Common Rail Diesel Engine


Automotive industry was born in the 19th century with complex mechanical systems. These systems were enhanced continuously by different people at different locations and from different companies. In earlier days the engines were used with low performance, low efficiency and high emission of exhaust toxic gases, which was due to un-optimised usage of fuels by the engines. But over a period of time, the revolution in the industrialization with the innovation of new technologies in the auto industry worked for better efficiency and low emissions. New environment safety and protection technologies also evolved in the automotive world.

Thus, the above achievements were made possible from one of the innovative technology from BOSCH called “Common Rail System”, which is the largest automotive producer in the world. The name CRS came to public few decades back in 1990s throughout the world, but in India the successful implementation and marketing came with its implementation in the M&M robust SUV(Sports Utility Vehicle) “Scorpio”.

The revolution made by the CRS compared to other immortal technologies like Inline Injection System, Unit Injection System is at the top of the sky due to its flexibility of usage in all kinds of vehicles say from passengers cars, commercial vehicles , off highways and in fact in ships too!!

So it is quite interesting to know what this CRS is and its unique features compared to other injection systems. In other injection systems ,for the injection of the diesel, the fuel is injected at the required time at high pressure to the combustion cylinder. So it is a complete close loop system, rather it is a dependent system. But in case of the CRS the pressurizing of the diesel is isolated from the injection done at the time of combustion. This has an enormous advantage with which vehicle’s electronic controller will have to concentrate only on the injection quantity with the already available pressurized fuel.

The CRS basically consists of electronic controller circuit, fuel tank, pressure controller, railtube having high pressure fuel, injector, sensors and actuators to control the desired pressure of the fuel in the railtube. The low pressure fuel from fuel tank is pressurized by the pressure controller and delivered to the tubepipe which is further distributed to all the injectors depending on its needs.” Since the pressurized diesel is available all the time, the electronic circuit decides when to inject and how much to inject. This can be considered as an advantage in injecting even minute quantities when ever fuel is needed in one combustion cycle!!.

Thus, mechanically it is made sure that the diesel is mixed properly with air by multiple fuel injections so that the combustion noise is reduced and even unburnt exhaust gases can also be burnt at specific intervals in order to reduce the emission. Even the pressure in the railtube is also varied by the electronic circuit, depending on the vehicle speed request from the driver. Thus the CRS gives a high performance of the vehicle with the efficient usage of fuel and reducing the emission of toxic exhaust agents upto certain level.

The main characteristics of Common Rail System, which give it advantage over other systems, are:
1.Injection Pressure is produced and governed relatively independent of the engine speed and can be selected freely within a wide range.
2.Injection begin and injection quantity can be freely selected.

The advantages of Common Rail resulting from the above mentioned characteristics are:
1. Combustion optimisation throughout the entire range and therefore reduction in exhaust emission.
2. Small and large injection quantities as well as simple application for different engines is possible (variety reduction).
3)Efficent and quick response to driver demands for torque and acceleration
4)Noiseless performance
5)Less emissions.

There is no doubt that the Common rail Diesel engine has become the backbone of Diesel vehicle industry.