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post #1 of 4 (permalink) Old 07-17-2004, 02:29 PM Thread Starter
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Direct Injection: What it is & why it's relevant

Although relatively little information is known about the new Toyota/Lexus RWD V6 family (the 3GR-FSE / 4GR-FSE) presently powering the latest JDM Toyota Crown and the upcoming new-generation Lexus GS and IS, one of its prominent characteristics, at least in its current Toyota Crown application, is Direct Fuel Injection.

What little I knew about Direct Injection is that its first production application was in certain JDM Mitsubishi models, that it provides both more power and better fuel economy than current Electronic Fuel Injection, and that it didn't immediately come to North America because DI, like modern Diesel engines sold in Europe, does not work well with our "dirty", high-sulfur fuel.

Recently, however, both BMW (in its 760i V12) and Isuzu (in its 3.5-liter V6) have brought direct injection to our shores. And Car & Driver editor Csabe Csere, in his June 2004 Steering Column, wrote an excellent, informative article about Direct Injection. Here's an edited version:

Will gasoline direct injection finally make it?
Powertrain experts have been touting gasoline direct-injection engines for many years. As has been the case with automated cars and carbon-fiber construction, the passage of time hasn't brought this particular future any closer—until now. With its redesigned A6, Audi is introducing a 3.1-liter V-6 that will finally bring direct injection to the mainstream in America.

Diesel engines have always used direct fuel injection. That means squirting fuel, under high pressure, into an engine's cylinders rather than into the intake manifold, which is the approach used on virtually every current gasoline engine. In a diesel, the process of injecting fuel directly into the combustion chamber at the top of the compression stroke initiates and controls combustion.

The first mass-produced car to use fuel injection was the Mercedes 300SL Gullwing, currently celebrating its 50th anniversary. With DI, the roadgoing SL generated about 10 percent more power and consumed about 10 percent less fuel than the carbureted engine that won Le Mans in 1952.

Within a few years, fuel injection began appearing in numerous street and racing cars. However, virtually all these applications employed indirect, or what's called port, injection. This meant that fuel was sprayed into the intake manifold behind each intake valve instead of directly into the cylinders. Port injection was cheaper because the injection took place at much lower pressure, the injectors were not subject to the searing heat of the combustion chamber, and the injection-timing requirements were relaxed.

Since there was no major performance difference between those port-injection systems and DI, the port systems soon dominated and were universally in use by the late '80s because they were the only fuel-metering system that could satisfy the ever-stricter emissions regulations.

DI, however, was not totally forgotten. In the '70s, Ford and Texaco worked on a system called Proco, for "programmed combustion." The goal was to use direct injection to achieve lean combustion, which requires a much lower than normal proportion of fuel to air, which can in turn improve fuel efficiency. But there was a limited understanding of combustion in the '70s, and the electronics were primitive, too, so the work did not advance.

But by the mid-'90s, technology had progressed to a point where Mitsubishi introduced a number of direct-injection engines in Japan.

These operated in lean mode during light-throttle use and switched to stoichiometric—a balanced fuel and air mixture—at high power. The problem was that in lean mode, the NOx emissions ran a little high. Furthermore, the normal three-way catalysts that attenuate the NOx emissions don't work well when fed the exhaust from lean combustion. Therefore, this type of direct injection was only feasible on small engines in small cars.

Recently, however, a couple of direct-injection engines have made it to this country. One is the 6.0-liter V-12 in the BMW 760Li, and the other is the 3.5-liter V-6 in the Isuzu Axiom.

Before getting into the DI details, you should know that the Audi engine, called FSI for "fuel stratified injection," is a showcase for modern engine technology. Its head and block are cast from aluminum. It has four valves per cylinder, operated by double overhead camshafts, each of which is adjustable over a 42-degree angle to optimize breathing and emissions at various rpm and throttle openings. Its valvetrain uses roller-finger followers for lower friction and greater valve lift. Its plastic intake manifold switches between runners that are short (15.6 inches) and long (27.2 inches) to enhance breathing across the rev range. The intake system even uses small retractable flaps in each intake port to increase turbulence during light loads.

