![]() ![]() Reducing the amplitude of these oscillations is an important objective of fuel injection system designers. The occurrence of high amplitude/low frequency pressure waves during the injection event represents one of the most important challenges in reducing the dwell time between multiple injections. In order to better control the pressure at the injector nozzle, some common rail injectors include an additional accumulator volume in the injector. Waves generated by sudden changes in pressure in one part of the system, such as when injection needle valve is opened, may become reflected at rigid terminations in the system and return to their origins, causing unwelcome consequences such as reduced injection pressure and variations in injection quantity. Just as is the case with P-L-N systems, common rail systems are also prone to effects related to wave dynamics in the rail and in fuel lines. In some cases, rail pressures can reach 300 MPa. The rail pressure can be controlled to a value that depends on the needs of any particular engine operating condition. In most cases, a metering valve at the high pressure pump controls the high pressure fuel delivery to the rail. The volume of the rail varies from only a few cubic centimeters in passenger cars, to as much as 60 cm 3 in heavy-duty applications. The rail is a thick walled tube designed to act as an accumulator to prevent significant pressure drop at the full fueling rate by providing hydraulic capacitance to the high pressure circuit. With increased use of multiple injections and the need to accurately control small fuel injection quantities starting at about the Euro 4 phase, manufacturers have paid more attention these seemingly mundane components. The sizing of these components has a significant impact on critical fuel injection variables such as the dwell time between multiple injections and the minimum fuel injection quantity. In modern common rail systems, the injector supply pipe dimensions and rail volume are critical parameters that can affect injection system dynamic performance. Several types of injectors can be used in common rail systems, including servo controlled electrohydraulic injectors and direct acting injectors. High pressure pump designs are evolving to achieve higher efficiency of the fuel injection system and to facilitate accurate rail pressure control. ![]() Radial, unit and in-line pumps are used in commercial common rail systems. Abstract: The components of a common rail fuel injection system include the rail, a high pressure pump and fuel injectors. ![]()
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