Common Rail Direct Injection : Functions, Design, Working, Types, Differences, Maintenance & Its Applications

The common rail direct injection, or CRDI, is a high-pressure diesel injection system developed by Robert Huber of Switzerland in the late 1960s. Further, it was created at the Swiss Federal Institute of Technology by Dr. Marco Ganser in Zurich and Ganser-Hydromag AG in 1995 at Oberägeri. This system was successfully used first in a production vehicle by Dr. Shohei Itoh & Masahiko Miyaki in the mid-1990s in Japan. The common rail fuel system was developed by a Japanese automotive parts manufacturer for heavy-duty vehicles. After that, Bosch obtained the technology from Elasis and developed it for mass production to make it a key component in the diesel engines development in the early 2000s. This article elaborates on common rail direct injection systems, working & their applications.

What is Common Rail Direct Injection (CRDI)?

The common rail direct injection or CRDI system is an advanced technology used where the highly pressurized fuel is supplied through a common rail to injectors in a diesel engine. This system stores fuel in a common rail at higher pressure by allowing efficient and precise fuel delivery to every cylinder. It uses a central fuel rail to stock up fuel in high pressure, after that it is supplied to individual injectors for every cylinder.

CRDI improves combustion efficiency and fuel economy, decreases emissions, and delivers more power to make it a staple within modern diesel engines. This technology has transformed the way diesel engines work by allowing for better performance and decreased environmental impact.

The CRDi system works by storing fuel in a common rail at high pressure and injecting it into the cylinders of the engine directly at accurately controlled timing & quantity. So this allows for better control above the fuel-air mixture which leads to better power, efficiency & decreased emissions as compared to older systems.

CRDI Functions:

The common rail direct injection system functions are discussed below.

• It delivers high-pressure fuel efficiently to injectors.
• It allows various injections for each cycle for better control.
• This system reduces vibration and noise in combustion.
• It improves combustion by particular fuel injection timing.
• It reduces emissions and improves fuel efficiency.
• This system holds a broad range of engine speeds & loads.
• It allows electronic control & adjustment for fuel delivery.
• This system enhances engine torque, power & overall performance.
• It provides stable fuel pressure mainly for all injectors.
• It helps in complying with severe emission standards.

Common Rail Direct Injection Design

The common rail direct injection system can be designed with different key components which are discussed below.

High-Pressure Fuel Pump

The high-pressure fuel pump in a common rail direct injection plays a key role in delivering fuel at the required pressure to the common rail for accurate injection. This pump can be driven through the engine which forces the fuel to a higher level range from 1,000 to 2,500 bar. After that, the ECU controls the fuel injection into the combustion chamber through the injectors.

This pump supplies pressurized fuel to the common fuel rail from the fuel tank. So it ensures that the fuel is delivered at the required force to meet the demands of accurate engine injection by contributing to efficient combustion.

Common Fuel Rail

The common fuel rail in a common rail direct injection system works as a high-pressure reservoir or distribution system that stores fuel from the high-pressure pump. After that, this rail can distribute the pressurized fuel to separate fuel injectors, controlled by the ECU (engine control unit). So it maintains constant fuel pressure through the system by optimizing the accuracy of injection & engine performance.

Injectors

Injectors are fundamental components in CRDi that are arranged in the engine cylinders and receive high-pressure fuel from a common rail and supply fuel into the combustion chambers. These are controlled precisely by the ECU (engine control unit) to deliver the correct amount of fuel at the correct time to ensure power generation, emissions control, and efficient combustion.

Injectors are controlled electronically by allowing exact timing and fuel injection quantity into every cylinder. So this system significantly improves performance, and fuel efficiency and decreases emissions as compared to previous fuel injection techniques.

Engine Control Unit

The engine control unit in a CRDI system is the central brain which manages and controls the fuel injection development. It gets data from different engine sensors and measures the timing & duration of optimal injection. After that, it controls the injectors by delivering fuel exactly into the combustion chamber. The ECU optimizes fuel delivery for efficiency, emissions compliance, and performance by ensuring the seamless operation of the CRDi system.

Working

The fuel is delivered from the fuel tank with a high-pressure pump to either the header or the accumulator. If the pressure of the accumulator goes beyond the predefined limit then a connected high-pressure relief valve steps in to lessen the excess pressure. After that, the stored fuel within the accumulator can be channeled to the engine cylinders through facilitated fuel lines by strong injectors.

Another high-pressure relief valve is used, which is set with a spring mechanism to maintain constant pressure for seamless operations. So this valve changes pressure and sends extra fuel to the fuel tank from the accumulator back.

