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.A mathematical model is suggested for injecting fuel by means of this pump-injector unit; and, based thereon, fuel supply characteristics for a multiphase injection, comprising one pre-main, one main and one post-main injections, have been calculated. The calculations were made for different main injection shapes: stepwise, trapezoidal, triangular and rectangular. It is shown that the suggested FSS allows implementing all the four shapes of the main injection, as well as setting the pressure for the pre- and post-main injections. The suggested FSS is highly promising, but needs further study.