Although they may not be hugely popular at this point in time, Twin-Charged Engines have made their presence felt in the past and are about to have a bit of a resurgence in the modern car scene.
A Twin-charged engine is an engine which utilises both a supercharger and a turbocharger. Historically, they have been used in everything from the tiny little Nissan March up to Industrial Mining Trucks.
Without doubt, the most famous Twin-charged engine, however, belonged to the awe-inspiring Group B Lancia Delta S4.
Lancia leveraged Twin-charging to gain an edge in world rallying when rally was at it’s craziest. The Twin-charged S4 was deployed against such savage machinery as the Audi Quattro and Peugeot 205 T16.
It was beating them too, until the tragic fiery deaths of Henri Toivenen and his co-driver, Sergio Cresto resulted not only in the end of the S4, but the end of Group B as a whole. If only Lancia had been foresighted enough to fit a proper fuel cell to go along with their brilliant engine.
But I digress.
When you look at the way current engine trends are going, you begin to understand why Twin-charging makes sense in today’s car.
The way to get better performance from an engine these days, while still keeping it compact, is to force induction through it via either a belt-fed supercharger, or, an exhaust-driven turbocharger. The problem with this, is that when you do either of these, fuel consumption goes through the roof(and emissions do too).
Each forced induction method has inherent problems. Belt driven superchargers work fine at lower revs, but make the engine hungry for fuel at the top end, because it takes more and more ancillary energy to keep the thing spinning.
Meanwhile, with higher effective operating revs, a turbocharged engine is great once it’s running up to speed, but not so effective down low. Trailing throttle and low revs are not the domain of the large turbo.
So a Twin-charged engine makes an attempt to overcome these problems by running both types of forced induction in tandem. At low revs, the supercharger is doing the work. It engages from idle speed and keeps spinning until the effective operating range of the turbo begins(typically around 2500-3500rpm).
It stays engaged for a brief moment in time after the turbo has begun spooling so that right in the mid-range of the motor, you receive double lots of boost pressure.
Shortly afterwards, an electromagnetic clutch is used to disengage the supercharger from the drivetrain, effectively stopping it from becoming a drain on the engine as the revs rise higher.
An air-flap is used in conjunction with the electromagnetic clutch. This air flap bypasses the supercharger and gives the incoming air a conventional path straight through the intercooler and into the intake manifold.
Add in modern day direct injection fuel systems and smart ECUs, and you can have a powerful, torquey and relatively light engine solution, while retaining compact installation size and thrifty fuel economy.
In the most modern of Twin-charged engines, for example that in the VW 118TSI, you cannot feel the changeover from supercharger to turbocharger no matter how hard you try. Such is the influence of modern engine management systems.
Expect twin-charged systems to become more and more common in years to come.
Michael Adams from Test Driven Australia
Article Originally Written for Infinite-Garage