Twice the advantage

The twin-charge TSI (twin-charger stratified injection) petrol engine is in the sleek Scirocco coupe. Photo / Alastair Sloane

Volkswagen's twin-charge technology dominated the 2009 engine "Oscars" in Germany by picking up three gongs: engine of the year, best "green" engine, and best engine in the 1 to 1.4-litre category.

It was one of the more significant results in the 11 years of the competition and comes as carmakers turn to technology to meet new emissions and fuel economy standards.

A panel of 64 judges from 32 countries choose the 1.4-litre TSI (twin-charger stratified injection) petrol engine as its standout performer, two years after the technology first appeared.

VW introduced the first of its 1.4-litre TSI engines in New Zealand in late 2007, replacing the 1.6 and 2-litre petrol units in the Golf hatchback line-up.

TSI had just been named the year's best new technology at the Frankfurt motor show. TSI uses a supercharger in tandem with a turbocharger. There is also a TSI engine that uses a turbocharger alone.

Said VW New Zealand general manager Dean Sheed at the time: "TSI is the future of smaller-capacity petrol engines as far as VW is concerned.

"The 1.4-litre engine has more power, better fuel economy and cleaner exhaust emissions. It's what our customers want."

The twin-charge TSI engine is now available in New Zealand in the sixth-generation Golf and new Scirocco coupe, where it produces 118kW at 5800rpm and 240Nm of torque between 1500-4500rpm. In contrast, the optional turbocharged 2-litre engine in the Scirocco puts out 147kW and 280Nm.

VW says its aim was to build a small-capacity petrol engine that provided performance and driveability that was about equivalent to the output of the carmaker's discontinued V5 2.3-litre, but with improved fuel consumption and lower emissions. Using a turbocharger alone to get more air into the engine didn't produce what VW wanted. A turbocharger runs off the engine's exhaust gases. The upside is that it doesn't sap engine power. The downside is the delay before exhaust gas pressure gets high enough to work the turbo to force more air into the mix. This is known as turbo lag.

A supercharger runs directly on engine power and works instantly. But the higher the revs the more power it draws from the engine. Result: it isn't as efficient at the top end.

TSI combines the advantages of turbocharger and supercharger but leaves the disadvantages behind, says VW.

Early tests of a 1.4-litre unit proved VW was on the right track. The TSI test engine produced 125kW (170bhp) of power at 6500rpm, and 240Nm of torque between 1500 and 4750rpm, similar output to the V5. It's this flat line of torque - at 1000rpm the engine is producing 175Nm - that contributes to improved driveability.

Between engine speeds of 2400 and 3500rpm, both the supercharger and turbocharger contribute to boost pressure. At 3500 rpm the supercharger is deactivated through a magnetic clutch, leaving just the turbocharger in operation. VW says the transition between the boosters is seamless.

TSI also improves fuel consumption at speed. At a constant 180km/h on a German autobahn, up to 40 per cent of fuel use in a standard car goes towards cooling its exhaust system. The TSI engine, says VW, doesn't use any additional fuel for cooling the exhaust until speeds exceed 210km/h. That was one of the engineering goals for the direct-injection 1.4 unit.

TSI also provides relatively low town-and-around fuel consumption - around 7 litres/100km in the Golf - and significantly cleaner exhaust emissions.

Dr Ruediger Szengel, head of petrol engine development for VW, accepted the engine of the year award.

He said: "Small engine capacity means low friction losses and high refinement.

"Induction boosting provides the ability to operate with long gearing, further benefiting fuel economy. Direct injection allows the use of a high compression ratio in conjunction with high boost pressures providing additional efficiency benefits.

"For similar reasons TSI technology avoids the need to inject extra fuel to cool the mixture at higher power outputs, providing TSI engines with a further fuel consumption saving over conventional, boosted petrol engines."