The direct-injection system then takes this hardware up a notch. First, the evaporation of the tiny droplets of fuel injected directly into the cylinder (at between 450 and 1700 psi) cools the intake mixture, producing a denser charge, which means more power.

Furthermore, the cooler charge is less prone to detonation. Further detonation resistance comes from more rapid combustion, which occurs because although the overall charge mixture is stoichiometric, the charge is locally richer in the vicinity of the spark plug. This causes the mixture to light off more vigorously and progress more quickly. Faster combustion means less spark advance, which is inherently more efficient and further reduces detonation sensitivity.

The payoff is a lofty compression ratio—12.5 to 1. That's one to two points higher than that of typical engines, which often require premium fuel. (The Audi) engine will be happy on a diet of regular.

Higher compression extracts more energy from each droplet of fuel. Peak power for the 3123cc FSI V-6 is 255 horsepower at 6500 rpm; peak torque is 243 pound-feet at 3250 rpm. That represents 77.8 pound-feet for every liter of displacement. The comparable figure for BMW's 3.0-liter six is 71.8, 74.3 for the Infiniti G35 V-6, and 75.9 for the Porsche 911 flat-six.

Fuel-economy results for the new A6 are not yet available but are expected to be better than the previous model's, despite a slight increase in weight and substantially more power. Such efficiency makes DI attractive to automakers ranging from General Motors to Mercedes-Benz. Expect to see lots more of it in the coming years.

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post #2 of 4 (permalink) Old 06-07-2005, 02:33 PM Thread Starter
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   has just posted an interesting, informative article on the Direct Injection present and future of Audi, arguably the most bullish automaker when it comes to DI.

Audi Winding Down IDI Development
By Herb Shuldiner

Audi plans to phase out conventional port injection for gasoline engines.

All future gasoline-engine research at Audi AG will focus on direct-injection technology, the company's chief powertrain engineer says.

Development of indirect-injection (IDI) systems, currently used for nearly all gasoline production vehicles, is being de-emphasized, says Axel Eiser, Audi's chief of engine development.

“In the long term, we'll phase out ported-engine research,” he says. “It will happen in less than 10 years.”

Eiser estimates a 5% higher cost to build a direct gasoline injection (DGI) engine compared with a conventional IDI gasoline unit. Despite the higher cost, Audi is developing an all-new DGI V-8 scheduled to debut in the U.S. in about 18 months.

Eiser discloses Audi's engine-development direction at a press preview for the A3 subcompact held here recently. The initial A3s sold in the U.S. come standard with Audi's first DGI engine to combine DGI with turbocharging: a 2L DOHC I-4.

The new 2L FSI (fuel straight injection) 4-cyl. generates 200 hp compared with the 170 hp for the 1.8L turbocharged IDI gasoline engine it replaces. In addition to improved horsepower, the FSI engine delivers about 6% better fuel economy, a 10% torque increase in the low range and a 4%-5% torque increase at mid-range engine speeds.

To optimize torque response, the 2L FSI engine's exhaust manifold and turbine housing are cast as one module. This design, says Audi, directs the exhaust to the turbine more directly and immediately.

Eiser's team also mounted the catalyst directly behind the turbocharger to speed heat-up and reduce emissions to attain U.S. Ultra-Low Emissions Vehicle (ULEV) standards.

A single-piston, high-pressure fuel pump delivers gasoline to the common fuel rail. The operating pressure is about 1,500 psi (103 bar). Dual overhead camshafts with continuously variable timing for the intake cam also contribute to higher torque at low rpm.

Roller finger followers help to reduce friction in the cylinder head. In addition, twin balance shafts reduce vibration and noise.

Eiser says new high-pressure fuel injectors, a new piston-bowl geometry and tumble-enhancing intake ports were specially designed for the 2L FSI engine.

