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Automakers Introduce New Gasoline Direct Injection Engines at Detroit

GM, Porsche and BMW are among the automakers announcing gasoline direct injection (GDI) engines in new models introduced at the North American International Auto Show in Detroit. Gasoline direct injection technology offers improved combustion and fuel efficiency, offering automakers either a way to deliver comparable power with lower fuel consumption, or increased power with less of a fuel consumption penalty.

Direct injection delivers precisely metered and timed fuel directly to the combustion chamber, enabling a more precise mixture formation. This also has a cooling effect in the chamber, enabling a higher compression ratio, and improving engine efficiency. Less fuel is required to produce the equivalent horsepower of a conventional port injection combustion system.

GM introduced its new 3.6-liter direct injection engine—first announced in May 2006—as the top-level engine for its new 2008 Cadillac CTS. The V-6 engine with variable valve timing (VVT) delivers an estimated 223 kW (300 hp) of power and 366 Nm (270 lb-ft) of torque. Designed to operate with regular unleaded gasoline, the new 3.6-liter direct-injection V-6 produces power similar to many V8 engines, but with better fuel economy.

The new engine delivers a 15% increase in horsepower; an 8% increase in torque, and a 3% improvement in fuel consumption compared to its predecessor. Additionally, the application of direct injection reduces cold-start hydrocarbon emissions by 25%.

This is GM’s third engine with gasoline direct injection. In 2006, the company also announced an Ecotec 2.0-liter four-cylinder Turbo engine with direct injection on the 2007 Saturn Sky Red Line and Pontiac Solstice GXP roadsters. A naturally aspirated Ecotec 2.2-liter direct injection engine has been offered on Opel models in Europe since 2004.

BMW, which announced a new in-line six-cylinder, 3.0-liter bi-turbo gasoline engine with direct injection (High Precision Injection) and fully variable camshaft control to optimize combustion in March 2006 (earlier post), announced its first four-cylinder, 2.0-liter gasoline direct injection engine, to be applied in its newly announced 320i Convertible.

One version of the earlier-announced 3.0-liter with High Precision Injection (HPI), applied in the new BMW 330i Convertible, delivers 200 kW (272 hp) with peak torque of 320 Nm (236 lb-ft). Average fuel consumption under the EU standard is 8.1 liters/100 kilometers (29.0 mpg US). Another version of the 3.0-liter straight six, applied in the 325i Convertible, develops maximum output of 160 kW (218 hp) and peak torque of 270 Nm (199 lb-ft), with fuel consumption of 7.9 liters/100 km (29.7 mpg US).

The new 2.0-liter HPI engine develops maximum output of 125 kW (170 hp) and peak torque of 205 Nm (151 lb-ft). This first representative of the new generation of four-cylinder power units combines gasoline direct injection through centrally arranged piezo injectors with infinite, fully automatic adjustment of the double-VANOS intake and outlet camshafts as well as the flexible DISA intake system switching to the right operating mode at all times. Average fuel consumption in the EU test cycle is 6.7 liters/100 kilometers (35.0 mpg US).

Porsche introduced its first GDI units with three new engines for its newly introduced second generation of the Cayenne family. For the high-end 2008 Porsche Cayenne Turbo, that means a twin-turbocharged 4.8-liter V8 that produces 500 hp (373 kW) and 516 lb-ft (700 Nm) of torque. Combined with a six-speed transmission, the turbo SUV accelerates from 0 to 60 mph in 4.9 seconds and has a top speed of 171 mph (275 km/h).

However, the direct injection technology enables an improvement in fuel efficiency of up to 11% in highway driving compared to the previous generation Cayenne Turbo. Estimated EPA fuel economy values for the new Cayenne Turbo are 13 mpg for city driving and 20 mpg on the highway.

The 2008 Porsche Cayenne S uses a normally aspirated version of the 4.8-liter V8 that generates 385 hp (287 kW) and 369 lb-ft (500 Nm) of torque. The Cayenne S V8 even meets ULEV (ultra low-emission vehicle) status and according to preliminary testing data offers 14 mpg in the city and 21 on the highway. That is an improvement of 3 mpg or around 15% for highway fuel economy.

