How Does A Common Rail Diesel Engine Work?

The high-pressure pump pressurizes the gasoline before transferring it to the rail, which acts as a pressure accumulator and reservoir. An electronically controlled valve regulates the pressure, ensuring that the rail maintains the precise pressure required by the ECU.

The gasoline then flows into the injectors, filling two spaces: one above and one below the nozzle’s needle. The two forces balance each other out, and a spring keeps the needle closed. When a solenoid or piezoelectric valve opens, the top compartment, known as the control chamber, can be vented.

This upper space empties out when the electronic control unit opens the valve. The pressure in the lower chamber lifts the needle up, opening the nozzle, and fuel is injected into the combustion chamber until the signal to the valve is cut and the valve closes again; at this point, the pressure in the control chamber causes the needle to close.

How a common rail fuel system works?

Fuel is delivered to the injectors via a high-pressure accumulator known as the rail in the common rail system. A high-pressure fuel pump supplies the rail. Electronically regulated pressure in the rail, as well as the start and end of the signal that triggers the injector for each cylinder.

What is the difference between common rail diesel and direct injection?

In a diesel or gasoline direct injection system, a common rail is one of the most critical components. The primary difference between a direct and a conventional injection is how the fuel is delivered and how it interacts with the incoming air. The gasoline is directly delivered into the combustion chamber with a direct injection system, skipping the waiting phase in the air intake manifold. The fuel is squirted directly where the combustion chamber is hottest, controlled by the electronic unit, resulting in a more equal and thorough burn.

Reduced exhaust and noise pollution, higher fuel efficiency, and enhanced overall engine performance are the key benefits of common rail direct fuel injection.

A high-pressure pump, injectors, a rail, and an electronic control unit make up the system.

A large metal cylinder serves as the common rail. It accepts high-pressure fuel from the pump and distributes it to the injectors. The current engines’ design has resulted in an increase in fuel pressure. For better fuel efficiency and performance, both diesel and gasoline engines are becoming smaller and lighter, which raises fuel pressure and establishes whole new demands for the production of a high-quality common rail.

First and foremost, the component’s geometrical precision is crucial. Better common rail performance is aided by precise design. Failures can result from even minor changes in size or shape. It’s important to define the proper specifications during the design phase, but it’s much more important to stick to them during the manufacturing process.

The importance of material selection should not be overlooked. Strength and corrosion resistance are ensured by good mechanical qualities. Steel and stainless steel are often used materials. The common rail for a diesel engine is constructed of steel, whereas the common rail for a gasoline engine is made of stainless steel, because the fuel is too corrosive for steel, and stainless steel has a higher corrosion resistance than steel.

The common rail’s quality is quite important. Breakages and leaks might occur as a result of damage, causing the vehicle to become immobile or catch fire. Therefore

Any common rail issues that may arise during the manufacturing process must be addressed. Forging is the most significant contribution to the effective prevention of component failures. By filling empty gaps inside the metal while deforming and shaping it with localized compressive stresses, forging, particularly hot forging, strengthens the material. A forged common rail is more durable and resists pressure and rust better.

What pressure does a common rail diesel run at?


Common rail systems were introduced to mainline industry in the late 1990s, and electronic control fuel systems were used primarily to fulfill pollution legislation.

A direct fuel injection system for petrol and diesel engines is known as common rail direct fuel injection. It uses a high-pressure (2,000 BAR – 29,000 PSI) fuel rail to supply individual solenoid valves on diesel engines, rather than a low-pressure fuel pump to feed unit injectors or pump nozzles.

Electronically controlled injectors spray very small volumes of diesel fuel into the engine. The engine control unit is in charge of them (ECU).

A mechanical high-pressure pump installed on the engine provides high-pressure gasoline. This high-pressure fuel is held in a reservoir known as the common rail until the injectors demand it.

The diesel is atomized into little droplets thanks to the high pressure. This translates to more efficient combustion, lower emissions, and quieter operation. All of these characteristics are present in modern common rail diesel systems.

In a common rail diesel system, the diesel fuel is always accessible for the engine to use, regardless of engine speed. It’s always there, and it’s available at a high pressure. This implies that even when the engine is just ticking over, or at low revs, high-pressure gasoline is available. Earlier conventional diesel systems, known as rotary diesel, are mostly regulated mechanically.

How does one of Ford Component Manufacturing’s metal pressed components get involved with this diesel system? To see the Copper Washers we press for the automotive sector, we must dig deep into the bowels of the car assembly. In a complex assembly, a simple metal pressed part plays a significant role.

