Lean burn limit and time to light characteristics of laser ignition in gas turbines

• Laser ignition of natural gas and air was conducted in a low pressure combustion test rig.
• Lean burn limit for laser ignition and standard high energy ignition was determined.
• Time taken to light at lean burn limit for laser ignition and standard high energy ignition was determined.
• Effect of air mass flow rate on combustion characteristics at air/fuel ratios approaching the lean burn limit was studied.

This work details a study of laser ignition in a low pressure combustion test rig, representative of an industrial gas turbine (SGT-400, Siemens Industrial Turbomachinery Ltd.) and for the first time investigates the effect of air mass flow rate on combustion characteristics at air/fuel ratios at the lean burn limit. Both the lean burn limit and time taken to light are essential in determining the suitability of a specified air/fuel ratio, especially in multi-chamber ignition applications. Through extension of the lean burn limit and reduction of the time taken to light, the operating window for ignition with regards to the air/fuel ratio can be increased, leading to greater reliability and repeatability of ignition. Ignition of a natural gas and air mixture at atmospheric pressure was conducted using both a standard high energy igniter and a laser ignition system utilizing a Q-switched Nd:YAG laser source operating at 1064 nm wavelength. A detailed comparison of the lean burn limit and time taken to light for standard ignition and laser ignition is presented.