Combustion modeling for non-premixed twin jet flow propane and methanol

doi:10.21203/rs.3.rs-3104900/v1

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Combustion modeling for non-premixed twin jet flow propane and methanol

https://doi.org/10.21203/rs.3.rs-3104900/v1

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In the present study, ANSYS Fluent Computational Fluid Dynamics is utilized to analyses the non-premixed twin jet flow for propane and methanol gas mixture in a combustion chamber the process takes place in species transport and finite rate/eddy dissipation is used, and the flow assumed to turbulent and k-Ɛ realizable is occupied. The effect of changed velocities in the inlet of pipe air and jet fuel and changes of shapes of jets like circular, rectangle, triangle, star, and square on the combustion process is enhanced. the temperature and species mass fraction as well as their contours are presented. Also, the heat release rate and combustion efficiency, and equivalent ratios.

Physical sciences/Energy science and technology

Physical sciences/Engineering

The increasing cost of experimental tests and the efforts to reduce the development time for modern combustor design. The efficient design of modern combustors needs the development of more efficient, reliable, and robust numerical models. A turbulent combustion model with detailed chemical kinetics is needed for accurate predictions of flame stability and pollutant emissions.

Jets issuing from two convergent nozzles issued with a certain distance is termed twin jets, the mixing in twin jets have a wide range in high-speed propulsion systems like noise reduction, thrust vectoring control, etc. twin jet also enhance the combustion efficiency reducing the combustion instabilities and significantly reduces emissions., in the early days mostly circular twin jets were used in manufacturing for easily of incorporation with gas turbine engines. The need for non-circular twin jets aroused as the necessity for faster large-scale and small-scale mixing increased spreading rate and better maneuverability. The RANS require relatively modest computing resource and time because they solve the averaged quantities and model the small-scale fluctuating quantities. Maele et al. [2] utilized and compared the RANS-based turbulence models, namely standard k-Ɛ, realizable k- Ɛ and RNG k- Ɛ turbulence models to the swirling flames in the Sydney burner. It was noticed that the realizable k-Ɛ model yielded a slightly better flow field. Dally et al [1] modified the value of a constant in the dissipation transport equation of the standard k-Ɛ model and found that the modified k-Ɛ gives better results than the Reynolds stress model RMS for bluff body flame. The comparison between the standard k-Ɛ model, the modified k-Ɛ model, and the RMS model is carried out by Frassoldati et al. [3] and they found that the modified k-Ɛ gives better predictions for fuel jet dynamics than RSM.

To accomplish RANS modelling of premixed turbulent combustion, Fiorina et al. [4] utilized the tabular chemistry acquired from the premixed flame let and the supposed probability density function (PDF) technique. They enquired a high-velocity variations flame with a thickened-wrinkled structure and suggested a scalar dissipation rate established on an appraisal of the conjugation between micro-mixing and flame wrinkling Bray et al. [5] employed simplified chemical kinetic processes in turbulent premixed flame models with significant Damköhler numbers for hydrogen-air and methane-air systems. The (PDF) of two independent scalar variables was utilized. Richardson et al. [6] enquired the mixing time scale in 3-D DNS with abbreviated CH4-air chemistry in the narrow reaction zones regime of turbulent Bunsen flames. They evidenced that the mixing rates are impacted by the steep slopes accomplished by flame structures with high Damköhler numbers. [7–11] furnish a detailed discussion of chemical kinetics reduction approaches with an emphasis on the combustion process.

Tang et al. [12] formulated a 3-D CFD model with an incorporated skeletal response mechanism for premixed H2-air combustion in a thermo-photovoltaic system's micro combustor. The radiation wall of the new combustor design indicated a greater peak mean temperature ascribable heat transfer enhancement, which was more noticeable at higher plate numbers. The thickened flame TF model is among the efficient ways for modelling the flame front in turbulent premixed combustion. To mimic pollutant production, ignition, and extinction, multistep reaction processes become progressively significant.

