Design News for Mechanical and Design Engineers

Stuttgart, Germany--If engineers at Robert Bosch GmbH have their way, your next car will be powered by a diesel engine.

The development of direct diesel injection technology has been an ongoing preoccupation at Bosch, which spends about 6 to 7% of its revenues on new product R&D. This year, Bosch expects to spend $425 million (Dm) on developing diesel fuel-injection equipment.

The goal? To help make diesel engines cleaner, quieter, and more economical to operate, Bosch's David Robinson told journalists at a recent press briefing here. He is executive vice president of sales and application engineering for Bosch's Automotive Equipment Group.

One of the major advantages of direct fuel injection, which can be accomplished in several different ways, is lower fuel consumption. Bosch engineers claim a 15 to 20% improvement in fuel economy, which, in turn, leads to lower engine emissions.

Direct diesel injection systems obtain their efficiency through a combination of high pressure and tight control over fuel delivery and injection timing. Indirect injection is inherently less efficient because it requires a divided combustion chamber, which results in a pressure drop and greater heat transfer.

Consisting of a high-pressure pump (up to 1,600 Bar), a fuel rail that functions as an accumulator, and injectors with fast-acting solenoid valves, it allows for the control of injection pressure over the entire range of engine operation (see diagram). In this way, says Bosch engineers, it is possible to control the moment, duration, and fuel quantity with an unprecedented level of accuracy.

The fact that the engine designer can select the exact sequence of injection--effectively optimizing the combustion process--results in a substantial reduction in fuel consumption, lower exhaust emissions, and less noise.

Up until recently, the bulk of direct injection technology was directed toward commercial vehicles. But Bosch sees a burgeoning market in passenger cars, particularly in Western Europe where more than 20% of the production cars today are powered by diesel engines.

That number is expected to grow, spurred on in large part by high fuel prices in Europe. Today, Volkswagen, BMW, and Mercedes are among the companies with production diesel-powered passenger cars in Europe. Even Chrysler offers versions of its Jeep Cherokee and Voyager SE (see sidebar) equipped with a diesel engine.

In contrast, the U.S., where the number of diesel-powered passenger cars make up a mere fraction of the market, presents a very different picture.

Therein lies precisely what Bosch sees as a great market opportunity. "GM has the Opel engine, and both Ford and Chrysler have diesel-equipped models," stresses Robinson. "In our opinion, if we can collectively move product into the U.S. market, the popularity of diesels will spread."

Despite the obvious savings in fuel economy associated with diesel engines, getting from here to there is not without its obstacles. For instance, with gas prices low, there is little incentive to purchase more fuel-efficient vehicles. And most drivers don't relish going to a truck stop, or perhaps some other out-of-the-way place, to fill up.

Bosch's biggest challenge, however, may be figuring how to obliterate some not-so-fond memories of diesel-powered cars of the early 1980s.