Infiniti Affirms Plans for Variable-Compression Engine

Nissan Motor Co.’s Infiniti arm is moving forward with plans to launch the industry’s first variable-compression-ratio engine next year in the QX50 midsize crossover vehicle.

Dubbed the VC-T (variable-compression turbo), the turbocharged 2.0-liter 4-cylinder unit promises to provide the performance of a gasoline-powered V-6 with the fuel-efficiency of a 2.0-liter diesel.

Mated with a continuously variable transmission, the VC-T is tuned to generate 268 hp and 288 lb-ft of torque in the QX50. Fuel efficiency is expected to be 27% better than the current QX50's 3.7-liter V-6.

The variable system features a multi-link design with an integrated piston/crank mechanism. This allows piston travel in the combustion chamber to be raised or lowered—thereby varying the combustion ratio—based on driving conditions and driver inputs.

A high-compression ratio (as great as 14.1) is used in city driving to optimize fuel efficiency and improve NVH characteristics. The engine switches to a low ratio (8.1) to boost power during acceleration and hill climbing. At the lower ratio, the turbocharger also increases power by pressurizing each cylinder with a denser mixture of fuel and air.

Nissan has been developing the engine for about 20 years. Company officials note that control systems have only recently advanced to the point to make the technology feasible to produce.

The VC-T engine is expected to be about 10% more expensive than a conventional 2.0-liter gasoline turbo but less expensive than a diesel engine. Fuel also will be pricier because the engine requires the use of premium-grade gasoline.

Watch a video about the technology here.