**2. Burner configuration and experimental set-up**

### **2.1 Basic configuration of the burner**

In air combustion, nitrogen leads to high fuel consumption and low combustion efficiency because nitrogen in the air acts as energy ballast. The substitution of air with pure oxygen leads to an increase in the laminar combustion rate up to 1300%, improves the thermal efficiency, increases the adiabatic flame temperature (2200 K for CH4-Air, 3090 K in oxy-combustion) reduce fuel consumption by 50% and, from an environmental point of view, reduce the formation of nitrogen oxides by

*Numerical and Experimental Studies on Combustion Engines and Vehicles*

The flames from multiple jets aligned have used in many industrial installation. Several studies have been published on the dynamic properties of non-reacting multiple jets [5–9]. Lee et al. [10] have studied the geometry parameters of diffusion flames and giving a number of variables such as the number of jets and the distance between the jets. Lenze et al. [11] have studied the influence of three and five non-premixed flames, with town gas and natural gas burners. Their measurements concern flame width, flame length and concentrations in confined and free

A new generation of highly separated fuel and oxidant injection burners is of great interest to industrialists. The idea of this burner consists of separating combustible and oxidant to dilute the reactants with combustion products before the

For this new combustion in a burner with three separated jets, the separation of jets provides a high dilution of reactants by combustion products in the combustion chamber. Consequently, this dilution decreases the flame temperature and decline in NOx production. In the literature, it has been proven that the separation of reactants are capable to change the flow structure, the flame characteristics, generates a better

Salentey et al. [16] was interested in the characterization the flames from multiple jets aligned through dynamic properties (speed of the jets and distance injectors) and the flame topology (stability, length, blow ...). Lesieur et al. [14] has studied numerically the characteristics of a burner with three jets, focusing on the mixing of the jets, their dynamics and the pollutant emissions. Boushaki et al. [12] was interested on two main areas for flow, passive control with changing the diameter of the burner in order to affecting the dynamics flow; and active control requiring external energy intake through actuators while retaining the geometry of the combustion chamber. The present chapter reports the results of a numerical and experimental investigation of the dynamic field on a burner with 25 kW power composed of three jets, one central jet of natural gas and two side jets of pure oxygen [19, 20]. One control systems, passive, is added to the basic burner to ameliore the combustion process to ensure the stabilization of flame and as well as pollutant reductions. The passive control is based on the inclined of side oxygen jets towards the central natural gas jet

Few works, are investigated the effect of equivalence ratios (in lean regime) on characteristics of non-premixed oxy-methane flames from burner with separated jets. However, the aim of this contribution is to investigate numerically the effect of different equivalence ratio on the combustion characteristics of a diffusion methane

The mixture of hydrogen and natural gas is a new mixed fuel. The use of a mixed mixture of fuel and hydrogen has the advantage of modifying very effectively the properties of the fuel while preserving the distribution facility. Due to this, the high molecular diffusivity of hydrogen, the extended flammability limits, the high laminar flame speed and the low ignition energy, the addition of hydrogen in the fuel makes it possible to work in a combustion poor. Increasing flammability limits in the presence of hydrogen offset the adverse effects of poor combustion such as local

thermal efficiency and as well as reduction of pollutant emissions [15–18].

up to 95% [4].

multiple flames.

mixing of the reactants [12–14].

in burner with three separated jets.

**18**

oxy-flame in a stabilized separated burner.

extinctions, radiation energy losses, and flame stretching [21].

The configuration of the burner illustrated in **Figure 1** consists in separating the fuel and oxygen per injection in order to increase the dilution of the reactants with the combustion products before the mixing of the reagents.

This burner consists of three non-ventilated jets, one central with internal diameter dg equal 6 mm that contains the fuel and two side jets with internal diameter dox equal 6 mm contain pure oxygen. Boushaki et al. [22] have studied this three-jet burner configuration. The separation distance between the jets (S) used is 12 mm. The gas density equal to 0.83 kg m<sup>3</sup> and the oxygen is supplied by liquid air with a purity of 99.5% with a density of 1.354 kg m<sup>3</sup> (at 1 atm and at 15° C). The thermal power (P) of the burner is equal to 25 kW, therefore the flow rate and the output speed of the natural gas are respectively mng = 0.556 g s<sup>1</sup> and Ung = 27.1 ms <sup>1</sup> .

