Spray and Vaporization Enhancement of Liquid Fuel with the Assist of Porous Media and Heating

Air-assist atomization is the main way to organize the liquid fuel combustion in gas turbine. The atomization and vaporization enhancement of n-heptane was investigated experimentally with porous media (PM) process, revealing the effects of atomizing air temperature, air-to-liquid mass ratio, and porous media heating power. The nickel foam has over 0.9 porosity, large specific surface area and excellent thermal conductivity make it the best choice of porous media. The n-heptane spray processed by nickel foam may present cohesion or sputtering effusion, and increasing air temperature, air flow rate or heating power can avoid liquid cohesion. Although the average velocity of the droplets is reduced significantly by nickel foam, the spray with porous media can obtain the Sauter mean diameter (SMD) about 15 mu m, equal to the no-PM case. Porous media heating performs remarkable improvement on the droplet size and distribution. The PM also results in obvious rises of spray temperature and the mass flow rate of n-heptane vapor. The air temperature and heating power perform with stronger than air flow rate. It is found by calculating the volumetric heat transfer power of nickel foam that PM substantially enhanced the fluid-solid heat transfer to six times with the addition of air temperature and porous media heating. A criterion number, theta(T) was proposed to evaluate the atomization and vaporization, and 400 K is the basic condition for better atomization. Both high air temperature and heating power may does not result in further improvement of theta(T) which presents similar peak values around 7.