Effect of hydrogen enrichment on the laminar burning characteristics of dimethyl-ether/methane fuel: Experimental and modeling study

In this work, the new laminar flame speeds of hydrogen/dimethyl-ether/methane/air mixtures (H2/DME/CH4) covering wide ranges of equivalence ratios (0.6-1.6) and hydrogen enrichment ratios (0%-100%) were measured using spherical expansion flame method. Four DME chemical reaction kinetic mechanisms (Zhao mechanism, Wang mechanism, Sandiego mechanism and Chen mechanism) were used to calculate the laminar flame speeds and compared with the experimental measured data. Results showed that the experimental data agreed well with the calculated values using Zhao mechanism. The laminar flame speeds were observed to increase significantly with hydrogen enrichment ratio and they can be divided into three stages depending on the hydrogen enrichment ratio in the H2/DME/CH4 fuel. Furthermore, the laminar flame speeds at fuel-rich conditions were more sensitive to hydrogen enrichment than fuel-lean conditions. In the increasing hydrogen atmosphere, the diffusional-thermal instability was enhanced for fuel-lean conditions, while it was effectively suppressed for fuelrich conditions. The hydrodynamic instability was enhanced for all cases, which was mainly due to the decrease of flame thickness. Numerical simulation revealed that with the enrichment of hydrogen, the laminar flame speeds have the strongest correlation with H + O radicals for the fuel-lean and fuel-rich conditions, while H radicals have the strongest correlation for the stoichiometric condition. Furthermore, the adiabatic flame temperature and thermal diffusivity can be enhanced with the enrichment of hydrogen.

Automated summary

This work measured the laminar flame speeds of hydrogen/dimethyl-ether/methane/air mixtures under different hydrogen enrichment ratios and compared the results using four DME chemical reaction kinetic mechanisms. The experimental data showed good agreement with the calculated values using the Zhao mechanism, and the laminar flame speeds were significantly affected by hydrogen enrichment ratios, especially under fuel-rich conditions. The study also revealed that hydrogen enrichment had different effects on diffusional-thermal instability and hydrodynamic instability depending on the fuel conditions.