Towards understanding multicomponent chemistry interaction using direct numerical simulation.
Technische Universität, Darmstadt
[Ph.D. Thesis], (2015)
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|Item Type:||Ph.D. Thesis|
|Title:||Towards understanding multicomponent chemistry interaction using direct numerical simulation|
In recent years the automobile and aviation industries, as well as other energy intensive branches, have moved towards downsizing as a new trend. Downsizing essentially means to reduce the dimensions of the device while power and efficiency is kept at least the same. The immediate consequence of downsizing for combustion devices is a higher area-to-volume ratio in which case the near-wall combustion attains greater influence on the overall behavior of the device. Although flame and wall do not interact everywhere in the combustor, their interaction has always significant influence on the combustion process especially in terms of unwanted byproducts such as unburnt hydrocarbons and NOx. On these accounts, the near-wall combustion and the flame-wall interaction becomes an increasingly attractive area of scientific investigation. There is especial interest in quenching the flame at the wall in researching flame-wall interaction(FWI). Based on orientation of the flame relative to the wall, one can think of two types of configurations for flame-wall interaction in laminar or turbulent flows, namely
- the flame front being parallel to the wall, that is also the flame propagating normal to the wall, which is called head-on quenching, and
- the flame front being normal to the wall, i.e. the flow runs parallel to the wall, which is called side-wall quenching.
Numerous experimental studies have been conducted in this area, but they have serious limitations. Flame-wall interaction has very short time scales and small characteristic lengths which require high precision measurements, overly sophisticated setups, and costly material. And yet the results are not up to par, because of technical limitations at this time. The flame quenching distance at atmospheric pressure is of the order of < 100 micrometer. There are not many reliable methods to capture flame-wall interaction at such small scales. This leaves CFD as the only feasible option which has only become possible by the arrival of the recent computing technologies. Although there is vast theoretical, experimental, and numerical body of research on the head-on configuration of the flame-wall interaction, there are few works concerning the side-wall configuration, either in laminar or in turbulent flame regimes. The main reason for that is the cost of computation. While the HOQ simulations can be performed using one-dimensional finite difference code, the side-wall quenching has to be simulated using two-dimensional domain, for the laminar combustion regime and three-dimensional domain, for turbulent flame-wall interactions. Improved computation capacity of research centers has made it possible to delve into this topic and better understanding the SWQ configuration. Gruber et al. have recently performed a three-dimensional direct numerical simulation to investigate the interaction between the wall and a turbulent hydrogen-air flame using multi-component reaction mechanism. Prior to his work there have been experimental and theoretical studies mostly, and numerically simulations were performed based on simple chemistry only. Lack of sufficient theoretical and numerical works in this area makes it more difficult to acquire enough information to characterize the flame-wall interaction in side-wall quenching. The aforementioned points are enough motivating to perform the sophisticated direct numerical simulations of combustion in the near-wall region using detailed chemistry. The goal of this work is first to investigate the flame-wall interaction in the head-on quenching configuration concerning different phases of simulation where the flame behaves differently from the transient phase exactly after simulation until after quenching. Secondly, the amount of produced carbon monoxide in different distances from the wall will be examined and compared to experiments. The last step is to gain better insight into the side-wall quenching of stoichiometric methane-air mixtures in configurations where the wall is parallel to the flow. The near wall combustion or the so called flame-wall interaction will be explored using two completely different possible quenching configurations and next, their similarity and differences will be studied. In order to make this possible, two quasi three-dimensional simulations for Side-Wall quenching were performed. To realize this, the readily available code (FASTEST-3D) was modified to calculate the mixture averaged flow properties of a gas mixture. The code was then extended to include mass fraction and energy transport equations for a multi-component gas mixture. In the simulations for both SWQ- and HOQ-configurations, the Smooke multi-component mechanism and the mix averaged transport coefficients calculation recommended by Hirschfelder are used.
|Place of Publication:||Darmstadt|
|Uncontrolled Keywords:||Multicomponent Chemistry, DNS, Numerical|
|Classification DDC:||600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften|
|Divisions:||16 Department of Mechanical Engineering
16 Department of Mechanical Engineering > Institute for Energy and Power Plant Technology (EKT)
|Date Deposited:||27 Nov 2015 08:35|
|Last Modified:||27 Nov 2015 08:35|
|Referees:||Janinicka, Prof. Johannes and Stephan, Prof. Peter|
|Refereed:||6 May 2015|