The following are the major components of the common rail system, as shown in the diagram:

  • The high-pressure pump is supplied with fuel by an electric feed pump (which is not present on all systems).
  • Filter – this must be updated according to the manufacturer’s instructions to ensure system cleanliness and longevity.
  • The high-pressure pump is the central component of the fuel system. This is where the pressure of diesel fuel is increased – it is engine driven, system dependent, and may generate in excess of 2,000 BAR – for comparison, a typical automobile tyre pressure is roughly 2.5 to 3.5 BAR.
  • Control valve for high pressure (not present on all systems) – electrically regulates the pressure generated by the pump (ECM Controlled)
  • The ‘common rail’ is where fuel is stored and delivered to injectors for injection.
  • Injectors – the ECM controls and operates the injectors in the common rail system after taking into account multiple sensor and signal inputs. Manufacturing tolerances and components are identical to those used in high-pressure pumps, and they are vital to the injector’s operation and longevity.
  • Engine Control Module (ECM), which collects feedback from the numerous sensors in the system and regulates the pressure and fuel injection accordingly, is the EDC control unit.

Finally, we can observe the Copper Washer, a metal pressing created by Ford Component Manufacturing for the automotive industry.

Hot combustion gases can enter the injector cavity if a pressed copper washer is missing or the injector is torqued incorrectly. When the engine is turned off, the lower fuel O-ring on the injector will fail, resulting in fuel leakage into the combustion chamber and hot combustion gases into the fuel system when the engine is operating.

Hydro-static engine lock-up and engine failure can occur if fuel leaks into the combustion chamber. When the engine is turned off and the fuel drips past the injector tip into the combustion chamber, this happens.

Fuel injector internal components will be seized and several injectors will fail as a result of combustion gases leaking into the fuel system. A combustion leak into the fuel system will contaminate all of the injectors since they share a common fuel rail within the cylinder head.

The presence of black soot on the bottom of the injector indicates that the injector was torqued incorrectly or that the pressed copper washer was missing.

Why do common rail injectors fail?

Today’s Common Rail injectors can make numerous injections in a single combustion cycle and inject fuel at far higher pressures – up to 30,000 psi – through clearances as small as 1 micron. While this has a number of advantages, including fewer emissions, increased fuel economy, and improved drivability, it also means they are more prone to wear and tear. In this article, we’ll look at the most prevalent reasons of injector failure, as well as the symptoms and how to detect them for the best injector service.

Why do Common Rail injectors fail?

Despite the fact that Common Rail injectors are built to last, developments in injection technology mean they are more susceptible to wear from issues such as:

  • Contamination by particles: With tolerances as tiny as a human hair, even the tiniest particles can cause substantial damage. These minute particles can damage the control valve and ball as a result of insufficient filtration, resulting in a weak seal between the two. This can change the fuel spray pattern over time, affecting the amount, timing, and distribution of gasoline injected.
  • Water contamination is another typical cause of Common Rail injector failure. Excess water in the fuel can contaminate the injectors. Water can infiltrate gasoline if it is not stored or handled properly, reacting with the chemicals to corrode metal surfaces and impair lubrication between moving parts. This can cause both the injectors and the high-pressure fuel pump to prematurely wear out.
  • Deposit formation: Any fuel left in the injector after the engine has been turned off will be effectively ‘baked’ by the residual heat, resulting in carbon deposits, commonly known as coking. These deposits will build up around the nozzle tip and the injector’s internal parts if they are not removed, causing the needle to stick. This can wreak havoc on both the number and timing of injections.
  • Incorrect installation: Inadequate installation might potentially lead to premature failure. A missing or improperly positioned nozzle washer, for example, will allow combustion residue to escape through the nozzle washer. Seal rings, on the other hand, can readily roll out of their grooves. While these may appear to be minor difficulties, they can lead to far more serious issues such as poor injector function, starting, and fuel efficiency.

Symptoms of a faulty Common Rail injector?

The spray of gasoline into the combustion chamber will very definitely be disrupted by a defective fuel injector. In the worst-case scenario, it may even prevent it from happening at all. In any case, it will have an impact on vehicle performance, resulting in a variety of symptoms:

