A Fuel-Sipping Engine

An engine from Lotus and Continental Powertrain consumes 15 percent less fuel.

A research project in the UK has developed a gasoline engine that it claims can reduce fuel consumption by 15 percent without losing power.

Trial combustion: A test engine from Lotus Engineering used to develop a new, efficient engine design. Credit: Lotus Engineering

The key to the new design is the way in which fuel and air are separately introduced into the engine cylinders. By experimenting with different regimes for directly injecting fuel while varying the opening and shutting the air inlet valves, the researchers say they have achieved the major breakthrough in performance--and developed a "concept-car engine" that is gaining interest from big auto makers.

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The aim of the project, a collaboration between two leading car engine development companies, Lotus Engineering and Continental Powertrain, and two universities, Loughborough and University College London, is to reduce losses caused by the engine throttle. In conventional engines, the throttle is kept partially closed except during full acceleration, obstructing the flow of air and reducing the pressure and density of the air that enters the cylinder. This forces the engine to work harder to pull air into the cylinder. That wasted energy can be saved by controlling the mass of air that enters the cylinder not with the throttle, but by varying the timing of valve openings at each cylinder. This also enables engines to be made smaller and more efficient.

Such adjustments aren't possible with conventional variable-valve engines, which use mechanical controls that restrict their operation. But Lotus Engineering has developed a hydraulic system that it says enables "complete control" of the timing, duration, and lift of the valves. The researchers concluded that the best configuration of valves was four for each cylinder, two for air intake and two for exhaust. According to the company's principal engineer, Graham Pitcher, engine output could be controlled by closing one intake valve and slightly opening the other.