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A new fuel supply system (FSS) for a diesel engine is suggested that allows controlling the pressure of the pre- and post-main injections, and changing the pressure curve of the main injection. The system comprises a pump-injector unit with an independent pressure control and a needle. The driving cam of the pump-injector unit is designed so that the downward plunger speed is constant. Due to this fact, the pressure in the high-pressure chamber of the pump-injector unit may also be constant and adjustable by means of a piezoelectric pressure-regulating valve (PRV). The PRV connects the high-pressure chamber of the pump-injector unit with the FSS. The passage area of the PRV depends on the voltage fed to the piezoelectric drive. Thus, by varying the voltage, we can change the pressure in the high-pressure chamber. The needle of the pump-injector unit is controlled hydraulically by a two-position valve. The valve drive can be of solenoid, piezoelectric or mechanical type.