CRDI_system

The common rail diesel injection system is assembled here. The high pressure pump, the rail model, connection pipe models developed in the other models are assembled here.

The high pressure pump receives fluid from a transfer pump (roughly 5 bar) and pumps it to the required level (500 to 1500 bar). The pump consists of three piston - chamber assembly. Each piston pump has an inlet check valve and outlet check valve. The operation of these three piston pumps are separated by a phase of 120 deg. The pistons are driven by the engine speed through a cam.

The combined outlet of all these three pumps are connected to the common rail volume as well as a pressure relief valve. The fuel injections are captured using flow sources to the connection pipes individually.

The experiment assumes an engine speed of 3000 RPM. The injection events are synchronized for this speed (4 cylinder engine assumed). Since pump shaft is connected through cam, the stroke is made to vary at half the speed of the engine.

Observation of hammer effect

The hammer effect is observed in the connection pipe pressures when the injection stops. The model is set up in such a way that the injection stop event is quick. This can be adjusted by varying the parameter 'falling' of pulse signals that act as an injection source. The default value is 0.1e-3. If this is increased to 1e-3, the hammer effect will be considerably reduced.

The following plot shows the injection events through injector mass flow rate at the bottom of the subplot. The connection pipe pressures are shown in colors blue, red, green and magenta in the top of the subplot. End of injection event in one cylinder is found to affect the pressures of the corresponding connection pipes (same colors are used for corresponding pressure and injection mass flow rate).

The result below shows injection event end through red colored line which is the injector mass flow rate. The green color line is the connection pipe pressure. This pressure shows a clear hammer effect oscillations during the injection closure event. Closer look at the green color plot below (connection line pressure) at around time=0.054 sec shows oscillations to contain two different predominant frequencies.