A Modified Implicit Iterative Difference Algorithm for Stiff Chemical Kinetic Equations in Complex Combustion System

He, Bo; Nie, Wan Sheng; Feng, Song; Li, Guo Qiang

doi:10.4028/www.scientific.net/amr.295-297.2333

Cited by 4 publications

(2 citation statements)

References 13 publications

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“…The use of a backward differentiation formula (BDF) implicit algorithm would improve computational stability but would not ensure a positive mass fraction in the integration. In this paper, a modified implicit iterative algorithm 38 is used for the integration of stiff chemical reaction ODE with operator splitting.…”

Section: Stiff Source Termmentioning

confidence: 99%

Unsteady Combustion Model of Nonmetalized Organic Gel Fuel Droplet

He¹,

Nie²,

He³

2012

Energy Fuels

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It is widely accepted that nonmetalized organic gel fuel droplets exhibit characteristic and complicated oscillations during both evaporation and combustion, in contrast to the quasi-steady combustion of conventional liquid droplets. In this paper, an unsteady combustion model for the gel droplet is developed, taking into consideration the interactions between oscillating evaporation and flame structures. This model is first validated against experimental results for droplets of an organic gel based on unsymmetrical dimethylhydrazine (UDMH) burning in various nitrogen tetroxide (NTO) oxidizing atmosphere. Using this newly derived model and a detailed UDMH/NTO gas phase chemical reaction mechanism, the combustion characteristics of spray-sized UDMH gel droplets are numerically simulated and discussed in detail. The simulation and experimental results for droplet diameter and temperature both exhibit the same trend during the combustion process. The simulation error for droplet lifetime increases with both droplet size and ambient pressure as a consequence of neglecting heat conduction of the suspending thread and nonideal gas behavior in the model. Numerical simulation results for the detailed flow field parameter variations of the spray-size gel droplet combustion show obvious oscillations in both droplet radius and UDMH vapor mass fraction at the droplet surface following the formation of a gellant film. The oscillation frequency gradually decreases as the film thickness increases and the fuel is depleted. Although the double-flame temperatures and their standoff ratios also oscillate as the gellant film swells and ruptures, their relative oscillation amplitudes are smaller than those of the droplet radius and the vapor mass fraction at the droplet surface. The temperature of the gas phase flow field is higher when fuel vapor at the droplet surface is more abundant, but there is usually a time lag between the gas phase temperature reaching its maximum and the gellant film bursting within each swell-burst period because of the finite fuel vapor diffusion velocity. The temperature of the droplets continues to rise even after reaching the boiling point of liquid UDMH, since the boiling of the relatively small amount of liquid UDMH in a spray droplet cannot absorb all the heat flux from the flame.

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Section: Stiff Source Termmentioning

confidence: 99%

Unsteady Combustion Model of Nonmetalized Organic Gel Fuel Droplet

He¹,

Nie²,

He³

2012

Energy Fuels

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“…有机凝胶液滴上述周期性膨胀-破裂占据了绝大部分液滴生存时间, 类似于液体多组分液滴"微爆"现象 [18] , 但强度更加剧烈. 文献 [16] [25] (Operator Splitting Algorithm), 以解决化学反应时间尺度与流动时间尺度存在明显差异的问题, 并提出和实现了一种改进隐式迭代算法 [26] , 提高了分离算法中刚性化学动力学方程积分效率和正定性.…”

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Prospects of UDMH Organic Gel Droplet Evaporation and Combustion Model

