## 1 Introduction  
The atmospheric environment is becoming worse, and the environmental protection consciousness of people is stronger than ever. To reduce the effects of the misuse of fossil fuels and their destructive impacts on nature, extensive efforts has been applied to develop hydrogen fuel as an alternative to hydrocarbon fuels [1; 2; 3; 4]. The pollutants produced by the combustion of hydrogen are lower and less damaging than those produced by the combustion of hydrocarbon fuels, therefore, hydrogen could be used as a novel, renewable and environmentally-friendly fuel. The hydrogen fuelled combustion system in operation would mean that there would be no ozone layer depletion, and greenhouse gasesand acid rain would be minimised. Hydrogen fuelled combustion of gas turbine engines has huge environmental advantages for the current system, because only water and nitrogen oxides (NO\({}_{\rm x}\)) are the emissions of hydrogen combustion [5; 6]. The hydrogen-enrichment of natural gas could be used to solve several drawbacks encountered for turbulent premixed combustion [7; 8; 9]. Using the CHEMKIN PREMIX code based on the GRI (Gas Research Institute) kinetic mechanism, the laminar burning velocities in a combustor with hydrogen-methane/air were calculated [10]. The methane reactivity could be enhanced slightly in lean mixtures conditions. Using Time-Resolved Particle Image Velocimetry, [PERSON] [11] investigated the transient interactions of premixed flames and toroidal vortex in combustors with hydrogen-enriched methane/air. The hydrogen presence would increase the main toroidal vortex velocity to affect the flow field and generate different sub-vortices. While the hydrogen substitutes for the methane, the vortex would wrinkle the flame front which induces the small flame pockets separates from the main front. Using a Large Eddy Simulation (LES) method, the unsteady propagation of the premixed flames around toroidal vortices in a combustor with hydrogen-enriched methane/air was simulated [12]. With the hydrogen mole fraction varying from 0 to 0.5 for lean mixtures, good predictions of experimental data could be obtained. The flame shape and structure affected by the vortex were presented. The hydrogen diffusion time was higher than that of the flame roll-up round the vortex. Hydrogen will be a great potential surrogate for fuel fossil fuels for gas turbine engines in the future, but currently, it is not widely used for gas turbine engines. Previous research on the application of hydrogen focused on internal combustion engines. For example, hydrogen has been seen as suitable for spark ignition engines as fuel, and compression ignition engines are also now in the process of modification to operate with hydrogen [2]. There are only sporadic studies of hydrogen applications for gas turbine engines. [PERSON] [13] investigated a low emission combustor using hydrogen lean direct injections. At an inlet temperature of 588 to 811 K and inlet pressure of 0.4 to 1.4 MPa, the NO\({}_{\rm X}\) emissions and combustion performance were measured, and the equivalence ratios were up to 0.48. With multiple injection points and quick mixing, all the injectors were installed to achieve lean direct injection (LDI) technology. The combination of nitrogen dioxide (NO\({}_{2}\)) and nitric oxide (NO) is usually called as NO\({}_{\rm X}\). The formation of photochemical smog, acid rain and harmful ozone is caused by such NO\({}_{\rm X}\) emissions as from aircraft engines [14; 15]. For fuelled hydrogen gas turbine engines, low NO\({}_{\rm X}\) emissions of combustion are usually required in order to meet the demand of environmental emissions regulations. The temperature, mixedness, residence time, and engine operation pressure would play an important role in NO\({}_{\rm x}\) emission production. For designing advanced gas turbine combustors in the future, locally leaner combustion should be developed to achieve low NO\({}_{\rm x}\) emissions [16; 17; 18].