But while many talk of futuristic hybrids, battery power and hydrogen, many automakers and suppliers already have gotten serious about saving CO2.
Several smaller engines already are in showrooms, and more are poised for launch.
Volkswagen cannot build enough of its downsized 1.4-liter TSI gasoline engine. The automaker is telling new customers not to expect delivery before 2009.
Renault launched its new Laguna sedan and wagon in 2007 with a 1.5-liter diesel as the base engine. Similarly, a 1.6-liter diesel is the smallest engine offered on the new Citroen C5, a rival to the Laguna.
"Every company is going for smaller engines," says Andrew Fulbrook, senior analyst at CSM Worldwide in London. "Right now it's the most cost-effective way of reducing CO2 emissions."
Robert Bosch GmbH, the world's largest auto supplier, has a stake in nearly every key CO2 technology. Bosch sees smaller engines as cost-effective.
-- GM: 1.6-liter turbo gasoline for sport version of Opel Corsa, Astra
-- Volkswagen: 1.4-liter TSI, replaces 1.6- to 2.0-liter gasoline engines
-- Fiat: 1-4-liter T-Jet, replaces 1.6- to 1.8-liter gasoline engines
-- Renault: 1.5-liter diesel in the Laguna, 1.2-liter gasoline turbo in the Twingo
-- Citroen: 1.6-liter diesel in the C5 offered as alternative to 1.8-liter gasoline engine
-- BMW: 2.0-liter twin-turbo diesel as performance option in 1 series
-- Ford: 1.6-liter turbo gasoline as alternative to 2.0- and 2.3-liter
-- Fiat: 900cc 2-cylinder gasoline and diesel for 500 and Panda
-- Renault: 900cc 3-cylinder turbo gasoline to replace 1.2-liter 4-cylinder; 1.4-liter turbo gasoline as alternative to 2.0-liter
-- Volkswagen: 600cc 2-cylinder and 900cc 3-cylinder for Up minicar
-- BMW: Twin-turbo diesel I-6 to replace diesel V-8
Prospect of fines"If we look at the CO2-reducing technology we have in our portfolio today and figure out how much it costs to reduce one gram of CO2, then hybrid is definitely on the very high end," Bernd Bohr, head of Bosch's automotive operations, told Automotive News Europe. "Turbocharging, downsizing and putting (in) gasoline direct injection costs about a third per gram of CO2 of what a hybrid costs."
Industry experts agree that the prospect of hefty fines in Europe for heavy CO2 emitters is driving development of technologies for smaller engines.
Making gasoline engines smaller can save up to 20 percent on CO2 emissions, says the Austrian engineering company AVL. Suppliers say this has exploded interest in environmental technologies.
"With the advent of these legal penalties, business planners suddenly have real (cost) sums to deal with," says Mark Criddle, senior manager at electric boosting specialist Controlled Power Technologies Ltd.
"Now automakers can put a figure in terms of euros per gram of CO2," Criddle says. "Everybody is seeing the price of fuel economy."
Also helping the downsizing move-ment is the disappointing fuel economy of many hybrids when used outside a city, says Richard Pearson, head of powertrain research at Lotus Engineering. Lotus is developing a smaller engine with Continental's powertrain unit and Emitec.
"Downsizing is a way of making a cost-effective and significant improvement to fuel economy that translates into the real world," Pearson says.
The gains may not be as great as with a hybrid, he says, but the solution is a lot cheaper. "They're better in real driving, not just in the test cycle," Pearson says.
Rinaldo Rinolfi, research and tech-nology vice president of Fiat Powertrain Technologies, says advanced downsized gasoline engines can bring a 20 to 25 percent CO2 reduction in urban driving and still save 10 percent while driving at high speeds.
"Further improvements of 3 percent can be obtained with stop-start and 5 percent with automated manual transmissions," he told Automotive News Europe in an e-mail.
Gasoline engines stand to gain most from downsizing. But to realize those gains, gasoline engines will need bigger changes in technology than the equivalent diesels.
For gasoline engines
-- Direct fuel injection
-- Turbocharger or supercharger
-- Variable valve timing on inlet and exhaust
For diesel engines
-- Common-rail fuel injection
-- Variable-geometry turbocharger
-- Variable valve timing
DownsidesPlus, the smaller engines present several problems that automakers must overcome before they will be fully acceptable to the consumer.
