Effect of H2 addition on combustion characteristics of dimethyl ether jet diffusion flame

In this paper, experiments and numerical calculations were conducted to investigate the effect of H2 addition on dimethyl ether (DME) jet diffusion flame behaviors, in terms of thermal and chemical structures, reaction zone size, flame entrainment, and NOx and CO emission indices. A wide range of H2 additions from pure DME to pure H2 were involved herein, while maintaining the volumetric flow rate of fuel mixture constant. The results indicate that when H2 mole fraction in the fuel mixture exceeded 60%, the blended fuel was converted to H2-dominated. Besides, the flames behaved rather distinctly at the DME- and H2-dominated regimes. With the increment in H2 addition, flame temperature, H2, H, O, and OH concentrations increased gradually, but concentrations of the intermediate hydrocarbons (such as CO, CH2O, CH2, and CH3) decreased on the contrary. Additionally, after the flame became H2-dominated, the species concentrations varied increasingly quickly with H2 addition. The reaction zone length and width decreased nearly linearly with H2 addition at the DME- and H2-dominated regimes. But the decreasing speed of reaction zone length became faster after the flame was converted to H2-dominated. At the DME-dominated regime, the dependence of flame entrainment coefficient (Ce) on H2 addition was rather small. While at the H2-dominated regime, Ce increased increasingly quickly with H2 addition. Moreover, with the increment in H2 addition, NOx emission index increased and CO emission index decreased gradually. In addition, at the DME-dominated regime, NOx emission index increased fairly slowly with H2 addition; while at the H2-dominated regime, it increased significantly. The optimal H2 addition to DME was 60 vol.% in the practical engineering.