Refining heavy-duty diesel fuel systems

  • 03-Feb-2014 03:16 EST
David Draper 1.jpg

Delphi's David Draper sees further integration of heavy-duty diesels with their fuel systems.

How are heavy-duty diesel fuel systems likely to evolve in Europe, now that Euro-VI, the tightest yet emissions regulations applied to heavy trucks and buses in the European Union, have come into force for all new vehicles?

As yet there are no further regulations under discussion, but further tightening of toxic emissions is not expected. Reducing fuel consumption and carbon dioxide emissions is generally reckoned to be the focus instead. Although further fuel-consumption reductions could be produced by improving aerodynamics, reducing friction, and recovering exhaust heat, engineers also are turning their attention to refinements in fuel systems that could improve efficiency as well.

Euro-VI injection pressures have risen to a maximum of around 2700 bar (39.2 ksi), and Delphi has engineered its systems to deliver up to 3000 bar (43.5 ksi). How necessary will that be?

“There is still work looking at the advantages of high pressures,” said David Draper, Heavy-Duty Diesel Systems Engineering Director at Delphi. “In certain circumstances and aftertreatment scenarios, higher pressures can be found to produce some improvements. It doesn’t feel at the moment like pressures will go much beyond 3000 bar.”

As Draper points out, injection pressures at Euro-VI settled at around 2500 to 2700 bar (36.3 to 39.2 ksi). Some manufacturers, notably Iveco, have achieved Euro-VI without exhaust gas recirculation (EGR), and that has reduced the need for higher injection pressures.

“For engines that are using the almost-no-EGR route, the maximum pressures ended up below 2000 bar,” said Draper.

That brought injection pressures lower than they have been for the past seven to eight years. “Along with those low pressures also came a need to change the injection characteristics and nozzle flow rates, so there was a whole package of things that had to happen for those low-EGR/no-EGR scenarios to work,” said Draper.

He thinks that this has changed all manufacturers’ approaches to emissions control and reckons they are now all looking at both low/no EGR and EGR with selective catalytic reduction (SCR) strategies.

“Whether you choose one or the other depends on what you want from the engine and the vehicle,” Draper explained. “Whilst some people say there is no penalty to be paid with the no-EGR route, our experience suggests that there is a BSFC (brake specific fuel consumption) penalty that comes with a no-EGR route today for Euro-VI. It’s not 10%, it’s not 5%, but we can’t see a way that a no-EGR engine really has the capability of running at the same efficiencies.”

Draper thinks there are around five or six options for heavy-diesel engine developments between now and around 2020. This would include an upgrade in around three years’ time, with a further upgrade, or new engines from around 2018 to 2020. From a fuel-injection system perspective, current systems offer good efficiency and low leakages.

“There is an option to almost stay with what you’ve got,” said Draper. “There are things we can do to improve injection performance without going up in pressure. As people look at noise and efficiency and are still trying to get a bit more from the combustion system, we see a trend that will perhaps mean more multiple injections than we saw at Euro-VI. To do that we probably would do it in a more efficient way in improving some of the internals in our injectors. Some OEMs may want more pressure as well...They might want to go up to 2700, 2800, or 2900 bar.

“Then looking at new or large upgrade engines, we are aiming at better ways to integrate the fuel-injection equipment (FIE) in the engine. Today, some fuel-injection equipment looks like it has just been bolted on the side as an optional extra. When we’re involved upfront with OEMs, looking at the basic engine, as we are today, we are looking at how we best integrate the fuel-injection equipment so that it literally looks like part of the engine structure.”

Draper offers the Paccar MX-11 11-L engine launched in Europe with DAF in 2013 as an example of an engine with much more integration than previously. The benefit is that the fuel-injection system can take better advantage of the engine’s cooling and oil systems.

“It just becomes another part of that structure that has to be cooled or lubricated,” he said.

This also gives greater thermal stability for the fuel system. There are packaging advantages, too. If a fuel pump is integrated and no longer needs to be driven from a drive belt, it can free up space for another pump or compressor. Integration can also reduce airborne noise from a remote fuel pump.

Delphi is now much more involved at an earlier stage with OEMs to ensure that systems are more fully integrated. It is a process that Delphi calls “DIF” for deeply integrated FIE.

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