Sereshchenko E.   Fursenko R.   Minaev S.  

Numerical simulations of ignition features of premixtures in three-dimensional vortex flows

Reporter: Sereshchenko E.

The ignition of turbulent flames is one of the most important problems in the combustion theory. It is relevant to many engineering applications such as investigations of various modes of engine operation required for a better control of fuel efficiency and idle stability of the engine operation. Frequently, the ignition occurs in flows that are highly turbulent and, therefore, involve a wide range of time and length scales. The deep understanding of ignition processes in such conditions is crucial for optimization of ignition systems. Ignition energy is an important property for devices requiring combustion events to be initiated at a predetermined location and time. Despite a number of investigations of ignition process in turbulent flow this important and extensively studied subject still has many unresolved fundamental issues. Detailed modeling of turbulent combustion meets significant difficulties associated with complicated interaction of chemical kinetics, hydrodynamics, radiation and heat and mass transport. Moreover, it may be difficult to distinguish the most important physical processes governing the flame ignition on the basis of detailed numerical simulations. As it was shown in [1,2] the basic characteristics of flame extinction and ignition in turbulent flow may be well described within the framework of reduced thermal – diffusion model with prescribed flow field roughly capturing the main features of turbulent flow.
This work presents the results of three – dimensional numerical simulations of ignition in regular vortexes describing by time – independent ABC – flow field in the cube with periodic boundary conditions in the frame of thermal – diffusion model. The effects of Lewis number, vortex size and the velocity amplitude on ignition energy are investigated. It was found that in large – scale vortex flow, the ignition energy is almost constant until the velocity amplitude exceeds a critical value. For the velocities higher than this critical value the ignition energy rapidly increases. Numerical results show that under a fixed velocity amplitude of the ABC – flow, there is a characteristic size of vortexes corresponding to the maximal ignition energy. Unlike the two – dimensional case [3], this critical wave number depends on velocity amplitude and Lewis number. It is shown that ignition energy is changing very slowly for Lewis numbers from 0.3 to 1.2, and then rapidly increases. Obtained results coincide with experimental data available in literature [4,5] and with previous theoretical results obtained for the spherical flame initiation in the quiescent mixtures [6,7]. It may be concluded that the reduced thermal-diffusion model combined with prescribed flow field yields results that qualitatively agree with experimental observations of the ignition processes in turbulent flow.

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[2] I. Brailovsky, G. Sivashinsky, Phys. Rev. E 51 (1995) 1172–1183.
[3] Sereshchenko E, Fursenko R, Minaev S, Shy S, Combus. Science and Technology 186(10-11) (2014) 1552–1561.
[4] C. C. Huang, S. S. Shy, C. C. Liu, Y. Y. Yan, Proc. Combust. Inst. 31 (2007) 1401–1409.
[5] S. S. Shy, C. C. Liu, W. T. Shih, Combust. Flame 157 (2010) 341–350.
[6] L. He, Combustion Theory and Modelling 4(2) (2000) 159–172.
[7] C Zheng, B Michael, J Yiguang, 47th AIAA Aerospace Sciences Meeting Including The New Horizons Forum and Aerospace Exposition, American Institute of Aeronautics and Astronautics, January 5–8, Orlando, FL, (2009).

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