Flame propagation of n-decane spray in microgravity

Flame propagation experiments on n-decane spray were performed in microgravity to investigate the flame propagation mechanism of a spray for less volatile fuels. After the spray was dispersed into an acrylic propagation tube with an inner diameter of 62 mm and a length of 535 mm, about 5 s were required for a quiescent spray to form under conditions of microgravity. The spray was ignited by an electrically heated nichrome wire just after the Sauter mean diameter (SMD) and the concentration of spray were measured by a laser droplet analyzer. The variation of flame propagation speed with the SMD was determined. Results showed that the change of the flame propagation speed with the SMD had a maximum for a constant equivalence ratio. This can be reasonably explained by analogy with the flame spread from a droplet to a neighboring droplet in a droplet array, that is, the flame spread of a droplet array and the flame propagation speed of spray reach a maximum when the spacing between a droplet and a neighboring droplet is approximately equal to the flame radius of the droplet. Therefore, all experimental data could be arranged on one curve when the lateral axis was taken as the spacing between droplets divided by the flame diameter. Even when methane of 1 vol %, which is outside the flammability limit, was added to spray with a constant overall equivalence ratio, the flame propagation speeds fell on the integrated curve.