Comparisons of the Uncoupled Effects of CO2 on the CH4/O2 Counterflow Diffusion Flame under High Pressure

Ying Chen,Xiaolei Zhang,Jingfu Wang,Conghao Li

doi:10.3390/app11041768

Abstract

A comprehensive numerical investigation of the uncoupled chemical, thermal, and transport effects of CO2 on the temperature of CH4/O2 counterflow diffusion flame under high pressure up to 5 atm was conducted. Three pairs of artificial species were introduced to distinguish the chemical effect, thermal effect, and the transport effect of CO2 on the flame temperature. The numerical results showed that both the chemical effect and the thermal effect of the CO2 dilution in the oxidizer side can decrease the flame temperature significantly, while the transport effect of CO2 can only slightly increase the flame temperature and can even be ignored. The reduction value of the temperature caused by the chemical effect of CO2 grows linearly, while that caused by the thermal effect increases exponentially. The RPchem and RPthermal are defined to explain the temperature reduction percentage due to the chemical effect and the thermal effect of CO2 in the total temperature reduction caused by CO2 dilution, respectively. The RPchem decreases with the increase of the pressure, the strain rate, and the CO2 dilution ratio, while the RPthermal behaves in the opposite manner. In the above conditions, the chemical effect plays a dominant role on the flame temperature reduction.

Highlights

To overcome the difficulties of the multiple goals of CCS [1,2,3], reduction of pollutants [3,4], and GHC reduction [5], the technology of Oxy-fuel combustion [6,7] based on the exhaust gas recirculation [8] has been proposed and developed by numerous scholars
laminar burning velocities (LBVs) of O2 /methane under various O2 mole fraction and equivalence ratios by numerical simulation under ordinary pressure; the results showed that the chemical effect was smaller than the thermal effect, but much bigger than the radiative effect in the calculation domain
The objective of the present study is to quantitatively explore the effects of CO2, which is added into the oxidant side of the CH4 /O2 counterflow diffusion flame on the flame temperature with high pressure and a large CO2 dilution ratio, and reveal the trends of the chemical effect and thermal effect of CO2 caused by pressure

Summary

Introduction

To overcome the difficulties of the multiple goals of CCS (carbon capture and storage) [1,2,3], reduction of pollutants [3,4], and GHC (greenhouse gas) reduction [5], the technology of Oxy-fuel combustion [6,7] based on the exhaust gas recirculation [8] has been proposed and developed by numerous scholars. Compared with air combustion (O2 /N2 ), the differences between CO2 and N2 regarding thermal properties, chemical properties, transport properties, and radiative properties [7,9,10] cause substantially complexities and challenges on the flame characteristics, especially for highpressure practical application, such as gas turbines [11]. For the isolate effect (uncoupled effect) of CO2 [13], numerical simulation becomes an efficient method

Objectives

Results

Conclusion