C175-20 Locomotive Engine Caterpillar

• Low-Pressure Fuel System

• High-Pressure Fuel System

• Electronic Control System for Fuel Delivery

These systems work together to ensure proper delivery of the fuel to each cylinder to achieve the required engine performance at all operation conditions.

Low-Pressure Fuel System

Illustration 1	g06105490
(1) Injector Cooling Circuit Back-Pressure Regulator

Illustration 2	g06105499
(2) Filter Outlet Pressure Sensor (3) Filter Inlet Pressure Sensor (4) Starting Priority Valve (5) System Regulator (6) Fuel Rail Pressure Sensor (7) Fuel Rail Temperature Sensor (8) Mechanical Fuel Transfer Pump (9) Fuel Transfer Pump Relief Valve (10) Fuel Transfer Pump Inlet Pressure Sensor (11) High-Pressure Fuel Pump (HPFP) Inlet Temperature Sensor (12) Secondary Fuel Filters

The basic function of the low-pressure fuel system is to provide fuel to the high-pressure fuel pump inlet at the:

• Proper Pressure

• Proper Temperature

• Proper Cleanliness Level

The fuel transfer pump (8) increases the fuel pressure for the transport through the secondary filters (12). The fuel transfer pump is equipped with a 950 kPa (138 psi) relief valve to prevent overpressure.

Pressure sensors are at the inlet (3) and outlet (2) of the secondary filters to monitor filter condition. A temperature sensor (11) measures the temperature of the fuel exiting the secondary filter. The fuel then reaches the high-pressure pump inlet where a system pressure regulator (5) maintains the pressure at 650 kPa (95 psi) to 950 kPa (138 psi).

During an engine start, a special starting priority valve (4) prevents flow to the injector cooling flow portion of the low-pressure fuel system until 250 kPa (36 psi) is reached. This action ensures adequate flow to the high-pressure pump at low engine cranking speeds. A certain amount of fuel flow bypasses the high-pressure pump and circulates through the injector cooling circuit. The injector cooling circuit back-pressure regulator (1) maintains the pressure in the injector cooling circuit at 350 kPa (51 psi). The unused fuel return then passes through the Mono-Block on the high-pressure pump and is returned back to the fuel tank.

Low-Pressure Fuel System Schematic

Illustration 3	g06112982
(A) Fuel Cooled Injectors (B) Double Wall Leakage Return (C) Injector Cooling Circuit Back-Pressure Regulator (D) Mono-Block (E) Fuel Cooled High-Pressure Pump (F) High-Pressure Pump Outlet (G) 2.6 mm Injector Cooling Supply Orifice (H) Anti-Reverse Flow Check (I) Fuel Transfer Pump Pressure Relief Valve (J) Low-Pressure Fuel System Regulator (K) Secondary Fuel Filters (L) Starting Priority Valve

The locomotive OEM system draws fuel from the tank and directs it through the primary fuel filters and fuel-water separator. The fuel is supplied to the mechanical fuel transfer pump. The fuel transfer pump must pressurize the fuel to approximately 250 kPa (36 psi) in order to open the check valve in the high-pressure fuel pump during engine starting.

The fuel transfer pump provides a fuel pressure of 600 to 850 kPa (87 to 123 psi) to the secondary filter inlet. After the fuel has been filtered, the fuel flows into the high-pressure fuel system. Some of the flow that is not used by the high-pressure fuel system is used to cool the injectors. The rest is recirculated back to the fuel transfer pump inlet. The pressure regulator is used to maintain the pressure in the low-pressure fuel system to a gauge pressure of 600 to 850 kPa (87 to 123 psi). Check valves are used to prevent fuel from draining from the high-pressure fuel system.

When the fuel system has air trapped in the fuel filters, lines, and other fuel system components, the engine could experience difficulty starting. The electric boost pump forces the air that is in the fuel out of the system through the injector cooling circuit.

Priming is required after servicing the fuel system such as changing the fuel filter. Priming is also recommended when the engine has not run for a long time. Refer to Locomotive OEM Operation and Maintenance Manuals for instructions on how to prime the fuel system.

Fuel Transfer Pump

Illustration 4	g06083236
(1) Fuel Transfer Pump (2) High-Pressure Fuel Pump

Illustration 5	g06083244
(3) Fuel Transfer Pump Pressure Relief Valve (4) Shaft Seal (5) Weep Hole (Do Not Obstruct)

The fuel transfer pump (1) is a fixed displacement gear pump that is driven by the high-pressure pump. The fuel transfer pump receives fuel from the primary fuel filtration unit. The pump sends the fuel through the secondary filters on the way to the high-pressure fuel pump. The fuel transfer pump also supplies cooling flow to the injectors, and the high-pressure pump.

