High-Pressure Oil: Powering Fuel Injectors For Optimum Performance

Fuel injectors are the primary means of getting fuel into a car's engine cylinder so that it can combust and the car can be driven. The fuel injector is supplied with pressurised fuel by the fuel pump in your car, and it is capable of opening and closing many times per second. When the injector is energised, an electromagnet moves a plunger that opens the valve, allowing the pressurised fuel to squirt out through a tiny nozzle. The nozzle is designed to atomise the fuel to make as fine a mist as possible so that it can burn easily. The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open, which is called the pulse width and is controlled by the engine control unit (ECU). The ECU also uses sensors to monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust, to fine-tune the fuel consumption and delivery so that the air-to-fuel ratio is just right.

One type of fuel injection system is the hydraulically activated, electronically controlled, unit injector (HEUI) fuel system, which was considered a modern marvel when it was introduced in 1994. Instead of a conventional injection pump, HEUI systems use a high-pressure oil pump that creates a volume of oil for the injectors to use. The injection pressure regulator is then responsible for creating injection pressures.

Another type of fuel injection system is the throttle body fuel injection system, which incorporates electrically controlled fuel-injector valves into the throttle body. More modern engines use multi-port fuel injection systems, which have a fuel injector for each cylinder, usually located so that they spray directly at the intake valve.

Injector firing process

The injector firing process involves several components working together to inject fuel into the engine's combustion chamber. Here is a detailed breakdown of the process:

Electronic Solenoid Activation:

The process begins when the electronic solenoid (A) receives an electrical signal from the Injector Drive Module (IDM) or Fuel Injection Control Module (FICM). This energizes the solenoid, initiating the fuel injection sequence.

Poppet Valve Operation:

The energized solenoid pulls the poppet valve (B) off its seat, closing the oil drain pathway. This action also opens the inlet for high-pressure oil to enter the injector.

High-Pressure Oil Transfer:

With the poppet valve open, high-pressure oil starts to flow through it and applies pressure to the intensifier piston (C). In the case of the 7.3L engine, the injection control pressure (ICP) of 3,000 psi is converted to an impressive 21,000 psi of fuel injection pressure.

Plunger and Nozzle Needle Movement:

The intensifier piston, with a larger surface area, transfers the high-pressure oil force to the plunger (D), forcing it downward. This downward motion also forces the nozzle needle to lift, pressurizing the fuel in the plunger cavity.

Nozzle Opening and Fuel Injection:

As the plunger moves downward, it eventually opens the nozzle (E), releasing the pressurized fuel into the combustion chamber. This precise injection of fuel is crucial for engine performance and efficiency.

Refilling the Injector:

After the injection, the void (F) created above the intensifier piston and plunger is refilled with high-pressure oil from the oil rails within the cylinder heads. This ensures that the injector is ready for the next cycle.

End of Injection:

To end the injection process, the PCM cancels the fuel delivery signal sent to the IDM, which in turn stops the electronic pulse to the injector solenoid. The poppet valve closes, preventing further high-pressure oil from entering the injector. The excess pressurized oil above the intensifier piston is drained, and the intensifier piston and plunger move upward, returning to their original positions.

The injector firing process is a complex sequence of events that involves precise timing and coordination between various components. It is a critical aspect of the engine's fuel injection system, ensuring the delivery of pressurized fuel into the combustion chamber for efficient engine operation.

High-pressure oil pumps

Unlike conventional pump systems, the HPOP doesn't create pressure in the usual way. Instead, oil pressure is determined by how much oil the pump sends through the pistons. Many HPOPs have seven pistons as part of a swashplate-style pump. The location and functionality of the pump depend on the manufacturer. For example, the Bosch high-pressure oil pump is gear-driven and works with a 7.3L Powerstroke engine, while a Siemens high-pressure oil pump is timed to the engine and sits in the crankcase of a 6.0L Powerstroke engine.

The HPOP is a relatively new invention, replacing the older HEUI (hydraulically activated, electronically controlled, unit injector fuel) system. While the HEUI system is considered outdated today, it was once a marvel of technology, offering computer-controlled timing advance, cleaner emissions, and increased horsepower and torque compared to its competitors. However, the HPOP has proven to be a more reliable and efficient way to ensure high-pressure oil reaches the parts of the engine that need it.

The HPOP works in tandem with other components, including the fuel injection system and the turbocharger, as part of a closed-loop injection control system. It plays a crucial role in ensuring the engine has the lubrication it needs to function properly and avoid damage.

The HPOP is designed to last a long time, but it will gradually lose its power. While it's rare for the pump to stop working entirely, a burning smell or blue smoke coming from the exhaust may indicate an oil leak. A lack of oil or oil pressure can be disastrous for the engine, as metal parts will start grinding against each other, leading to blown gaskets, leaks, and other issues.

To maintain the HPOP and ensure optimal performance, it's essential to change the oil regularly and clean the oil filter to remove excess dirt and soot. Additionally, the oil cooler should be checked to prevent the oil from becoming too hot, as this can affect its ability to lubricate engine parts effectively.