  • Check engine light: If the engine isn’t working as it should, the engine management light will illuminate. To confirm the fault code, you’ll need a diagnostic scan tool.
  • Rough idling: When fuel delivery is limited, the RPM at idle drops, resulting in a rough idle. The car will eventually stall if this value becomes too low.
  • Engine knock: When the fuel isn’t ignited properly, for example, due to an incorrect air-fuel mixture, it can lead to premature detonations, which are audible as a knock or ping from the engine.
  • Engine surge can also be caused by a defective injector supplying too much gasoline to the cylinder. Under sustained load and throttle, engine rpm will continue to fluctuate if this happens.
  • Engine misfire: if the fuel supply is disrupted, the engine’s cylinders may be unable to produce adequate power to the vehicle, resulting in misfiring.
  • Fuel leakage: if there is fuel on the injector’s exterior or nearby, the injector could be destroyed. Alternatively, the seal could have deteriorated.
  • Fuel efficiency is poor because the ECU compensates for defective injectors by over-fueling. As a result, the engine runs rich, consuming more gasoline than is required.
  • Increased emissions: a faulty injector can cause incomplete combustion of diesel fuel, resulting in higher emissions in diesel cars.

How to diagnose a faulty Common Rail injector

If you suspect the Common Rail diesel injector is to blame for any of the aforementioned problems, it’s critical to undertake a thorough diagnosis to determine the actual cause:

  • Identify the error code: The first step in diagnosing Common Rail issues is to check the vehicle’s onboard diagnostics (OBD). You may quickly discover trouble codes and narrow down your diagnosis by using a high-quality all-makes diagnostic tool like Delphi Technologies’ DS solution.
  • Check the injectors: If the OBD has generated a fuel injection system error code, the injector functionality should be checked. The injectors can be connected to tools like Delphi Technologies’ Sealed Rail Diagnostic Kit, which eliminates the requirement for a complete system removal and retrofit. It gathers and measures back leakage flow from injectors, indicating which injectors may be defective and need to be replaced. Garages can save time and money by changing individual injectors rather than the entire set.
  • Check the Common Rail pump’s function: Next, install the Sealed Rail Kit directly onto the pump’s high-pressure outlet pipe and crank the engine to record system pressure. The findings are displayed digitally by the Sealed Rail Kit, and if the value differs from the specified pressure measurement for the vehicle application, the pump may be defective.
  • Confirm whether the pump is mechanical or electrical: If you suspect the Common Rail pump is defective, utilize Delphi’s False Actuator Kit in conjunction with the Sealed Rail to investigate further. The vehicle’s actuator is temporarily replaced, allowing the pump to generate full system pressure. If the False Actuator is in place and the pump generates the correct pressure, the vehicle actuator is likely to be faulty and should be replaced. If the pressure remains below the acceptable level, the Common Rail pump may have a mechanical problem that requires repair or replacement.
  • With Delphi Technologies’ Electronic Injector Test Kit, you can check for an open coil circuit and a coil internal short circuit, as well as inspect the coil insulation to the injector body and measure the coil’s resistance and inductance, all with a single tool. This will enable you to quickly and easily discover any electronic faults, whether inside or outside the car. It should be noted that an electronic failure in a Common Rail solenoid injector cannot be fixed.
  • Diagnose and treat early-stage valve lacquering: If no defects are found during the aforementioned testing, it’s likely that valve lacquering is present. The Electronic Injector Test Kit also allows you to check if the injector is moving freely by performing a ‘buzz’ test. If not, use in conjunction with the Injector Solvent Cleaning Kit to remove any lacquering from the valve.

How to replace a Common Rail injector

Once you’ve found the faulty injector, replace it according to best practices by following these steps:

  • To begin, use a diagnostic tool to ensure there is no residual pressure in the system.
  • The injector pipe should then be removed, and any exposed pipes should be covered to avoid contamination.
  • Get rid of the back leaks. Depending on the application, you may also need to unhook the glow plug connector.
  • After that, remove the electrical connector as well as the holding clamp, and pull the injector out of the seat.
  • It’s critical to take note of the new correction code before installing the replacement injector.
  • Remove the nozzle’s protective cap and carefully slide the new injector into place.
  • Replace the retaining clamp and torque it according to the vehicle manufacturer’s recommendations.
  • Install a new high-pressure pipe and torque it to the right specs with the appropriate tooling.
  • Finally, using a diagnostic tool, reprogramme the ECU with the new rectification code. This will guarantee that the pulse times are adjusted and that the proper fuel delivery is maintained.

How to look after Common Rail injectors

Another strategy to keep your clients pleased is to offer basic maintenance recommendations. Regular TLC, like many other parts, will assist keep the injectors in good working order for a longer period of time.