These features optimize mixture preparation and in-cylinder charge motion necessary for a turbocharged DGI engine. The result is quick and efficient burn of the intake charge and improved torque and fuel economy.

Eiser emphasizes Audi's FSI technology continues to advance. “We will make evolutionary improvements every two or three years, but the overall principle will remain for about the next 10 years,” he says.

The next big steps will be building all ancillaries - water and oil pumps - directly into the engine and designing for variable demand.

Eiser notes that with most conventional power-steering systems, for example, the unit's parasitic draw from the engine is constant, regardless of need. Variable-demand ancillaries, perhaps electrically driven or electronically controlled, siphon less energy from the engine.

Eiser also predicts increased use of turbocharging will support a trend toward smaller-displacement engines. “FSI is a better base for turbocharging,” he says. “But we're evaluating supercharging as well.”

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post #3 of 4 (permalink) Old 06-07-2005, 09:06 PM
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To elaborate a little, direct injection's most attractive feature is atomization. The fact that the fuel is under so much pressure aids in dispersement when it enters the chamber as it wants to spread out and balance from higher to lower pressures. The fuel also does not sit on the back of the valve, allowing it to mix more evenly with the air in the cylinder. This lack of puddling, that normally occurs on the back of the valve, and the intake manifold when the car is cold increases performance and lowers emissions output, compared to it's port injection counterpart. The reason it increases power and torque is due to a more controlled flame front and travel rate. This allows for timing to not be as advanced, and allows for more individual explosions to happen in a smaller time, which in turn means that more are happening at once.

The more fuel and air you can ignite off at one time, the more you can optimize the amount of cylinder pressure pushing down on the crank via the leverage of the rod. The closer we can get to the otto cycle, the more efficient the engine is. The amount of torque an engine makes is an average of the total BMEP (brake mean effective pressure) over time, the less time needed to complete combustion, the higher the average is, and the higher torque is read. You are able to use more of the potential energy of gasoline, in a smaller cycle of time. Direct injection does not allow gasoline molecules to band together, as they have a natural chemical tendancy to do when they are let loose into the atmosphere. The even distribution of the fuel will also minimize hot spots and spontaneous combustion, allowing for the higher compression and lower octane.

The next step after direct injection will be what Smokey Yunick has done already (pioneered), 15 years ago. It will come full circle and oppose some of the methods that direct injection employs to increase efficiency. This future system will actually heat up both the air and the fuel, as well as put the charge air under pressure, but the fuel under high pressure. If the fuel can be introduced in a venturi, it will change matter states into a gas and permeate the oxygen, mixing thoroughly and evenly throughout. It can then be kept heated so that the fuel does not reach a 'dew point' and condense, and then homogenized and perfectly mixed so that the fuel air mixture is perfectly even among the air entering the chamber. Timing can be reduced even further, the rate of burn and BMEP will be higher giving better performance. NOx will be higher because that is a by product of higher cylinder pressures or increased torque. This is why Hondas are so good with emissions, they do not have any torque whatsoever (the machines that build them have more torque then Honda engines themselves). Anyway, all of this will take place a few feet away from the cylinder, to allow for the change in states, the homogenization and proper distribution. The result will mirror Smokey's findings: 2.0L engine, 250 normally- aspirated horsepower and 60 miles per gallon. Smokey's design was a little different than mine: he heated the fuel to achieve a gaseous form, whereas I would want to play with pressure to get the fuel to a gaseous form, which I think would yield better results, and allow for any crud that is left in the fuel from the pump to also enter the chamber and be burned, and is a bit safer. My design is just a tweak of his, though, the man was a genius.


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post #4 of 4 (permalink) Old 09-05-2006, 10:54 AM Thread Starter
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An informative article from

Directly speaking - a look at developments in GDI
by Matthew Beecham

Despite a slow start, gasoline direct injection (GDI) technology is becoming popular, representing the next weapon in the emissions battle.

