Have you ever wondered how a common rail diesel injection works? Well, we got you covered.
Common rail diesel injection systems have become the go-to choice for modern diesel engines due to their superior performance characteristics, lower emissions, and improved efficiency.
These injection systems have largely replaced mechanical injectors and HEUI systems, both of which were unable to achieve the high injection pressures and multi-event injection capabilities of common rail systems.
This article will provide an in-depth look at the workings of common rail diesel injection systems, their components, advantages, and their usage in various engines.
The Basics of Common Rail Diesel Injection
A common rail diesel injection system, simply known as a common rail system, is a high-pressure fuel injection mechanism used in modern diesel engines.
It consists of a low-pressure fuel pump (lift pump), high-pressure fuel pump (injection pump), Piezoelectric fuel injectors, and the associated rail system.
This configuration allows for higher injection pressures, which in turn reduce emissions and improve overall engine efficiency.
The Evolution of Diesel Injection Systems (Historical Context)
Before the widespread adoption of common rail systems, diesel engines primarily relied on mechanical injectors and HEUI (hydraulically actuated, electronically controlled unit injector) systems for fuel injection.
However, these older systems were unable to achieve the high injection pressures and precise control offered by common rail technology.
This led to the development and eventual dominance of common rail systems in modern diesel engines.
Components of a Common Rail Diesel Injection System
A typical common rail diesel injection system consists of the following main components:
Low Pressure Fuel Pump (Lift Pump)
The low pressure fuel pump, or lift pump, is responsible for delivering fuel from the fuel tank to the high pressure fuel pump (injection pump).
Its primary purpose is to ensure a consistent supply of fuel to the injection pump.
The pressure of the fuel entering the injection pump is relatively low and does not have a significant impact on the actual injection pressure.
High Pressure Fuel Pump (Injection Pump)
The high pressure fuel pump, or injection pump, is responsible for maintaining extremely high pressure within the common rail(s).
In an inline-6 (I-6) engine, there is a single common rail that feeds each injector, while a “V” engine utilizes two common rails, one for each engine bank.
The rail pressure, or pressure of the fuel system at the outlet of the high pressure pump, can reach pressures in excess of 30,000 psi.
Piezo Electric Fuel Injectors
Piezo electric fuel injectors are a crucial component of common rail diesel injection systems.
These injectors are controlled by the PCM/ECM (Powertrain Control Module/Engine Control Module), which initiates injection events by energizing an injector.
When an injector is energized, fuel flows through the injector nozzle, atomizing as it enters the combustion chamber.
Rail System
The rail system in a common rail diesel injection system is responsible for connecting the high pressure fuel pump to the injectors. It consists of a pipe or rail that holds fuel at a constant high pressure, ready to be injected into the combustion chamber when required.
Examples of Common Rail Diesel Engines
Many modern diesel engines employ common rail diesel injection systems, including the following popular examples:
- 6.6L Duramax diesel: All generations of this engine use a high-pressure common rail injection system.
- 5.9L Cummins: This engine was upgraded to a common rail system for the 2003 model year (24v model).
- 6.4L International and 6.7L Ford Power Stroke: Both of these engines feature common rail systems.
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The Future of Common Rail Diesel Injection
As the demand for cleaner, more efficient engines continues to grow, common rail diesel injection technology will play an increasingly important role in the development of new engines.
With its ability to deliver high pressures, precise control, and reduced emissions, common rail systems offer a promising solution for meeting the challenges posed by ever-tightening emissions regulations.
Advantages of Common Rail Diesel Injection Systems
There are several benefits to using common rail diesel injection systems in modern diesel engines:
Improved Combustion Efficiency
One of the most significant advantages of common rail systems is their ability to achieve greater combustion efficiency.
This is because the high rail pressure results in better atomization of fuel, which in turn leads to more efficient combustion.
Lower Emissions
Common rail diesel injection systems have been proven to produce lower particulate emissions compared to mechanical injectors and HEUI systems.
This is due to the improved combustion efficiency and the ability to fire an injector multiple times per single combustion event.
Greater Performance Potential
The high injection pressures and multi-event injection capabilities of common rail systems allow for greater performance potential in modern diesel engines.
