valve is closed high pressure fluid in the accumulator chamber 18 is trapped thus creating a store of energy in the form of compressed fuel immediately following the closing of valve 44a the pressure of the fuel extant in the accumulator chamber acting upon the differential area of the valve means 19 i e the projected area of the tip 21 versus the cross sectional area of passage 39 minus that of the passage 42 causes valve tip 21 to lift from its seat and the secondary or accumulator phase of injection commences with fuel being discharged through the large orifice 22 into the precombustion chamber 12 there is some overlap of the primary phase and the secondary phase of injection the primary phase continues until the pressure of the fluid in chamber 43 decreases to a level which allows the check valve 34 to seat against valve seat 36 the secondary phase continues after termination of the primary phase until the pressure p 2 in the accumulator chamber decreases to a level which allows valve tip 21 to seat against the casing 14 thus terminating the secondary injection phase when the primary phase of injection through the small orifice 33 occurs on each.