Direct injection means injecting the fuel directly into the cylinder instead of premixing it with air in separate intake ports. That allows for controlling combustion and emissions more precisely. But it demands more advanced engine-management technologies.

On the face of it, GDI offers a potential 20% improvement in fuel economy and emissions compared with conventional gasoline engines. The original promises put forward for the first generation GDI systems, however, were certainly overstated. The fuel economy benefits that were touted at the time were largely based on a stop-go driving mode in Japan. However, in Europe and more so in the US, a lot of the driving situations simply don't lend themselves to getting this type of performance out of GDI. Also, there were some technical shortcomings from the first generation systems that, in addition to the fuel economy, did not really come through.

Since then, the technical focus on developing GDI has centered on reducing fuel consumption while boosting performance through homogeneous combustion. “In the old days, you had injection systems to increase the absolute power of an engine,” said Eduard Rikli, CEO, of the Swiss-based Mikron Technology Group “These days, however, that is still the case but a much larger proportion is covered by systems aimed at keeping fuel consumption and emissions as low as possible. We shall see that trend for years to come.”

On balance, the reasons for the slow adoption of GDI are many and varied although principally result from the economic balances and compromises which have to be made with the introduction of any new technology. “The vehicle manufacturers have to make considerable investment in significantly changed cylinder head designs, engineering capacity and the general infrastructure associated with a new technology,” said John Clack, commercial manager, automotive, Bosch UK. “In the US, despite the recent increases in crude oil prices, they have maintained a low fuel price policy. This has offered little incentive for the introduction of fuel saving technologies, whether GDI or diesel.

In Europe the emphasis has been on CO2 reduction and here, because of its higher thermal efficiency, diesel offers distinct fuel saving advantages. This, coupled with the fact that many European countries have fuel taxation strategies which greatly benefit diesel has resulted in a dramatic growth of diesel engined vehicles at the expense of gasoline.” However, Clack believes that forthcoming emission legislation could be the key for the future expansion of GDI technology. In the US GDI engines already comply with SULEV legislation with simpler exhaust gas treatment than is required with port fuel injection to the extent that costs for the overall system are on a par. In Europe, local air pollutant limits are the key. “If future legislation brings limit values in line for both diesel and gasoline then the likely requirement for expensive exhaust after-treatment on diesel could move the overall cost/benefit equation in favour of gasoline,” said Clack. In late 2005, Bosch launched its second generation gasoline direct injection systems.

Michael Crane, North America director of powertrain gasoline systems, Siemens VDO Automotive, believes that adoption of GDI technology in the US has lagged both Europe and Asia mainly because market drivers like fuel consumption and carbon dioxide have been stronger in those regions. He said: “With the advent of significantly higher fuel prices and potential CAFE increases in North America, OEMs are just now turning to direct injection as a viable means of reducing fuel consumption while simultaneously improving both engine performance and emissions.”

Crane argues that GDI is not a panacea for fuel economy, but has multiple advantages that make it very attractive under both current and projected market conditions. “Moving the fuel delivery point from the intake ports to the cylinder eliminates the hang-up or storage of fuel in the ports, promotes more precise fuel delivery, and allows an increase in compression ratio. These features combine - often in synergy with other engine improvements like turbocharging and downsizing - to deliver increased fuel economy, reduced cold start emissions, and better engine performance. GDI is unique in that the consumer realizes the best of all worlds with no compromises.”

Crane also reckons that there is little doubt that homogeneous or stoichiometric operation will be the roll-out strategy for GDI in North America, pointing out that VW/Audi, Lexus, BMW, and Mazda are all employing this strategy today and the first domestic GDI engine will be introduced later this year in GM's Pontiac Solstice. He said: “Stratified charge, lean-burn operation is feasible with GDI and can yield double-digit reductions in fuel consumption; however, this strategy requires advanced aftertreatment to control the excessive oxides of nitrogen that are produced under such conditions. The incremental on-cost and operating costs associated with the advanced after treatment required to meet the stringent regulatory requirements in the US make this an unlikely scenario for the next several years.”

