CRDi engine | Working Of Common Rail Diesel injection System

Notes on Common Rail Direct Injection (CRDi)

The term ‘CRDi’ commonly refers to diesel engines. Although, there is a similar technology which the petrol engines also use 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 combustiontakes 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.
The CRD-i technology works in tandem with the engine ECU which gets inputs from various sensors.
A Common Rail system uses a ‘common-for-all-cylinders’ fuel-rail or in simple words a ‘fuel distribution pipe’.

Diesel Common rail — Diesel – Common rail

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 –

High Pressure Fuel Pump
Common Fuel Rail
Injectors
Engine Control Unit

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.

Advantages & Disadvantages of CRDi

Advantages

CRDi engines are advantageous in many ways. Cars fitted with this new engine technology are believed to deliver 25% more power and torque than the normal direct injection engine. It also offers superior pick up, lower levels of noise and vibration, higher mileage, lower emissions, lower fuel consumption, and improved performance.

In India, diesel is cheaper than petrol and this fact adds to the credibility of the common rail direct injection system.

Disadvantages

Like all good things have a negative side, this engine also have few disadvantages. The key disadvantage of the CRDi engine is that it is costly than the conventional engine. The list also includes high degree of engine maintenance and costly spare parts. Also this technology can’t be employed to ordinary engines.

Applications

The most common applications of common rail engines are marine and locomotive applications. Also, in the present day they are widely used in a variety of car models ranging from city cars to premium executive cars.

Some of the Indian car manufacturers who have widely accepted the use of common rail diesel engine in their respective car models are the Hyundai Motors, Maruti Suzuki, Fiat, General Motors, Honda Motors, and the Skoda. In the list of luxury car manufacturers, the Mercedes-Benz and BMW have also adopted this advanced engine technology. All the car manufacturers have given their own unique names to the common CRDi engine system.