Gau et al. [13] demonstrated incomplete combustion in either laminar or turbulent settings for the coupling of the TF model with multistep reaction mechanisms and concluded that the modified dynamic thickening flame sensor is appropriate for multistep reaction. Natural-gas fuel had much poorer combustion efficiency and greater combustor pressures for relighting than the other fuels. The poor performance of natural gas is demonstrated to be caused by the chemical stability of the methane molecule, demonstrating that the utilization of natural gas fuel consequences in importantly lower combustion efficiency at severe operating conditions, peakier values of combustor pressure (lower flight altitude) for altitude ignition and blowout, and a greater proclivity for combustion instability than either ASTM A-l or propane fuel. Wear, Jerrold D.

The present work improvement Variations in the forms of nozzles in the jet, as well as velocities of air input and fuel velocities, control the burning of propane and methanol in dual jets flow in a basic combustion chamber as represented in Fig. 1.

3.1 The Species Model

The species were modeled using the model developed by Westbrook and Dryer (1981). This basic model has a single chemical reaction and five species.

3.2 Turbulent Gaseous Combustion Model

The finite-rate/eddy dissipation model was used to simulate the turbulence-chemistry interaction (gaseous combustion). In essence, the net rate of response is the lowest of the following.:

The kinetic rate of chemical synthesis or depletion
The rate at which reactant eddies dissipate.
The rate at which product eddies dissipate.

3.3 Boundary Conditions

The inlet conditions of Air/fuel, Methanol/fuel, and Propane/fuel are tabulated in Table 1. Also, the species mass fraction was determined according to the studied equivalence ratio.

Table 1

Inlet conditions of the combustion chamber
Inlet	Inlet velocity of the air pipe (m/s)	Turbulence intensity	Turbulence length scale (m)	Inlet temperature (k)
Air/fuel	12, 6, 5, 2.5	3.6%	0.003	298
Methanol/fuel	2.22,1.2, 1.5, 2	3.6%	0.003	298
Propane/fuel	2.22, 2, 1.2, 1.5	3.6%	0.003	298

Combustion gases outlet gauge pressure is zero with a backflow temperature of 923 K. Outlet species mass fractions depend on the equivalence ratio. Wall boundary condition has no-slip adiabatic conditions.

3.1 Stability and Convergence

It is difficult to obtain a convergent solution for reacting flow because of the strong impact of the chemical reaction on the basic flow pattern and the strong coupling between mass and momentum equations and species transport equations. Also, the large heat release from the reaction causes high-density change and a large acceleration in the flow. These coupling issues are solved by using two steps solution technique. When the reaction rate kinetics is more rapid than the rate of convection and diffusion the solution of species transport becomes more difficult and such a system is termed as “stiff” and the coupled solver is recommended for laminar flow and eddy dissipation concept is recommended for turbulent flow.

3.2 Two-step procedure

To reach a stable converged solution in a reacting flow two-step process can be a practical solution. This can be achieved by solving the governing equations with disabling the reaction i.e. (cold/non-reacting) flow. After reaching the basic flow pattern the reaction can be enabled.

3.3 Ignition in a combustion simulation

Practically, to initiate the spontaneous ignition for fuel/air mixture, the temperature of the mixture should exceed the activation energy threshold requirements. The same issue is made in the current simulation. A finite rate eddy dissipation model for chemistry-turbulence interaction is used. The initial spark was supplied by patching a high-temperature field (1000 K) into the computational domain of combustion. It is noted that the initial patch does not affect the final steady-state solution.

3.3.4 The solver

The gradient least square cell-based method was applied for spatial discretization schemes and the second-order upwind scheme was employed for density, momentum, modified turbulent viscosity, and energy equations. Under relaxation factor of 0.8 was used for species, energy, and density while a value of 0.6 was applied for momentum, turbulent kinetic energy, turbulent kinetic dissipation rate, and turbulent viscosity.

