DIESEL FUELS & DIESEL FUEL SYSTEMS

Application and Installation GuideDiesel Fuels & Diesel Fuel SystemsControl Module (ECM) to control theamount of fuel injected into thecylinders. A solenoid on eachinjector receives voltage signals fromthe ECM to become energized. Theinjectors will inject fuel only whilethe injector solenoid is energized.The ECM controls the amount offuel that is injected by varying thesignals that are sent to the injectors.By controlling the timing and theduration of the voltage signal, theECM can control injection timing andthe amount of fuel that is injected.HEUI Fuel SystemThe Hydraulically actuatedElectronically controlled UnitInjectors (HEUI) use a hydraulicpump and engine oil to generate fuelinjection pressure, and an ECM tocontrol the pressure and amount offuel injected into the cylinders.The operation of the HEUI fuelsystem is completely different fromany other type of fuel system that isactuated mechanically. The HEUIfuel system is completely free ofadjustment. Changes in performanceare made by installing differentsoftware in the ECM.Common Rail Fuel SystemUnlike the MEUI fuel system, in acommon rail fuel system injectionpressure is created external to theunit injectors in a high-pressure fuelpump which is driven off the engine.The pump pressurizes a highpressurefuel manifold that runsalong both sides of the enginefeeding high pressure fuel to theinjectors. The electronic fuelinjectors at each cylinder control thedelivery and timing of the fuelinjection(s). Similar to some othersystems, the common rail fuelsystem has capability of multipleinjections for a given combustionevent.The main components of acommon rail system include thehigh-pressure pump, the highpressurelines and rail system, andthe injectors. The low-pressure fuelsystem utilizes similar componentsto the unit injector fuel system. SeeFigure 2 for a schematic of thecommon rail fuel system.The common rail fuel system doesnot continually circulate fuel throughthe entire system like the unitinjector fuel system. Instead, smallamounts of fuel are bypassed duringthe injection event. Due to the veryhigh pressure in the fuel manifold,more heat is put into the fuel thanon previous systems. Because of theadditional heat added to the fuel, itis critical that the fuel inlettemperature is maintained withinguidelines provided for the enginemodel. Recommended, andsometimes required, is the use of afuel cooler to maintain theappropriate inlet fuel temperature.Otherwise, the overheated fuel willhave very low viscosity and filmstrength which makes the fuelsystem components, especially theinjectors, more susceptible todamage from fuel contaminants andwear, hence the importance ofproper filtration practices oncommon rail engines.©2005 Caterpillar®All rights reserved. Page 9