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After rocky start, direct-injection engines make a comeback, although challenges remain

WIM OUDE WEERNINK | Automotive News Europe
Posted Date: 5/27/05
Better fuel economy and lower emissions from gasoline direct-injection engines are getting closer.

Most European automakers are preparing GDI engines for introduction in the next few years, starting with an engine developed jointly by BMW AG and PSA/Peugeot-Citroen SA.

GDI technology had a rocky start. Mitsubishi launched a range of GDI engines in Europe in 1998, claiming a 15 percent reduction in gasoline consumption and lower emissions. They were based on engines used in Japan.

But many European customers complained they were not getting 15 percent better fuel economy. Worse, some catalytic converters, which remove oxides of nitrogen, or NOx, were fouled by the high-sulfur gasoline sold in many European countries. Other drivers complained of rough transitions as the engines switched from lean-burn mode to homogeneous-burn mode when they accelerated.

Mitsubishi withdrew GDI engines from Europe, blaming the lack of low-sulfur gasoline. PSA also halted GDI sales in 2001, saying fuel economy was disappointing.

Other companies continued development. DaimlerChrysler has offered lean-burn GDI engines since 2000 in markets with low-sulfur gasoline.

In 2001, Volkswagen AG and Audi AG boosted sales of gasoline direct-injection engines after retuning them for performance rather than fuel economy.

Last year, BMW introduced a similar concept for its V-12 engines.

Supplier Siemens VDO Automotive Corp. believes GDI can capture 30 percent of gasoline-engine sales in Europe by 2008.

New approach

The industry's approach to GDI has changed from a lean-burn focus on reducing gasoline consumption to homogeneous combustion to boost performance. Engineers made the air-gasoline mixture richer, going from a lean mixture of more air and less gasoline to the ideal mixture of exactly the air necessary to burn the gasoline completely.

One major reason for the change in emphasis is manufacturing cost. Lean-burn technology needs special exhaust gas treatment to reduce NOx emissions.

"It does not work with a traditional catalytic converter," said Paul Kapus, head of gasoline engine development at Austrian engine developer AVL List GmbH. "You need a NOx catalyst that can regenerate."

That can add several hundred dollars per unit in production costs.

"Homogeneous combustion allows you to focus more on performance and does not need costly exhaust gas aftertreatment," said Rudolf Krebs, head of engine development at Audi. "But you still need low-sulfur fuels."

Precision tuning

Homogeneous combustion also needs more precise air-gasoline mixtures within the cylinder to avoid uneven burning that creates pollutants.

Designers are adding high-pressure injectors for even finer gasoline mists and positioning intake valves to promote swirling that helps provide even mixing and creates a concentrated ball of air-gasoline mixture near the spark plug. It works even better with turbochargers because the injected gasoline cools the incoming air.

"A second effect is a more spontaneous reaction at lower engine speeds," Krebs said. "It reduces turbo lag."

Performance-tuned GDI engines with turbochargers or superchargers can improve fuel efficiency by as much as 7 percent. BMW says the turbocharged version of its PSA joint-venture engine gets 15 percent better fuel consumption.

In many ways, GDI technology development parallels modern common-rail diesel engines.

One similarity is using common-rail systems to boost the pressure of diesel fuel delivered to injectors. Pressures that once were 580 pounds per square inch are now up to 1,595 psi. Krebs expects gasoline injectors to rise to 2,176 psi.

Other GDI developments include faster piezo injectors replacing magnetic-valve units and the introduction of multiphase injection.

Leading GDI suppliers include Siemens VDO, which plans to introduce piezo injectors by 2006; Robert Bosch GmbH, which makes control units, injectors and pumps; and Japan's Hitachi Ltd. for injection pumps.

Tasks remain

But challenges remain.

One is improving gasoline-injection patterns for more even burning. Many automakers will reposition injectors at the top of the cylinder rather than at the side. Vertical injectors are closer to spark plugs.

"They make for better mixture composition, allowing higher compression ratios and improved fuel efficiency," AVL's Kapus said.

Despite the new emphasis on performance, the promise of GDI engines nearing the fuel efficiency of diesel engines is alluring.

"We see split technologies," said BMW spokesman Wieland Bruch. "We will focus on Valvetronic variable camshaft timing and lift for America and China but develop lean-burn GDI elsewhere."

Both Valvetronic and direct injection reduce throttle losses (from air-flow friction) in induction systems. That's a key goal, said Fritz Indra, GM Powertrain's former boss of advanced engineering, who retired April 1. With reduced throttle losses, GDI engines can equal or even better diesel engines," Indra said.

Costs remain a barrier to widespread GDI application. VW says it will compensate for higher costs on GDI engines by economies of scale.

Because of cost, some automakers say entry-level models may continue using conventional indirect port-injection gasoline engines. But BMW says that, eventually, all of its gasoline engines will use GDI.

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Very interesting developments. From what I remember, the Audi direct injection engines seem to be getting good reviews from the press. The benefits, whether they are increased economy or increased performance certainly are intriguing.

The real question is ho w much more the technology will cost once it is widely available. Same goes for other technologies like Hybrids. The added cost of the technology is going to have to be justified for it to really take off and be accepted.

For example, JD Power (I believe they did the study) estimates that there is a very limited market for hybrids despite their current growth, and that they will reach a maximum market share of around 3.5% at their peak. One of the big reasons is that the added cost of the technology doesn’t pay for itself. I suppose the same will go for GDI engines.
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