Utilizing direct-fired sCO2 oxy-combustion is attractive for power generation applications because of the cycle’s inherent carbon capture, high efficiency, and small machinery footprint. However, there is a large amount of uncertainty regarding the combustion process of natural gas in carbon dioxide diluent at supercritical pressures. One such area of uncertainty is in regards to the ignition system. The performance of most common ignition systems is not proven at the elevated pressures and densities typical of these cycles.
This paper presents an evaluation and down-selection of potential ignition systems considered for a sCO2 oxy-combustor igniter. The ignition systems considered include spark ignition, laser ignition, heating element auto-ignition, external preheat auto-ignition, ignition using solid or liquid fuels, and external torch ignition. After a preliminary review, spark ignition and laser ignition were chosen for system reliability and repeatability. To further quantify the practicality of each system, a spark igniter and laser igniter were lab-scale tested to determine breakdown energies associated with these igniters. The spark igniter was tested using gaseous CO2 and SF6 (to attain higher fluid densities). The laser igniter was tested using supercritical CO2 and gaseous CO2. An additional round of testing was conducted using the laser igniter in a constant volume combustion chamber (CVCC). Natural gas was combusted with oxygen in varying levels of CO2 dilution to determine the required laser power for stable, reliable ignition and to quantify the high dilution flammability limit. Based on these test results, a laser igniter was selected as the most practical option for high-pressure sCO2 combustor ignition.