Fuel System 3408E and 3412E Part 3 - Caterpillar Electronic Engine
Fuel System - 3408E and 3412E Industrial Engines
Components of the HEUI Injector
The HEUI injector serves four functions. The HEUI injector pressurizes supply fuel from 450 kPa (65 psi) to 160 MPa (23500 psi). The HEUI injector functions as an atomizer by pumping high pressure fuel through orifice holes in the unit injector tip. The HEUI injector delivers the correct amount of atomized fuel into the combustion chamber and the injector tip disperses the atomized fuel evenly throughout the combustion chamber.
Components of the HEUI injector
(1) Solenoid
(2) Poppet valve
(3) Intensifier piston
(4) Plunger
(5) Plunger cavity
(6) Barrel
(7) Nozzle assembly
The HEUI injector consists of five basic components:
-Solenoid (1)
-Poppet valve (2)
-Intensifier piston (3)
-Plunger (4)
-Barrel (6)
-Nozzle assembly (7)
Solenoid
The solenoid (1) is an electromagnet. When the solenoid is energized, the solenoid creates a very strong magnetic field. This magnetic field attracts the armature which is connected to the poppet valve (2) by an armature screw. When the armature moves toward the solenoid, the armature lifts the poppet valve off the poppet valve's lower seat. Energizing the solenoid and lifting the poppet valve off the poppet valve's lower seat is the beginning of the fuel injection process.
Poppet Valve
The poppet valve (2) has two positions which are opened and closed. In the closed position, the poppet is held on the lower poppet seat by a spring. The closed lower poppet seat prevents high pressure actuation oil from entering the unit injector. The open upper poppet seat vents oil in the cavity that is above the intensifier piston (3) to the drain port. The oil is vented to the drain port through the upper portion of the unit injector. In the open position, the solenoid (1) is energized and the poppet valve is lifted off the poppet valve's lower seat. When the poppet valve is lifted off the poppet valve's lower seat, the lower poppet seat opens allowing high pressure actuation oil to enter the unit injector. When the high pressure actuation oil enters the unit injector, the high pressure actuation oil pushes on the top of the intensifier piston. The poppet is closed against the upper seat of the poppet valve and this blocks the path to the drain port. Blocking the path to the drain prevents the leakage of high pressure actuation oil from the unit injector.
Intensifier Piston
The surface area of intensifier piston (3) is six times larger than the surface area of plunger (4). This larger surface area provides a multiplication of force. This multiplication of force allows 24 MPa (3500 psi) of actuation oil to produce 162 MPa (23500 psi) of fuel injection pressure. When poppet valve (2) moves away from the lower poppet seat, high pressure actuation oil enters the unit injector. When the high pressure actuation oil enters the unit injector, the high pressure actuation oil pushes on the top of the intensifier piston. Pressure rises on top of the intensifier piston and the pressure pushes down on the intensifier piston and the plunger. The downward movement of the plunger pressurizes the fuel in plunger cavity (5). The pressurized fuel in the plunger cavity causes nozzle assembly (7) to open. When the nozzle assembly opens, the fuel delivery into the combustion chamber begins. A large O-ring around the intensifier piston separates the oil above the intensifier piston from the fuel below the intensifier piston.
Barrel
The barrel (6) is the cylinder that holds plunger (4). The plunger moves inside the barrel. The plunger and barrel together act as a pump. Both the plunger and the barrel are precision components that have a working clearance of only 0.0025 mm (0.00010 inch). These tight clearances are required in order to produce injection pressures that are over 162 MPa (23500 psi) without excessive leakage.
Note: A small amount of controlled leakage is required in order to lubricate the plunger which prevents wear.
Nozzle Assembly
Nozzle Assembly
(1) Inlet fill check ball
(2) Case
(3) Check
(4) Tip
(5) Tip orifice holes
The nozzle assembly is similar to all other unit injector's nozzle assemblies. Fuel that has been pressurized to the injection pressure flows from the plunger cavity through a passage in the nozzle to the nozzle tip (4). Fuel flow out of the tip is stopped by check (3), which covers the tip orifice holes (5) in the end of the tip. The force of a spring holds the check down in the closed position. This prevents the leakage of fuel out of the tip and this prevents the leakage of combustion gas into the unit injector when the cylinder fires.
