Diesel Engine Fuel System

The fuel system on a diesel engine is a highly specialized set of components which must deliver the correct amount of fuel to the cylinder at the precise moment it is needed. A well-designed fuel system enables the engine to produce maximum power at maximum efficiency with a minimum of exhaust emissions.

Caterpillar diesel engines are all furnished with a fuel system based on a conventional design, utilizing unit injectors, but with differing means of injector actuation and control.

The engine driven transfer pump delivers fuel to the unit injectors via the secondary fuel filter. The pump is equipped with a pump-mounted safety valve and the fuel flow at rated rpm is listed in the technical data and varies with engine speed

Diesel Engine Fuel System

BRANCH-AUTOMOBILE ENGG.

SEMESTER-4^TH SEM,Summer-2022

NAME-Er.SIDHARTHA KUMAR MOHANTA

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Types of Diesel Fuel Injection Systems

Diesel fuel injection systems can be classified into three categories, as follows:

1. Pump-Line-Nozzle
2. Unit Injector
3. Common Rail

Diesel Engine Fuel System

Fuel System must ensure:

• The fuel is clean.
• There is no air or water in the fuel.
• The fuel is at the correct pressure.
• The fuel is at an acceptable temperature.

Fuel System

Diesel Fuels

1. Diesel fuel quality is an important factor in satisfactory engine life and performance.
2. Fuels must provide adequate combustion without producing excess contaminates that can harm the engine. Additionally, fuel selection involves economic and environmental considerations.
3. The availability of certain grades of diesel fuels may be cost prohibitive or inappropriate for various applications

Basic Fuel System

The basic fuel system common to all Caterpillar diesel engines, includes;

• A engine driven fuel transfer pump.
• A secondary fuel filter
• Unit fuel injectors
• A fuel pressure regulator.

Optional;

• Flexible hoses
• Manual fuel priming pump
• Duplex filter

Diesel Engine Fuel System

1. MUI Fuel System
2. EUI Fuel System
3. HEUI Fuel System
4. Common Rail Fuel System
5. ACERT Fuel Technology

Basic Fuel System

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• Common Rail Fuel System
• In this system fuel pressure is created to external to the injectors in a high –pressure fuel pump which is driven by engine. High pressure manifold that runs both sides of engine feeding high pressure fuel to the injectors. The electronic fuel injectors at each cylinder control the delivery and timing of the fuel injection(s).

Diesel Fuel System

High Pressure Rail

High Pressure Injection Pump

Advanced Efficiency Secondary Fuel Filters

Fuel Tank

Cooler

(optional)

Primary Fuel Filter/ Water Separator

Diesel Fuel System Design Considerations

Diesel fuel supply systems must ensure continuous and clean supply of fuel to the engine’s fuel system.

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The diesel fuel supply system typically has three major components: a fuel storage system, a fuel transfer system and a fuel filtration system.

Design Considerations

• Fuel Storage System;

Design Considerations

• Auxiliary, Day Tank are required in the following conditions;
• The main fuel tank is located on the same level but more than 15m (50ft) away.
• The main fuel tank is located 3.7m (12ft) or more below the engine.
• The main fuel tank is located above fuel injectors.
• Fuel Tank Material;
• Low carbon rolled steel are best.
• Zinc, either in the form of plating or as a major alloying component should not be used with diesel fuels.

Design Considerations

• Fuel Supply Piping;
• Fuel pressure measured in the fuel return line should be kept below 27kPa (4psi) for all models except 3300 (3psi) and 3600 (51psi) series.
• Black iron pipe is best suited for diesel fuel, copper may substituted.
• Valves and fittings may be cast iron or bronze. Do not use brass components; they may contain zinc.
• Fuel Filtration System;
• Primary fuel filter
• Water separator – Water in diesel fuel is absolutely unwanted. It is extremely important to maintain the water & sediments level at or below 0.1%.

Design Considerations

• Fuel Temperature;
• Fuel temperature supplied to engine can affect unit injector life and maximum power capability.
• The minimum allowable viscosity at the injectors is 1.4 cSt.
• Maximum fuel temperature limit of 66°C regardless of viscosity.
• Maximum allowable inlet fuel temperature to transfer pump:

– C7, C9, C15, C18, C27, C32 is 80°C (176°F)

– C175 is 70°C (158°F)

Additional Considerations

• Fuel Coolers
• Fuel Heaters
• Additional information can be found in Diesel Fuels & Diesel Fuel System Application & Installation Guide (LEBW4976)

Common Rail System

• Most flexible fuel system injection strategy

–Similar to HEUI system, injection quantity and pressure not tied to engine speed/load.

• Allows for noise reduction and less fuel consumption
• More flexible system for future engine rating expansion
• Supports increased injection pressure
• Current version easier to package in the engine head on HD engines

Fuel Filter

• All ACERT engines MUST use only CAT supplied secondary fuel filters. These are designed with the needs of the system in mind.
• Pre-Filters/Primary Filters must meet Caterpillar engine design requirements.
• No modifications are permitted between secondary filter and engine fuel return connection.

Fuel Oil System Considerations

• Fuel Storage
• Fuel Tank Size and Location
• Sufficient Capacity for Normal Comsumption
• Ability to Dissipate Heat
• Location Relative to Fuel Injectors
• Drainablility and Cleanability of Fuel Tanks
• Fuel Cleanliness
• Primary Fuel Filtration
• Duplex Filter with Differential Pressure Gauge
• Sized for Engine‘s Fuel Consumption Rate
• Both Filtration and Water Separation
• Fuel Purification

NETSCo

Fuel Transfer Pumps

Caterpillar engine-mounted transfer pumps are positive displacement gear-type or piston-type pumps, with a limited prime and lift capability.

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Caterpillar fuel pumps’ prime and lift capability is 3.7 m (12 ft), but pipe size, routing, and ambient temperature will impact this capability.

Fuel system Installation

Fill line - Located above the high fuel level, with outlet baffled to prevent agitation of sediment in the tank.

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Delivery line - Located near the bottom but not so low as to pick up collected sediment or condensation.

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• Return line - To carry excess fuel back to the auxiliary tank. Should have its outlet baffled for the reason described above.
• Overflow line - Allows excess fuel to return to the main tank in event of overfilling of the auxiliary tank.

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