Common rail direct fuel injection is a modern variant of direct injection system for diesel engines. It features a high-pressure (1000+ bar) fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding pump nozzles or high-pressure fuel line to mechanical valves controlled by cams on the camshaft. Third generation common rail diesels now feature piezoelectric injectors for even greater accuracy, with fuel pressures up to 180 MPa / 1800 bar, although a new version of Delphi’s proven diesel common rail system will allow compliance with Euro 6 and US Tier 2 Bin 5 without costly next-generation injection technologies.furkan_imsCRDI-IT STANDS FOR COMMON RAIL DIRECT INJECTION
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Solenoid or piezoelectric valves make possible fine electronic control over the injection time and amount, and the higher pressure that the common rail technology makes available provides better fuel atomisation. In order to lower engine noise, the engine's electronic control unit can inject a small amount of diesel just before the main injection event ("pilot" injection), thus reducing its explosiveness and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting, and so on. Some advanced common rail fuel systems perform as many as five injections per stroke.
Common rail engines require no heating up time, and produce lower engine noise and lower emissions than older systems.
In older diesel engines, a distributor-type injection pump, regulated by the engine, supplies bursts of fuel to injectors which are simply nozzles through which the diesel is sprayed into the engine's combustion chamber. As the fuel is at low pressure and there cannot be precise control of fuel delivery, the spray is relatively coarse and the combustion process is relatively crude and inefficient.
In common rail systems, the distributor injection pump is eliminated. Instead an extremely high pressure pump stores a reservoir of fuel at high pressure—up to 2,000 bar (200 MPa)—in a "common rail", basically a tube which in turn branches off to computer-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid. Driven by a computer (which also controls the amount of fuel to the pump), the valves, rather than pump timing, control the precise moment when the fuel injection into the cylinder occurs and also allow the pressure at which the fuel is injected into the cylinders to be increased. As a result, the fuel that is injected atomises easily and burns cleanly, reducing exhaust emissions and increasing efficiency.
Most European automakers have common rail diesels in their model lineups, even for commercial vehicles. Some Japanese manufacturers, such as Isuzu, Toyota, Nissan and recently Honda, have also developed common rail diesel engines. Some Indian companies have also successfully implemented this technology, notably Mahindra & Mahindra for their 'Scorpio-CRDe' and Tata Motors for their 'Safari-DICOR'.
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Modern diesels owe their resurgence in popularity to advances in fuel delivery and engine management systems that allow the engines to return power, performance and emissions equivalent to their gasoline counterparts, while simultaneously producing superior fuel economy.
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