Experimental Investigation of CH4-Humid Air Flame Characteristic of a Novel Micromix Concept Model Burner

The temperature and humidity of the combustion chamber inlet air under the humid air turbine cycle (HAT) vary dramatically, with the highest air temperature of approximately 900 K and high humidity of about 0.3 kg/kg. Compared with conventional lean premixed combustion, which may cause risks such as flashback and autoignition under high-temperature conditions, micromix combustion has the characteristics of small mixing scale, compact flame, flashback resistance, and low emissions, and has been implemented in HAT cycle combustion chambers. In this work, a 9-nozzle micromix model burner with a 3 × 3 array arrangement was designed based on the flow field organization of multiple micromix round jets. The effects of heat load (30∼55 kW), air temperature (300∼630 K), and steam ratio (0∼0.143 kg/kg) variation on the combustion and pollutant emission characteristics of methane-humid air micromix flame at atmospheric pressure conditions were experimentally investigated. Intensified Charge-Coupled Device (ICCD) is adopted to detect OH* chemiluminescence distribution thus investigating the turbulence-reaction interactions and the characteristics of the reaction field. And the effect of humidity on NOx emission was qualitatively analyzed by combining it with a reactor network model. Results indicated that compact flames were achieved for different cases with flame heights of about 85∼185 mm. The steam ratio has a significant influence on the flame structure and NOx emission. Compared with the dry air condition, the flame length increased by nearly 50% while the steam ratio reached 0.143 kg/kg, and the NOx emission was kept at a relatively low level of about 5 ppm (@15% O2) under the designed operating condition. The in-depth understanding of humid air micromix combustion technology is a significant step toward the design of future stability combustors for the HAT cycle.