The needle valve in the above diagram is responsible for changing the opening & closing of the nozzle throughout the fuel spray into the cylinders. The cam orders the upward and downward nozzle’s motion with its conveyed movement throughout a rocker’s arm and connects the lever to a spring. In the stay period of the cam, the spring, in tandem with the needle valve avoids fuel injection into the cylinder.

The gland packing plays a key role in this system by ensuring a suitable fuel level over the valve seat to assist the best fuel injection into the cylinders. The wedge is central in this system, which rules the amount of injected fuel into the cylinder in position with the power requirements of the engine. So this wedge can be activated manually based on specific needs.

Specifications:

The specifications of common rail direct injection, or CRDi, include the following.

• The common rail of CRDi, like a high-pressure fuel rail, is a reservoir that holds fuel at a stable high pressure, normally ranging from 1,000 and 2,500 bar.
• The ECU (Electronic Control Unit) controls the fuel injectors, high-pressure pump, and engine components to improve the quantity and fuel injection timing.
• Fuel Injectors of this system are piezo-electric or solenoid-controlled injectors that spray fuel at high pressure into the combustion chamber.
• The high-pressure fuel pump generates the required high-pressure fuel for the CRDi system.
• The pressure regulator of this system helps to maintain the proper pressure within the common rail.
• Various sensors provide data to the electronic control unit to control the system.

Types of CRDi Engines

CRDi engines are available in two different types based on the injector actuator, like piezoelectric-type and solenoid-type which are explained below.

Solenoid Injectors

Solenoid injector uses magnetic force to control the fuel valve or fuel injection, and also a solenoid coil to generate a magnetic field to shift a valve for fuel injection control. Once these injectors are energized and the coil pulls a solenoid valve to open the injector and allows fuel to spray into the engine. These injectors provide reliability and durability; however, they can also have mechanical moving parts which can fail eventually.

Solenoid injectors are used normally in common-rail systems, where they get control signals from the engine control unit. These can also used in a wide range of pressure levels found in IndiaMART, Diesel Geeks and Bosch Mobility.

Piezoelectric Injectors

A piezoelectric injector works with piezoelectric elements by changing electrical energy into mechanical movement by enabling quicker and more accurate fuel control. These are equipped with a ceramic element whose arrangement can be changed whenever subjected to an electrical voltage to activate the injection needle. As compared to solenoid types, its benefits lie in the faster injection process control & more precise injection quantity.

Piezoelectric injector pressure levels from Bosch ranges from 2,000 bar to 2,700 bar. So these are used in light duty vehicles and the premium car segment. The injector with a modular design can be adapted to the requirements of customer. When piezo actuator is incorporated in the housing, then injector can be significantly slimmer as compared to solenoid valve injectors. Thus they need much less installation space.

Difference between CRDi and Normal Diesel

CRDi diesel engines and normal diesel engines differ from each other mainly in their fuel injection system. But, CRDi engines provide a more efficient and sophisticated fuel injection system as compared to normal diesel engines, which can lead to various benefits in fuel economy, performance, overall engine operation, emissions, etc. So the difference between CRDi and normal diesel includes the following.

CRDi Maintenance

CRDi systems need specific maintenance to ensure the best performance and long life. By below maintenance practices below, we can achieve optimal performance and longevity.

• CRDi engines must use premium diesel fuel to keep injectors clean.
• Oil must be changed at the suggested intervals because diesel engines can be more prone to fuel strength to decreases the effectiveness of oil.
• Add fuel system cleaners occasionally to the fuel tank to eliminate deposits & keep the injector clean.
• Check injectors frequently for every 20,000 miles, and clean and replace them if required.
• Frequently change oil, fuel, and air filters to avoid contaminants from going into the engine.
• Keep away from hard driving and short start-stop journeys because they increase deterioration of the fuel injection system.
• It is significant to check and replace related components and high-pressure fuel pumps regularly to maintain constant fuel pressure.
• CRDi engines need specialized maintenance because of their high-pressure systems and complex technology.
• Direct injection builds carbon on intake valves, thus fuel system cleaners must be added.

Common Rail Direct Injection Symptoms

CRDi systems in diesel engines usually experience many issues that are visible as different symptoms like engine misfires, rough idling, poor fuel economy, excessive exhaust smoke, fuel leakage, and engine knocking. In addition, different problems like hard starting, difficulty accelerating, and no start can also indicate CRDi injector problems.

• If the common rail directs injection systems aren’t delivering the proper amount of fuel, then the engine may face misfires.
• A faulty CRDi can lead to inefficient fuel consumption.
• Uneven fuel delivery causes a rough idle or even the engine to stop.
• Incomplete combustion because of the injector issues can result in improved emissions, which can be noticeable as smoke.
• Improper combustion or premature detonation can cause an engine to rattle or knock.
• Problems with the injector function or fuel pressure can make starting the engine hard.
• A faulty injector may lead to hesitation or decreased power output in acceleration.
• The ECU may notice a fault and activate the check engine light.
• Physical harm to the injector can cause fuel leaks.