4.1 Model Validation

To check the reliability of the present model, its predictions were compared with that of previous work of Liu Jing et al. [15] and Anetor et al. [17], Numerical analysis of the effect of swirl angel and fuel equivalence ratio on the methanol combustion characteristics in a swirl burner Reasonable agreement is observed in Fig. 2 that the slight differences between the results may be due to the difference in geometry dimensions, Fig. 2 is the result of research journal Liu jing et al. [15] comparison with Figs. 4 and 5 is the result of modeling which is the same boundary condition and the same dimension of Liu jing et al. [15] we find the same result which is motivated to use the MUTHURAM A [16] and reach the shown result below where BA2 is blade angel 60º+60º as in Fig. 3 which is the blade inclination angle butted inside the combustion chamber after the jets as the research MUTHURAM (16).

4.2 Effect of change shapes on combustion honors

The effect of two different shapes (circular, elliptic) which affect the combustion temperature, eff., HHR and equivalent ratio with the variety of different velocities like air or fuels, we divide the result into two parts one with circular and its variation of velocities on the temp., eff., HRR, equivalent ratios, the other is the effect of the elliptic shape of the inlet pipe with velocity variation of air and fuel at the temp., eff. And so on.

4.3 Elliptic shape

4.3.1 Effect of change velocities on efficiency, HRR, and Equivalent ratios

The effect of velocity in the range of study from lean to chemically correct gas mixture on the combustion process is illustrated in Fig. 5 We make a ratio between V_air and F_uel where we input velocity in air pipe and velocity in two fuel pipes and make a ratio in excel sheet as an X-axis and various in Y- axis of eff., HRR, and so on, We find at percent 13% which represents V_air =12, V_fuel=1.5 and 30% which represents V_air =5, V_fuel=1.5 also affect the eff. To be high then the other values of velocities make it fluctuate until the reaction zone reaches its minimum value then it decreases. Also, the equivalence ratio increases with the increase in the percent velocity of reaction products increases and this is due to the decrease of the excess air in the fuel/air mixture Fig. 6. Also, the fuel species starts from the inlet boundary value and is kept constant for some distance till the reaction starts then it decreases reaching zero value at the which the reaction stops. Also, the HRR is the maximum value at (v_air =12,vf = 2.22) then the curve is fluctuate at (v_air=2.5,v_fuel=1.5) then increased at percent 40% then slightly decreased this is the effect of variation of velocity to the inlet pipes which connected to the combustion chamber is changed the values of eff. and so on. Figure 7 illustrates the HRR varied values.

4.3.2 Effect of inlet methanol, propane, and Air Temperature

The inlet effect of methanol, propane, and Air temperature on the combustion process is given in Fig. 9. The temperature distribution along the centerline of the combustion chamber is illustrated in Fig. 8. It is shown from the figure that as the inlet temperature decreases, the combustion process starts nearer to the mixture inlet and higher product temperature is attained. And the variance velocity is the nearer same temperature it is shown that the curved is increased until the temperature reaches 1100 k as shown, Also the photo in Fig. 9 is the shape of flame in the combustion chamber at V_air = 12 and V_fuel=2.22 m/s. This value of velocity has changed the shape of curvature as shown in Figs. 8 and 9.

4.4 The effect of variation of shape and velocity on combustion behavior

4.4.1 Circular shape:

The change of the shape of pipes at the inlet where one of three inlet pipes is varied like elliptic or circular is changed the result and values of the result as shown.

4.4.2 Effect of change velocities on efficiency, HRR, and Equivalent ratios

As shown in Fig. 10 there are extremely different values of efficiency than the elliptic shape, we find variation when variate velocity and shape of the inlet pipes at this Fig. 10 the eff. It decreased slightly from the top point at the percent of velocity 13% which represents (v_air=12, v_fuel=1.5), and then decreased to 56.3% at percent 60% of velocity which represent (v_air=2.5, v_fuel =1.5)

In Fig. 10 in contrast to Fig. 11 the equivalence ratio increases with increasing the percent of velocity where the max. equivalence ratio at 60% velocity ratio (v_air=2.5, v_fuel=1.5).

