INVESTIGATION OF AUTOIGNITION DELAYS IN A SHOCK TUBE UNDER SUPERCRITICAL CARBON DIOXIDE CONDITIONS

Ph.D. Thesis Proposal by

Miad Karimi

(Co-Advisor: Professor Devesh Ranjan)

(Co-Advisor: Professor Wenting Sun)

March 16th, 12:00pm-2:00pm

Montgomery Knight Rm 317

Abstract:

The United States gets majority of its total energy from oil, coal, and natural gas, all of which are fossil fuels. However, the emission from the combustion process poses climate and environmental concerns. Carbon dioxide (CO2) and Nitrogen oxides (NOX) are the principal byproducts of fossil fuels combustions and considered as pollutants. Large amount of CO2 is produced due to carbon being the main constituents of such fuels (60–90 percent of the total mass). Having these species as pollutants, it is important to investigate alternative ways for combustion to occur in order to reduce the emissions. One solution is to separate the carbon by sequestering the CO2 from the exhaust. In this technique, natural gas/syngas and pure oxygen are diluted with carbon dioxide (CO2) before entering the combustor. As a result, the main products of combustion are water (H2O) and CO2 which act as the working fluid to drive the turbines. This technology recycles the flue gas back into the combustor to maintain the temperature and heat flux profiles. A further advantage of removing air from combustion process is significant reduction in NOx emission. In recent years, substantial progress has been made toward developing directly fired supercritical carbon-dioxide (sCO2) power cycles. A pressurized oxy-combustion power cycle has the dual benefit of very high efficiency while simultaneously allowing nearly a complete capture for carbon sequestration. Unlike the operating conditions of conventional gas turbines for ground power generation (~ 20 bar), the sCO2 power cycle requires combustors to operate at much higher pressures (in the range of 100 to 300 bar) and inlet temperature of approximately 900 K. One of the key requirements in designing such combustors is the comprehensive knowledge of chemical kinetics, in particular autoignition delay properties at those conditions. Simulation results using well-known chemical kinetics mechanisms reveals discrepancies in prediction of autoigniton delay times of natural gas/syngas in highly diluted CO2 environments above the critical points. Therefore, experimental data is needed to validate the existing chemical kinetics models which consequently contributes to sCO2 power cycles combustor designs. The goal of the current study is to obtain a comprehensive knowledge of oxy-combustion chemical kinetics of methane, syngas and natural gas at elevated pressures and temperatures. ­­Currently, the effect of CO2 addition in autoignition delay time is understood and studied at conditions well below its critical point. However, no experimental data or detailed analyses are available in literatures above the critical point. Hence, the current study will provide the experimental data along with sensitivity and reaction flux analysis results to fill the existing knowledge gap in oxy-combustion field of study. Conclusions and outcomes of the study is valuable for sCO2 power cycle combustor designs.

Committee:

Dr. Devesh Ranjan, Co-Advisor, ME/AE, Georgia Institute of Technology

Dr. Wenting Sun, Co-Advisor, AE, Georgia Institute of Technology
Dr. Suresh Menon, AE, Georgia Institute of Technology
Dr. Timothy Lieuwen, AE, Georgia Institute of Technology
Dr. Peter Loutzenhiser, ME, Georgia Institute of Technology