Effects of CH4 mixing on the laminar burning velocity and Markstein length of RP-3/air premixed flame

Experiments have been carried out in a constant volume combustion bomb to investigate the effects of initial temperature (450 and 480 K), initial pressure (0.1 and 0.3 MPa) and CH4 mixing ratio (0, 0.2, 0.4, 0.6, 0.8, 0.85, 0.9 and 0.95) on the laminar burning velocity and Markstein length of homogeneous, quiescent CH4/RP-3/air mixture over wide equivalence ratio from 0.7 to 1.4. Results show that with the increase of initial temperature from 450 to 480 K, no cellular structure in flame is observed, but obvious cellular structure is observed when initial pressure increases to 0.3 MPa at equivalence ratio of 1.2. The laminar burning velocity reaches its maximum in slightly rich mixture (phi = 1.1) and with the increase of initial temperature and decrease of initial pressure the peak laminar burning velocity of CH4/RP-3/air mixture increases. It is found that the laminar burning velocity of CH4/RP-3/air mixture decreases slowly when methane mixing rate increase from 0 to 0.8, but decreases rapidly from 0.8 to 0.95. Analysis results show that at equivalence ratio of 1.1, the Arrhenius factor exp (-T-a/2T(ad)) has greater effect on the laminar burning velocity of CH4/RP-3/air mixtures when the methane mixing ratio is larger than 0.8. At equivalence ratio of 0.8 (lean mixture), with the increase of CH4 mixing ratio the Le-1 decreases, which leads to the decrease of Markstein length and make the premixed flame tends to be unstable, while at equivalence ratio of 1.4 (rich mixture), with the increase of CH4 mixing ratio the Ze and delta increase, which stabilizes the premixed flame.