Experimental study on the pre-evaporation pulse combustion of liquid fuel within a porous medium burner

Experimental studies are conducted to investigate the behaviors of pre-evaporation pulse combustion of liquid fuel within a porous medium burner. A controllable electric preheating system is developed to enhance the evaporation of droplet spray and auto-ignite the flammable vapor without second ignition. Base on the stability analysis of the preheating temperature and the calibration of the fuel flow, the characteristics of the pulse flame in a single injection duration are observed in detail. The thermal characters in terms of the temperature distribution are investigated, and the influences of equivalence ratio and the air flow on the temperature are discussed in the present work. Experimental results show that the pulse flame propagates in the manner of four-phases, i.e., the quasi-steady flame, the transient flame, the free flame and the preheating flame. While the quasi steady flame keeps in a moving state with speed around 0.1 mm/s magnitude order, the propagation of transient flame is similar to a deflagration process with a significant speed of 1.2 m/s magnitude order. The minimum preheating temperature for full evaporation and sustainable combustion is necessary about 1023 K, and the maximum flame temperature achieves up to around 1300 K. As the equivalence ratio increases, an evident temperature improvement and a larger high temperature zone appear, however the propagation speed of the quasi-steady flame almost keeps constant. An increasing air flow plays a limited effect on the maximum temperature while it actually leads to a faster speed of the high temperature zone.