Главная Препринты Influence of the Initial Parameters of the Air Suspension Flow on the Flame Propagation Velocity

Influence of the Initial Parameters of the Air Suspension Flow on the Flame Propagation Velocity

Язык труда и переводы:
УДК:
536.46
Дата публикации:
12 января 2023, 21:03
Категория:
Секция 03. Основоположники аэрокосмического двигателестроения и проблемы теории и конструкций двигателей летательных аппаратов
Авторы
Тизилов Андрей Сергеевич
Togliatti State University
Егоров Александр Григорьевич
Togliatti State University
Аннотация:
The implementation of projects for the creation of advanced propulsion systems on powdered metal fuel (PMF) depends on the organization of an efficient working process in the combustion chamber. This paper presents the results of a study of the influence of the initial parameters of the flow of an air suspension of aluminum particles on the flame propagation velocity. The nature of the dependence of the flame propagation velocity u_f on the excess air coefficient  in the turbulent flow of an air suspension of ASD-1 and ASD-4 aluminum powders has been established. The velocity of flame propagation increases with an increase of the initial air temperature and a decrease the size of aluminum particles. The nature of the influence of the initial turbulence on the flame propagation velocity depends on both the particle size and the diameter of the combustion chamber.
Ключевые слова:
flame, air suspension, combustion chamber, excess air coefficient
Основной текст труда

Russian scientists Yu.V. Kondratyuk and F.A. Zander was the first to express the idea of the possibility and necessity of using light metals and their compounds for fuels in liquid-propellant rocket engines. The use of powdered metal fuel (PMF) essentially opened up a new direction in jet engine building. Possessing a high calorific value and high density, PMFs can significantly increase such important characteristics of propulsion systems as specific thrust impulses.

With regard to intra-chamber processes in power plants, experimental and theoretical studies should be aimed at studying those characteristics that determine the ignition and completeness of combustion of powdered metal fuel [1]. One of these characteristics is the flame propagation speed. In this regard, experimental data are needed that will make it possible to establish regularities and reveal the features of combustion and flame propagation in a turbulent flow of airborne particles of metal particles. Aluminum is one of the most accessible metals as a powdered metal fuel.

This paper presents the results of studies of the influence of the initial parameters of the air suspension flow: aluminum particle size, velocity, turbulence, and air temperature on the flame propagation velocity. This work is a continuation of the research, the results of which were presented in [2].

The most important characteristic of powdered metal combustibles is the particle size. In recent years, quite a lot of experimental results have been obtained to determine the law of combustion of aluminum particles, allowing us to state that in the size range d_{32}< 10 \mu m m, there is a change in the combustion mode. In the specified range of sizes, the combustion mode of aluminum particles changes from diffusion-controlled to kinetic, i.e., a transitional combustion mode is realized.

It was found that in the air suspension flow with ASD-4 with an average particle size d_{32}= 7.4 \mu m , the combustion of which proceeds in the kinetic mode, the dependence U_{f}=(\alpha )  corresponds to theoretical concepts. According to which, at values ​​of 0.2 and in air suspensions of aluminum particles, heat release, temperature and flame front propagation velocity take maximum values ​​[2,3,4].

In the air suspension flow with ASD-1 with an average particle size d_{32}=17.4\mu m , it was found that the flame propagation speed increases with a decrease in the excess air coefficient in the range of \alpha =3.0...0.2 , and there is only one maximum on the U_{f}=(\alpha )  dependence curve, which corresponds to the value of the excess air coefficient \alpha \approx 0.2 . This is explained by the fact that ASD-1 aluminum particles with an average size d_{32}=17.4\mu m  burn in air at atmospheric pressure in the diffusion mode. In this case, with an increase in the mass concentration, the total surface area of ​​the particles increases, in connection with which an intensification of the processes of radiative heat transfer between the particles is observed, leading to a corresponding increase in the speed of propagation of the flame front.

It has been established that for an air suspension of ASD-1 powder with an average particle size of aluminum d_{32}=17.4\mu m , a dependence was obtained indicating that an increase in the initial air temperature leads to an increase in the flame propagation velocity U_{f} . The maximum values ​​of the flame propagation speed correspond to the values ​​of the excess air coefficient \alpha =0.2...0.3 . In this case, the boundary of the rich limit of flame propagation shifts towards stoichiometry ( \alpha =1.0 ), remaining in the region of the over-enriched composition of the air suspension.

It was found that with an increase in the flame propagation velocity U_{f} , respectively, and with an increase in the air suspension flow velocity U_{0} , the range of mixture compositions within which flame propagation is possible narrows. It was found that in the model of a combustion chamber with a diameter of 0.04 m at a speed U_{0}  of less than 40 m/s, there was no steady propagation of the flame front. This fact confirms the existence of a critical value of the Reynolds number for the process of unsteady flame propagation in reacting air suspensions of aluminum particles.

It has been established that in the air suspension flow with ASD-1 aluminum particles in the range of \alpha =0.1...0.8 , an increase in the initial turbulence \epsilon _{0}  from 12 to 22% and a turbulence scale l_{0}  from 0.01 to 0.07 mm leads to an expansion of the flame propagation limits and increase the speed of flame propagation. It was also found that the presence of a grate in the inlet channel l=  at 0.07 m in the combustion chamber leads to an increase in the flame propagation velocity in the air suspension flow from ASD-4, and to a decrease in the air suspension flow from ASD-1.

The revealed regularities of the influence of the initial parameters of the air suspension flow on the speed of flame propagation can find practical application in the organization of the combustion process in the chambers of propulsion systems on powdered metal combustible fuel.

Литература
  1. Yagodnikov D.A. Vosplamenenie i gorenie poroshkoobraznyh metallov [Ignition and combustion of powdered metals]. Moscow, BMSTU Press, 2009, 432 p. (In Russ.).
  2. Egorov A.G. O skorosti rasprostraneniya plameni v aerovzvesi chastic alyuminiya [On the Flame Propagation Velocity in the Aerosuspension of Aluminum Particles]. Physics of Combustion and Explosion. 2020, vol. 56, no. 1, pp. 48–58. (In Russ.).
  3. Malinin V.I. Vnutrikamernye processy v ustanovkah na poroshkoobraznyh metallicheskih goryuchih [Intra-chamber processes in installations on powdered metal fuels]. Perm, Ural Branch of the Russian Academy of Sciences Publ., 2006, 262 p. (In Russ.).
  4. Poletaev N.I. Svyaz' skorosti rasprostraneniya pylevogo plameni s rezhimom goreniya chastic goryuchego [Correlation between the propagation velocity of a dust flame and the mode of combustion of fuel particles]. Physics of Combustion and Explosion, 2016, vol. 52, no. 6, pp. 60–69. (In Russ.).
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