Print 103 comment(s) - last by randomly.. on Aug 29 at 12:13 PM

The upcoming Chevrolet Cruze will use a turbocharged 1.4-liter four-cylinder gasoline engine.

The Pontiac Solstice GXP uses a turbocharged, direct injection 2.0-liter four-cylinder engine.

Chevrolet Malibu Hybrid
GM goes high-tech to improve fuel efficiency

General Motors has seen the writing on the walls when it comes to efficient vehicles. Although gas prices have dropped more than 15 cents in the past few weeks, Americans are still gravitating towards smaller vehicles that are easier on the wallet when the times comes to fill up the tank.

GM has spent the past few years working on a number of technologies to bring lightweight, advanced, and fuel efficient powertrains to its vehicles and a number of them are already available or will soon be hitting the general populous.

GM's reinvigorated powertrain efforts revolve around traditional gasoline engines, diesels, hybrids, and Homogeneous Charge Compression Ignition (HCCI) engines according to Automotive News. GM is also looking to replace nearly all of its existing four and five-speed automatic transmissions with more efficient six-speed units.

For its gasoline engines -- much like Ford's efforts with its EcoBoost lineup -- GM is looking towards direct injection (DI) and turbocharging to extract V6 performance from four-cylinder engines and V8 performance from six-cylinder engines. GM's current turbocharged DI 2.0-liter four-cylinder engine can be found in the Pontiac Solstice GXP, Saturn Sky Red Line, Chevrolet HHR SS, and the Chevrolet Cobalt SS. In its current form, the engine delivers an impressive 260 HP and 260 lb-ft of torque.

In the near future, GM will apply turbocharging to its existing DI 3.6-liter six-cylinder engine to boost output from roughly 300 HP to around 400 HP. On the lower end of the spectrum, a new 1.4-liter turbocharged four-cylinder engine will finds its way into the Chevrolet Cruz -- the replacement for the Chevrolet Cobalt -- in place of the existing 2.2-liter normally aspirated (NA) four-cylinder engine.

On the diesel front, GM points to its upcoming 4.5-liter V8 diesel engine which will be used in its light-duty pickups and full-size SUVs. According to GM, the engine itself is 75 pounds lighter than traditional diesel engines and will allow its hefty trucks to achieve 26 MPG on the highway.

When it comes to hybrids, GM is already making ground with its mild hybrid system in the Chevrolet Malibu Hybrid and Saturn Aura Green Line. Eventually, the company's more efficient two-mode hybrid system -- currently used in full-size pickups and SUVs -- will find its way into the Saturn Vue Green Line and GM's other mid-size cars and SUVs.

Finally, GM is also banking on HCCI technology to extract diesel-like fuel economy from a gasoline engine. DailyTech first brought you news of this technology when Mercedes unveiled its F700 research vehicle. According to GM, adding HCCI to a gasoline engine boost fuel economy by 15 percent and significantly reduced harmful tailpipe emissions.

GM hopes to stay a step ahead of its competitors with its upcoming powertrain advances; however, its competitors likely aren't sitting still when it comes to their own efforts in striving for greater performance and engine efficiency.

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RE: Good to see
By randomly on 8/26/2008 7:06:20 PM , Rating: 2
a properly turbocharged engine at full throttle will be more efficient than a NA engine because of the improved thermodynamic efficiency.

RE: Good to see
By ziggo on 8/26/2008 10:23:05 PM , Rating: 2
False. Turbocharged engines are a wonderful thing. But from a thermodynamic efficiency standpoint they do not help. The energy used to compress the incoming air is essentially captured from the exhaust stroke, causing the exhaust pressure to be higher than for a NA engine.

At full throttle turbo engines have to run pretty rich to keep cylinder temps down. Also turbocharged engines generally have lower compression ratios, which is the only factor for the thermodynamic efficiency of a pure otto cycle.

The major benefits are size and weight. They also allow a smaller displacement engine to act like a larger one when necessary. Thus you can act like a small engine when cruising at low loads and still have the power on demand like a larger engine.

RE: Good to see
By Spuke on 8/26/2008 10:38:30 PM , Rating: 2
At full throttle turbo engines have to run pretty rich to keep cylinder temps down
Not with Direct Injection you don't. DI, boosted engines are run lean as hell. You also don't have to run as low of a compression ratio either as VW's run 10:1 and GM runs 9.2:1. I wouldn't be surprised if these new DI, turbo engines coming from Ford and GM run even higher than 10:1.

RE: Good to see
By ziggo on 8/27/2008 10:52:36 AM , Rating: 2
I have a DI turbo engine. My target afrs are still around 12 under full boost. The compression ratio isn't stellar either.

It could be designed to help, but the engine I have uses the DI cushion to up the boost to 16lbs. In any case, from a thermodynamic efficiency standpoint, NA cars are the way to go.

RE: Good to see
By Spuke on 8/27/2008 11:20:13 AM , Rating: 2
I have a DI turbo engine. My target afrs are still around 12 under full boost. The compression ratio isn't stellar either.
Ours are WAY leaner. Different tuning I suppose. What kind of turbo are you guys using? We have a K04 variant and it is capped to 20 psi in stock form.

RE: Good to see
By randomly on 8/29/2008 12:13:48 PM , Rating: 2
It's not necessarily true that the energy the turbo uses to compress the incoming air is captured from the exhaust stroke because of critical or choked flow. The mass flux of air becomes independent of the downstream pressure and so the turbo does not change the back pressure on the exhausting piston. The energy is drawn by the turbo results in a lowering of the exhaust temperature, and thus you are extracting more thermodynamic energy than you were before. This increases the engine efficiency.
This is particularly effective on Diesel engines.

If you are forced to lower the compression ratio because you running near the predetonation limits of the engine with a particular fuel you of course lower the efficiency of the engine which may chew up most of the added gain from the turbo.

The drawback to turbos are the added expensive, complexity, maintenance, and response lag. But properly used they CAN improve the thermodynamic efficiency of an ICE.

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