When the injection pressure increases to approximately 28 MPa (4000 psi), the hydraulic force from the fuel overcomes the spring force. When the spring force is overcome by the hydraulic force, the check moves away from the tip. When the check moves away from the tip, the check is in the open position. The amount of pressure that is required to open the check is called the Valve Opening Pressure (VOP). The fuel flows out of the tip orifice holes in the end of the tip and the fuel flows into the combustion chamber. The check remains open and fuel continues to flow out of the tip until fuel injection pressure drops below 28 MPa (4000 psi). When the pressure drops, the check closes and fuel injection is stopped. The amount of pressure that allows the check to close is called the Valve Closing Pressure (VCP).
Note: VOP and VCP will vary among applications and horsepower ratings in order to meet exhaust emission standards. The above values were used as illustrations only.
The inlet fill check ball (1) unseats during upward travel of the plunger in order to allow the plunger cavity to refill. The inlet fill check ball seals during the downward stroke of the plunger in order to prevent fuel injection pressure leakage into the fuel supply.
Read More:
Fuel System C11 and C13 - Caterpillar Electronic Engine
Fuel System C15, C16, and C18 - Caterpillar Electronic Engine
Fuel System C7 and C9 - Caterpillar Electronic Engine
Operation of the HEUI Injector
There are three stages of injection with the HEUI injector:
-Pre-injection
-Injection
-End of injection
Pre-Injection
Pre-injection cycle
(1) Drain port
(2) High pressure oil inlet port
(A) Low pressure oil
(B) Fuel supply pressure
(C) Actuation oil pressure
(D) Mechanical movement of internal components
During the pre-injection cycle, all internal components have returned to the spring loaded position. The solenoid is not energized and the lower poppet seat is closed. The lower poppet seat blocks high pressure oil inlet port (2). Actuation oil pressure is blocked from entering the unit injector. The plunger and the intensifier piston are at the top of the bore and the plunger cavity is full of fuel. Fuel pressure in the plunger cavity is equal to the fuel supply pressure. The fuel supply pressure is approximately 450 kPa (65 psi).
Injection
Components of the HEUI Injector
The HEUI injector serves four functions. The HEUI injector pressurizes supply fuel from 450 kPa (65 psi) to 160 MPa (23500 psi). The HEUI injector functions as an atomizer by pumping high pressure fuel through orifice holes in the unit injector tip. The HEUI injector delivers the correct amount of atomized fuel into the combustion chamber and the injector tip disperses the atomized fuel evenly throughout the combustion chamber.
Components of the HEUI injector
(1) Solenoid
(2) Poppet valve
(3) Intensifier piston
(4) Plunger
(5) Plunger cavity
(6) Barrel
(7) Nozzle assembly
The HEUI injector consists of five basic components:
-Solenoid (1)
-Poppet valve (2)
-Intensifier piston (3)
-Plunger (4)
-Barrel (6)
-Nozzle assembly (7)
Solenoid
The solenoid (1) is an electromagnet. When the solenoid is energized, the solenoid creates a very strong magnetic field. This magnetic field attracts the armature which is connected to the poppet valve (2) by an armature screw. When the armature moves toward the solenoid, the armature lifts the poppet valve off the poppet valve's lower seat. Energizing the solenoid and lifting the poppet valve off the poppet valve's lower seat is the beginning of the fuel injection process.
Poppet Valve
The poppet valve (2) has two positions which are opened and closed. In the closed position, the poppet is held on the lower poppet seat by a spring. The closed lower poppet seat prevents high pressure actuation oil from entering the unit injector. The open upper poppet seat vents oil in the cavity that is above the intensifier piston (3) to the drain port. The oil is vented to the drain port through the upper portion of the unit injector. In the open position, the solenoid (1) is energized and the poppet valve is lifted off the poppet valve's lower seat. When the poppet valve is lifted off the poppet valve's lower seat, the lower poppet seat opens allowing high pressure actuation oil to enter the unit injector. When the high pressure actuation oil enters the unit injector, the high pressure actuation oil pushes on the top of the intensifier piston. The poppet is closed against the upper seat of the poppet valve and this blocks the path to the drain port. Blocking the path to the drain prevents the leakage of high pressure actuation oil from the unit injector.