Finally, the entry-level Cayenne is powered by a 3.6-liter V6 that produces out 290 hp (216 kW) and 283 lb-ft (383 Nm) of torque. The new Cayenne gains LEVII emission status and preliminary fuel economy testing showed estimated EPA fuel economy figures of 18 mpg in the city and 22 on the highway. That is a fuel economy improvement of 3 mpg for city driving.

In addition to direct injection, the 2008 Porsche Cayenne S and 2008 Cayenne Turbo’s 4.8-liter V8 features VarioCam Plus valve control, a technology that enhances performance through infinite valve timing and valve lift adjustment on the intake side.



In other words, trying to make a gas engine more like a diesel. And where do they introduce this technology? In the same oversized pigs that they keep telling us that they think that people want.


Before anyone jumps in to berate the Cayenne, an improvement from 15 to 18mpg average over a 12,000 mile year will save 133 gallons of gas.

To achieve the same effect with a 35mpg Civic (say) you'd have to average 57.4 mpg.

Its easier to improve a Cayenne to 18mpg average than it is to improve a sedan from 35 average to 57mpg average


Before you look stupid read the text and you will see gm STARTED with smaller cars and smaller engines.

Roger Pham

True imitation of Diesel cycle is not quite advantageous with gasoline engine due to the higher particulate matter (PM) and NOx emission, but, with Hydrogen or methane/hydrogen mixture, PM is almost non-existent and NOx can be much lower from limited-temperature combustion moderated by highly-controlled fuel injection.
If you wanna exceed Diesel fuel efficiency with very low emission level (SULEV), bet on Hydrogen or CNG/hydrogen mixture with direct injection, while using glow plug or hot ceramic plug to assist with ignition, due to the higher self-ignition temperature of H2 or CNG.


It sure would be nifty to have valvetronic and GDI all in one head...I doubt there is enough room though. Diagrams always seem to show the valvetronic components taking up a good bit of space. I don't know about BMW's system but Mitsubishi uses upright intake runners that come down into the head from above (rather than from the side) to induce a reverse tumble which makes an ultra-lean a/f ratio easier to attain.

Rafael Seidl

GDI should not be seen as turning a spark ignition engine into a diesel. The mixture is still homogenized prior to ignition by a spark plug. The main advantages are improved scavenging (since there is no risk of additional unburnt HC getting into the exhaust), evaporative cooling during the compression stroke (permitting more efficient higher compression ratios) and much reduced fuel uptake by the engine oil during cold starts (yielding long oil change intervals).

Further improvements in fuel economy are possible with stratified injection in part load, in which a locally stoichiometric mixture near the tip of the spark plug is surrounded by pure air. Running globally lean sharply reduces throttling losses but requires the application of a more expensive lean-burn NOx aftertreatment system. Moreover, only second-generation spray-guided GDI delivers sufficiently low PM emissions in stratified mode to make do without a DPF. Mercedes' new M 272 DE V6 engine implements these technologies.

BMW uses stratified spray-guided GDI in the 335i and the fully variable Valvetronic valve train in the 325i. Note that combining them makes little sense, as each is quite capable of minimizing throttling losses by itself.

VW/Audi have abandoned stratification for now (confusingly, they retained the FSI/T-FSI moniker) and returned to homogenous GDI using injectors positioned on the side of the head and special piston crown geometry.



When you say combining GDI and Valvetronic makes little sense I strongly disagree. They are not just trying to create fuel efficient engines but powerful ones as well. A GDI engine with the ability to alter the valve lift (in addition to valve timing provided by vanos) can allow for a much higher performance level than a static valve lift setting and GDI.

Rafael Seidl

Patrick -

a powerful engine is one that delivers high rated power at full load. If you keep your displacement constant, increasing rated power means increasing specific power.

