What Is A CRDI Engine?
-by Maulik Joshi (B.E. Mech.)
CRDI =>COMMON RAIL DIRECT INJECTION
Most of the people who used to be called “gearheads” will at least be familiar with the term CRDI and how it applies to engines for cars and trucks. The letters stand for common rail direct injection, which is a fairly recent design for diesel engines that may also be suitable for passenger automobiles. Though originally intended for commercial use, this design is now in wide use around the globe.
The method is chosen by more and more manufacturers and by individual users because it is fuel efficient as other diesel technologies were. However, CRDI has also provided a tremendous boost in diesel-engine performance. The improvement is mainly due to the common-rail design, which has tubes that connect all the injectors. These injectors are based on the direct-injection concept, as was the case in the past. But the common-rail design was quite a step forward.
Fuel in the common tube or “rail” is under a set amount of pressure which causes the fuel to be “atomized” or broken down to its smallest particles. This allows the fuel to combine with the air much more efficiently. With proper direct injection, fuel use is highly efficient, with much less waste fuel escaping the system unused.
The newest electronic technology has also allowed CRDI engines to better control the amount of fuel used, the pressure within the system and the timing of both the injection of fuel and the electronic charge applied to make the fuel burn. Injectors in the common rail direct injection engine have controls on the injector heads that allow slight variances in the amount of fuel put into the cylinders.
As is the case with almost all automobiles, trucks and motorized equipment today, a “computer” or electronic “brain” controls the various factors, including amount of fuel, timing of injection, timing of the charge and the pressure within the tubes or common rails. According to those who have used this technology in both test and commercial applications, the CRDI method greatly reduces engine and vehicle vibration, allows the engine and vehicle to run more quietly and reduces the cost of operation significantly.
For the most part, traditional, classic carburetion engines have been replaced by such methods as MPFI or multi-point fuel injection designs for gasoline engines and CRDI or common rail direct injection for diesel engines. MPFI was first developed some years ago in response to the call for more fuel-efficient engines. The need for better emission standards made MPFI popular, since it allowed for better gas mileage in automobiles.
CRDI for diesel vehicles has improved performance by as much as 25 percent, according to some studies. This gives the vehicle more power and makes the technology more attractive for passenger vehicles. These engines run much more smoothly, with efficiency greatly enhanced by higher pressure possible in the common-rail or tube design. While the CRDI engine is a little more expensive than previous technologies, the savings in fuel cost can help recoup the initial expensive over time.
How the CRDI engine works?
A CRDi engine is based on direct injection technology and has common rails i.e. tubes which inject pressurised fuel directly into the engine.
The common rail connects all the injectors and contains fuel at a constant high pressure. A small amount of fuel is supplied to the engine before and after the actual supply of charge. The high pressure in the common rail ensures that upon injection, the fuel atomises to a very high degree and mixes consistently with the air, thereby leaving minimal unburnt fuel.
In a CRDi engine, fuel quantity, engine pressure and timing of fuel injection are controlled electronically. The injectors have variable control heads which ensure that a highly precise amount of diesel goes into each cylinder. The onboard computer makes sure that the fuel is injected at the just the precise moment. This significantly improves engine efficiency and reduces noise and vibrations as compared to the conventional diesel engines.
This is for the CRDi. But needless to say that you will understand it better if you know the basic functioning of an internal combustion engine.
The common rail connects all the injectors and contains fuel at a constant high pressure. A small amount of fuel is supplied to the engine before and after the actual supply of charge. The high pressure in the common rail ensures that upon injection, the fuel atomises to a very high degree and mixes consistently with the air, thereby leaving minimal unburnt fuel.
In a CRDi engine, fuel quantity, engine pressure and timing of fuel injection are controlled electronically. The injectors have variable control heads which ensure that a highly precise amount of diesel goes into each cylinder. The onboard computer makes sure that the fuel is injected at the just the precise moment. This significantly improves engine efficiency and reduces noise and vibrations as compared to the conventional diesel engines.
This is for the CRDi. But needless to say that you will understand it better if you know the basic functioning of an internal combustion engine.
Components of CRDi
PRE SUPPLY PUMP
- The electric fuel pump comprises of:
- 1.Electric Motor
- 2.Roller-Cell Pump
- 3.Non Return Valve
- electric
- roller
- gear
- roller
- gear
- Rail-pressure sensor (RDS).
- Injector
High pressure pump
- The pump plunger moves downwards
- The inlet valve opens
- The fuel is drawn in to the pumping element chamber(suction stroke)
- At BDC, the inlet valve closes
- The fuel in the chamber can be compressed by the upward moving plunger.
- High- pressure accumulator (Rail).
Pressure-control valve (DRV)
Responsible for maintaining the pressure in the rail at a constant level.
ECU with Sensors
- Common Rail is an EDC controlled injection system
- The ECU controls & monitors the complete injection process
- The sensors delivers all the measured values which are required in the process
Rail-pressure sensor(RDS)
- Measures the pressure in the rail.
- Inputs the information to the ECU.