Intensifier Piston
The surface area of intensifier piston (3) is six times larger than the surface area of plunger (4). This larger surface area provides a multiplication of force. This multiplication of force allows 24 MPa (3500 psi) of actuation oil to produce 162 MPa (23500 psi) of fuel injection pressure. When poppet valve (2) moves away from the lower poppet seat, high pressure actuation oil enters the unit injector. When the high pressure actuation oil enters the unit injector, the high pressure actuation oil pushes on the top of the intensifier piston. Pressure rises on top of the intensifier piston and the pressure pushes down on the intensifier piston and the plunger. The downward movement of the plunger pressurizes the fuel in plunger cavity (5). The pressurized fuel in the plunger cavity causes nozzle assembly (7) to open. When the nozzle assembly opens, the fuel delivery into the combustion chamber begins. A large O-ring around the intensifier piston separates the oil above the intensifier piston from the fuel below the intensifier piston.
Barrel
The barrel (6) is the cylinder that holds plunger (4). The plunger moves inside the barrel. The plunger and barrel together act as a pump. Both the plunger and the barrel are precision components that have a working clearance of only 0.0025 mm (0.00010 inch). These tight clearances are required in order to produce injection pressures that are over 162 MPa (23500 psi) without excessive leakage.
Note: A small amount of controlled leakage is required in order to lubricate the plunger which prevents wear.
Nozzle Assembly
Nozzle Assembly
(1) Inlet fill check ball
(2) Case
(3) Check
(4) Tip
(5) Tip orifice holes
The nozzle assembly is similar to all other unit injector's nozzle assemblies. Fuel that has been pressurized to the injection pressure flows from the plunger cavity through a passage in the nozzle to the nozzle tip (4). Fuel flow out of the tip is stopped by check (3), which covers the tip orifice holes (5) in the end of the tip. The force of a spring holds the check down in the closed position. This prevents the leakage of fuel out of the tip and this prevents the leakage of combustion gas into the unit injector when the cylinder fires.
When the injection pressure increases to approximately 28 MPa (4000 psi), the hydraulic force from the fuel overcomes the spring force. When the spring force is overcome by the hydraulic force, the check moves away from the tip. When the check moves away from the tip, the check is in the open position. The amount of pressure that is required to open the check is called the Valve Opening Pressure (VOP). The fuel flows out of the tip orifice holes in the end of the tip and the fuel flows into the combustion chamber. The check remains open and fuel continues to flow out of the tip until fuel injection pressure drops below 28 MPa (4000 psi). When the pressure drops, the check closes and fuel injection is stopped. The amount of pressure that allows the check to close is called the Valve Closing Pressure (VCP).
Note: VOP and VCP will vary among applications and horsepower ratings in order to meet exhaust emission standards. The above values were used as illustrations only.
The inlet fill check ball (1) unseats during upward travel of the plunger in order to allow the plunger cavity to refill. The inlet fill check ball seals during the downward stroke of the plunger in order to prevent fuel injection pressure leakage into the fuel supply.
Read More:
Fuel System C11 and C13 - Caterpillar Electronic Engine
Fuel System C15, C16, and C18 - Caterpillar Electronic Engine
Fuel System C7 and C9 - Caterpillar Electronic Engine
Operation of the HEUI Injector
There are three stages of injection with the HEUI injector:
-Pre-injection
-Injection
-End of injection
Pre-Injection
Pre-injection cycle
(1) Drain port
(2) High pressure oil inlet port
(A) Low pressure oil
(B) Fuel supply pressure
(C) Actuation oil pressure
(D) Mechanical movement of internal components
During the pre-injection cycle, all internal components have returned to the spring loaded position. The solenoid is not energized and the lower poppet seat is closed. The lower poppet seat blocks high pressure oil inlet port (2). Actuation oil pressure is blocked from entering the unit injector. The plunger and the intensifier piston are at the top of the bore and the plunger cavity is full of fuel. Fuel pressure in the plunger cavity is equal to the fuel supply pressure. The fuel supply pressure is approximately 450 kPa (65 psi).
Injection