D fuel grain diameter H fuel grain height P ′ fluctuating combustion chamber pressure P ig igniter pressure P stationary combustion chamber pressure Vr average regression rate t 0 ignition instant t b burn time t d instant the burning surface hits the head end t p instant the pixel p turns white LP8#03 Third LP8 run, first with the transparent head end LP8#11 Eleventh LP8 run, second with the transparent head end