Fuel injection nozzles

The design of fuel injection nozzles is critical to the performance and emissions of modern diesel engines. The injector nozzle's parameters, such as the injector seat, sac, nozzle hole size, and geometry, influence the combustion characteristics of the diesel engine. Additionally, the stability of emissions and performance over the engine's lifetime, as well as the mechanical durability of the injector, are affected by these design parameters.

The injector nozzle must produce a fuel spray that meets the performance and emissions requirements of the target market. The specific requirements for injection nozzles depend on the type of fuel system. For example, in a common rail fuel system, the nozzle operates under demanding tribological conditions and must be carefully designed to prevent leakage. In unit injector or unit pump systems, pressure pulsing creates demanding fatigue strength requirements, while in pump-line-nozzle systems, the hydraulic dead volume must be minimised.

In high-pressure oil injection systems, such as the HEUI (Hydraulically Activated, Electronically Controlled, Unit Injector) fuel system, a high-pressure oil pump is used instead of a conventional injection pump. This pump creates a volume of oil for the injectors to use, rather than pressure. The injection pressure regulator, controlled by the PCM (Powertrain Control Module), is responsible for creating injection pressures. In the case of the 7.3L Power Stroke engine, the injection pressure regulator generates pressures ranging from 450 to 3,000 psi.

The injector firing process in a HEUI injector can be understood through the following steps:

• The electronic solenoid is energised by the IDM (Injector Drive Module), causing the poppet valve to lift and opening the inlet for high-pressure oil.
• High-pressure oil transfers its pressure through the poppet valve, acting on the intensifier piston.
• The intensifier piston forces the plunger down, which pressurises the fuel in the plunger cavity and opens the nozzle, injecting fuel into the combustion chamber.
• The void created by the downward movement of the intensifier piston and plunger is refilled with high-pressure oil from the oil rails within the cylinder heads.
• The nozzle uses a check ball to seal during the plunger's downstroke, preventing high-pressure fuel leakage.

The design and functionality of fuel injection nozzles play a crucial role in achieving optimal combustion, ensuring stable emissions, and maintaining the durability of the injector and the engine as a whole.

Fuel injector cleaners

There are several fuel injector cleaners on the market, such as Chevron Techron, Lucas Fuel Injector Cleaner, and STP Super Concentrated Fuel Injector Cleaner. These products contain concentrated detergents that help dissolve and remove the harmful deposits that have built up on the fuel injectors.

The usage instructions for fuel injector cleaners may vary slightly between products, but generally, you simply pour the entire contents of the bottle into your gas tank before or after fuelling. It is recommended to use fuel injector cleaners regularly, such as with every oil change or after a certain number of miles (for example, every 4,000 miles).

Some people may be sceptical about the effectiveness of fuel injector cleaners, but there are many positive testimonials online. For example, one person with almost 220,000 miles on their car's fuel system saw an improvement in their mileage after using a fuel injector cleaner. They also noted that buying the product in bulk was the best way to maximise gains while keeping costs down.

It is important to note that fuel injector cleaners should not be used as a substitute for proper maintenance and repairs. If you are experiencing issues with your car, it is always best to consult a trusted mechanic for advice.

Fuel injection system components

Fuel injection systems are made up of several components, which work together to deliver the right amount of fuel into the engine. The main components include:

The Fuel Tank

The fuel tank stores the fuel and helps maintain its temperature below the flash point. It is also designed to be corrosion-resistant and leakproof, with the ability to withstand pressures of at least 30 kPa. Additionally, the fuel tank is equipped with a safety valve to relieve excessive pressure and dissipate heat from the fuel returning from the engine.

The Fuel Feed Pump

The fuel feed pump supplies fuel from the fuel tank to the injection pump. It has a spring-loaded plunger that is actuated by a push rod from the camshaft. When the push rod is at its minimum position, the spring force on the plunger creates suction in the pump, drawing fuel from the fuel tank. When the camshaft is turned to its maximum lift position, the plunger is lifted upwards, closing the inlet valve and forcing fuel through the outlet valve.

The Injection Pump

The injection pump, also known as the fuel injection pump, is responsible for delivering the right amount of fuel to the injector under high pressure. The pressure can range from 120 to 200 bar, and the fuel is injected at the correct instance into the injector fitted in each cylinder head. There are two types of injector pumps: distributor type pumps and jerk-type pumps.

The Injector

The injector is a critical component of the fuel injection system. It is an electronically controlled mechanical device that sprays or injects the fuel into the engine, creating a suitable air/fuel mixture for optimal combustion. The injector is located in the combustion chamber, inlet manifold, or throttle body. Injectors that also control the metering of fuel are called injection valves, while those that perform all three functions (metering, atomization, and injection) are called unit injectors.

The Electronic Control Unit (ECU)

The ECU, also known as the engine control unit or engine management system, plays a crucial role in the fuel injection system. It collects information from various engine sensors to determine the precise amount and timing of the fuel dose required for each cycle. Based on this information, the ECU sends a command electrical signal to the fuel injector coil, activating the injector and allowing fuel to pass into the engine. The ECU controls not only the fuel injection but also the ignition timing and other engine functions.

Frequently asked questions