Burning velocity measurements of fluoropropanes by the spherical-vessel method

Burning velocity measurements of six types of fluoropropanes including structural isomers were carried out in order to understand the flammability of hydrofluorocarbons (HFC). The burning velocity (Su) was determined by applying a spherical flame model to the pressure rise during combustion, which was measured at room temperature and at initial pressures of 80–107 kPa over a wide range of HFC/air concentrations. The maximum Su of 1-fluoropropane (HFC-281fa), 2-fluoropropane (HFC-281ea), 1,3-difluoropropane (HFC-272fa), 2,2-difluoropropane (HFC-272ca), 1,2,3-trifluoropropane (HFC-263ea), and 1,1,1-trifluoropropane (HFC-263fb) was 35.0, 31.8, 31.9, 21.2, 25.7, and 14.5 cm s−1, respectively. Note that the maximum Su of HFC-263ea was appreciably higher than that of HFC-272ca, which shows the importance of the F-atom distribution, as well as of the F/H ratio in the HFC molecule. The results of equilibrium calculation for these HFCs showed that Su is positively correlated with the flame temperature and the concentrations of the active chain carriers H and OH in the flame. We conducted a trial to interpret the magnitude of Su by means of the effects of substituents for C1–C3 HFCs. As a result, it has been found that the order of inhibition efficiency for Su decreases in the order of CF3 > CF2 > CF.