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Mercedes-Benz Re-Thinks Direct Injection

Benz Now Back On Track with CGI Direct Injection

Believe it or not, gasoline direct injection is a technology thats near sixty years old. Sixty years old? It makes you wonder what automakers were doing all the while with less efficient, conventional port fuel injection. Its funny how only now, in the middle of the first decade of the 21st century, were starting to hear about this alternative injection method, employed in Mitsubishis, Mazdas, Volkswagens and BMWs, among others. The real innovator, however, was Mercedes-Benz, which, way back in 1954 employed the worlds first fuel injection system in the classic 300 SL Gullwing coupe. It also happened to be the worlds first gasoline direct injection system, which

Direct injection, as we know it in the automotive world, started here, with the 300 SL. (Photo: Mercedes-Benz U.S.A.)

was derived from the Benz-designed engine featured in a Messerschmitt fighter aircraft a decade earlier.

The term gasoline direct injection, incidentally, comes from the process in which fuel is delivered to the engine; it is injected directly into the combustion chamber, through a common high-pressure fuel rail. About three years ago, when gasoline direct injection technology was still in its modern-day infancy, few

CLKs like these were the first modern non-diesel Benzes to feature CGI. (Photo: Mercedes-Benz U.S.A.)

cars featured it. At the time, the leading automaker was Mitsubishi, with its Carisma compact sedan and a few European-market Pajeros, while Volkswagen and Audi had just started featuring their version, called FSI. Of course, not one to be left behind, Mercedes-Benz once again invested in direct injection, developing its own version called Stratified-Charge Injection Gasoline, or CGI for short. Benz applied this technology to one engine, a 1796 cc (1.8L) inline four-cylinder that made 168-horsepower. It was available in the CLK and

Stunning. Beautiful, Powerful. Im not just talking about the CLS exterior, Im talking about the new CGI engine. (Photo: Mercedes-Benz U.S.A.)

the C-Class as a sort of mid-range engine, but it was neither quick nor glamorous, and the power that was produced wasnt particularly smooth nor was it delightful to listen to. It did what was expected of it, namely, cut back on tailpipe emissions and fuel consumption. Needless to say, almost everyone forgot about CGI.

Outside of Stuttgarts inner circle, no one knew exactly why Mercedes-Benz didnt advance this technology during the three years that it was on the market. It was unexplainable why Benz didnt scale up CGI production for its class-leading twin-turbo V12s, or its big, burly V8s,

Ceramic and metal piezoelectric injectors are what make the new CGI system so impressive. (Photo: Mercedes-Benz U.S.A.)

or at least employ it in more engines to compete with Audi and BMW. Instead, they did something much better with their time, something that Mercedes-Benz used to be very good at; they strove for perfection behind closed doors. At this years Geneva motor show, alongside a slew of 63-series AMG muscle sedans and coupes, Mercedes-Benz brought out its first vehicle to feature its all-new direct injection technology, the CLS350 CGI.

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-Bs long history building common-rail turbodiesels, namely piezoelectric injectors. You may have heard this term being mentioned

Some of the engines components were re-worked for heavier duty use. The engine must deal with up to 2,900 psi! (Photo: Mercedes-Benz U.S.A.)

once or twice in the news - always with reference to diesels - but its never meant a whole lot to anyone in North America. While theyre 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 theyre 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

CGI system is able to run lean, even in times when others cant. (Photo: Mercedes-Benz U.S.A.)

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 Benzs 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

292-horsepower and 269 lb-ft of torque are generated by the improved engine. (Photo: Mercedes-Benz U.S.A.)

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 CGIs 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 75 mph.

As it now seems, the payoff for Mercedes playing the waiting game has been well worth it, with results that are well beyond expectations when compared to the standard 3.5-liter V6. All things considered, the automakers 3.5-liter V6 engine is a respectable power source, and can be found extensively throughout the Mercedes-Benz range in everything from its C-Class sedan to the ML-Class SUV. In current production guise it makes 272-horsepower

The CLS350 CGI will replace the standard CLS350 in Western Europe. Will Benz do the same with 3.5-liter models in North America? (Photo: Mercedes-Benz U.S.A.)

and 258 lb-ft of torque, but adding the revised CGI injection system to the same engine generates more power and more torque, delivering 292-horsepower and 269 lb-ft of torque. And it gets better, as fuel consumption is down to as little as 26 mpg from 23 mpg on a mix of city and highway. The CGI version of the CLS is also quicker to 60 mph by 0.3 seconds, taking just 6.6 seconds.

Having positioned itself on the cutting edge of diesel technology with Bluetec, and now gasoline direct injection with CGI, Mercedes-Benz has returned to its tradition of perfection through innovation. Mercedes intends to replace the standard CLS350 with the new CLS350 CGI model, and eventually will phase out the non-CGI versions of other cars in favor of this powerplant. In the not too distant future, its also expected that Mercedes will add CGI to its smaller V6s and to its V8s as well. Theres been no word on whether Benz will offer CGI in North America, but with better quality fuels on the way and many competitors offering direct injection gasoline engines, its only a matter of time.

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