A variable-compression engine introduced by Saab Automobile AB last week could reach production in three to four years, says Saab's chairman.
The technology behind the engine 'has been a tough nut to crack,' said Bob Hendry, chairman of Saab and Adam Opel AG, both subsidiaries of General Motors. 'We think we've cracked it.'
Saab is becoming known for unusual engine concepts. At the 1995 Frankfurt auto show, the company unveiled several bizarre designs, including a piston with an integrated spark plug and a turbocharged engine that ingested windshield-washer fluid to reduce its emissions and improve fuel economy. Neither has made it into production.
However, Hendry said Saab still has a year of development before it can consider whether to commit to the variable compression engine. He added that Saab is looking for an independent engine development company to assist on the project.
Saab also believes that by adding direct injection and other technology, the variable-compression engine could run on either gasoline or diesel fuel. It currently can operate on gasoline, ethanol or methanol.
The five-cylinder, 1.6-liter concept engine, unveiled at the Geneva auto show, can cut fuel consumption 30 percent and reduce carbon dioxide emissions an equal amount, according to Saab. The company added that the engine will meet all current and expected emissions requirements worldwide.
The engine achieves compression ratios ranging from 8: 1 to 14: 1 through an adjustable upper section of the engine that consists of the cylinder head and integrated cylinders. Saab calls the upper section the 'monohead.' A hydraulic system adjusts the slope of the monohead in relation to the lower engine section as much as 4 degrees. That changes the volume of the combustion chambers.
The optimum compression ratio is determined by a special version of the Saab Trionic electronic engine-management system, the in-house system Saab has used on its turbocharged engines since 1991.
The engine runs at its highest efficiency for normal driving conditions at a stoichiometric 14: 1 ratio, when its performance is comparable to other 1.6-liter engines. When the compression ratio is lowered to 8: 1, the engine performs like a 3.0-liter engine with 225 hp and higher torque.
The lower ratio generates more power because the engine uses a mechanical compressor for supercharging. It delivers a maximum boost pressure of 2.8 bar, much higher than Saab's current turbocharging system.
A DISSENTING VOICE
'Compression ratio has always been an obstacle' since Saab began working on variable compression technology in 1981, said Per Gillbrand, Saab senior technical adviser for drivetrains and director of the engine project. But improvements in fuels and engine technology have solved that problem, he said.
Gillbrand, the pioneer behind Saab's turbocharging technology, is optimistic about the future of the engine, and he said he is receiving good feedback from consultants. 'I've never been on an engine project so scrutinized by experts,' he said.
But not everyone at GM is sold on the variable compression engine. Fritz Indra, executive director of advanced engineering for the GM Powertrain Group, said the Saab concept is a good experiment but might not be practical. He said if it does go into production, it would only be for an expensive niche vehicle.
That's all right with Gillbrand, who is well aware of Indra's skepticism. Said Gillbrand: 'Saab is a niche car anyhow.'