Common Rail Fuel Injection System Components

20 Май 2015 | Author: | No comments yet »

Common Rail Fuel System Components

Hannu Alessandro Ferrari

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Abstract . The components of a common fuel injection system the rail, a high pressure and fuel injectors. Radial, and in-line pumps are used in common rail systems. pressure pump designs are to achieve higher efficiency of the injection system and to facilitate rail pressure control. types of injectors can be used in rail systems, including controlled electrohydraulic injectors and acting injectors.

Piping and Rail

In modern common systems, the injector supply dimensions and rail volume are parameters that can affect system dynamic performance. The of these components has a significant on critical fuel injection such as the dwell time multiple injections and the minimum injection quantity. With use of multiple injections and the need to control small fuel quantities starting at about the 4 phase, manufacturers have more attention these mundane components.

The rail is a thick walled designed to act as an accumulator to prevent pressure drop at the full rate by providing hydraulic to the high pressure circuit. The of the rail varies from a few cubic centimeters in passenger to as much as 60 cm 3 in heavy-duty applications. In cases, a metering valve at the pressure pump controls the pressure fuel delivery to the The rail pressure can be controlled to a that depends on the needs of any engine operating condition. In cases, rail pressures can 300 MPa.

Just as is the case with systems, common rail are also prone to effects to wave dynamics in the rail and in lines. Waves generated by changes in pressure in one part of the such as when injection valve is opened, may become at rigid terminations in the system and to their origins, causing consequences such as reduced pressure and variations in injection

In order to better control the at the injector nozzle, some rail injectors include an accumulator volume in the injector.

Inlet Pipe Effects. The of high amplitude/low frequency waves during the injection represents one of the most important in reducing the dwell time multiple injections. Reducing the of these oscillations is an important of fuel injection system A significant attenuation of pressure can be achieved by selecting the appropriate for the injector inlet pipe [2193] .

The energy stored in pressure induced by injection events the same injection duration and pressure remains almost when the geometrical parameters of the supply pipes are modified. owing to the fact that the stored in a sinusoidal pressure-wave increases with the square of its amplitude and frequency, hydraulic modifications leading to increased amplitudes should yield frequencies and vice versa .

Since the frequency of the pressure is strictly related to the geometric of the high-pressure circuit, the focus is on the circuit in order to maximize the of the waves. Physical modeling shows that this increases with the injector pipe aspect ratio, is the ratio of the length to the internal and this is confirmed by experiments. pressure-wave oscillations in this way is an active damping strategy.

Alternatively, the introduction of orifices at the to pipe connections or inside the can be used. This is considered a damping strategy. For a particular duration and rail pressure, an will generally decrease the fuel quantity when to a hydraulic layout without an The relative reduction is variable, but is less than 10%. An will also reduce system hydraulic efficiency.

Volume Effects. A relatively volume accumulator has traditionally considered fundamental to dampen the fluctuations caused by the fuel delivered by the pump and the fuel-injection in common rail systems. studies with a fuel system for light vehicles has that the progressive reduction in the volume from 20 to 3 cm3 has no impact on the of these pressure fluctuations and negative impact on injector [2978] [2979]. The high-pressure capability of the system in these resulted from the synergic of both the system high-pressure capacitance and the pressure control Although the duty cycle of the pressure control valve or the fuel metering valve at the inlet (FMV) depended on the size, the high-pressure control was capable of keeping the pressure adequately close to the nominal for the range of accumulator volumes This finding has been to the design of newer generation rail systems for passenger which use smaller rail then in the past.

This finding also the door to the possibility of removing the entirely from the high-pressure In fact, such a system referred to as Common Feeding, has developed [2979]. It uses a hydraulic accumulator volume in the pump which is then directly to the injector feed The pressure sensor, PCV and FMV are also integrated. The resulting injection has low hydraulic inertia that rise to fast dynamic during transients and reduced costs. Furthermore, this matches the requirements of easy on the engine.

It should be noted that a accumulation volume is required in the circuit to avoid an excessive in the pressure level during the event. Effective monitoring of the in the high pressure circuit requires a minimum volume to pressure control system The minimum volume for these is about one order of magnitude than the standard rail [2979] .

Mercedes-Benz C 250 CDI BlueEFFICIENCY Prime Edition
Mercedes-Benz C 250 CDI BlueEFFICIENCY Prime Edition
Mercedes-Benz C 250 CDI BlueEFFICIENCY Prime Edition

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