Development and Application of an Eight-Step Global Mechanism for CFD and CRN Simulations of Lean-Premixed Combustors

Abstract

In this paper, the development of an eight-step global chemical kinetic mechanism for methane oxidation with nitric oxide formation in lean-premixed combustion at elevated pressures is described and applied. In particular, the mechanism has been developed for use in computational fluid dynamics and chemical reactor network simulations of combustion in lean-premixed gas turbine engines. Special attention is focused on the ability of the mechanism to predict NOx and CO exhaust emissions. Applications of the eight-step mechanism are reported in the paper, all for high-pressure, lean-premixed, methane-air (or natural gas-air) combustion. The eight steps of the mechanism are as follows: (1) oxidation of the methane fuel to CO and H2O, (2) oxidation of the CO to CO2, (3) dissociation of the CO2 to CO, (4) flame-NO formation by the Zeldovich and nitrous oxide mechanisms, (5) flame-NO formation by the prompt and NNH mechanisms, (6) postflame-NO formation by equilibrium H-atom attack on equilibrium N2O, (7) postflame-NO formation by equilibrium O-atom attack on equilibrium N2O, and (8) postflame Zeldovich NO formation by equilibrium O-atom attack on N2.

Optimized Reduced Chemistry and Molecular Transport for Large Eddy Simulation of Partially Premixed Combustion in a Gas Turbine

“…In a first test of this new approach applied to methane-air combustion, the chosen global mechanism to be optimized is composed of four reactions, which are given in (Westbrook and Dryer, 1984;Jones and Lindstedt, 1988;Meredith and Black, 2006;Slavinskaya and Unkhoff, 2008;Novosselov and Malte, 2008;Marzouk and Huckaby, 2010;Abou-Taouk et al, 2012; however for unsteady flow simulations in complex geometries, they offer an interesting alternative to single-step chemistry, or to tabulated chemistry which may be difficult to handle in the case of multiple injections leading to large lookup tables requiring huge amount of computing memory. The seven species involved allow for reproducing the adiabatic flame temperature over the range of equivalence ratios considered, as illustrated in Figure 1.…”

Assessment of an Equivalent Reaction Networks Approach for Premixed Combustion

“…The ERN concept was first developed by Bragg (Bragg, 1953;, and has been applied to various combustion systems such as industrial burners , boilers (Faravelli et al, 1997;Faravelli et al, 2001;, confined swirling flames (Frassoldati et al, 2005) and gas turbine combustors (Andreini and Facchini, 2004;Novosselov and Malte, 2008;Fichet et al, 2010). The basic idea of the ERN method is to reduce the computational cost of turbulent combustion modelling, while maintaining the computational accuracy of the chemistry.…”

Combustion features of a bio-fuelled micro-gas turbine

“…In accordance with the considerations that have been drawn in the previous sections, a comprehensive analysis of both combustion development with syngases and internal EGR effect requires the adoption of an appropriate kinetic scheme [9,21,22], together with an accurate solution of the flow field throughout the combustion chamber. The latter, of the tubular lean-premixed type and 400 mm long, is depicted in Figures 5 and 6 and it has been studied in many authors' works [1 -6] under a wide variety of aspects and operating conditions.…”

“…2) An eight-step scheme [21] that is outlined by the equation set (5). This kinetic scheme includes the methane partial oxidation together with the CO 2 dissociation and a refined mechanism for the thermal and prompt NO formation, which has been already employed by the authors in a number of previous articles [4,5]:…”