Causes

The causes of CRDi include the following.

• Contaminated fuel can harm injectors.
• Insufficient fuel filtration can lead to the entry of debris into the system & harm injectors.
• Deterioration of the ball seat in the injector can cause it to leak.
• Extreme fuel return can cause various issues with the injector.
• Problems with the control pressure of the injector can lead to other issues.
• Small particles in injectors can corrode sealing surfaces to cause them to fail.
• Water within the fuel can cause deterioration, which leads to parts sticking or debris.
• Low-quality fuel can cause paraffin crystals can lead to injector failure.
• Leaking joints or damaged fuel tanks can introduce impurities into the system.
• Damaged or missing sealing rings can cause performance issues or leaks.
• Improper component tightening can lead to damage or leaks.
• If the nozzle is not properly cleaned before installation, then it causes debris to stay within the system.
• Using non-OEM quality or remanufactured parts can lead to reliability problems.
• Issues with the ECM or its connections can influence the fuel delivery system.
• Sensor issues can also cause faults.

Future Trends

The CRDi engine concept in automotive technology is continuously enhancing. So, some future trends within this technology are discussed below.

• Dual-stage injection systems implementation in CRDi attains lower emissions and higher efficiency.
• CRDi technology expanding to gasoline engines for improved fuel economy and performance.
• Incorporating this technology with alternative fuels like hydrogen and biofuels for sustainable mobility.
• Using lightweight materials can enhance fuel efficiency and decrease overall vehicle weight.

Advantages

The common rail direct injection system’s advantages include the following.

• There is a substantial increment in torque and power as compared to fixed direct injection engines.
• It needs minimal investment for execution.
• Improving acceleration and attaining better pick-up performance.
• Delivering improved mileage & fuel efficiency.
• Significantly decreases emissions to the lowest level.
• It reduces fuel consumption for inexpensive operation.
• CRDi technology provides several benefits over usual diesel engines to make it an ideal choice for current vehicles.
• These engines optimize fuel delivery to provide superior fuel efficiency & decreased consumption.
• The precise fuel injection control can improve power output & engine reaction.
• CRDi engines generate less dangerous emissions because of better combustion, which obeys severe ecological regulations.
• This system decreases vibration and engine noise, which leads to a smoother and quieter ride.
• The controlled injection decreases stress on different engine components, which leads to improved engine life.
• CRDi engines provide superior cold-starting capabilities by ensuring smoother operation in lower temperatures.

Disadvantages

The common rail direct injection system’s disadvantages include the following.

• Higher vehicle costs because to the advanced features in technology.
• Its maintenance cost is high.
• These components are expensive.
• Its design is complex.
• These are sensitive to fuel quality, which leads to potential problems with impure fuel.
• Injector issues and wear may change engine performance.
• System difficulty can result in complex repairs.
• It is prone to water contamination and electromagnetic interference, which leads to damage.
• Availability of limited service centers in some regions.
• Higher noise can occur at higher RPMs because of increased fuel pressure.
• It generates PM (Particulate Matter) and NOx (Nitrogen Oxide) emissions.

Common Rail Direct Injection Applications

The applications of common rail direct injection include the following.

• Modern diesel-powered cars provide better performance and fuel economy.
• Buses and trucks equipped with these engines take advantage of decreased operating costs & lower emissions.
• Construction and agricultural machinery utilizes these engines to enhance durability and efficiency.
• Marine vessels rely on CRDi engines to achieve fuel efficiency and deliver higher power for extended journeys.
• CRDi engines power marine vessels, providing fuel efficiency and increased power, which is crucial for long journeys.
• Various applications, such as generator sets and fixed power generation, employ CRDi systems.
• These engines enhance the durability and efficiency of construction and agricultural machinery.
• Buses, Trucks & other commercial vehicles use CRDIs, which lead to reduced emissions and lower operating costs.
• Many modern diesel-powered cars use CRDi engines, which provide a fuel economy & performance balance.

This overview highlights the common rail direct injection (CRDi) system, which modern diesel engines use to achieve significant improvements in efficiency, performance, and emissions compared to earlier systems. CRDi allows improved combustion, resulting in improved power output by decreasing emissions and fuel consumption by controlling fuel delivery throughout a high-pressure common rail. Thus, the CRDi diesel-powered cars examples are: Hyundai Creta, Mahindra XUV700, buses & trucks with CRDi engines. Here is a question for you: CRDi is also known as?