Analysis of the performance of a low-power atmospheric burner for gas appliances for households and their impact on the emission and stability of the burner
The paper presents results of theoretical numerical research dealing with CO and NO X emission performed in the process of optimization of the performance of low-power atmospheric burners. The theoretical part of this paper, whose main goals were better understanding of the complex issues of methodology and establishment of performance prediction and optimization of low-power atmospheric gas burner included numerical variation of independent parameters, such as burner geometry, the coefficients
... of primary and secondary air and different gaseous fuels including biogas. The findings of theoretically obtained performance prediction and optimization of atmospheric burners were experimentally investigated in purpose built test rigs for a number of variable parameters. The obtained results fully justified the proposed models of performance prediction and burner optimization. In this paper the results of theoretical research performed within the process of optimizing the performance of low power atmospheric burners are presented. In the theoretical phase, the main goals were to better understand the complex problems of atmospheric burner operation and to form a methodology for predicting the performance and optimization of low-power atmospheric burners, introducing burner geometry, primary and secondary air coefficients, as well as gaseous fuel types including pure methan CH 4 (99.73 purity)  and biogas. Althugh this combustion system has a long tradition, is quite surprising that the issue of atmospheric burners is relatively modestly represented in the available literature. In this respect, the authors had no opportunity to compare their work with the some similar research of this issue in virtually all its aspects. The main objectives to be achieved by the construction and the development of modern atmospheric burners include the following categories: the stability of the work, the dynamic range of operation, emissions, lifetime of a burner, the degree of usefulness of the gas devices (consumers) in which the burner is to be installed, and the price of the burner. Design of a flexible burner incorporates a proper procedure and implementation of CFD codes but first of all understanding of chemical reactions that take place, how they affect the flame behaviour and how the flame interacts with the flow field. The combination of commercially available chemical reactions, flow codes and reduced chemical kinetics mechanisms with semi empirical models of low heat value fuels combustion were needed to be developed to enable reliable and fast numerical analysis of practical burners when more parameters are varied. Sub-task was defined as a fundamental research of chemical reaction mechanisms, modelling of emissions and flame structure in premixed combustion systems. Modeling of premixed flame systems Forming of the mathematical model or modeling of the combustion process, in this case consists of a fundamental part that includes: the phenomenology of chemical reactions and flame propagation, then variables that affect these phenomena (excess air coefficient, type of fuel, etc.). In premixed combustion, the fuel and oxidizer are already mixed at the molecular level before the fuel mixture is ignited. Combustion with a premixed flame is more complex for modeling than combustion with an unprmixed flame. Appropriate restrictions are set along with the goal.  The reason for this is that combustion with a premixed flame takes place in a thin layer whose geometry is affected by turbulence. In subsonic flows, the flame front propagation is determined by the laminar flame front propagation and turbulent vortices. [11, 15] The laminar flame front propagationis determined by the complex effect of the simultaneous action of chemical reactions and the phenomenon of heat transfer and propagation with flow right next to reactants that have yet to enter the thermochemical reaction.  The effect of turbulence is reduced to the contraction and expansion of the flame in the laminar flame zone, increasing the laminar flame zone and, consequently, the effective flame front propagation. [4, 16] Large vortices tend to deform the laminar flame zone, while small vortices, if smaller than the thickness of the laminar flame, penetrate the laminar flame zone and intend to modify the laminar flame structure.  3. Modeling of chemical reactions, emissions of combustion products and flame structure 3.1. The goal of modeling Flame structure and emissions were modeled using the CHEMKIN program (Reaction Design, California USA). This program contains various models of chemical reactors. The one corresponding to the burner simulation with a laminar methane/air premixed flame was selected. This onedimensional model of the reactor allows the calculation of: temperature profile, concentrations of the main components, intermediate elements and then flame propagation ratio as a function of distance. The flame structure and burner emissions with a laminar premixed methane/air flame  were calculated at an initial temperature of 298 K and at a pressure of 1.