Direct-injection engines make a comeback

[Globalist]

Direct-injection engines make a comeback


By Wim Oude Weernink
Automotive News / May 23, 2005

GDI pros and cons
ADVANTAGES
Lower fuel consumption
Better performance, especially low-end torque

DISADVANTAGES
Higher cost of emissions controls and add-on equipment
Global lack of low-sulfur gasoline


How GDI engines work

In a gasoline direct-injection engine, gasoline is injected into each cylinder, where it mixes with air drawn from the intake port and is ignited by a spark plug. With conventional port injection, the air and fuel are mixed just outside the intake valve before being drawn into the cylinder.

There are two types of GDI engines. Lean-burn GDI uses less gasoline in the air-fuel mix than the theoretical, or stoichiometric, ideal. The injector and piston head are designed to keep the fuel centered on the spark plug. Lean-burn engines are extremely fuel efficient at low speeds, but high-sulfur gasoline can increase NOx emissions. The NOx levels must be lowered using a self-regenerating catalytic converter, which only works well on low-sulfur gasoline.

Homogeneous GDI engines use only the amount of air necessary to completely burn the fuel in the cylinder. The air-fuel mixture must be uniform to avoid emitting partially burned fuel. Fuel consumption is greater, but performance and low-end torque are improved.
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.

[Globalist]

GDI is the way to go. I am wondering why nobody tried RQL (Rich-Quench-Lean) approach like in gas turbines.

You start rich, and you quench it with EGR (preferentially cooled EGR), then stage the air (through a by-pass) to complete the reaction. That's the perfect recipe for NOX reduction because cooled EGR will knock NOX and increase efficiency.

If someone tries the idea and it works. I will ask for $1/engine (produced) :-)

[327]

did I or they miss something? Multi port injection has been around for quite a while now

[Globalist]

Originally Posted by 327

did I or they miss something? Multi port injection has been around for quite a while now

GDI is different from MPFI in the location of fuel injectors. In GDI injector is located in the cylinder head.

[327]

Originally Posted by Globalist

GDI is different from MPFI in the location of fuel injectors. In GDI injector is located in the cylinder head.

Oh i see, thanks

[Michael_S]

Didn't GM already own this technology in some of the 2003 Isuzu SUVs?
3.5 liter V6 that got 20 more horsepower and 2 mpg better than the previous generation...

... and then all of the models that offered it were killed. Why in the blue blazes did they get rid of it?

http://www.popsci.com/popsci/bown/20...534655,00.html

[doh]

It is good news, and technology is getting better. Yamaha, Ficth and others have been able to perfect it in outboards. Autos can benefit immensely from it.

[AMcA]

In other words, the good old reciprocating engine will live on! No wankels, no water engines, no turbines, no cars powered by flatulence.

Hooray!

[Bvonscott]

Sounds complicated to me. Anyone have a "lamens terms" description of how it works? Or a website?

[moman]

Originally Posted by Bvonscott

Sounds complicated to me. Anyone have a "lamens terms" description of how it works? Or a website?

It's quite simple. The fuel injector in screwed into the cylinder like a spark plug. Air comes through the intake valve, mixing with the fuel in the cylinder.
Conventional fuel enjection (port/sequential) has the fuel injector positioned above the intake valve, and fires when the valve is opened, in essence mixing the air/fuel mixture slightly above the valve.

The drawback I see is having another screw hole in an aluminum head. There are enough helicoils done now removing spark plugs every 5 years. Try removing a fuel injector after 15 years!

[mastrdrver]

This is something the teams have been doing in Top Fuel and Funny Car for quite a few years now, just without the electronics.

[IAMCANADIAN]

they should use it in GM's to give it MORE POWER and BETTER EFFICIENCY

[FightingChance]

Better hope the on-board ECM doesn't screw up though ;]

Serious, this would be a boon to tuners, would it not? If one could interface directly with the software, you could change timing and flow and all that, right?

[redimpss5]

Umm, someone forgot to show up at school. Top fuel injects at the exhaust, but hey..is that a hemi? (1962) MPI, DFI, TPI, TFI What ever you call it, as long as it has a PCM involved, all is well.

[moman]

Originally Posted by FightingChance

Better hope the on-board ECM doesn't screw up though ;]

Serious, this would be a boon to tuners, would it not? If one could interface directly with the software, you could change timing and flow and all that, right?

you can do all of that today.