Common Rail Direct Injection (CRDi):
Most modern engine's fuel systems use ‘Common Rail Direct Injection’ or CRDi which is an advanced technology. Specifically, the term ‘CRDi’ commonly refers to diesel engines. Although, there is a similar technology which the petrol engines also use. However, it is known as Gasoline Direct Injection (GDI) or Fuel Stratified Injection (FSI). Both these technologies have a similarity in design since they consist of a common “fuel-rail” which supply fuel to injectors. However, they considerably differ from each other in pressures & type of fuel used.
In Common Rail Direct Injection, commencement of combustion takes place directly into the main combustion chamber located in a cavity on the top of 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 CRDi line diagram:
The CRD-i technology works in tandem with the engine ECU which gets inputs from various sensors. It then also calculates the precise quantity of fuel and timing of injection. The fuel system features engine 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 open 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 CRDi System –
Working of CRDi -
A high-pressure pump generates pressurised fuel. The pump compresses the fuel at the pressures of about 1,000 bar or about 15,000 psi. It, then, supplies the pressurised fuel via a high-pressure pipe to the inlet of the fuel-rail. From there, the fuel-rail distributes it to the individual injectors which then inject it into the cylinder's combustion chamber.
Most modern CRDi engines use the Unit-Injector system with Turbocharger which increases power output and meets stringent emission norms. This 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 CRDi engine animation here: