What Is a Unit Injector?

In today’s modern age, people are always seeking new ways to improve their vehicle’s performance and efficiency. One such accessory for machinery powered by a diesel engine is the renowned unit injector. But what is a unit injector, and how can its application benefit your vehicle?

This article explains the importance and advantages of this type of fuel injection system by highlighting its uses and applications. To better understand how these systems impact your machinery, it also covers the different types of unit injectors and their characteristics. Continue reading to discover what is the purpose of a unit injector and its benefits!

What Is a Unit Injector?

In simple terms, a unit injector acts as a specific type of fuel injection system created by combining an injector nozzle and a high-pressure fuel pump. While the use of the injector is for directing the flow of high-pressure fluids, the pump is responsible for bringing fuel into the engine’s cylinders. 

Since such a fuel injector pump is most commonly installed in machinery run by a diesel engine, its main purpose is to deliver fuel into the combustion chamber through a direct injection. By injecting the right fuel quantity at precisely the right moment, it creates a cleaner and more efficient combustion.

Source: shutterstock.com / Photo Contributor: Kankawee Chotima

Unit injector components

Each unit injector consists of several basic components, which are as follows:

• Spring-loaded plunger – The central part of the unit injector which is responsible for generating the high-pressure
• Barrel – Designed to withstand high pressures; the barrel houses the plunger and helps it generate high-pressure
• Solenoid valve – Used to regulate the pressure build-up
• Nozzle valve – Enhances atomization and is used to spray the pressurized fuel into the combustion chamber
• Fuel supply port – Provides a pathway so the fuel can enter the unit injector from the fuel supply system

How unit injectors work

Since fuel injectors remove the need for high-pressure fuel pipes, they focus on accurate fuel injection and timing. To supply the necessary fuel at the precise moment, each unit injector is mounted directly on the engine and aligned with each cylinder. 

The unit injector builds up pressure with a plunger that compresses the fuel by moving up and down. Since this component is driven by the camshaft, it needs to be synchronized with the engine's crankshaft so the fuel injection happens at exactly the right moment in the engine’s cycle. 

Once the fuel has been pressurized, it’s moved to the nozzle, which is secured in place by a nozzle holder. Here, the fuel is broken into tiny droplets, a process known as atomization, and sprayed directly into the combustion chamber. As these fuel droplets mix with the air present in the chamber, they ignite and produce a controlled combustion that powers the engine.

What Is a Unit Injector Used For?

After elaborating on what is unit injection system, it’s important to highlight its uses and capabilities. Designed for high performance and control, this fuel system is most commonly installed in machinery that requires durability, high power, and fuel efficiency. So, some of the most common applications of unit injectors include the following:

• Commercial vehicles
• Heavy-duty trucks
• Industrial machinery
• Agricultural machinery
• Marine engines in ships

Types of Unit Injectors

Having covered the fundamentals of unit injectors, it’s essential to explore the various types available and their unique characteristics. Below are the three most common types of unit injectors:

• Mechanical unit injectors – Most commonly found in older diesel engines, mechanical unit injectors are mechanically operated by using a camshaft to drive the plunger and control the fuel injection timing. Although they are fairly low-priced and easy to maintain, they produce higher emissions and less fuel efficiency. 
• EUI (electronic unit injectors) – Commonly found in modern diesel engines, these unit injectors have an electronically controlled solenoid valve that manages the injection timing and duration. However, the plunger is still driven by a camshaft and it requires an ECU (electronic control unit) to operate. Even though they are more expensive and are more complex to maintain, EUIs have precise control over the fuel injection and better fuel efficiency.
• HEUI (hydraulically actuated electronic unit injectors) – Most common in heavy-duty machinery, HEUIs use hydraulic pressure to drive the plunger while the injection timing is controlled electronically. Although they’re the hardest to maintain, they allow the best control over the injection and drastically enhance the efficiency and power.

Conclusion

What is a unit injector? This component enhances your vehicle’s efficiency by directly injecting pressurized fuel into the combustion chamber. With different types of unit injector systems available, you can choose between mechanical, electronic, or hydraulically functioning options based on your needs. If you’re interested in upgrading your vehicle with a durable and reliable unit injector, check out the top-tier fuel injection pumps that Goldfarb & Associates offers for both new and remanufactured parts.