In Japan, Mitsubishi Motors was the first to introduce GDI technology, launching it on the Galant/Legnum’s 4G93, which was later rolled out in Europe in 1998. In 1999, PSA Peugeot Citroen borrowed (under license) the GDI technology from Mitsubishi Motors and introduced a GDI engine although this was subsequently withdrawn from the market in 2001.

Osamu Fukasawa of Denso Corp’s powertrain management systems engineering department agrees that GDI technology has not spread rapidly although he reckons that the technology has the potential to outperform the port injection gasoline engine in terms of reducing fuel consumption, increasing engine output, and exhausting cleaner emission. However, Fukasawa believes that the biggest problem of GDI is high cost relative to port fuel injection systems. “GDI technology requires high pressure pump and high pressure injectors,” said Fukasawa. “Further, if GDI technology is used to reduce fuel consumption, NOx would be increased in the exhaust to necessitate the NOx removal system such as NOx catalyst, resulting in further increased cost. Also with using NOx catalyst, the sulfur contained in gasoline would become a factor. Stringent emission regulations for PM would be another reason to prevent GDIs to spread in the market.”

Bosch’s Clack agrees that GDI component cost is higher than for port fuel injection, but points out that it is possible to save cost in exhaust treatment systems such that the overall effect can be neutral.

Although GDI does not compete head-on with variable valvetrain, it is regarded as a complimentary technology. In comparing the cost of GDI with variable valvetrains, Dr Walter Piock, manager, advanced gasoline – innovation Centre, Delphi Powertrain Systems, told us: “It is difficult to give precise figures. As a guide, choosing a direct injection over a MPFI system means you must replace the injectors and the fuel rail and introduce a high pressure pump in addition to the feed pump from the tank. So the major cost driver here is the fuel pump. If you look to implement a new valvetrain system then you have to completely change the cylinder head and implement high precision parts to the different cylinders. As a very rough guess, compared to a sophisticated VVA [variable valve actuation], I would say that a homogenous direct injection gasoline system would cost slightly more than half.”

Piock also sees a number of synergies between GDI and diesel direct injection in terms of the injectors, pumps, sensing, and control software. He said: “The fuel system pressure is one order of magnitude different which requires different concepts and designs for gasoline and diesel injection systems. While modern passenger car diesel engines are dealing today with 1600 to 1800-bar fuel pressure gasoline direct injection systems are working with less than 200-bar. Homogenous systems with the main injection during the intake stroke have currently operating pressures up to 150bar. For stratified systems, operating pressures currently go up to 200-bar. In addition we have to consider the use of more corrosion and wear resistant materials and sometimes special coatings as gasoline does not have the same protective properties as diesel.

In addition to different pressures, some of the latest diesel injection systems deal with up to seven injections in one engine cycle in order to improve fuel economy and noise generation and to meet the emission regulations, i.e. two pre-injections, one main injection and two or three post injections. On the gasoline side of the business, however, clean and efficient combustion can be achieved without this level of control.” As far as the control software is concerned, Piock also sees some similarities between diesel and gasoline fuel injection systems in terms of fuel handling, control and cylinder balancing. “The handling and modeling of these systems is very similar,” said Piock.

Although GDI will continue to be a weapon in the technology armory of the OEMs in their fight to reduce CO2, Denso’s Fukasawa predicts that homogeneous GDI will be the mainstream technology with a 10% share in Japan by 2010. He said: “The key points would be to realize the high potential of GDI relating to fuel consumption, engine output and emission, while lowering costs. Stringent fuel consumption regulations would be another factor that would accelerate the growth of GDI.” In North America, Siemens VDO’s Crane forecasts that 2 – 5% of the North American gasoline engine market will use direct injection by 2010.

Just-auto forecast market penetration could reach 12% in Western Europe by the end of this decade. However, if the fuel economy benefits can be truly demonstrated and GDI is proven to be a better solution over competing technologies, the potential market could be much higher.

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