Experimental investigation of transient ignition dynamics of hydrogen enriched methane diffusion impinging flames

Abstract

The ignition characteristics of hydrogen enriched methane diffusion impinging flames are investigated experimentally. Keeping the total fuel flow rate constant, the hydrogen volume percentage is set at 40% and 60% respectively, while a pure methane flame is also involved for comparison. Two traditional optical diagnostics, high speed colour and schlieren imaging techniques have been used to tackle the fast transient ignition process with advanced digital image processing algorithms. The weak blue flame during the ignition process, which is hardly seen on the original high speed images, has been enhanced selectively to reveal the complete flame structure. The flow field velocity during the ignition process has been estimated using an optimised schlieren motion estimation method. The relative velocity between the flame and flow velocities has also been resolved and analysed. The results indicate that the flow field velocity increases with increasing hydrogen percentage. The maximum velocity detected in the test cases can be as high as over 3.5 m/s when the hydrogen volume percentage is at 60%. The techniques used in the current study are simple to set up and convenient to use, which have shown enormous potential to be applied in the experimental investigations into more complex combustion configurations.