Advances in turbocharger design, manufacturing and materials are expected to boost the growth of turbocharged petrol direct injected engines by 30% over the next five years, according to supplier BorgWarner.

“Gasoline-engine turbocharging is not focused exclusively on increasing engine output, but also on combining exceptional engine performance with fuel economy,” said BorgWarner turbo & emissions systems head Roger Wood.

“These are among the most important challenges facing automakers all over the world. BorgWarner is at the forefront of the industry in terms of providing the technology solutions that enable our customers to meet the challenges of improving fuel economy and engine performance. In addition to conventional turbochargers, variable turbine geometry (VTG) technology will play a significant role in gasoline engines.”

Several automakers around the globe are exploring application possibilities for VTG technology in petrol engines. Worldwide, the use of turbocharged petrol direct injected engines is expected to grow to 2m engines in 2011 from about 0.5m in 2006. About 70% of these engines are expected to be produced in Europe, with the rest of in Japan, China and North America.

Downsized petrol engines with VTG technology can achieve the same output and dynamic engine response as normally aspirated engines with a larger displacement. At the same time, these improvements are achieved with much lower fuel consumption. Fuel savings are estimated at 15% and 20% compared to a larger traditional or port injected petrol engine without a turbocharger.

Until recently, VTG technology was limited to diesel engines. The technical challenge lay in developing materials capable of withstanding the much higher exhaust gas temperatures that are generated in petrol engines. In cooperation with Porsche, BorgWarner developed the first turbocharger with VTG technology for the 911 Turbo.

The key feature of the turbocharger is its adjustable guide vanes. At low engine speeds and low exhaust gas flow rates, the vanes in a closed position develop a high boost pressure. This pressure falls as the vanes are opened. As a result, the bypass system with the wastegate valve that is a feature of conventional turbochargers can be eliminated. The entire exhaust gas flow can then pass through the turbine wheel and be immediately converted into increased boosting. This considerably improves engine response in the lower rpm range, compared to a conventional turbocharger with a wastegate typically used in petrol applications.

To address the challenge of high exhaust temperature, high-temperature-resistant alloys are used for the VTG cartridge and vanes.

BorgWarner Turbo & Emissions Systems expects this technology to become established on a broad number of applications over the next decade.