There is enough difference in a curved manner between circular HRR and elliptic HRR but at different velocity ratios it is the same in increasing and decreasing but the values are different as in Fig. 12 which is represent equivalent ratio as y-axis and velocity ratio in x-axis where the equivalent ratio increases with increasing velocity ratio as shown in the figure.

4.4.3 Effect of inlet methanol, propane, and Air Temperature

The inlet effect of methanol, propane, and Air temperature on the combustion process is given in Fig. 14. The temperature distribution along the centerline of the combustion chamber is illustrated in Fig. 13. It is shown from the figure that as the inlet temperature decreases, the combustion process starts nearer to the mixture inlet and higher product temperature is attained. And the variance velocity is the nearer same temperature but different at v_air =2.5,v_fuel=1.5 It is shown that the curved is increased until the temperature reaches 2550 k as shown, Also the photo in Fig. 13 is the shape of the flame in the combustion chamber at V_air =2.5 and V_fuel=1.5. This value of velocity is changed the shape of curvature as shown which is different to the curved temperature of elliptic.

4.5 Combustion Performance Parameters

4.5.1 Combustion Efficiency

The combustion efficiency is calculated as follows:

The heat liberated from the combustion process is directed to heat both the Q _heat to Q _fuel plus Q _air where Q_fuel and Q_air represent inputs but Q_heat represents the output

1. Q = m. cp (T-T) (1)

Q_air=m_aircp_air (T_out -T_gi) (2)

Q_input =m_f × l_cv +Q_air (3)

So, the efficiency of the combustion process can be expressed as:

η = Q_h/Q_input (4)

Figure 5 shows the variation of the combustion efficiency with the velocity ratio for different velocities. be high then the other values of velocities make it fluctuate until the reaction zone reaches its minimum value then it decreases. Also, the equivalence ratio increases with the increase in percent velocity of reaction products increases and this is due to the decrease of the excess air in the fuel/air mixture.

4.5.1 Heat Release Rate

The heat release rate HRR is calculated from:

HHR = Q_release/A_s (5)

Where, A_s is the unit surface area of the combustion chamber

Q _release= Q_fuel + Q_air/2

From the findings of the current work, there is a difference in the effect of using an inlet circular pipe than an elliptic as shown in the result it is the effect on eff., equivalent ratio, and HRR Also the temperature curve there is different in the values and shape of the curve, Also the velocity variance affects the shape and values, we observed in the temp. the curve for the circular shape that the value of velocity V_air =2.5, V_fuel=1.5 m/s is the optimum values that highest the temp. as a maximum value than other velocities so we conclude or recommended to use these values as an optimum value in this test rig.

AVAILABILITY OF DATA AND MATERIALS

The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request

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No competing interests reported.

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Combustion modeling for non-premixed twin jet flow propane and methanol

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Version 1

Abstract

Figures

INTRODUCTION

Survey

PROBLEM DEFINITION

3.1 The Species Model

3.2 Turbulent Gaseous Combustion Model

3.3 Boundary Conditions

Method of Solution

3.1 Stability and Convergence

3.2 Two-step procedure

3.3 Ignition in a combustion simulation

3.3.4 The solver

RESULTS AND DISCUSSIONS

4.1 Model Validation

4.2 Effect of change shapes on combustion honors

4.3 Elliptic shape

4.3.1 Effect of change velocities on efficiency, HRR, and Equivalent ratios

4.3.2 Effect of inlet methanol, propane, and Air Temperature

4.4 The effect of variation of shape and velocity on combustion behavior

4.4.1 Circular shape:

4.4.2 Effect of change velocities on efficiency, HRR, and Equivalent ratios

4.4.3 Effect of inlet methanol, propane, and Air Temperature

4.5 Combustion Performance Parameters

4.5.1 Combustion Efficiency

1. Q = m. cp (T-T) (1)

4.5.1 Heat Release Rate

CONCLUSIONS

Declarations

AVAILABILITY OF DATA AND MATERIALS

References

Additional Declarations

Supplementary Files

Status:

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