07-02-2012, 11:31 AM
COMMON RAIL DIRECT INJECTION (CRDi) AS A POWER GENERATING UNIT IN AUTOMOTIVE SYSTEM
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INTRODUCTION
While the Japanese are leading in petrol direct injection technology, Germany's Bosch, working in conjunction with several European car makers, Have pioneered Common-Rail Direct Injection for diesel engines. Compared with petrol, diesel is the lower quality ingredient of petroleum family. Diesel particles are larger and heavier than petrol, thus more difficult to pulverize. Imperfect pulverisation leads to more unburnt particles, hence more pollutant, lower fuel efficiency and less power. Common-rail technology is intended to improve the pulverisation process.To improve pulverisation, the fuel must be injected at a very high pressure, so high that normal fuel injectors cannot achieve it.
METHODS OF FUEL INJECTION
Mechanical and electronic injection
Older engines make use of a mechanical fuel pump and valve assembly which is driven by the engine crankshaft, usually via the timing belt or chain. These engines use simple injectors which are basically very precise spring-loaded valves which will open and close at a specific fuel pressure. The pump assembly consists of a pump which pressurizes the fuel, and a disc-shaped valve which rotates at half cranksThe valve has a single aperture to the pressurized fuel on one side, and one aperture for each injector on the other. As the engine turns the valve discs will line up and deliver a burst of pressurized fuel to the injector at the cylinder about to enter its power stroke.
Direct Injection
Recently many diesel engines feature direct injection (DI). The injection nozzle is placed inside the combustion chamber and the piston incorporates a depression where initial combustion takes place. Direct injection diesel engines are generally more efficient and cleaner than indirect injection engines, but tend to be noisier, which is being addressed in newer common rail designs.Some recently designed hi-tech petrol engines utilize direct injection as well.
ITS FUNCTION
A pump inhales the fuel from the tank (ELECTRONIC PUMP) and continuously sends the quantity of requested fuel towards a second pump (HIGH PRESSURE PUMP) by making it pass first through the fuel filter that purifies it from any impurity which would cause a premature wear of its components
