C6.6 Industrial Engine Fuel Injection Caterpillar


Fuel Injection
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C6.6 Industrial Engine [KENR9109]
1.1. Introduction
2.2. High Pressure Fuel System
3.2. Components of the Fuel Injection System
4.1. Primary Filter/Water Separator
5.1. Secondary Fuel Filter
6.1. Fuel Pump Assembly
7.2. Shutoff
8.2. Control
9.1. Fuel Injectors
10.1. Fuel Manifold

Introduction



Illustration 1g02402177
Typical example
(1) Fuel strainer
(2) Electric transfer pump
(3) Primary fuel filter
(4) ECM that is fuel cooled.
(5) Secondary fuel filter
(6) Fuel Injection Pump
(7) Inlet pressure regulator
(8) Fuel manifold (rail)
(9) Pressure relief valve
(10) Electronic unit injector
(11) Fuel cooler (optional)
(A) Fuel tank

Fuel is drawn from the fuel tank through a fuel strainer to an external electric transfer pump. The fuel then flows to the 10 micron primary fuel filter and a water separator.

The fuel may flow to a fuel cooled ECM. The fuel then flows to a 4 micron secondary fuel filter.

The fuel flows from the secondary fuel filter to a pressure regulator. A pressure regulator that is installed in the low-pressure fuel system controls the fuel pressure to the fuel injection pump. The pressure regulator regulates the fuel at a pressure of 150 kPa (22 psi) when the engine is at idle speed.

From the pressure regulator, the fuel flows to the fuel injection pump. The fuel is pumped at an increased pressure of 200 MPa (29000 psi) to the fuel manifold (rail).

Fuel that has too high a pressure from the fuel manifold (rail) returns through the pressure relief valve to the return line. Fuel that is leak off from the electronic unit injectors flows to the return line. The fuel may then flow through an optional fuel cooler on the way back to the fuel tank.

High Pressure Fuel System



Illustration 2g02216334
Typical example
(1) Fuel injection pump
(2) Fuel temperature sensor
(3) Suction control valve for the fuel injection pump
(4) Pressure relief valve
(5) Electronic unit injector
(6) Fuel manifold (rail)
(7) Fuel pressure sensor
(8) Fuel transfer pump

The fuel injection pump (1) feeds fuel to the high-pressure fuel manifold (rail) (6). The fuel is at a pressure of 200 MPa (29000 psi). A pressure sensor (7) in the high-pressure fuel manifold (rail) (6) monitors the fuel pressure in the high-pressure fuel manifold (rail) (6). The ECM controls a suction control valve (3) in the fuel injection pump (1) in order to maintain the actual pressure in the high-pressure fuel manifold (6) at the desired level. The high-pressure fuel is continuously available at each injector. The ECM determines the correct time for activation of the correct electronic unit injector (5) which allows fuel to be injected into the cylinder. The leakoff fuel from each injector passes into a drilling which runs along the inside of the cylinder head. A pipe is connected to the rear of the cylinder head in order to return the leakoff fuel to the fuel tank.

Components of the Fuel Injection System

The fuel injection system has the following mechanical components:

  • Primary filter/water separator

  • Electric transfer pump

  • Fuel transfer pump

  • Secondary fuel filter

  • Fuel injection pump

  • Fuel injectors

  • Fuel manifold

  • Pressure relief valve

  • Fuel pressure sensor

  • Fuel temperature sensor

The following list contains examples of both service and repairs when you must prime the system:

  • A fuel filter is changed.

  • A low-pressure fuel line is replaced.

  • The fuel injection pump is replaced.

  • The ECM is replaced.

For the correct procedure to prime the fuel system, refer to Systems Operation, Testing and Adjusting, "Fuel System - Prime".

Primary Filter/Water Separator



Illustration 3g02214535
Typical example

The primary filter/water separator (1) is located between the electric lift pump and the secondary fuel filter. The primary filter/water separator (1) provides a 10 micron filtration level.

The primary filter/water separator can either be engine mounted or supplied loose. The primary filter/water separator is supplied with water in fuel switch (2).

Secondary Fuel Filter



Illustration 4g02214536
Typical example

The secondary fuel filter (1) is located after the primary fuel filter. The secondary fuel filter (1) provides a 4 micron filtration level.

Fuel Pump Assembly



Illustration 5g02216343
Typical example

The fuel pump assembly consists of a low-pressure transfer pump and a high-pressure fuel injection pump. The pump assembly is driven from a gear in the front timing case at engine speed. The fuel injection pump (1) has three plungers that are driven by a camshaft. The fuel injection pump (1) delivers a volume of fuel three times for each revolution. The stroke of the plungers are fixed.