A downsized gasoline engine needs direct injection and a turbocharger to provide sufficient power under high demand. But the bigger the turbocharger for high-end power, the greater the inertia created by its mass.
That inertia slows the turbocharger's boost response and can result in a lack of torque at low engine speeds, says Lotus' Pearson.
"The Lotus approach is not to be too aggressive in the downsizing to preserve the naturally aspirated (off-boost) response," Pearson says. "Other designs that chase higher power and torque figures have high boost but suffer significant transient response problems."
Lotus compensates for the torque deficit though use of a variable valve train, Pearson says.
Volkswagen solves the problem on its high-specification TSI 1.4-liter gasoline engine by adding a supercharger to complement the existing turbocharger.
VW will not discuss the cost, but the industry consensus is that the engine probably costs about 2,000 to 2,500 euros ($3,000 to $3,800) more. That is about the same price premium paid for a high-end diesel compared with an equivalent gasoline engine.
For Criddle at Controlled Power, electric boost is the answer. The company was formed in the United Kingdom in January to develop former Visteon technologies, notably the VTES electric supercharger.
Criddle says VTES has the potential to deliver near-maximum torque "almost from idle speed" and eliminate waiting for turbocharger blades to reach working speeds.
He says using a supercharger for low-speed boost would allow engineers to design an accompanying turbocharger optimized for higher-speed use.
-- Mahle: 1.2-liter, 161-hp 3-cylinder gasoline
-- AVL: 2.0-liter, 200-hp DGI-tc gasoline concept shown in 2005
-- Ricardo: 2/4SIGHT gasoline concept: Switching between 2- and 4-stroke operation cuts CO2 by 27%
-- Lotus-Continental: 1.5-liter, 160-hp 3-cylinder gasoline turbo with integrated exhaust manifold
Twin-turbo solutionEngineers agree that current gasoline turbocharger designs are compromised. The units have to be small enough to give acceptable performance at low speed, but small units are vulnerable to overheating at high loads. For this reason, extra fuel is added — and thus wasted — to keep them cool enough.
A different solution, says CSM's Fulbrook, is a twin-turbo set similar to units used on some BMW and PSA/Peugeot-Citroen models. A smaller turbocharger works for low loads, and a larger one starts working when demand is higher.
"Honeywell and BorgWarner make enough of these," Fulbrook says. "I can't imagine they will be that expensive."
The other vital enabling technology for downsizing — gasoline direct injection — is now being built in millions of units by suppliers Bosch, Delphi, Continental and others and has developed economies of scale, Fulbrook says.
A further issue is vibration. Two- and three-cylinder engines have different noise vibration and harshness characteristics than standard four-cylinder units and require balance shafts, another item that absorbs energy.
Industry insiders say a diesel engine developed to meet Euro 6 emissions rules, which take effect in 2014, could cost the consumer about $1,500 more than today's Euro 4-tuned equivalent.
Fiat's Rinolfi estimates that it would cost $600 to $750 to reduce CO2 by 10 percent through downsizing; to reduce CO2 emissions by 20 to 25 percent, the cost would be $1,100 to $1,200.
Which is cheaper?So would a downsized gasoline unit including features such as electronic valve control and turbochargers still be cheaper than a Euro 6 diesel?
The answer may depend on whether automakers choose stratified rather than homogeneous combustion.
The technology for homogeneous burning is simpler and cheaper. Stratified combustion offers greater fuel and CO2 savings but requires more expensive aftertreatment for nitrogen oxide emissions.
Analyst Fulbrook thinks that even with stratified charge combustion, a downsized 1.3-liter tuned for Euro 6 might be slightly cheaper than a comparably performing diesel. "It certainly won't be more," he says. "A Euro 6 diesel hybrid will definitely be more expensive."
Cost is one factor that will determine whether sales of gasoline-powered new cars will rebound in Europe after a decade of decline against the diesel.
The other factor is whether automakers can convince customers that smaller engines really can deliver the same power and performance as the larger engines they replace.
Says Fiat's Rinolfi: "Since downsized gasoline engines will have both CO2 levels and fun-to-drive behavior similar to diesels, they will progressively take market share from diesels in particular in the lower segments."