Numerical investigation of coal flamelet characteristics in a laminar counterflow with detailed chemistry

- The characteristics of coal flamelet in a counterflow are numerically investigated.
- The effects of various operating conditions on the flamelet behaviors are studied.
- Unlike the gaseous mixture fraction, the coal mixture fraction is non-monotonic.
- Negative flame index can be obtained in the rapid devolatilization region.

The characteristics of flamelets in coal flames stabilized in a laminar counterflow are numerically investigated with detailed chemistry. The behaviors of coal flamelet are compared with those of the gas flamelet. In addition, the effects of strain rate, coal particle mass flow rate and coal particle size on the behaviors of coal flamelet are studied in both the physical space and the mixture fraction space. The results show that the characteristics of coal flamelet are significantly different from those of the gas flamelet. On the one hand, unlike the monotonicity of the gaseous mixture fraction, the coal particle mixture fraction is non-monotonic due to the interphase mass transfer. On the other hand, due to the non-monotonicity of coal particle mixture fraction, the thermo-chemical quantities in the coal flame cannot be uniquely identified by a single variable of mixture fraction as those in the gas flame. It is also found that the strain rate, coal particle mass flow rate and coal particle size have significantly effects on the behaviors of coal flamelet.