Production of Delphi’s Direct Acting Diesel Common Rail (DADCR) system has started, following a five-year development program in France, Luxembourg, and the UK. The system incorporates direct-acting piezo injectors—claimed by the company as a "world first" that can operate at pressures up to 2000 bar (29 ksi) and will help meet Euro 6 emissions standards. Initial application of the technology will be on Mercedes-Benz’s OM651 four-cylinder 2148-cm³ diesel engine, which will power a 2009MY car.
The system has been designed to reduce both noise and emissions (including a 30% cut in particulate matter); improve fuel consumption, power, and torque; and help provide generally enhanced refinement and driveability. The technology is said to mark the advent of a new generation of injection technology.
The system’s injector needle is set in motion directly by a piezo-ceramic actuator instead of using an electrohydraulic circuit found on most other systems. The DADCR system allows the injector to spray fuel into the combustion chamber with much improved momentum and accuracy due to what the company describes as "extremely fast" opening and closing of the needle valve, independent of injection pressure.
"Consumers will be able to drive this system on the roads on a premium vehicle before the end of this year," said Jose Avila, General Manager, Delphi Diesel Systems, based in Luxembourg.
AEI has previously reported on the technology during its development phase, but now more comprehensive details have emerged. Delphi claims that it is the first time that a production system has incorporated an injector needle that is directly activated by the piezo stack, so removing the hydraulic circuit and its associated lag and energy consumption, while providing "significant" additional control possibilities for engine designers.
The company cited as other benefits: through-life stability of operation; robustness of injected quantities for varying injection patterns; and low shot-to-shot variation of injected quantities.
The new Delphi system was aimed at achieving several salient performance requirements that the company expected to be enablers for future emissions legislation. These included high mean effective injection pressure (square rate of injection at any pressure up to 2000 bar); multiple injection flexibility (seven or more injection events); fast opening/closing of the throttle needle (about 3 m/s); and proportional control of needle lift by the engine control unit, thus allowing the rate of injection to be mapped into it—and elimination of back-leak flow.
The principle of the new system does not require a return flow to operate, stated Delphi. Thus, all fuel is injected and no fuel is wasted in a return flow. This improves the injection system’s thermal circuit to such an extent that, even at a rail pressure of 2000 bar, fuel cooling is not required.