Technical: Direct Injection

With Bosch gasoline direct injection, drivers benefit from higher torque at low speeds and therefore enhanced driving enjoyment. At the same time, the system reduces fuel consumption by up to 15 percent.

“Gasoline direct injection is now heralding the same kind of revolution that we previously saw in diesel engines,” says Dr. Rolf Bulander, the member of the board of management of Robert Bosch GmbH responsible for powertrain technology. In Europe, the technology is already on the way to becoming standard, and Bosch components can be found in sporty compact cars, touring sedans, SUVs, and sports cars.

Starting in 1951, Gutbrod was the first automaker to use Bosch gasoline direct injection in selected models of its Superior subcompact car. From 1954, Bosch made this technology available for large-scale series production in the Mercedes-Benz SL 300, the legendary “Gullwing.” The basic technical principle has remained the same over the years: the injectors spray the fuel straight into the combustion chamber in such a finely atomized state that it is immediately combustible. The fact that the fuel vaporizes permits greater compression, because the combustion chamber is additionally cooled. Although the new combustion method saved a lot of fuel, it took a long time before the technology gained widespread acceptance. Over decades, the company further developed gasoline direct injection with innovations such as laser drilling for the injection holes, which enables particularly exact mixture formation and clean combustion. This innovation earned Bosch, Trumpf, and the University of Jena the German Future Prize in 2013.

At the start of the new millennium, tough emissions standards in Europe brought gasoline direct injection to the mass market. This pattern is repeating itself, because vehicles will be allowed to emit on average only 95 grams of CO2 per kilometer by 2021. As a result, approximately half of new European vehicles with gasoline engines will have direct injection by as soon as 2016. “We are currently doing excellent business in Europe with gasoline direct injection. But in a few years, there will be lots of action in the U.S. and China too,” Bulander says. In these markets, the innovative injection systems are still largely restricted to imported vehicles. However, with automakers in China and the U.S. facing tough new emissions legislation in the future, they will increasingly adopt the new technology.

This will boost the fuel economy of U.S. pick-up trucks, European sedans, and medium-sized Asian cars in equal measure, saving motorists money at the pump. In addition, the economical systems make a valuable contribu-tion to the environment. This effect is already measurable in Europe, the cradle of and lead market for the innovative technology. In 2013, some 40 percent of all new cars on the continent were equipped with gasoline direct injection. Bosch experts estimate that these new vehicles save a total of around 1.2 million metric tons of CO2 a year, because they consume less fuel. “With innovative technology, Bosch is making powertrain systems energy-efficient, reducing emissions, and slashing the costs for every kilometer driven,” Bulander explains.

Yet the potential of gasoline direct injection does not end with making internal-combustion engines more efficient: it is also the ideal basis for electrifying gasoline engines. Its optimum design for downsizing allows for compact engines with few cylinders, which can be supplemented by electrical components. In such cases, a highly efficient IC engine forms the core of the powertrain and can be supported by electrical components during its less efficient running phases or even switched off altogether – such as in plug-in hybrids, which can drive up to 60 kilometers powered by electricity alone. “Gasoline direct injection and electrification complement each other perfectly,” Bulander says. Big reductions in CO2 emissions can be achieved by a combination of electrical components and direct injection.

Bosch’s boost recuperation system is a good example of how this works. The 48-volt hybrid goes perfectly with downsized engines. A particularly strong generator supports the engine at low speeds or during acceleration by working as a motor. This electrification measure alone can reduce fuel consumption by up to 15 percent. In real driving conditions with the coasting function that shuts off the engine, additional reductions of 10 percent are possible. That makes for total fuel savings of up to twenty-five percent. The system can thus help to meet strict emissions standards in the compact class.

For larger vehicle classes, a plug-in hybrid with gasoline direct injection can help achieve these targets. Here, greater electrification combined with more efficient direct injection results in a greater potential for savings than the boost recuperation system. The following rough calculation shows the advantage for drivers with an annual mileage of 15,000 kilometers: a person who commutes 20 kilometers to and from work every day in pure electric mode would end up driving about 10,000 kilometers a year – or two-thirds of their annual mileage – without using gasoline. For the remaining 5,000 kilometers, they would profit from the efficient gasoline direct injection. In total, the fuel savings enabled by the plug-in hybrid’s electrical components and gasoline direct injection would exceed 70 percent.

Explained: Gasoline Direct Injection