In the shrinking combat zone between gasoline and diesel engine technology, tactical maneuvers are under way that could see significant advances by the compression-ignition side.
Past strategic movements by diesel have been countered by major gasoline victories in recent years, including very effective downsizing that has seen the emergence of 3-cylinder solutions allied to highly effective turbocharging. These moves have demonstrated that spark ignition is taking the offensive in the campaign for lower CO2 emissions. Diesel, though, seemed to be resting on its laurels.
But much is happening in diesel-combustion technology, asserts John Fuerst, President of Delphi's Powertrain Division. This may be surprising, because it could be assumed that after decades of development across the industry, data would be extensive. But there is far more work to be done, and a considerable part of it will be at Delphi’s new Advanced Diesel Injection and Combustion Center in Luxembourg.
Located at Delphi’s established Customer Technology Center, the new facility brings together diesel and gasoline research in one location. It will help coordinate research with customers’ advanced engineering groups. Speaking at its official opening, Fuerst told AEI that the Center’s teams of specialists are set to achieve “significant progress” in the simultaneous improvement of power and emissions.
“Our big investment in Luxembourg is our advanced combustion and injection spray laboratory," he said. "When we prioritize our development activities, CO2 always comes first, but other controlled emissions are also getting a lot of attention (including NOx) as we work to get more power and efficiency."
Fuerst noted that Delphi's main investments are in analytical systems that allow engineers and scientists to see inside the combustion chamber in real time during the injection and combustion events. "With better combustion, we get improved fuel consumption and lower emissions without using extra control systems,” he said.
New injection-spray analysis tools
Delphi regards its Luxembourg spray chamber, one of many laboratories at the site, as being “unique,” with an ability to monitor droplet images using a camera capable of up to one million images per second.
Control of the injection event is a common issue for the laboratories at the Luxembourg Center. This is achieved through ultra-precise control of the opening and closing of the injector. The new spray characterization laboratories are already revealing how fuel droplets and ligaments are forming as injectors close, which Delphi states is a source of emissions that can be reduced via further refinement of injector valve and nozzle design.
The Center also has a very comprehensively equipped climatic and altitude wind tunnel with -30° to +50°C thermal capability and wind speeds of up to 160 km/h (100 mph) with a second tunnel capable of 250 km/h (155 mph).
But a serious drawback of diesel engine technology remains cost. At present, a typical gasoline engine may be only about half the cost of a diesel unit. Fuerst explained that eliminating complexity would contribute to reducing the cost of a diesel engine and would enhance reliability.
“Where possible, we want to reach our targets by making existing technologies better—and that includes simpler—as well as offering higher performance,” he said.
Fuerst is convinced that cost reduction has great potential and that it can complement a weight reduction—and vice versa. An example concerns Delphi’s advances, and potential advances, in fuel pump design. The company’s first generation of pumps were made of steel and weighed around 5 kg (11 lb). The current generation retains steel for the pressure head but incorporates an aluminum housing, halving weight and “significantly” reducing cost.
There is more to be achieved by working closely with an OEM to eliminate the pump housing and use the engine block or cylinder head, with the high-pressure pump positioned on either. The pump would then be actuated by a lobe (or several) on a rotating shaft—ideally the existing camshaft or crankshaft. “So the current housing and drive system can be eliminated and weight cut to around 1 kg (2.2 lb),” stated Fuerst.
Although Delphi has not issued a precise figure, cost reduction is expected to be up to 30% and a CO2 advantage would also be gained. A version of this application—which is relatively simple and low cost—is currently available for vehicles sold in India. The Luxembourg Center is now working on the next generation for use by European vehicles. This will focus on higher injection pressures, weight reduction, and enhanced levels of integration.
3000-bar injection on the way
The cost gap between gasoline and diesel engines will narrow, Fuerst believes, particularly as emissions standards are converging. However, at present quantifying that improvement in cash and timescale terms remains challenging, and will always be subject to variation as new technologies are introduced.
Common rail pressures are set to rise markedly. To meet Euro 5 requirements for light-duty vehicles, sub-2000 bar (29,000 psi) systems were the norm. “To meet Euro 6 and Euro 6C requirements, additional pressure does bring value," noted Fuerst. "Our light-duty system currently offers up to 2200 bar, with 2500 bar ready for next-generation systems.”
Heavy-duty engine applications are already up to the mid-2000s, and 3000 bar (43,511 psi) is approaching. Pressure levels of this magnitude are also likely for cars and light commercial vehicles.
Delphi is also focused on reducing diesel NVH. “We are continuing to refine multiple injection strategies—using more events—to further control combustion noise through a smooth rate of heat release; but higher peak combustion pressures will always create noise concern,” he explained.
Delphi also considers through-life efficiency: “We have to make sure that as the vehicle ages, noise and emissions stay low, and that performance change is minimized.”
The Luxembourg complex has an NVH laboratory that spans a frequency range of 125 Hz to 10 kHz where Delphi engineers work to reduce sound at source level.
Reducing diesel-hybrid costs
While gasoline engine cylinder capacities continue to shrink, a minimum size for diesels is more complex to establish. Fuerst sees around 400 cm3 per cylinder as a possible minimum when all aspects are taken into consideration. Turbo-matching and surface area-to-volume are concerns.
“We see some engine manufacturers reconsidering and going up from 400cc. If 400cc is seen as a bit of a barrier, then it follows that downsizing will stop at 1.2 L for three-cylinder diesels,” he said.
Diesel hybrids continue to be controversial within the industry due to cost, compared with straight diesel powertrains and gasoline hybrids. Although Delphi has technologies on the pioneering Peugeot 3008 diesel-hybrid, Fuerst questions the payback to the end customer—a diesel hybrid may cost €3500 more than a straight gasoline-powered vehicle, he noted. But if Delphi can help lower the cost of diesel engines, that would make a difference in the cost of hybridized diesel vehicles.
If electric vehicles—probably in the form of a fuel cell solution—ever achieve a market breakthrough, could the need to constantly strive to improve combustion engines fade into irrelevance? Fuerst said there are many “if and buts” to the answer, but he's certain that the ICE will continue to be further developed "for many years to come.”