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Hydraulic Electronic Unit Injector Fuel System

Posted on 3/28/2016 11:30:35 AM

HEUI is short for Hydraulic Electronic Unit Injector.
Differently with mechanically fuel injection systems,HEUI system don't require mechanical adjustment. 
Meanwhile softwware in the ECM is also different which make its performance different.

The engine uses an HEUI in each cylinder.A solenoid on each injector controls the amount of fuel delivered bythe injector. An engine speed/timing sensor detects top dead center (TDC). All fuel injection is timed off theoccurrence of TDC. The ECM determines how much fuel is to be delivered based on the difference betweendesired and actual speed. The ECM then sets the timing from TDC for each cylinder based on data received fromthe coolant temperature sensor, inlet air manifold temperature, atmospheric pressure sensor, and turbochargeroutlet (boost) pressure sensor. In order for best performance of engine,fuel economy,and white smoke control,the timing and uel delivery is controled by the ECM.

The HEUI fuel system uses a hydraulically actuated electronically controlled unit injector. A plunger and barrel in the fuel systems for diesel engine is used to pump fuel under high pressure into the combustion chamber.The performane of engine is controled by the precise amount of fuel pumped into the combustion chamber. The engine oil under high pressure,instead of a fuel injection pump camshaft lobe,is used by HEUI to power the plunger.The HEUI uses engine lubrication oil that is pressurized from 870 psi (6 Mpa) to 3500 psi (24 Mpa) to pump fuelfrom the injector.Like a hydraulic cylinder,HEUI operated to multiply the force of the high-pressure oil. HEUI produces very high injection pressures through multiplying the force of the high-pressure oil,which is achieved by applying the force of high-pressure oil to a piston.The pistonis larger than the plunger by approximately six times. The piston pushes on the plunger. The engine lubricationoil under high pressure is called the actuation pressure of the oil. The actuation pressure of the oil generates the injection pressure delivered by the unit injector, increasing the pressure by a factor of six.The injection pressure of the fuel depends on actuation pressure.During conditions of low speed such as idle and start, lowinjection pressure is used. High actuation pressure during high idle and acceleration results in high injection pressure of the fuel.Infinite control of injection pressure is provied by the HEUI fuel system.

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