This translates to better power, torque, and overall engine performance.
Reduced Engine Noise
Common rail injection systems typically lead to reduced engine noise compared to older injection systems.
This is because the high pressure fuel injection results in a smoother, more controlled combustion process.
Combustion Optimization in Common Rail Systems
Balancing Nitrogen Oxide Formation, Soot Particulates, and Fuel Consumption
In diesel engines, there is a three-way interaction between nitrogen oxide formation, soot particulate production, and fuel consumption.
More intensive combustion leads to lower particulate emissions and fuel consumption, but it also results in higher nitrogen oxide emissions.
Conversely, retarded combustion leads to lower nitrogen oxide formation but increased fuel consumption and particulate emission levels.
Engine developers must find a compromise between these extremes for every point on the engine performance map.
This involves harmonizing the effect of the fuel injection system with other internal engine measures, such as exhaust gas recirculation, which primarily reduces nitrogen oxide emissions, and external exhaust aftertreatment systems.
The Role of Injection Rate and Pressure
The two key parameters in fuel injection that affect fuel consumption and emissions are injection rate and injection pressure.
Common rail systems offer precise control over these parameters, enabling engine developers to optimize combustion for maximum efficiency and minimal emissions.
Applications of Common Rail Diesel Injection Systems
Common rail diesel injection systems have been used in various engine models, including:
6.6L Duramax Diesel
All generations of the 6.6L Duramax diesel engine employ a high pressure common rail injection system.
This has contributed to the engine’s strong performance and low emissions.
5.9L Cummins
The 5.9L Cummins engine was upgraded to a common rail system for the 2003 model year (24v model).
This change resulted in improved engine performance and reduced emissions.
International 6.4L and Ford 6.7L Power Stroke
Both International’s 6.4L and Ford’s 6.7L Power Stroke engines feature common rail diesel injection systems.
These systems have been instrumental in helping these engines achieve higher levels of performance and efficiency.
Evolution of Common Rail Diesel Injection Systems
Over the years, common rail diesel injection systems have evolved and improved, with notable examples being:
ACRS: Amplified Common Rail System
Introduced by Detroit Diesel in 2007, the ACRS (Amplified Common Rail System) was a revolutionary injection system used in the DD15 engine.
The ACRS system was designed to overcome the limitations of unit injectors, which performed best only at higher RPMs.
The ACRS system could deliver up to 38,000 PSI injection pressures, with rate-shaping capabilities to reduce peak cylinder pressure and temperature, thus reducing Nox emissions.
MaxxForce Engines
Navistar introduced the MaxxForce engines in 2007, which featured a slightly different form of common-rail system.
The MaxxForce engines utilized a system that did not amplify the pressure inside the injector, but instead used piping capable of withstanding the full pressure throughout the system.
This allowed for peak torque down to 1,000 RPM, a characteristic not achievable in most engines below 1,200 RPM.
Cummins XPI Common-Rail System
Cummins, in collaboration with Scania, developed their XPI common-rail system to meet the stricter Nox emissions standards in 2010.
The XPI system utilized a copper zeolite catalyst to make the SCR (Selective Catalytic Reduction) process more efficient.
Meeting Emission Standards with Common Rail Systems
Modern diesel engines must adhere to strict emission regulations, and common rail diesel injection systems have played a crucial role in meeting these standards.
The high injection pressures and multi-event injection capabilities of common rail systems have helped reduce engine emissions, particularly Nox and particulate matter.
The SCR process, which involves using DEF (Diesel Exhaust Fluid) to convert Nox into harmless nitrogen and water, has become a popular solution for meeting Nox emission standards.
Common rail systems have been instrumental in allowing engines to utilize SCR technology effectively.
How a Common Rail Diesel Injector Works and Common Failure Points >> Check out the video below:
Conclusion
Common rail diesel injection systems have become an essential component of modern diesel engines, offering improved efficiency, lower emissions, and better overall performance.
With continuous advancements in technology and stricter emission regulations, it is likely that common rail systems will continue to play a vital role in the diesel engine industry.
Whether you are an industry professional or simply interested in learning more about diesel engines, understanding the workings of common rail diesel injection systems is essential.