The injector will use only part of the fuel that is delivered by each stroke of the pistons in the pump. The suction control valve (3) for the fuel injection pump (1) is controlled by the ECM. This maintains the fuel pressure in the fuel manifold (rail) at the correct level. A feature of the fuel injection pump (1) allows fuel to return to the tank continuously.

The fuel temperature sensor (2) measures the temperature of the fuel. The ECM receives the signal from the fuel temperature sensor (2). The ECM calculates the volume of fuel.

The fuel injection pump has the following operation:

  • Generation of high-pressure fuel

The fuel output of the fuel injection pump is controlled by the ECM in response to changes in the demand of fuel pressure.

Shutoff

The engine shuts off by preventing the electronic unit injectors from injecting. The ECM then closes the suction control valve to prevent the pressure in the fuel manifold (rail) from increasing.

Control



Illustration 6g02210619
Typical example of the electrical control system for the fuel system
(1) Electronic Control Module (ECM)
(2) Throttle position sensor
(3) Wastegate regulator
(4) Fuel rail pressure sensor
(5) Inlet manifold pressure sensor
(6) Atmospheric pressure sensor
(7) Coolant temperature sensor
(8) Inlet manifold air temperature sensor
(9) Secondary speed/timing sensor
(10) Primary speed/timing sensor
(11) Fuel injection pump
(12) Suction control valve for the fuel injection pump
(13) Fuel temperature sensor
(14) Electronic unit injectors

The ECM determines the quantity, timing, and pressure of the fuel in order to be injected into the fuel injector.

The ECM uses input from the sensors on the engine. These sensors include the speed/timing sensors and the pressure sensors.

The ECM controls the timing and the flow of fuel by actuating the injector solenoid.

The amount of fuel is proportional to the duration of the signal to the injector solenoid.

The ECM controls the fuel pressure by increasing or decreasing the flow of fuel from the fuel injection pump.

Fuel Injectors



Illustration 7g02290433
Typical example
(1) Electrical connections
(2) Bolt
(3) Clamp
(4) Combustion washer
(5) O-ring
(6) Fuel inlet

Note: If a replacement electronic unit injector is installed, the correct injector code must be programmed into the electronic control module. Refer to Troubleshooting, "Injector Code - Calibrate" for more information. The code that is required is located at Position (X). Record Code (X) before the electronic unit injector is installed.

The fuel injectors contain no serviceable parts apart from the O-ring seal and the combustion washer. The clamp and setscrew are serviced separately.

The pressurized fuel from the fuel manifold is injected into the combustion chamber by the electronic unit injector. The desired injection timing, injection quantity and injection pattern are controlled by the ECM depending on engine operating conditions.

The injection process is controlled using a two-way valve. The supply of electrical current to the solenoid controls the two-way valve. When the two-way valve is not energized the out orifice is closed and there is no fuel leak. In this condition the pressure in the control chamber and the pressure at the nozzle needle are the same. In this condition the spring pressure on the command piston keeps the needle closed.

When an injection of fuel is required, the electrical current from the ECM charges the solenoid, which in turn energizes the two-way valve and lifts the valve. When the valve lifts the valve uncovers the out orifice. The fuel starts to flow and reduces the pressure in the control chamber. When the pressure difference at the nozzle needle exceeds the combined pressure of the control chamber pressure and the spring pressure, the nozzle lifts to start the injection process. The fuel coming out of the nozzle is atomized and injected as a very fine spray.

When the injection needs to be stopped the electrical current to the solenoid is cut off and the pressure difference in the control chamber starts increasing. The increased pressure difference stops the injection process when the combined pressure exceeds the nozzle pressure.

The electronic unit injectors can be instructed to inject fuel multiple times during the combustion process. A close pilot injection occurs before the main injection. The close pilot injection helps to reduce NOx and noise. The main injection period helps to increase the torque of the engine. The after injection period helps to reduce the amount of smoke that is produced.

Fuel Manifold



Illustration 8g01911496
Typical example

The fuel manifold (2) stores high-pressure fuel from the fuel injection pump. The high-pressure fuel will flow to the injectors.

The fuel pressure sensor (3) measures the fuel pressure in the fuel manifold (2).

The pressure relief valve (1) will prevent the fuel pressure from getting too high.

The fuel pressure sensor must be replaced with the fuel manifold (rail). The pressure relief valve can be serviced as a separate component.

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