Fuel injection systems
STATE OF THE ART Perhaps the clearest evidence of how far diesel power has come is provided by two recently announced developments, from Volvo and Volkswagen. Volvo’s new i-ART generation of diesels, due later this year, ramps fuel injection pressures up to an unprecedented 2,500 bar (the highest prior to this has been 2,200 bar) and incorporates combustion pressure sensors to enable precise injection rate shaping at all times. “The system measures the
pressure pulse going through the injector,” says Derek Crabb, head of powertrain at Volvo and the architect of the new-generation engines. “The higher pressure allows you to inject more fuel, but what you’re really after as an engineer is better spray pattern, so you get more effective combustion. The droplets become smaller and break up, giving more complete combustion, without leaving residuals that generate hydrocarbon emissions.” While Crabb is reluctant to give
precise details on the performance improvements delivered by the new technology, he says it is “a major help” in achieving the new Euro 6 and possibly future Euro 7 standards, and that the gains are worth “several per cent” when it comes to fuel economy.
CAD view of next-generation Volvo cylinder head incorporating Denso feedback-control injectors
Further major gains could be had
in the area of NVH, hints Crabb, where careful control of the pilot phase of the injection pulse can help spread out the combustion event and thus reduce the noise profile of the engine. Whereas the Volvo engine is expected to major on efficiency and low emissions, the high-performance diesel referred to by VW group CEO Martin Winterkorn is unashamedly
WHY PRECISION MATTERS Absolute accuracy and consistency between the injectors on an individual engine can make it not only smoother, but also more powerful, cleaner and longer lasting. Denso’s fourth-generation injectors feed back their precise characteristics to the engine management system, so the electronics can automatically compensate for any wear that occurs or for any differences between individual injectors. “With a conventional engine, you have to calibrate it to, say, 80% of the
emissions limits just to allow for variability from engine to engine,” says Derek Crabb, head of powertrain at Volvo. “That way, you give away economy, performance and refinement.” With a technology that is able to compensate for variability and in-
service drift, he says, engines can be tuned much closer to the 100% box and still stay within the legislative limits over their lifetime. “We can then get back performance, get back fuel economy. That’s basically what we’re doing with this system.”
Injectors will soon be capable of
2,500 - 3,000 bar
aimed at high power outputs. Though few firm details have so far been given, what Prof Winterkorn did say was that, with 3,000 bar injection, the engine would achieve a specific power of 100kW (134Bhp) per litre; sources within VW point to two-stage supercharging, with an electric turbine feeding into an exhaust-driven turbo. BMW has already reached a
claimed 93 kW per litre with a triple
May/June 2013
www.automotivedesign.eu.com
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