Variable valve lift reduces throttling losses in part load. At rated power, you're using maximum lift anyhow so variable lift contributes exactly zilch to rated power.

Stratified GDI also reduces throttling losses in part load. At rated power, GDI is always homogenous. The gain in specific power stems from the evaporative cooling. This lets you increase the compression ratio by about one unit, e.g. from 10.5 to 11.5 for a naturally aspirated and from 9 to 10 using a boosted engine, both running on RON 95 gasoline. At constant fuel flow, the theoretical power gain is on the order of 2.3% for the NA and 3% for the boosted engine. In a real implementation, this is modulated by increases in heat transfer and internal friction losses.

In other words, if you want a substantial increase in specific power, you need to increase fuel flow per thermodynamic cycle. This implies taking in more oxygen, to maintain stoichiometric combustion and keep the three-way catalyst operational. To achieve this, you need to increase the density of the fresh charge, e.g. by boosting and intercooling.



Lets say you set an engine up with a static level of valve lift that gets moderate fuel efficiency, good emissions and decent power.

Do you really think that will outperform the same engine which is able to have increased valve lift over the compromised setting? You are considering that the valve lift is maximized for power in the static engine setup BUT it is NEVER setup strictly for maximum power in even high performance cars as they would not meet emissions at low rpm and torque would suffer at low rpm. Typically, on a head with a static valve lift scheme you will have the lift such that it is great for mid-range rpm (and variable valve timing can make up for some low and high rpm power/emissions/fuel economy adjustments). Valvetronic would allow you to increase valve lift even further at high rpm for exceptionally high rpm power and then settle down to the mid-range and low lift range for fuel economy/torque/emissions at low-mid rpms.

Nuno Pereira

I can´t see how variable vavle lifting reduces throttling losses.It was told the cause for that is air pressure. During the intake stroke, at part load, the pressure in the crankcase is higher than the one on the top of the piston (diferences of pressure)which requires energy to be overcome. The same effect is easily obtained with a sering. All it takes is a finger to stop the air entering the sering. It will be impossible to overcome the atmospheric pressure if the piston is forced (we´re not strong enough)but if this was done in vacuum there would be no problem.
Now tell me how variable valve lifting can solve the problem (beside Atkinson cycle obviously). To avoid throttling losses, the cilinder has to be fully filled so the both pressures on each side of piston are the same


It isn't variable valve lift that reduces the throttling losses but in this case BMW's Valvetronic. Valvetronic removes the throttle body "butterfly" valve and there will thus be no vacuum in the intake manifold for the valves to have to fight against to open. Throttling (in the case of BMW's valvetronic ONLY) is controlled by the variable lift nature of the valves. Essentially the accelerator is "connected" to the valve lift rather than the throttle plate.


Valvetronic removes the throttle body "butterfly" valve and there will thus be no vacuum in the intake manifold for the valves to have to fight against to open. Throttling (in the case of BMW's valvetronic ONLY) is controlled by the variable lift nature of the valves.

OK, call them valve losses then, or the more generic pumping losses. You'll still have to restrict the airflow and incur those losses as long as you're stuck with a fixed air-fuel ratio.



Valvetronic (and other variable valve timing devices for a lesser degree) reduces pumping losses as follows. Suppose engine is working on half throttle – takes ½ of full charge of intake air. In classic design, piston on intake stroke sucks air with ½ of atmospheric pressure, and piston should work against half atmospheric pressure all stroke down. Now in Valvetronic design piston sucks air with atmospheric pressure half of the stroke (no negative work), then intake valve closes and second half of intake stroke piston is working against vacuum from zero to ½ atmospheric, or on average ¼ atmospheric for ½ stroke. Amount of negative work piston is doing in second case is 4 times less then in first case. It is very primitive illustration, in reality it is not as dramatic, but you can get the picture where reduction in pumping losses is coming from.


Thanks, that almost made sense. It's not quite adiabatic, so perhaps you can get an advantage, though it's still not clear to me how.



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