The control characteristics of the high-pressure common rail fuel injection system on small-quantity fuel injection largely determine its control precision and stability for the multiple-injection fuel quantity. In addition, the disturbance effect of fuel injection can be fully utilized by adjusting the injection volume and injection interval, thus increasing the mixing rate of the fuel and gas, improving the combustion process in the cylinder and reducing the emissions of soot and NOx. The small-quantity and multiple injection processes can effectively improve the fuel spray process and reduce the impinging fuel volume in the cylinder. The precise control of small-quantity fuel injection is one of the main technical characteristics of high-pressure common rail fuel systems. This process wastes 80–100 μs before the current is large enough to generate a sufficient electromagnetic force to open the ball valve, which is not conducive to the rapid response of the injector. The electromagnetic force to drive the ball valve is minimal, increasing with the square of the electric current. In addition, the gap between the electromagnetic coil and the armature is the largest when the solenoid valve is opened. When the common rail fuel pressure is high, the injector has an obvious fuel leakage, resulting in a waste of energy. This approach requires a higher energy loss when the injector is working. As the core component of the fuel-injection system, most injectors currently use solenoid valves as the drive control mechanism. The system can independently adjust the fuel injection parameters without being affected by the engine operating conditions and can effectively reduce the emissions and fuel consumption of a diesel engine, making it the mainstream of current diesel fuel injection systems. The high-pressure common rail injection-system has the characteristics of a high injection pressure and an adjustable injection rate. However, these behaviors reduce the control margin for the pulse width, especially in small pulse width regions. Under the condition of a small-quantity fuel injection of 20 mm 3, decreasing the inlet orifice diameter and increasing the outlet orifice diameter shortened the minimum control pulse width and fuel injection duration required for the injector injection, which is beneficial for multiple and small-quantity fuel injection. The bypass valve significantly accelerated the establishment of the control-chamber pressure, reduced the pressure fluctuation in the chamber, shortened the closing delay and duration of the needle valve, and reduced the rate of the fuel-quantity change so that it provided a greater control margin for the pulse width over the same fuel volume change interval. The results show that the linearity of the curve of the injection volume with the pulse width was relatively poor, and there was a significant inflection point when the piezoelectric injector worked in the small pulse width region (PW < 0.6 ms). The effects of key structural parameters of the injector on the delivery, control-chamber pressure fluctuation, and small-quantity injection characteristics were studied. The small-quantity fuel injection with different driving voltages, pulse widths, and rail pressures was analyzed. Considering the nonlinearity of a piezoelectric actuator, the complete electro-mechanical-hydraulic model of the piezoelectric injector was established and verified experimentally, which showed that it could accurately predict the fuel injection quantity. The piezoelectric injection-system provides a reliable approach for precise small-quantity fuel injection due to its fast, dynamic response.
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