By creating an engine with variable compression ratios, Saab thinks it may have found a way to dramatically increase fuel economy and engine performance per litre of displacement.
The Saab Variable Combustion (SVC) engine unveiled at the Geneva Motor Show solves the problem of the fixed compression ratio in a conventional engine -- that it's a compromise designed to suit a wide variety of operating conditions, including city traffic, highway driving at constant speed, or high-speed freeway driving.
The compression ratio of the SVC engine is continually adjusted to provide the optimum value for varying driving conditions -- 14:1 at low load in order to maximize the use of the energy in the fuel, and to 8:1 at high load to enable the engine performance to be enhanced by supercharging without inducing knock.
As a result, claims Kevin Smith of Saab Cars USA, "the SVC concept reduces the fuel consumption of a conventional naturally aspirated engine by up to 30 percent while at the same time providing impressive performance."
The supercharged 5-cylinder SVC concept engine has a displacement of 1.6 liters and is said to be as fuel-efficient under normal conditions as a conventional engine of the same size.
But, when desired, it is also supposed to be able to deliver power comparable to a highly tuned 3-liter engine -- 225 horsepower and 224 pound-feet of torque, to be exact. Per litre of displacement, that means the engine produces 150 horsepower and 147 pound-feet of torque.The SVC engine uses a cylinder head with integrated cylinders (aka the monohead) and a lower portion consisting of the engine block, crankshaft and pistons.