combustion chambers” [4]. Flame stabilization, or attachment is theorized to occur when the local velocity of the fluid flow is less than the flame speed. A common feature in flames is a flame base, or edge flame, which attaches to a surface and displays a small dark space in between the flame and the surface. Takahashi et al found that the highest reactivity spot, called the reaction kernel, is formed in a relatively low (<1600K), fuel lean zone of the flame base [4]. Furthermore, the geometric irregularity of the flame base allows for the back-diffusion of radical species, like OH, against the incoming oxidizing stream. The photograph in Figure 1 is not of sufficient quality to show the details of the flame base. But, the stationary reaction kernel located in the flame base “provides a continuous ignition source and sustained stable combustion fast enough to consume the incoming reactants” [4]. Thus, flame stabilization displays a flame base that contains a reaction kernel, and although Figure 1 does not contain sufficient detail to highlight the flame base or reaction kernel, one must exist for flame stabilization.

Figure 2. Experimental Set-up

Below is a list of some parameters that give a little more insight into the photograph.

Size of field of view o Approximately ≈ 2.2 ft by 3.6 ft (height by width respectively)
Distance from lens to object o ≈ 2.5 ft
Lens focal length and other lens specs.

Jet Diffusion Flame: Visualization of a Turbulent Flame Impinging on a Wall, Papers of Mechanical Engineering

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Jet Diffusion Flame