fuel accumulator common rail 64 are obtained by non return valves 62 and 63 the hydraulic fluid pump valve 46 and the fuel injection valve 49 are preferably operated under the control of the electronic powertrain controller 22 fig1 it is assumed initially that the fuel pump piston 52 is in the top end position and that the chamber 57 at the hydraulic end 53 of the fuel pump piston 52 contains hydraulic fluid the combustion fuel has been drawn into chamber 61 from the reservoir 60 through the one way valve 62 as the piston 52 was returned to the top end position in the last cycle the hydraulic fluid pump valve 46 is operated so that pressurized hydraulic fluid from the hydraulic accumulator 16 is supplied to the chamber 57 at the hydraulic end 53 of the fuel pump piston 52 the hydraulic fluid advances the fuel pump piston 52 toward the bottom end position to the right in fig6 compressing the spring 59 and pumping the highly pressurized fuel through the one way valve 63 into the fuel accumulator common rail 64 against the fluid pressure of the fuel accumulator common rail 64 when the chamber 57 has been depressurized the spring 59 returns the fuel pump piston 52 back into top end position to the left in fig6 drawing fuel from the reservoir 60 through non return valve 63 into the chamber 61 at the fuel end 54 of the fuel pump piston 52 for the next cycle when injection valve 49 is opened under the control of the electronic powertrain controller 22 the pressurized fuel in the accumulator common rail 64 is forced into the channel 50 and through the nozzles 51 and directed into the combustion chamber 24.