Evaporation and ignition of droplets in combustion chambers modeling and simulation
Evaporation and ignition of droplets in combustion chambers modeling and simulation
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DOI：
10.1016/j.actaastro.2011.06.021
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发表时间：
2012-01-01
影响因子：
3.5
通讯作者：
Nerchenko, V. A.
中科院分区：
文献类型：
--
作者：
Betelin, V. B.;Smirnov, N. N.;Nerchenko, V. A.
在对液体燃料喷入燃烧室热气氛、混合气形成、点火和燃烧过程进行计算机模拟时，需要对蒸发过程进行充分的模拟，这对于具有强热质扩散流的曲面是非常重要的。最广泛分布的烃燃料的燃烧在气相区域中发生。因此，燃料从液滴表面的蒸发也成为该过程的限制因素之一。在描述液滴与流动的热力相互作用时，考虑了液滴雾化、蒸发、液滴雾化的非平衡效应和相变等问题。本文将讨论小液滴的非平衡蒸发过程。如前所示，对于许多类型的广泛使用的液体，考虑蒸发中的非平衡效应对于液滴直径小于100 μ m是至关重要的，而表面张力效应基本上只表现为小于0.1 μ m的液滴。研究加热气流中单个液滴的行为可以区分液滴加热和蒸发的两种情况。小液滴经历连续加热，然后由于蒸发的热损失而冷却，然后快速加热直到其寿命结束。较大的液滴可以直接加热到临界温度，然后迅速蒸发。液滴雾化干扰加热，蒸发和燃烧的情况。燃油喷射和燃烧室内热空气自燃的情况有三个特征阶段。在喷射喷射的第一阶段，液滴非常迅速地蒸发，从而冷却喷射点处的气体，液体射流非常短并且变为蒸汽射流。在第二阶段，液体射流变得更长，这是因为蒸发速率由于温度降低而减小。但燃油蒸气的燃烧开始，使液滴的热流增加，加速了蒸发。液体射流的长度再次减小，并保持恒定，略有振荡。(C)2011爱思唯尔有限公司保留所有权利。
Computer simulation of liquid fuel jet injection into heated atmosphere of combustion chamber, mixture formation, ignition and combustion need adequate modeling of evaporation, which is extremely important for the curved surfaces in the presence of strong heat and mass diffusion fluxes. Combustion of most widely spread hydrocarbon fuels takes place in a gas-phase regime. Thus, evaporation of fuel from the surface of droplets turns to be one of the limiting factors of the process as well. The problems of fuel droplets atomization, evaporation being the key factors for heterogeneous reacting mixtures, the non-equilibrium effects in droplets atomization and phase transitions will be taken into account in describing thermal and mechanical interaction of droplets with streaming flows. In the present paper processes of non-equilibrium evaporation of small droplets will be discussed. As it was shown before, accounting for non-equilibrium effects in evaporation for many types of widely used liquids is crucial for droplet diameters less than 100 mu m, while the surface tension effects essentially manifest only for droplets below 0.1 mu m. Investigating the behavior of individual droplets in a heated air flow allowed to distinguish two scenarios for droplet heating and evaporation. Small droplets undergo successively heating, then cooling due to heat losses for evaporation, and then rapid heating till the end of their lifetime. Larger droplets could directly be heated up to a critical temperature and then evaporate rapidly. Droplet atomization interferes the heating, evaporation and combustion scenario. The scenario of fuel spray injection and self-ignition in a heated air inside combustion chamber has three characteristic stages. At first stage of jet injection droplets evaporate very rapidly thus cooling the gas at injection point, the liquid jet is very short and changes for a vapor jet. At second stage liquid jet is becoming longer, because evaporation rate decreases due to decrease of temperature. But combustion of fuel vapor begins which brings to increase of heat flux to droplets and accelerates evaporation. The length of the liquid jet decreases again and remains constant slightly oscillating. (C) 2011 Elsevier Ltd. All rights reserved.