How Do Fuel Injectors Work?

The best fuel injectors allow an engine to achieve maximum power output while minimizing fuel consumption and emissions. Advanced injector technologies improve combustion efficiency by ensuring precise fuel delivery and optimal air-fuel mixing. As a result, they play a vital role in reducing carbon and greenhouse gas emissions.

In this article, we’ll explore what a fuel injector is and how it operates across various powertrain types — including diesel, natural gas, and hydrogen engines, as well as hydrogen fuel cell vehicles.

What Does a Fuel Injector Do?

A fuel injector precisely controls the delivery of fuel into an engine’s internal combustion chamber, where it mixes with air and ignites to generate power. Within this chamber, the chemical energy contained in fuels such as diesel, hydrogen, or natural gas is converted into mechanical energy that drives the vehicle. When triggered by the electronic control unit (ECU), the injector releases an exact quantity of fuel at the optimal moment, ensuring efficient combustion, improved performance, and reduced emissions.

How Does a Diesel Injector Work?

A diesel fuel injector is composed of a solenoid (an electromagnet), a nozzle, and a needle valve housed within the injector body. In modern direct-injection diesel engines, fuel is injected directly into the combustion chamber rather than the intake port.

Inside the cylinder, air is compressed by the upward movement of the piston. As the piston approaches the top of its stroke, the engine control unit (ECU) sends an electrical signal to the solenoid, which lifts the injector needle and allows high-pressure fuel—reaching up to 37,000 psi (2,550 bar)—to be sprayed through the nozzle into the combustion chamber. The extreme heat from the compressed air causes the air-fuel mixture to auto-ignite, producing the power that drives the pistons.

The combination of very high injection pressure and ultra-fine nozzle holes ensures thorough atomization and precise fuel-air mixing, enabling engines to meet stringent emissions standards. Additionally, modern diesel injectors can deliver multiple injection pulses during a single combustion cycle, improving combustion efficiency, reducing noise, and lowering emissions.

How Does a Natural Gas Injector Work?

Natural gas engines operate in a similar way to gasoline engines, as both rely on a spark plug to ignite the air-fuel mixture—unlike diesel engines, which use compression ignition.

In these systems, natural gas is compressed and stored in a high-pressure tank, usually positioned at the rear of the vehicle. The gas then passes through a pressure regulator, which reduces its pressure to a suitable level for precise fuel delivery through the injector. When the electronic control unit (ECU) sends a signal, the injector opens and releases the correct amount of fuel into the intake air stream. This air-fuel mixture then flows into the combustion chamber, where it is ignited by the spark plug, generating power.

Natural gas is a lower carbon-intensity fuel compared to diesel, making it a key technology for fleets seeking to reduce carbon emissions today. Moreover, when sourced as Renewable Natural Gas (RNG), it can even achieve negative carbon intensity, offering an immediate and impactful path toward cleaner transportation.

How does a hydrogen ICE injector work?

Hydrogen engines have a high degree of components in common with natural gas and diesel engines. Cummins’ hydrogen engines are built on the cutting-edge fuel-agnostic engine platform. Though they share common components, hydrogen engines have specific requirements for regulating and injecting fuel. This is because hydrogen is more flammable than diesel and is easier to ignite in a combustion chamber. Because of this, hydrogen engines can have “pre-ignition” issues, which may cause backfiring. One way to overcome pre-ignition issues is for an engine to use a direct injection system. Direct injection systems introduce hydrogen directly into the cylinders. Cummins is currently developing a 15-liter hydrogen engine that uses direct injection.

What is the injector system in fuel cell vehicles?

Hydrogen fuel cell vehicles harness electrical energy produced by splitting a hydrogen atom into protons and electrons and reacting it with oxygen. On fuel cells, the hydrogen delivery system must provide sufficient fresh flow of hydrogen to the anode side of the fuel cell stack to meet the electrical power demands of the application. This can be accomplished using either a hydrogen injector or proportional valve, both of which accurately regulate the flow of hydrogen to the stack. Unlike diesel, natural gas, and hydrogen internal combustion engines (ICE), fuel cells do not have any carbon or pollutant emissions. The byproducts of splitting a hydrogen atom in a fuel cell are electricity, heat, and water vapor.

What is the role of fuel injectors in the energy transition?

Fuel injectors are more than just a component in engines — they play a vital role in the global energy transition from fossil fuels to cleaner energy sources. By optimizing fuel consumption in traditional diesel engines and enabling the use of alternative fuels such as natural gas, hydrogen internal combustion engines (ICE), and hydrogen fuel cells, fuel injectors support trucking fleets’ efforts to reduce carbon and greenhouse gas emissions.