Ward’s 10 Best Highlights Gasoline Direct Injection (GDI) Engines

10 December 2005

Different types of gasoline direct injection.

Ward’s has announced its 10 Best Engines awards for 2006 with a focus on improved fuel economy as well as performance.

Ward’s editors noted the importance of two engineering developments on this year’s list: gasoline direct injection (GDI) technology and forced induction. Bill Visnic, Ward’s senior technical editor, called direct injection technology “the most important development the powertrain sector has seen in this decade.”

A gasoline direct injection (GDI) engine sprays the fuel directly into the combustion chamber of each cylinder (as opposed to a port fuel injection (PFI) or carburetor engine) and delivers significantly increased performance and decreased fuel consumption and emissions.

First-generation GDI systems are wall-guided—the spray hits the wall, and the formation of the fuel-air cloud depends mainly on the charge movements. A spray-guided technique uses the injection procedure itself and not the charge movement to ensure that a combustible mixture is brought to the sparkplug at exactly the right time, regardless of pressure and temperature conditions.

Three of the 10 Best feature gasoline direct injection:

• The Audi 2-liter TFSI (Turbocharged Fuel Straight Injection), combined with a variable-geometry turbocharger delivers 200 hp (147 kW). The injector, located on the admission side in the cylinder head, is served by a high-pressure pump driven by the camshaft and a pressure reservoir shared by all cylinders—the common rail system.

  The injector regulates fuel delivery with millisecond intervals, at injection pressures of up to 110 bar. By comparison, a manifold injection system operates at between four and six bar.

  With the 2.0-liter TFSI, the Audi A3 accelerates from 0–100 km/h in 7.0 seconds with combined fuel consumption of 8.8 liters/100km (26.7 mpg US) and CO₂ emissions of 211 g/km.

• The Mazda 2.3-liter DISI (Direct Injection Spark Ignition) combines with turbocharging to generate 256 hp (191 kW) with combined fuel consumption of about 12.7 l/100km (22.3 mpg). (Earlier post.)

• The normally aspirated Toyota 3.5-liter engine uses two injectors per cylinder to combine direct injection with a conventional port fuel-injection system. The high-pressure fuel system uses a pump driven by a dedicated lobe on the exhaust cam. A proprietary direct injection injector generates a fan-shaped spray pattern.

  The port injectors are secondary injectors. Unlike traditional staged injection where the secondary injectors come online as boost is introduced or high load is realized, this engine runs only the direct injectors at high loads. The engine—the 2GR-FSE—delivers 306 hp (228 kW) and combined cycle fuel consumption of about 11.9 l/100 km (23.7 mpg).

Other engine makers are moving rapidly to implement more sophisticated GDI schemes.

BMW, for example, has stated that it will implement spray-guided direct injection on all its gasoline models in the future, as well as regenerative braking and stop/start functionality. (Earlier post.)

DaimlerChrysler has shown a concept hybrid applying a spray-guided GDI V6 in a hybrid powertrain for a S-Class car. (Earlier post.)