Common Rail Direct Injection (CRDi):
Most modern engine's fuel systems use an advanced technology known as CRDi or Common Rail Direct Injection. Both petrol end diesel engines use a common 'fuel-rail' which supplies the fuel to injectors. However, in diesel engines, manufacturers refer to this technology as CRDi whereas Petrol engines term it as Gasoline Direct Injection (GDI) or Fuel Stratified Injection (FSI). Both these technologies have a similarity in design since they consist of “fuel-rail” which supplies fuel to injectors. However, they considerably differ from each other on parameters such as pressure & type of fuel used.
In Common Rail Direct Injection, the combustion takes place directly into the main combustion chamber located in a cavity above the piston crown. Today, manufacturers use CRDi technology to overcome some of the deficiencies of conventional diesel engines which were sluggish, noisy and poor in performance when implemented, especially in passenger vehicles.
Following is the schematic Common Rail Direct Injection line diagram:
The CRDi technology works in tandem with the engine ECU which gets inputs from various sensors. It then calculates the precise quantity of fuel and timing of injection. The fuel system features components which are more intelligent in nature and controls them electrically / electronically. Additionally, the conventional injectors are replaced with more advanced, electrically operated, solenoid injectors. They are opened by an ECU signal, depending upon the variables such as engine speed, load, engine temperature etc.
A Common Rail system uses a ‘common-for-all-cylinders’ fuel-rail or in simple words a 'fuel distribution pipe'. It maintains optimum residual fuel pressure and also acts as a shared fuel reservoir for all the injectors. In CRDi system, the fuel-rail constantly stores and supplies the fuel to the solenoid valve injectors at the required pressure. This is quite opposite to the fuel injection pump supplying diesel thru’ independent fuel lines to injectors in case of earlier generation (DI) design.
Components of Common Rail Direct Injection System –
1. High Pressure Fuel Pump
2. Common Fuel Rail
Working principle of Common Rail Direct Injection -
A high-pressure pump supplies pressurized fuel. The pump compresses the fuel at the pressures of about 1,000 bar or about 15,000 psi. It, then, supplies the pressurized fuel via a high-pressure pipe to the inlet of the fuel-rail. From there, the fuel-rail distributes the fuel to individual injectors which then inject it into the combustion chamber.
Most modern CRDi engines use the Unit-Injector system with Turbocharger which increases power output and meets stringent emission norms. Additionally, it improves engine power, throttle response, fuel efficiency and controls emissions. Barring some design changes, the basic principle & working of the CRDi technology remains primarily the same across the board. However, its performance depends mainly on the combustion chamber design, fuel pressures and the type of injectors used.
The manufacturers use custom acronyms to make their diesel CRDi product stand out in the competition.
• TDI™ - Turbocharged Direct Injection – It is developed, produced & trademarked by Volkswagen group that comprises of a turbo-diesel engine combined with Cylinder-Direct Injection.
Watch Common Rail Direct Injection engine animation here:
Keep reading: Electronic fuel injection technology >>