The first study in this document is the control technique, consists in inclining the side oxygen jets towards the natural gas jet as shown in **Figure 1**. The angle of oxygen jets (ϴ) compared to the vertical direction varies from 0 to 30° (0, 10, 20, and 30°), however, we will present the effect of angle of the side oxygen jets on the dynamic fluid, for many detail you can see [12].

The combustion is carried out inside a square chamber of 60 60 cm2 section and a height of 1 m. The side walls are water cooled and refractory lined inside the combustion chamber. a converging 20 cm high and a final section of 12 12 cm is placed at the end of the chamber to limit the entry of air from above. In order to allow optical access to all flame zones, six windows are provided in each face of the chamber.

The Particle Image Velocimetry (PIV) was used as a measurement technique to characterize the experimental dynamic field. The PIV technique requires a laser sheet that clarifies the flow area studied a CCD camera, control equipment and an acquisition PC. The laser used is the Nd-YAG Bi-pulse with frequency 10 Hz and wavelength of 532 nm. The laser chain used is composed by a first divergent cylindrical lens and then by a second convergent spherical lens. The Mie signal emitted by the particles is collected by CCD camera of type a Lavision FlowMaster (12-bit dynamic and resolution 1280 1024 pixels).

**Figure 1.** *Schematic view of the burner.*

## **3. Numerical method**

The steady equations for conservation of mass, momentum, energy and species have been used in this numerical simulation. The second order equations for turbulence kinetic energy *κ* and its rate of dissipation ε have been used to modulate the turbulence. The general form of the elliptic differential equations for an axisymmetric flow is given by Eq. (1).

Here *S*<sup>Φ</sup> is the source term and ΓΦ is the transport coefficient.

$$\frac{\partial}{\partial \mathbf{x}} (\rho U \Phi) + \frac{\mathbf{1}}{r} \frac{\partial}{\partial r} (r \rho V \Phi) = \frac{\partial}{\partial \mathbf{x}} \left( \Gamma\_{\Phi} \frac{\partial \Phi}{\partial \mathbf{x}} \right) + \frac{\mathbf{1}}{r} \frac{\partial}{\partial r} \left( r \Gamma\_{\Phi} \frac{\partial \Phi}{\partial r} \right) + \mathbb{S}\_{\Phi} \tag{1}$$

where *ρ* is the density, P is the mean pressure and *μ* is the viscosity.

*μ<sup>e</sup>* is the effective viscosity is determined from *μ<sup>e</sup>* ¼ *μ* þ *μt*, where *μt*is the turbulent viscosity, which is derived from the turbulence model and expressed by: *<sup>μ</sup><sup>t</sup>* <sup>¼</sup> *<sup>C</sup>μρ <sup>κ</sup>*<sup>2</sup> *ε* .

The Finite Eddy Dissipation Model (EDM) is used to simulate the turbulence/ chemistry interaction. This model is based on the hypothesis that the chemical reaction is fast in relation to the transport processes of the flow.

**Table 1** summarizes the volumetric flow rates, the velocities, Reynolds number respectively of methane and oxygen of equivalence ratio (0.7, 0.8 and 1).

Reynolds Number is defined by the following equation:

$$Re = \left(\rho \,\mathrm{d}\_{\mathrm{gn}} \,\mathrm{U}\right) / \mu \,\tag{2}$$

**Table 2** summarizes the parameters of this numerical study including methane, hydrogen and oxygen flow rates, velocities, percentage of hydrogen and equiva-

**Φ =1 P=25 kW**

**)** *m*\_ *<sup>O</sup>***<sup>2</sup> (g.s**�**<sup>1</sup>**

0% H2 0.49 0 2.07 27.07 27.06 20% H2 0.46 0.012 2.03 31.3 26.66 40% H2 0.40 0.02 1.98 37.07 25.9

**)** *U*ng **(m.s**�**<sup>1</sup>**

. The GAMBIT is used to

**)** *UO***<sup>2</sup> (m.s**�**<sup>1</sup>**

**)**

Fluent 6.3.2 is used to solve the steady equations for conservation of mass, momentum, energy and species. The finite volume method is used with second order upwind. In fact, convergence criterion of residuals for energy equation and

construct the grid; the computational domain has been extended 100 cm in the axial direction and 30 cm in the radial direction. A total number of 28,700 quadrilateral cells were generated using non-uniform grid spacing to provide an adequate reso-

The axial velocity profile at the inlet, of the methane is supposed constant. At the

