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Injection ingenuity

6th November 2008
Page 48
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Page 48, 6th November 2008 — Injection ingenuity
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With new engine emissions standards coming, injection system companies have created a number of different applications to meet the criteria.

Words: John Kendall Euro-5 emissions standards are due to take effect for new vehicles from next year. bringing in much tighter limits for emissions of oxides of nitrogen (NOx) compared with Euro-4, while leaving other exhaust emission limits untouched.

Reducing NOx emissions from a diesel engine tends to bring an increase in particulate emissions or vice versa: and is one of the main reasons exhaust after-treatment has been needed since Euro-4 limits were drafted in.

But halving particulate emissions limits for Euro-4 — and imposing a further reduction in NOx limits — has meant a rethink when it comes to fuel injection strategies.

Put simply, increasing injection pressures helps to promote more complete combustion i.e. more of the fuel that is injected is burned. At the same time, producing the number of injection pulses that will be needed to control the combustion process more precisely swings the balance in favour of common-rail systems and away from electronic unit injector (EUI) and unit pump (EUP) systems.

Common-rail systems

The reasoning behind choosing common-rail systems is simple enough. They can hold a greater volume of fuel under pressure, which allows for more injection pulses than would be possible from ELJI or EUP systems.

So, it comes as no surprise that Delphi, which has relied on EUI and EUP for its heavy diesel injection systems, announced at the Hannover Show last month that it will be switching to common-rail systems in order to meet the Euro-6 standard and beyond (Euro-6 emissions limits are due to take effect from 2013).

Delphi displayed three common-rail systems at the show, which will help the firm cater for a wider variety of engine designs, with capacities between four and 16 litres.

First, there will be a 'conventional' common-rail system, which will be called 'high-pressure heavy duty common rail'. Fuel pressure will be generated by a cam and plunger pump lubricated with engine oil.

Two further systems will complete Delphi's commonrail offerings. The company describes these as 'distributed pump common rail' because both integrate the firm's EUP and EUI pumping technology into the systems.

Satisfying requirements

Taking a 13-litre engine as an example, Delphi expects that a system fed by three pumps would satisfy most needs, while two pumps should do the job for smaller engines.

The EUP-based application has been named F2 P The cam-driven pumps supply fuel to the rail, which supplies the injectors. The EUI-derived system combines the unit pumps with a common rail set-up by modifying the EUI components. Take the example of the 13-litre sixcylinder engine, fitted with three pumps, again. The pumps would be activated by the overhead cam, just like Delphi's current E3 EUI injector, which can already deliver injection pressures of up to 2,500bar.

While the pump and injector are housed in the same body, like the E3, the two elements remain separate. The pump feeds pressurised fuel directly to the rail, which supplies fuel back to the injector part of the device. For the three cylinders that are not fitted with the pump/injector, a more conventional and straightforward common-rail injector is used.

To help raise the rail pressure, the camshaft carries two lobes, giving two pump strokes per revolution in place of the single stroke for current EUP and EUI systems.

To achieve the required injection pressures and satisfy the 1.6 million-kilometre durability requirements. Delphi has had to work on the geometry of the sealing cones.

To control all three common-rail systems, Delphi has developed the new ETC3 electronic truck controller. The air-cooled engine management system will control all engine and duty functions. A fuel-cooled option for extreme operating conditions will also be on offer.

Delphi reveals that the ETC3 controller will be ready for production in 2010, and expects the new range of heavy-duty common-rail systems to go into production from around 2012. •

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