Mercedes-Benz Re-Thinks Direct Injection
So, what new thing does the new and improved CGI bring to the world of direct injection? A surprising number of new things, actually, and much came from M-B’s long history building common-rail turbodiesels, namely piezoelectric injectors. You may have heard this term being mentioned once or twice in the news - always with reference to diesels - but it’s never meant a whole lot to anyone in North America. While they’re an essential part of the modern performance diesel motor, they have little value on this side of the Atlantic, as North American regulators are too busy banning them to welcome the cutting edge diesel technology. Nevertheless, piezo injectors differ from the injectors used in standard gasoline direct injection engines in that they’re made of metal and ceramic which change their state in a matter of milliseconds, when subjected to an electrical current. When an electrical current passes through the injectors, the characteristics of the injectors change, enabling them to quickly start and stop injecting fuel.
The use of piezoelectric injectors, as opposed to regular fuel injectors changes key elements of the combustion process. By nature, piezo injectors are precision components, designed to deliver an extra-fine spray of fuel. Combined with their ultra-quick change of state, and a fuel-line pressure over 200 bar (2,900 psi - some 50 times greater than a normal fuel injection system), fuel delivery ’strokes’ are optimal and consistent. What is unique about Benz’s CGI system is that through the use of piezoelectrics, fuel can be delivered to the engine multiple times during the combustion cycle and not just at one point. This allows for further improvements on power and torque, all while reducing emissions and overall waste gasses.
The fuel savings generated by direct injection engines come from their unique ability to run lean, a term used to describe a mixture of gasoline and air that is used for combustion. The injection spray in any direct injection system is ultra-fine and evenly distributed, allowing the engine to run lean, but under high compression. As a result, less fuel is used and therefore fewer emissions are produced. CGI moves the game up one step further with multiple-stage injection. The majority of direct injection systems only run on lean mode when engine loads are low, such as during low-speed cruising. The CGI’s multistage injection provides sufficient power and torque to ensure that the car can run lean during acceleration, and sustain that lean fuel to air mixture at speeds above 120 km/h.