Fuel-Injected Cars: Maintaining Optimum Fuel Pressure

Fuel injectors are a modern necessity for all automobiles. They are electronically controlled mechanical equipment, placed at a particular angle to inject the right amount of fuel into the engine's combustion chamber. The injectors are designed to open and close multiple times per second, with their position varying according to different engine designs. They are usually mounted on the engine head, with a tip inside the combustion chamber, and they control the fuel-to-air ratio to ensure perfect combustion. Fuel injectors have become essential to meet stricter emissions requirements and improve fuel efficiency. They provide a more precise delivery of fuel, resulting in enhanced combustion efficiency, increased power output, and reduced emissions.

Fuel injectors

A typical fuel injection system consists of several components, including the fuel injectors themselves, a fuel rail, a rail pressure sensor, a medium-pressure fuel pump, and various sensors. The fuel pump pressurizes the fuel, increasing its pressure from around 40-60 psi to between 1500-4500 psi. The fuel injectors are then responsible for spraying this pressurized fuel directly into the cylinders.

The fuel rail plays a crucial role in delivering the fuel from the pump to the injectors, while the rail pressure sensor measures the pressure in the rail and sends this information back to the engine control unit (ECU). This allows the ECU to adjust the fuel pressure as needed to ensure optimal engine performance.

There are two main types of fuel injectors: mechanical and electronic. In a mechanical system, the injector is spring-loaded into the closed position and is opened by fuel pressure. On the other hand, an electronic injector is also held closed by a spring but is opened by an electromagnet built into the injector body. The duration for which the injector stays open, known as the pulse width, is determined by the ECU, which calculates the appropriate amount of fuel needed by the engine.

By using fuel injectors, modern engines benefit from improved fuel efficiency, enhanced power output, and reduced emissions. The precise delivery of fuel through fuel injectors ensures a more accurate fuel-to-air mixture, resulting in a smoother and more efficient combustion process.

Fuel pump

A fuel pump is a crucial component in liquid-fuelled engines, such as petrol or gasoline and diesel engines. Its primary function is to transfer fuel from the fuel tank to the device where it is mixed with intake air, such as the carburettor or fuel injector. The type of fuel pump used depends on the type of engine and fuel injection system employed.

In carburetted engines, commonly found in older cars, lawnmowers, and power tools, low-pressure mechanical pumps mounted on the engine are typically used. These pumps operate at a relatively low fuel pressure of 10-15 psi and can be either diaphragm or plunger pumps.

On the other hand, fuel-injected engines utilise either electric fuel pumps or high-pressure mechanical pumps. Electric fuel pumps are often mounted inside the fuel tank and are used for lower-pressure manifold injection systems. High-pressure mechanical pumps, on the other hand, are mounted directly on the engine and are employed for high-pressure direct injection systems. These modern direct-injection engines operate at significantly higher pressures, up to 30,000 psi, and have various configurations, including common rail radial piston and inline designs.

The role of the fuel pump is to ensure the fuel reaches the engine, where it can be injected and combusted. In the case of fuel-injected petrol engines, the electric fuel pump located inside the fuel tank transports fuel to the engine, while a separate fuel pump pressurises the fuel to around 40-60 psi for direct-injection systems.

The placement of the electric fuel pump is flexible, as it does not rely on mechanical power from the engine. However, it is typically submerged in fuel at the bottom of the tank to ensure cooling and minimise the risk of fire.

Fuel rail

A fuel rail is a critical component of the fuel injector in a car. It is responsible for the stable supply of fuel to the injector, which in turn supplies it to the engine combustion chamber. The fuel rail helps achieve high levels of fuel efficiency and environmental performance.

In the context of fuel injection, a fuel rail is a pipe that supplies pressurised fuel to all of the injectors. Fuel injection has been the primary means of getting gasoline into the engine cylinder of modern cars since the 1990s. Fuel injectors deliver precise bursts of fuel, ensuring that the fuel is well mixed with the air before it enters the chamber.

There are two types of fuel injection systems: indirect injection and direct injection. In indirect injection, the fuel is injected into the inlet manifold or inlet port, rather than directly into the combustion chamber. This ensures that the fuel is well mixed with the air before it enters the chamber. In direct injection, the fuel is injected directly into the cylinder filled with compressed air.

Fuel pressure sensor

The engine control unit (ECU) uses information from various sensors to fine-tune fuel consumption and delivery, ensuring the correct air-to-fuel ratio. This includes data from the mass airflow sensor, oxygen sensor, throttle position sensor, coolant temperature sensor, voltage sensor, manifold absolute pressure sensor, and engine speed sensor.

The ECU adjusts the fuel rate based on input from the throttle valve position sensor, which detects how much air is entering the engine. This ensures that there is no hesitation when the gas pedal is pressed, as adequate fuel is supplied to match the air intake.

The fuel injectors are controlled by the ECU and are supplied with pressurized fuel by the fuel pump. They open and close multiple times per second, releasing pressurized fuel through a tiny nozzle that atomizes the fuel, creating a fine mist for easy combustion. The amount of fuel supplied is determined by the duration the fuel injector stays open, known as the pulse width.

Engine control unit (ECU)

An engine control unit (ECU) is a device that controls various subsystems of an internal combustion engine. The ECU is often referred to as the "brain" of the engine. It is a computer, a switching system, and a power management system all in one small case. The ECU controls the injection of fuel and, in petrol engines, the timing of the spark to ignite it.

The ECU has to deal with many variables when deciding the correct mixture ratio of air and fuel. Not only is the amount of mixture important, but the ratio of that mixture has to be correct. Too much fuel and too little oxygen, and the combustion is dirty and wasteful. Too little fuel and too much oxygen, and the combustion is slow and weak.

The ECU uses sensors to monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. It then uses this information to fine-tune the fuel consumption and delivery so that the air-to-fuel ratio is just right. This is known as "closed-loop control".

The ECU has many sensors that feed it information, including:

• Accelerator pedal position sensor
• Camshaft position sensor
• Coolant temperature sensor
• Crankshaft position sensor
• Inlet manifold pressure sensor (MAP sensor)
• Intake air temperature
• Intake air mass flow rate sensor (MAF sensor)
• Oxygen (lambda) sensor
• Throttle position sensor

The ECU can then perform an action on the engine, allowing the correct amount of power to control actuators precisely. This includes controlling fuel injector pulse width, the exact timing of the ignition system, the opening of an electronic throttle body, or the activation of a radiator cooling fan.

The ECU has many internal power requirements, and in order for many sensors and actuators to work, the correct voltage has to be supplied by the ECU to components around the car. This could be a steady 5 volts for sensors, or over 200 volts for the fuel injector circuits.

The first stage of ECU operation is power management, where various voltages are regulated and the power-up of the ECU is handled. The microprocessors can then begin to boot up, and the main microprocessor reads software from the memory and performs a self-check. It then reads data from the numerous sensors on the engine and converts them into useful information.

The ECU is constantly making calculations and adjustments to ensure the engine is running efficiently and the correct amount of fuel is being supplied.

Frequently asked questions