Dieseltester

CRDI test bench

What is Electronic Common Rail Direct Injection (CRDI)

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. It's the high pressure fuel rail and the computer controlled electronic injectors that make all the difference. In the common rail system, the fuel pump charges the fuel rail at a pressure of up to 25,000 psi--but unlike indirect injection pumps--it is not involved in fuel discharge. Under the control of the onboard computer, this fuel quantity and pressure accumulates in the rail independently of engine speed and load. Each fuel injector is mounted directly above the piston within the cylinder head (there is no pre-chamber) and is connected to the fuel rail by rigid steel lines that can withstand the high pressure. This high pressure allows for a very fine injector orifice that completely atomizes the fuel and precludes the need for a pre-chamber.

The actuation of the injectors comes via a stack of piezo electric crystal wafers that move the jet needle in tiny increments allowing for the spray of fuel. Piezo crystals function by expanding rapidly when an electric charge is applied to them. Like the fuel pump, the injectors are also controlled by the the engine computer and can be fired in rapid succession several times during the injection cycle. With this precise control over injector firings, smaller, staggered quantities of fuel delivery (5 or more) can be timed over the course of the power stroke to promote complete and accurate combustion. In addition to timing control, the short duration, high pressure injections allow a finer and more accurate spray pattern that also supports better and more complete atomization and combustion.

Through these developments and improvements, the modern common rail direct injection diesel engine is quieter, more fuel efficient, cleaner, and more powerful than the indirect mechanical injection units they have replaced.

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