The mean velocity fields carried out by PIV in non-reacting flow are represented on **Figure 2**. From initial state where ϴ = 0° to inclined state where ϴ = 30°, the dynamic field changes with the change of flow structure. The jets fusion point

*Mean velocity fields for jet oxygen angle 0° and 30° (longitudinal velocity in color scale) in non-reacting flow.*

lution near the jet axis and close to the burner where gradients were large.

axis of symmetry, *<sup>r</sup>* <sup>¼</sup> 0, *<sup>V</sup>* <sup>¼</sup> 0 and <sup>∂</sup>Φ*=∂<sup>r</sup>* <sup>¼</sup> <sup>0</sup> ð Þ <sup>Φ</sup> <sup>¼</sup> *<sup>U</sup>*, *<sup>κ</sup>*, *<sup>ε</sup>* . At the outlet, the fully-developed condition of pipe flow is adopted <sup>∂</sup>Φ*=∂<sup>x</sup>* <sup>¼</sup> <sup>0</sup> ð Þ <sup>Φ</sup> <sup>¼</sup> U, V, *<sup>κ</sup>*, *<sup>ε</sup>* . The velocities are assumed to be zero at the wall, and these no-slip boundary conditions are appropriate for the gas. These equations, called "wall functions," are introduced

for all other equations equal respectively 10�<sup>6</sup> and 10�<sup>3</sup>

**)** *m*\_ *<sup>H</sup>***<sup>2</sup> (g.s**�**<sup>1</sup>**

*A New Combustion Method in a Burner with Three Separate Jets*

and used in finite difference calculations at near-wall points.

**4.1 PIV measurements on burners with inclined jets**

**4. Inclined effects on dynamic**

*m*\_ CH**<sup>4</sup> (g.s**�**<sup>1</sup>**

*DOI: http://dx.doi.org/10.5772/intechopen.90571*

*Flow rates and exit velocities of fuels and oxygen.*

lence ratio.

**Figure 2.**

**21**

**Table 2.**

A global equivalence ratio can be defined as the molar ratio of methane and oxidant at the injection to molar ratio methane and oxidant in stoichiometric conditions, as:

$$\Phi = h \begin{pmatrix} \frac{Q}{Q\_{O2}} \end{pmatrix} \Big/ \begin{pmatrix} \frac{Q\_{CH4}}{Q\_{O2}} \end{pmatrix}\_{\text{subnis}} \tag{3}$$

where Q is the volumetric flow rate.

The second numerical study in this document is the effect of hydrogen to dynamic of flame. One of the jet transports the fuel, natural gas + hydrogen, and the other the pure oxygen. The values of the flow rates of fuel and the exit velocities are regrouped in **Table 2**.

We shall consider an overall irreversible reaction between methane/hydrogen and pure oxygen:

$$\left(\left(1-\text{a}\right)\Phi\text{CH}\_4 + \text{a}\Phi\text{H}\_2 + \text{a}\Phi\text{O}\_2\bullet\text{b}\Phi\text{CO}\_2 + \text{c}\Phi\text{H}\_2\text{O}\tag{4}\right)$$

α is the percentage of hydrogen and written as:

$$\alpha = \frac{\text{\%H}\_2}{\text{\%H}\_2 + \text{\%CH}\_4} \tag{5}$$


**Table 1.** *Dynamic conditions of the burner.*


20% H2 0.46 0.012 2.03 31.3 26.66 40% H2 0.40 0.02 1.98 37.07 25.9

*A New Combustion Method in a Burner with Three Separate Jets DOI: http://dx.doi.org/10.5772/intechopen.90571*

**Table 2.**

**3. Numerical method**

metric flow is given by Eq. (1).

*<sup>∂</sup><sup>x</sup>* ð Þþ *<sup>ρ</sup>U*<sup>Φ</sup>

1 *r ∂ ∂r*

where Q is the volumetric flow rate.