  • Inspect injectors on a regular basis – every 20,000 miles is a good rule of thumb, although it may be sooner if you make frequent shorter trips.
  • To maintain engine parts clean and free of deposits, use a premium quality fuel with additional detergents.
  • To keep your fuel injection system in good shape, add a fuel system cleaning to your tank on a regular basis.
  • To maintain your engine working at its best, change the oil on a regular basis. It can deteriorate over time, losing its ability to clean, cool, and lubricate the engine.
  • Air, oil, and gasoline filters should all be replaced on a regular basis. Filters that are dirty or clogged allow impurities into the engine, causing damage to critical components and lowering engine performance and efficiency.
  • Take into account your driving style. Shorter start-stop journeys and vigorous driving will put more strain on the fuel injection system, resulting in more wear and tear.

You’ll be able to determine likely causes, speed your diagnosis procedure, and perform a best-practice injector replacement if you follow the above guidelines – resulting in a high-quality, long-lasting repair that you and your customers can rely on.

How common rail direct injection operates on diesel engines?

Modern diesel engines use a common rail fuel injection system. Common rail systems offer a level of flexibility that can be used to achieve best-in-class emission control, power, and fuel efficiency. Original Equipment Manufacturers (OEMs) may now design for maximum performance and end-user value across a broad range of machines and applications.

For the flexibility they enable while satisfying the most strict pollution control standards, a growing number of modern diesel engines use common rail direct injection (CRDi) fuel systems.

Fuel is delivered to the engine under pressure and electronically controlled precision in common rail systems. This gives a level of flexibility that can be used to achieve best-in-class emissions control, power, and fuel consumption.

Perkins’ electronic product lines in the 400, 850, 1100, and 1200 Series use CRDi technology.

How does CRDi work?

Fuel is held at changeable pressure in an electronically controlled engine’s cylinder or’rail,’ which is connected to the engine’s fuel injectors via individual pipes, making it a ‘common rail’ to all injectors. The pressure is controlled by the fuel pump, while the timing and amount of fuel injected are controlled by the fuel injectors, which work in tandem with the fuel pump. Earlier mechanical systems, on the other hand, relied on the fuel pump for pressure, timing, and quantity.

The CRDi system also has the advantage of injecting the gasoline directly into the combustion chamber. In older engines, the indirect injection (IDI) system pumped fuel into a pre-combustion chamber before feeding it to the main combustion chamber.

What is the advantage of CRDi?

CRDi uses a programmable control module to ensure that the fuel injection timing, quantity, and atomization or fuel spray are all regulated electronically. Multiple injections at any pressure at any time (within pre-defined restrictions) are possible, offering a level of flexibility that can be used to improve power, fuel efficiency, and pollution control.

Perkins has a lot of experience with CRDi when it comes to electronically regulated engines. We deliver a competent and capable product at the forefront of prime mover solutions thanks to the experience we’ve accumulated over the last ten years.

How will you notice the benefits of common rail?

Because of the scheduling flexibility, CRDi improves noise, vibration, and harshness (NVH). Your engine is quieter and has a higher sound quality. It’s also more fluid. Because higher injection pressure provides a finer spray of fuel (atomisation) that burns more efficiently, you’ll see a reduction in fuel usage.

Meeting emission regulations requires improved combustion efficiency. Soot or particles in the exhaust and deposits in the engine waste less fuel. A cleaner-running engine is better for the environment — and less expensive to own. Cleaner operating increases your engine’s long-term longevity and reliability.

Our engines have been built to handle more demanding working conditions. Improved fuel filtration, for example, ensures that the fuel injected from the common rail is of greater purity. To keep your engine running effectively and within the limitations of the applicable emission requirements, clean servicing procedures are required.

“A cleaner-running engine is better for the environment — and for your wallet.” Cleaner running increases your engine’s long-term durability and reliability.”

Are common rail engines good?

The common rail diesel engine improves emission management and fuel and power economy. To put it another way, common rail diesel engines can provide more power to a vehicle while using less fuel and emitting fewer pollutants.

As a result, it complies with government regulations that seek to limit the amount of carbon emissions emitted by a vehicle. Here are five benefits of a common rail diesel engine over a direct injection engine.

What causes ignition to occur in a diesel engine?

Compression ignites the fuel in diesel engines. Because of the ideal gas law, the temperature of gas molecules rises as the volume decreases (unless the gas is cooled at the same time). This is what diesel engines rely on. The air in the cylinder is compressed by a piston (see figure 1), causing it to become extremely hot. After that, the diesel is atomized in the injectors and sprayed into the hot air as a mist. The heated air ignites the gasoline quickly, creating ignition.

This ignition causes the diesel to burn with oxygen from the atmosphere, converting chemical energy into higher temperature, allowing the gas to push back out on the piston, as seen in Figure 1.

Diesel engines employ a glow-plug, which is a hot piece of metal, to help ignite the diesel when it is cold.