18787A18 Mercury CYLINDER HEAD ASSEMBLY

Illustration 1 g02192355
Fuel system schematic (typical example)
The fuel supply circuit is a conventional design for engines that use fuel injectors. The fuel supply circuit uses a fuel transfer pump to deliver fuel from the fuel tank to the electronic fuel injectors. The transfer pump is a fixed displacement gear pump.The fuel flows then through a fuel filter before entering the fuel supply manifold. A fuel priming pump is located on the fuel filter base in order to fill the system. The system must be primed after the filter changes. The system must be primed after draining the fuel supply and return manifolds, when the fuel injectors are replaced.The fuel flows continuously from the fuel supply manifold through the fuel injectors. The fuel flows when either the supply or the fill port in the injector is not closed by the injector body assembly plunger. The fuel that is not injected into the cylinder is returned to the tank through the fuel return manifold.A pressure regulating valve is at the end of the fuel return manifold. The pressure regulating valve controls the entire fuel system pressure. The regulation provides proper filling of the fuel injectors.The electronically controlled mechanically actuated fuel injector system provides total electronic control of injection timing. The injection timing is varied in order to optimize the engines performance.The timing ring is part of the rear gear group. A signal is generated by the engine speed/timing sensor. This information is for detection of crankshaft position and for engine speed. Other information and these data allow the ECM to send a signal to the injector solenoids. The fuel injector solenoid is energized in order to begin fuel injection. The fuel injector solenoid is de-energized in order to end fuel injection. Refer to Systems Operation, "Fuel Injector".Gas System
The Electronic Control Module (ECM) provides control of the air/fuel mixture to the engine. Illustration 2 is a diagram of the fuel system main components. The flow of fuel through a typical fuel system is explained below.Refer to the Application and Installation Guide, LEBW5336, "Gaseous Fuel Systems" for more information on fuel system specifications and installation. The publication is available from the Electronic Media Center.
Illustration 2 g03383996The fuel flows from the main gas supply through a knock-down regulator. A knock-down regulator is a second regulator that is needed when the gas supply pressure is too high for a single regulator to manage. From knock-down regulator, the fuel flows to the fuel filter. Usually, the fuel filter is a component of the design at the particular site. The customer is responsible for supplying clean, dry fuel to the engine. The fuel filter may be supplied by Caterpillar or by the customer. To prevent particles from entering the engine, a 1 micron filter is recommended. Use a filter that is properly sized for the required gas pressure.For installation of the fuel filter, the recommended location is close to the engine before the engine gas pressure regulator. Pressure gauges in the gas lines on each side of the fuel filter are recommended in order to monitor the filter differential pressure. A manual shutoff valve in the gas line before the fuel filter will facilitate servicing of the filter.The filtered fuel flows to the gas pressure regulator.The regulator is supplied by Caterpillar.A maximum inlet fuel pressure of 690 kPa (100 psi) is required.A regulated pressure of 10.3 to 24.1 kPa (1.5 to 3.5 psi) is recommended.The required fuel pressure stability is 1.7237 kPa ( 0.25 psi).Less gas pressure may result in reduced power. More gas pressure may result in instability.The fuel flows through the gas pressure regulator to the Gas Shutoff Valve (GSOV). The GSOV is supplied by Caterpillar. The solenoid for the GSOV may be connected to engine wiring harness or to a harness that is supplied by the customer. In either case, the customer may install a switch that can interrupt the circuit.The control system is configured for a GSOV that is energize-to-run. This means that the GSOV must be energized in order for the engine to run. The GSOV may be energized by the customer equipment or by the ECM. When the GSOV is energized, the valve opens and the fuel flows to the engine. When the control system shuts down the engine, the voltage is removed from the solenoid. The valve closes and the fuel is shut off.
Illustration 3 g03379490
Typical left-hand view
Flow of fuel through the quad turbocharger arrangement
(1) Fuel control valve The fuel flows from the electronically controlled fuel control valve (1). The ECM issues a command signal to the fuel control valve via the CAN data link. The fuel control valve regulates the flow of fuel to the engine.
Illustration 4 g03379492
Typical top view of a 3512C
(2) Air inlet tubes
(3) Turbocharger compressor
(4) Mixing tubes The fuel control valve controls the volume of fuel that flows to mixing tubes (4) attached to air inlet tubes (2). The inlet air that is necessary for combustion also enters the air inlet tubes. The air/fuel mixture enters turbocharger compressors (3).
Illustration 5 g03379589
Flow of air and fuel through the aftercooler and air inlet manifold
(5) Aftercooler
(6) Air inlet manifold
(7) Spark arrestor The air/fuel mixture flows from the air inlet pipes through aftercooler (5) and air inlet manifold (6). The temperature of the compressed air/fuel mixture is reduced in the aftercoolers. The cooler temperature increases the density of the air/fuel mixture, which results in more efficient combustion. The manifold distributes the air/fuel mixture through spark arrestors (7) to the cylinders for combustion.