Effect of CO₂ Dilution on Methane/Air Flames at Elevated Pressures: An Experimental and Modeling Study

Abstract

This study reports experimental and kinetic modeling results on the effects of CO2 dilution on laminar premixed methane/air flames, based on spherically propagating flames and one-dimensional adiabatic planar flame simulations, at elevated pressure. The laminar burning velocities of air mixtures with CH4 and CO2 at different dilution ratios were measured. In order to have a comprehensive understanding of the effects of CO2 dilution both chemically and physically, sensitivity analysis, chemical reaction rate analysis, and mole fraction analysis of active radicals were carried out using the Aramco 1.3 kinetic mechanism. The chemical impact of the addition of CO2 was segregated from its physical effects using fictitious species, FCO2 with the same thermochemical and transport characteristics as CO2, but does not participate in any chemical reactions. The CO2 dilution percentage varied was from 0 to 70% (by volume) to measure S L o at 300 K, 1 and 5 bar, and equivalence ratios (Φ) of 0.6 to 1.4. Results show that increasing CO2 dilution ratio decreases the S L o of these CH4/CO2/air mixtures. The results simulated using Aramco 1.3 illustrate that the chemical effect is less important at elevated pressure than at ambient pressure. The H and OH radical reduction rates are remarkably reduced at elevated pressure, where H radicals are primarily controlling the combustion. Elementary reactions with a negative sensitivity coefficient exhibit higher sensitivity toward pressure compared to the dilution effect, while elementary reactions with a positive sensitivity coefficient were equally sensitive to both pressure and dilution effects. The increase in initial pressure suppresses the peak net reaction rates for all the elementary reactions, with increasing CO2 concentration.

Propagation Characteristics of Stoichiometric Inert-Diluted Methane–N2O Flames

“…The kinetic modeling of fuel–air flames in the presence of CO 2 (fuels: H 2 , CH 4 , and C 2 H 4 ), performed by Liu et al, , could segregate the chemical impact of CO 2 addition from its physical effects when CO 2 was replaced by a fictitious species FCO 2 , which has the same thermochemical and transport characteristics as CO 2 but does not participate in any chemical reaction. Later, such a procedure was used in the kinetic modeling of many other flames. − These studies have shown that compared to the chemical effect, the thermal effect plays a more important role in the laminar burning velocity reduction of CO 2 -diluted flames than N 2 -diluted flames.…”

A Comprehensive Experimental and Kinetic Study of Laminar Flame Characteristics of H2 and CO Addition to Oxygenated Gasoline

“…Two ignition electrodes were shaped into a V shape to produce a 1 mm gap for sparks and connected to a high-voltage (TREK, 40/15-H-CE) power supply. More details regarding the current setup can be found in refs , and .…”

“…In this section, the data processing is presented briefly, while the details can be found elsewhere. 22 The Schlieren images were converted into eight-bit bitmap image files. Removing a prekernel image produced a flame image without the infusion of the spark plug.…”

“…In this section, the data processing is presented briefly, while the details can be found elsewhere . The Schlieren images were converted into eight-bit bitmap image files.…”

Effects of CO2 Dilution and CH4 Addition on Laminar Burning Velocities of Syngas at Elevated Pressures: An Experimental and Modeling Study

“…Previous works , compared the reduction in S L with different diluents and ranked the order as He< Ar< N 2 < CO 2 , with CO 2 being the inhibitor most effective in decreasing flame temperature and S L . The effects of CO 2 addition on the S L of syngas and hydrocarbon fuels include the dilution effect; thermal-diffusion and chemical effects are investigated under atmospheric and elevated pressures ,,,− [Khan, 2021 #44]. CO 2 gas is also used as an exhaust gas in recirculation to suppress thermal-NO x formation in oxy-fuel combustion. , Han et al reported that the chemical retarding effect of CO 2 addition increased as pressure increased and the direct reaction effect through CO 2 + H = CO + OH always dominated the decrease of adiabatic flame temperature.…”