Hidden Potential

Their reputation is not the best – but combustion engines have become cleaner and more fuel-efficient in recent years. Because gasoline and diesel will remain the most important automotive powertrains until the fuel cell is ready for series production, their fuel consumption must be further reduced. At DaimlerChrysler, much is being done to reach that goal.

49°N/9°E The dark green Mercedes-Benz CLS 350 GGI races through a steeply banked curve. Peter Lückert expounds on engine technology and fuel efficiency with a relaxed air, as if admiring the scenery on a Sunday drive in the country. In reality, his route is the test track at the DaimlerChrysler plant in Untertürkheim – more often home to prototypes equipped with technologies not yet ready for production. The car Lückert brings to a stop at the end of a long straightaway has been on the market since the summer of 2006. Today it gets a chance to demonstrate its capabilities on the test track, showing off an engine that DaimlerChrysler considers a milestone in fuel efficiency – and one Peter Lückert regards with pride as Head of Development, Combustion Engine Drive Systems.

“What’s most decisive today is a new engine’s fuel savings” Peter Lückert, Head of Development, Combustion Engine Drive Systems

CGI stands for a technology DaimlerChrysler calls “sustainable engine management.” Stratified Charged Gasoline Injection, is full name, denotes spray-guided direct injection of fuel into the cylinder, where the gasoline is made to ignite through a highly sensitive process: A newly developed piezo injector releases precise doses of fuel in fractions of a second in optimal position with relation to the ignition spark, achieving minimal energy waste. The 3.5-liter six-cylinder engine consumes 10 percent less fuel than earlier models whose injectors were located outside the combustion chamber in the air intake. Despite the drop in fuel consumption, the engine gains 20 horsepower and achieves 270 foot-pounds (365 newton-meters) of torque, making it “perceptibly more agile in initial acceleration,” as Lückert remarks. But the power bonus is merely a welcome side effect. “What’s most decisive today is a new engine’s fuel savings,” he believes. Direct injection – with its more efficient combustion – is seen by major carmakers like DaimlerChrysler as the most promising technology of the immediate future.

Enlarge Alternatives are being sought for in many directions, and vast amounts of money are invested in researching environmentally friendly natural gas, hydrogen, and electric powertrains, as well as regenerative synthetic fuels. But most of those technologies are years away from market readiness. DaimlerChrysler has invested 1.5 billion euros to date in fuel cell technology, and maintains the world’s largest test fleet, with over 100 vehicles. Prototypes like the Mercedes-Benz A-Class F-Cell and the Mercedes-Benz F 600 are seen as part of a technological avant-garde. Many automobile manufacturers regard hydrogen as the ultimate fuel of the future.

But with its untenable production costs and nonexistent fueling infrastructure, fuel cell drive is not ripe for production. Furthermore, hydrogen cannot yet be obtained in adequate quantities with regenerative methods. Hybrid technology is a further possibility to use combustion engines more efficiently. But combining a combustion engine with an electric motor is a realistic option only in city traffic. Over long distances, it offers no decisive advantage. The technological challenge is thus to realize additional potential fuel efficiency in highway driving as well. DaimlerChrysler has concentrated on implementing hybrid drive where it is most effective: in city buses. The company is developing a “toolbox” of flexible hybrid modules for passenger cars, and the future policy of DaimlerChrysler will be to design all passenger cars to allow a hybrid option.

Conventional powertrains must gain in fuel-efficiency

Thus, until further advances are made, it remains impossible to imagine everyday automotive life without combustion engines. A McKinsey report entitled “DRIVE” predicts that gasoline and diesel powertrains will remain dominant through 2020. Additional possible fuel savings are estimated at 30 percent for gasoline engines and 20 percent for diesel – and such savings are urgently necessary. Greenpeace cites a figure of 900 million automobiles worldwide, producing 4 billion tons of CO2 annually, or 2.3 kilograms of CO2 for every liter of fuel burned (nearly 20 pounds per gallon) – a heavy burden on the environment. And the number of cars will continue to increase. It will reach two billion by 2030, meaning that manufacturers must move quickly to improve fuel efficiency.

Enlarge   European producers set a benchmark by promising to reduce the CO2 emissions of their fleets by approximately 25 percent between 1995 and 2008, to an average of 140 grams per kilometer (225 grams per mile). Given their varying product portfolios, different manufacturers had different target values. DaimlerChrysler was able to reduce the average CO2 emissions  of its European Mercedes car fleet by 20 percent since 1995 – and in Germany since 1990, by 30 percent. The average fuel consumption of the Mercedes car fleet has fallen by 3 liters per 100 kilometers since 1990: Back then, a Mercedes-Benz S-Class got 16 miles to the gallon (14.5 liters per 100 kilometers), while today a Mercedes-Benz S 320 CDI with comparable performance achieves 27 mpg (8.5 liters/100 km). Fuel consumption was lowered by nearly 45 percent – but of course it is still significantly higher than that of subcompact cars like the smart with its 67 miles per gallon (a mere 3 liters/100 km).

Improving fuel efficiency for premium segment vehicles and especially for SUVs with off-road capability remains a challenge that manufacturers like DaimlerChrysler must face. Of all new Mercedes-Benz automobiles sold in Europe today, 38 percent use less than 6.5 liters of fuel per 100 kilometers, achieving mileage in excess of 36 mpg. That is a step in the right direction, but further steps will be necessary if environmental goals are to be reached.
The current trend is “downsizing”: With intelligent injection technology, turbochargers, and compressors, smaller engines generating higher performance can be operated under part load for lower emissions and reduced fuel consumption. Today’s engines draw 50 percent more power from a given quantity of fuel than the engines of 1990. Diesel engines especially – thanks to common-rail direct injection and precise piezo injectors – are more powerful, quieter, and less thirsty. The new generation of four-cylinder diesels from DaimlerChrysler to be rolled out next year uses half a liter less fuel per 100 kilometers than current engines. Above all, the new diesel engines are cleaner: At the latest North American International Auto Show in Detroit, DaimlerChrysler presented the cleanest diesels on earth, the Mercedes-Benz E 320 BLUETEC and the Mercedes-Benz Vision GL 320 BLUETEC.