FUEL PRESSURE CONTROL OPERATION[MZ-CD 1.6 (Y6)]
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• The engine management system on the common rail injection system is able to provide the optimum injection pressure for each operating condition.
• Via the high pressure chambers of the common rail fuel pump, fuel is compressed and fed to the common rail.
• In the process, the delivery quantity is regulated by the fuel metering valve by varying the opening cross section of the fuel metering valve accordingly.
• The fuel pressure is regulated in such a way that the optimum pressure is available for each operating condition.
• This reduces noise emissions when the fuel is being burned.
• In addition, the engine management system can also meter the fuel very accurately which has a positive effect on exhaust emissions and fuel consumption.
• The fuel pressure sensor continuously informs the PCM about the current fuel pressure.
• Pressure is regulated via the fuel metering valve by reducing the cross section of this valve accordingly. As a result, the fuel pump delivers a smaller amount of fuel (or no fuel at all, depending on requirements) until the desired fuel pressure is reached.
• Fuel pressure is dependent on engine speed and engine load.
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1
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Fuel pump
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2
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High-pressure chambers for high-pressure generation
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3
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Fuel feed
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4
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Fuel metering valve
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5
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Fuel pressure sensor
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6
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Common rail
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7
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Solenoid valve
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8
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Nozzle needle
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9
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Fuel injector
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10
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Fuel flow
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Switching Off The Engine
• Because of the way the diesel engine works, the engine can only be switched off by interrupting the fuel supply.
• In fully electronic engine management this is done by setting the default PCM injected quantity = 0. The solenoids for fuel injection are therefore no longer energised and the engine is switched off.
Pressure Drop After Engine Is Switched Off
• After the engine has been switched off, pressure is reduced through leakage past the fuel injectors. The rate of pressure reduction depends on how high the fuel pressure and fuel temperature are. For safety reasons, a certain period of time has to elapse before the high‐pressure system is opened after engine shut‐off.