α is the percentage of hydrogen and written as:

**Configuration** *<sup>ϕ</sup>* **<sup>Q</sup>**\_ **CH4**

*Dynamic conditions of the burner.*

regrouped in **Table 2**.

and pure oxygen:

**Table 1.**

**20**

*∂*

*ε* .

by: *<sup>μ</sup><sup>t</sup>* <sup>¼</sup> *<sup>C</sup>μρ <sup>κ</sup>*<sup>2</sup>

The steady equations for conservation of mass, momentum, energy and species have been used in this numerical simulation. The second order equations for turbulence kinetic energy *κ* and its rate of dissipation ε have been used to modulate the turbulence. The general form of the elliptic differential equations for an axisym-

> ΓΦ ∂Φ *∂x*

The Finite Eddy Dissipation Model (EDM) is used to simulate the turbulence/ chemistry interaction. This model is based on the hypothesis that the chemical

**Table 1** summarizes the volumetric flow rates, the velocities, Reynolds number

A global equivalence ratio can be defined as the molar ratio of methane and oxidant at the injection to molar ratio methane and oxidant in stoichiometric conditions, as:

*stoichio*

ð Þ 1 � α ΦCH4 þ αΦH2 þ aΦO2 ➔ bΦCO2 þ cΦH2O (4)

þ 1 *r ∂ ∂r*

*r*ΓΦ ∂Φ *∂r* 

*Re* <sup>¼</sup> <sup>ρ</sup> dgn <sup>U</sup> *<sup>=</sup>***<sup>μ</sup>** (2)

þ *S*<sup>Φ</sup> (1)

(3)

(5)

Here *S*<sup>Φ</sup> is the source term and ΓΦ is the transport coefficient.

*∂ ∂x*

where *ρ* is the density, P is the mean pressure and *μ* is the viscosity. *μ<sup>e</sup>* is the effective viscosity is determined from *μ<sup>e</sup>* ¼ *μ* þ *μt*, where *μt*is the turbulent viscosity, which is derived from the turbulence model and expressed

respectively of methane and oxygen of equivalence ratio (0.7, 0.8 and 1).

ϕ ¼ *h <sup>Q</sup> QO*2 *= QCH*<sup>4</sup> *QO*<sup>2</sup> 

The second numerical study in this document is the effect of hydrogen to dynamic of flame. One of the jet transports the fuel, natural gas + hydrogen, and the other the pure oxygen. The values of the flow rates of fuel and the exit velocities are

We shall consider an overall irreversible reaction between methane/hydrogen

<sup>α</sup> <sup>¼</sup> %H2

**<sup>Q</sup>**\_ **o2**

**l s** %H2 þ %CH4

**l s**

Confi 1 1 0.767 1.534 27.13 27.13 12,272 Confi 2 0.8 0.767 1.917 27.13 33.86 12,272 Confi 3 0.7 0.767 2.19 27.13 38.69 12,272

*U*ng **<sup>m</sup>**

**s**

*UO***<sup>2</sup>**

**m s**

**Re gn**

ð Þ¼ *rρV*Φ

*Numerical and Experimental Studies on Combustion Engines and Vehicles*

reaction is fast in relation to the transport processes of the flow.

Reynolds Number is defined by the following equation:

*Flow rates and exit velocities of fuels and oxygen.*

**Table 2** summarizes the parameters of this numerical study including methane, hydrogen and oxygen flow rates, velocities, percentage of hydrogen and equivalence ratio.

Fluent 6.3.2 is used to solve the steady equations for conservation of mass, momentum, energy and species. The finite volume method is used with second order upwind. In fact, convergence criterion of residuals for energy equation and for all other equations equal respectively 10�<sup>6</sup> and 10�<sup>3</sup> . The GAMBIT is used to construct the grid; the computational domain has been extended 100 cm in the axial direction and 30 cm in the radial direction. A total number of 28,700 quadrilateral cells were generated using non-uniform grid spacing to provide an adequate resolution near the jet axis and close to the burner where gradients were large.

The axial velocity profile at the inlet, of the methane is supposed constant. At the axis of symmetry, *<sup>r</sup>* <sup>¼</sup> 0, *<sup>V</sup>* <sup>¼</sup> 0 and <sup>∂</sup>Φ*=∂<sup>r</sup>* <sup>¼</sup> <sup>0</sup> ð Þ <sup>Φ</sup> <sup>¼</sup> *<sup>U</sup>*, *<sup>κ</sup>*, *<sup>ε</sup>* . At the outlet, the fully-developed condition of pipe flow is adopted <sup>∂</sup>Φ*=∂<sup>x</sup>* <sup>¼</sup> <sup>0</sup> ð Þ <sup>Φ</sup> <sup>¼</sup> U, V, *<sup>κ</sup>*, *<sup>ε</sup>* . The velocities are assumed to be zero at the wall, and these no-slip boundary conditions are appropriate for the gas. These equations, called "wall functions," are introduced and used in finite difference calculations at near-wall points.