The fuel transfer pump is mounted on the high-pressure pump (2). A relief valve (3) in the fuel transfer pump limits the outlet pressure to 950 kPa (138 psi). Other important parts include the shaft seal (4) and the weep hole (5) which prevent fuel in oil contamination.

High-Pressure Fuel System

Illustration 6	g06082425
(1) Injector (2) Accumulator-Quill Tube (3) Line Support Clamps (4) High-Pressure Injection Lines (5) Pump to Accumulator High-Pressure Lines (6) High-Pressure junction Block (7) High-Pressure Fuel Pump

The common rail high pressure fuel system on this engine consists of high-pressure fuel accumulator-quill tubes (2) that maintain a volume of fuel that is used to supply each cylinder as needed and high-pressure fuel lines (4) to transport fuel between the high-pressure fuel pump (7), high-pressure accumulator quill tubes (2), and the common-rail injectors (1).

The main components of this system Illustration 6 are between the high-pressure fuel pump (7) and the injectors (1):

• High-Pressure Fuel Pump to Junction Block Lines

• High-Pressure Junction Block

• Accumulator Quill Tubes

• Accumulator Quill to Accumulator Quill Fuel Injection Lines

The low-pressure fuel system provides fuel at the proper pressure, temperature, and cleanliness level to the high-pressure fuel pump. The high-pressure fuel pump pressurizes the fuel to the level required for the engine operating condition. System pressure in the high-pressure fuel system is controlled electronically via a fuel control valve, which regulates the amount of fuel that is allowed to enter the inlet of the pump. A pressure relief valve mounted on the high-pressure pump manifold mechanically limits the maximum fuel pressure in the system in the event of a malfunction.

High-Pressure fuel flows from a manifold on the high-pressure pump (7) to a high-pressure junction block (6), which distributes fuel to each engine cylinder bank via double-walled high-pressures lines (4). The double-wall serves to prevent the escape of any high-pressure fuel in the event of fuel leakage from the high-pressure system and therefore ensures safe containment of the fuel in the event of a high-pressure leak. The fuel is then transported through the high-pressure lines (4), through the accumulator quill tubes (2), and to the injectors (1). If leakage into the double-wall system occurs, the necessary repairs need to be performed as quickly as possible to prevent further damage to the high-pressure fuel system.

Fuel is transported to the modular accumulator-quill tubes via the double-walled injector lines. The modular accumulators contain an integral metallic filter to prevent debris from getting to the injectors as well as an integral flow limiting device that shuts off flow to the cylinder and prevents over fueling in the event of higher than expected fueling. Refer to Systems Operation, "Accumulator-Quill Tube", for information that is related to the operation of the accumulator-quill tubes.

The accumulator-quill tubes (2) transport high-pressure fuel through each cylinder head directly to electronically controlled injectors (1) that provide the proper injected fuel quantity and timing for the particular operating conditions. Refer to Systems Operation, "Fuel Injector" for information that is related to the operation of the fuel injectors (1).

High-Pressure Fuel Pump

Illustration 7	g06108774
(1) High-Pressure Fuel Pump

Illustration 8	g06108778
(2) Fuel Control Valve (3) Temperature Sensor - Dry Well Port (4) High-Pressure Manifold (5) Rail Pressure Sensor Port (6) Low-Pressure Mono-Block (7) High-Pressure Pump Inlet (8) Magnetic Oil Drain Plug

Illustration 9	g06112996
(9) Double-Wall O-ring (10) Rail Pressure Sensor

Note: The fuel rail pressure sensor is installed into the high-pressure fuel pump. This sensor has an integral crush washer and can only be used one time. Once it is removed from the high-pressure pump, it must be replaced with a new sensor.

The common rail fuel system high-pressure fuel pump on this engine is driven by an idler in the engine gear train. The flow of the low-pressure fuel into the high-pressure fuel pump is controlled by the fuel control valve (1). The fuel control valve (1) controls how much fuel is allowed into the pump, which determines the pressure in the high-pressure fuel rail.

The high-pressure pump receives fuel from the fuel transfer pump at 600 kPa (87 psi) to 850 kPa (123 psi) and to the required injection pressure. It provides pressurized fuel to the fuel injectors through the high-pressure fuel lines and accumulators.

The high-pressure manifold mounted to the top of the pump contains the rail pressure sensor port, dry-well temperature sensor port, pressure relief valve, and the outlet port for high-pressure fuel. The pump also has a low-pressure mono-block (6) on the rear of the pump, which houses low-pressure fuel system valves and regulators and the high-pressure pump fuel inlet port.

Note: The high-pressure manifold (4) and the low-pressure mono-block (6) are not serviceable and should not be tampered with and/or disassembled.

Note: If replacing the oil-lubricated high-pressure pump, it may contain residual oil from the performance testing completed at the factory. All oil and fuel connections and passages are plugged/capped with protective covers. Care should be taken to ensure removal of these protective covers upon installation.