Nissan’s premium arm Infiniti will unveil its 2.0-litre variable-compression petrol engine at the Paris motor show next month – and tests have shown it is just as efficient as a similar capacity diesel unit, says the company.
It is already being hailed in Europe as the ‘most advanced internal combustion engine ever created.’ The turbocharged 2.0-litre VC-T is said to offer the power of a 3.5-litre V6, but with around 27 per cent better fuel economy.
Nissan’s chief powertrain engineer Shinichi Kiga told European news outlets: “This is original and unique technology – a world first.” The carmaker claims it offers 10 per cent more performance and is at least 10 per cent more fuel-efficient than comparable turbocharged 2.0-litre petrol rivals.
Said Infiniti president Roland Krueger: “This is the result of 20 years of research for Infiniti and is the next step towards meeting emissions regulations.”
The engine has been developed entirely in-house at Infiniti and will at first go into the QX50 (at top), a mid-sized SUV. It is not known if the company will licence the technology to the Renault-Nissan Alliance and its links with Mercedes-Benz.
So how does it work in the in-line four-cylinder? Unlike a traditional petrol engine with a constant compression ratio of around 10.5:1, for example, the technology adjusts the ratio while the engine is in operation.
It alters the volume of the air/petrol vapour in the combustion chamber between the piston at top dead entre, or the top of its stroke, and bottom dead centre, or its lowest point in the up-and-down movement.
This varies the compression ratios, from a low 8.0:1 for better performance, to a high 14.0:1 for improved fuel economy. The engine automatically applies the optimum ratio depending on driving conditions.
Nissan engineers say the VC-T engine has a maximum output of 200kW/390Nm and that pairing it with a continuously variable transmission (CVT) is the best solution for maximum efficiency.
In a nutshell, the VC-T engine uses an actuator that pushes a control arm to change the angle at which the piston’s connecting rod meets the crankshaft. It’s a complex system that changes the stroke the piston reaches within the cylinder. It also eliminates the need for counter-rotating balance shafts, a requirement in all in-line fours.
By changing the stroke length, the engine can vary the compression ratio. Lowering the compression ratio allows the turbocharger to produce more boost without the risk of premature detonation, or ‘pinging’.
Increasing the ratio, say on a motorway cruising at 100km/h, improves fuel economy. ”Sophisticated engine control logic”, says Infiniti, along with electronic valve timing and direct fuel injection, allows VC-T to switch between normal and Atkinson cycle operation on the move.