He¹,

Nie²,

Zhuang³

2013

Acta Chim. Sinica

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The organic gel propellants have the advantages of both solid and liquid propellant, but the catching fire and burning process of organic gel droplet appears obvious vapor ejection and flame disturbance. This unsteady combustion phenomenon of organic gel droplet is different from the quasi-steady combustion of conventional liquid droplet and produces great influence on the spray combustion flow field of gel liquid rocket engine and its optimization design. Based on the unsteady evaporation characteristics inside UDMH (unsymmetrical dimethylhydrazine) organic gel droplet and the micro molecule structure of organic gel propellant, three kinds of liquid phase evaporation model, the unsteady multicomponent evaporation model, the interface tracking multiphase flow evaporation model and the discrete element multiphase flow evaporation model, are proposed. The unsteady multicomponent evaporation model regards the gel droplet as a binary multiconponent droplet, in which the gellant inside the gel droplet is been equivalent to a species with low volatility and high boiling temperature. In order to depict the shape and location variety of vapor bubble inside the gel droplet more precisely, the interface tracking multiphase flow evaporation model regards the gel droplet and the vapor bubble inside it as a single fluid, and uses the Level Set function tracking the interface location of vapor bubble. Based on the micro molecule structure of organic gel propellant, the discrete element multiphase flow evaporation model for the gel droplet regards the gellant and vapor bubble as the aggregation of micro-particles with different properties respectively, and uses the Lagrange method tracking the movement and aggregation of each kind micro-particle. The multicomponent evaporation model has been implemented in our foregoing work, so a summary of the model is presented. And next the main difficulties and the technique preparation about the last two multiphase flow models have been presented and analyzed in detail. In view of mixing and combustion process of gas phase surrounding the UDMH organic gel droplet, we propose that the finite rate chemical reaction model and the flamelet model should be used for the stagnation ambient and convective ambient respectively. The difficulties and numerical methods for handling the stiff chemical source term in finite rate chemical reaction model have been presented. And next the consistent flamelet model which takes consideration of species diffusion coefficient and non-unity Lewis number is presented. It would be more precise for the temperature and species interpolation of the gel droplet laminar non-premixed combustion flow field.

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Effects of NTO Oxidizer Temperature and Pressure on Hypergolic Ignition Delay and Life Time of UDMH Organic Gel Droplet

He¹,

Nie²,

Feng³

et al. 2013

Propellants Explo Pyrotec

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Organic gel propellants are promising candidates for a variety of rocket motor and scramjet applications, since they are intrinsically safe and provide high performance. It is well known that organic gel fuel droplets exhibit distinct combustion characteristics compared with conventional liquid fuel droplets, and furthermore an understanding of the ignition delay and lifetime of these droplets is critical to the improvement of combustor design. In this work, investigations of the combustion of unsymmetrical dimethylhydrazine (UDMH) organic gel droplets in different nitrogen tetroxide (NTO) oxidizing atmospheres were conducted using two sets of experimental apparatus. The combustion characteristics under different conditions of temperature and pressure were compared and analyzed based on the flame shapes observed during experimentation. From these trials, an unsteady combustion model was developed and used for the numerical simulation of spray‐sized UDMH organic gel droplet combustion in an NTO atmosphere. The hypergolic ignition and burning characteristics of the organic gel droplets under conditions simulating either engine startup or steady state combustion were compared, and changes in ignition delay and droplet lifetime with ambient temperature and pressure were analyzed. The experimental and numerical results show that the UDMH organic gel droplets exhibit periodic swell‐burst behavior following the formation of an elastic film at the droplet surface. Each droplet burst results in fuel vapor ejection and flame distortion, the intensity of which declines with increasing ambient pressure. However, the swell‐burst period is extended with increasing ambient pressure, which results in potential flameout. Under conditions of low temperature and pressure similar to those at engine startup, the ignition delay and lifetime of spray‐sized gel droplets decrease with increasing temperature or pressure, although there is a sharp increase in droplet lifetime when the ambient pressure reaches a critical value associated with flameout. The ignition delay was found to be a rate‐limited phenomenon linked to the droplet heating rate. The proportion of ignition delay and droplet lifetime due to droplet heating‐up decreased with increasing temperature or decreasing pressure. Conversely, at high temperatures and pressures simulating the engine’s steady state operating conditions, the droplets were observed to flameout after several swell‐burst periods and both ignition delay and lifetime decreased monotonically with increasing temperature or pressure. The ignition delay time was determined to be rate‐limited by gas phase chemical reactions and contributed very little to the overall droplet lifetime compared with the engine startup condition.

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A Modified Implicit Iterative Difference Algorithm for Stiff Chemical Kinetic Equations in Complex Combustion System

Cited by 4 publications

References 13 publications

Unsteady Combustion Model of Nonmetalized Organic Gel Fuel Droplet

Unsteady Combustion Model of Nonmetalized Organic Gel Fuel Droplet

Prospects of UDMH Organic Gel Droplet Evaporation and Combustion Model

Effects of NTO Oxidizer Temperature and Pressure on Hypergolic Ignition Delay and Life Time of UDMH Organic Gel Droplet

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