#Common-rail Diesel, the most widely used injection system by all manufacturers

15 / November 2023
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Common-rail Diesel, the most widely used injection system by all manufacturers

Seletron Performance

Why has the common-rail Diesel remained the injection system used by all manufacturers?


In the '90s, there were a series of innovations regarding diesel injection systems. We transitioned from purely mechanical rotary injection pumps to electronically controlled rotary injection pumps (similarly for less common inline pumps). Then came radial piston injection pumps with a complex electronic control system based on CAN, PDE injection systems (pump-injector elements), and towards the end of that decade, common rail systems became widespread. But what are the reasons for sticking with this injection system for over 20 years? Let's explore them!


Flexibility of Diesel Injection System


The common-rail system consists of a centralized high-pressure pump and a rail (hence the name) that distributes pressurized diesel to various injectors through metal pipes. The same system, by adding or removing pipes and injectors, can be used on 4-cylinder engines as well as 3, 5, 6, or 8 cylinders, changing only the engine management.


Diesel Pressurization Pressure


The common-rail system, as of now, has reached pressures of 2500 bar, an optimal value that allows highly effective fuel atomization. Previous injection systems did not reach these values.


Decoupling of Injection Phase from Crankshaft Position


All previous injection systems, whether with distributor pumps or injector-pump modules, were constrained by the crankshaft position. Only at certain crankshaft degrees could the injection system generate injection pressure. The common-rail system is the only one capable of maintaining constant diesel pressure regardless of the engine phase and its rotation speed (provided it is at least at idle speed).


Injection Precision


Injectors used in common-rail systems can rely on extremely high supply pressure. Moreover, these injectors are very precise in dosing the diesel flow and can perform multiple separate injections for each combustion phase. Specifically, piezoelectric-controlled injectors (which we have also discussed in our technical column) are even more precise than electromagnetic-controlled injectors, ensuring optimal mixing of fuel and oxidizer.


Simplicity of Pump Construction


The high-pressure diesel pressurization pump, despite being built with extremely low tolerance components and special materials, is inherently simpler than a rotary distributor injection pump, an inline injection pump, and even more so than a radial piston injection pump. The pump has three pumping elements, a bypass modulator that regulates pressure, and a few other elements (the pressure sensor used as system feedback is mounted on the rail).


These characteristics have made the common-rail system (which, we remind you, was invented in Italy and is now used worldwide) the most suitable for handling multiple injections with great precision, having very high injection pressure, operational flexibility, and the ability to manage precise post-injections useful for controlling particulate filter regeneration phases.


If you want to upgrade your common-rail Diesel car, browse our cataloghttps://seletron.com/en/shop/ and look for the enhancement kit suitable for your specific engine. You can immediately get:


  1. Increased power
  2. Increased torque
  3. Better acceleration
  4. Improved responsiveness
  5. Higher speed
  6. Greater elasticity
  7. Optimized fuel consumption


If you enjoyed this article explaining why the common-rail Diesel system has remained the injection system used by all manufacturers and want to learn more about the other injection systems we mentioned, you can delve deeper by reading these interesting and comprehensive articles on:


How an inline injection pump works



Preview: Since we have talked in previous months about the operation of electronically controlled rotary injection pumps, then about those with radial pistons, and then moved on to injection systems with injector-pump elements and later to common-rail systems, some have noticed that we have not talked about inline injection pumps for Diesel engines. We have not done so because the market for cars with engines that use an electronically controlled inline injection pump is so small that it has no impact on our company, which deals specifically with electronic enhancements (Diesel and gasoline).


How a rotary injection pump works



Preview: As you may know, we conducted a kind of survey through newsletters to understand which topics you are most interested in. This is to better focus on the interests of our followers. Following this survey, we realized (with pleasure) that many are particularly interested in very technical topics related to the detailed functioning of our additional control units. We are not only referring to mechanics and tuners but also to individuals who - perhaps like you reading this - have a thirst for information to satisfy their curiosity related to the automotive sector, especially the world of engines.


How a radial piston injection pump works



Preview: Here we are with the second appointment related to the specific functioning of our additional control units for power increase on Diesel engines equipped with an injection system composed of the more complex radial piston injection pump called VP44. Perhaps we should speak in the past tense, as for many years, cars with this injection system have not been produced, and consequently, the demand for additional control units to enhance these engines - which we will see now - has decreased to rare requests. Now, let's see the constructive differences of these injection pumps compared to the previous rotary ones we talked about in the previous article. (Here is the link to the article on additional control units vp37).


How the injector-pump system works



Preview: Welcome back, as promised, to talk in detail about additional control units for Diesel engines that use PDE systems, namely injector-pump systems. We have talked in previous articles about other injection systems, particularly the first electronic injection control system through a rotary electronically controlled pump, then the second evolution of centralized injection pump, namely the one with radial piston pumps. Today, we talk about the first non-centralized Diesel injection system, created with independent modules for each cylinder, elements composed of a high-pressure pump mounted in the same body as the electronically controlled injector.


How the common-rail Diesel system works



Preview: First of all, we thank the Italian engineer Mario Ricco for having this excellent insight. The common rail system originates in Italy, happening in the early '90s, but to see the first cars with this modern injection system on the road, we have to wait until 1997 when the Alfa 156 1.9JTD and the Mercedes C-Class with the 220CDI were introduced to the market. The first one mounts the first 4-cylinder 1900 with two valves per cylinder and a single overhead camshaft, uses a fixed-geometry turbocharger with an intercooler, and delivers a power of 105 horsepower. The Mercedes, on the other hand, produces the first 2200 with 4 cylinders and a power of 125 hp used on the C-Class. Both engines use this new Bosch-engineered and produced injection