Injection hurtles forward: Bosch's gas/diesel injection projects

Automotive Industries, Nov, 2003 by Jonathan Walker

At a recent International Press Briefing held at the company's vehicle testing facility in Boxberg, Germany, Robert Bosch GmbH demonstrated its latest product and development projects in both gasoline and diesel fuel injection systems.

On the diesel side, May 2003 saw the launch of Bosch's third generation common rail system using compact, rapid-switch piezoelectric inline injectors.

According to Dr. Ulrich Dohle, President of the Diesel Systems Division at Bosch, the improved response of the new common-rail system gives the potential to reduce pollutant emissions within the engine by up to 20 percent, compared with current magnetic or piezoelectric systems. As such, the technology will make a major contribution compliance with the upcoming emissions legislation stages in Europe (EURO IV, EURO V).

In addition, the company is aiming, in 2005, to introduce an improved variable injector nozzle, intended to make diesels quieter and cleaner, as well as working on solutions for the exhaust emission treatment systems which will become obligatory for some cars and commercial vehicles.

"In Bosch's conventional Common-Rail system the injector is controlled by a magnetic coil," Dohle explains. "In the new piezoelectric injectors, we exploit the expansion of piezo crystals in an electrical field to produce an injector actuation effect switching in less than ten thousandths of a second, less than half the time required by a magnetic switch. A package of several hundred very small, thin crystals is used."

To exploit piezo technology, Bosch has integrated the actuator into the injector body. The movement of the piezo package is transferred to the rapid-switch nozzle needle without friction. "There are no mechanical components," Dohle confirms. "The advantages over magnetic and existing conventional piezo injectors lie in a more precise dosing and an improved atomization of the injected fuel within the combustion chamber. The higher switching speed of the injector means that the intervals between the individual fuel injections can be reduced, giving a more flexible control of the injection process."

A quieter diesel engine with improved fuel efficiency, cleaner combustion and more power results. In addition, the return flow of fuel not required for injection is very small--in a common rail system returned fuel represents the dissipation of the energy used to pressurize the rail. "This has allowed us to further reduce the delivery rate and thus the energy requirement of the high-pressure pump in the common rail system," Dohle says.

"The low tolerances for injection quantity and timing mean that the fuel dosage at the injector is very exact. This results in lower levels of exhaust pollutants. For example, one or two pre-injections of fuel prevent the emission of white and blue smoke just after a cold start and combustion noise is reduced. A supplementary injection following immediately on the main injection lowers the emission of soot particulate and a further injection can regenerate particulate filters, if fitted."

Overall, Dohle states, Bosch's third generation Common-Rail system with piezoelectric inline injectors is capable of reducing engine exhaust emissions by up to 20 percent compared with existing magnetic or piezoelectric systems.

Dohle notes that in 2006 Bosch is planning further common rail innovations. Ideas under consideration are injection pressures of over 2000 bar and injectors with variable injection geometry.

On the gasoline injection side, Dr. Rolf Leonhard, vice president development, Gasoline Systems Division looked back on an involvement which started in 2,000 in the form of the DI-Motronic electronic gasoline direct injection system.

"With its stratified charge technology, DI Motronic has reduced fuel consumption by about 10 percent compared with port fuel injection systems," Leonhard notes. "In the future, additional DI-Motronic features are set to make gasoline engines even cleaner and more fuel efficient."

Leonhard also stresses the importance of this technology with regards to the European automotive industry's commitment to reduce the average level of carbon dioxide emissions to 140 g per kilometer for new cars by 2008.

In combination with turbocharging, gasoline direct injection would also be a powerful tool in engine downsizing. A further Bosch development--new supplementary electric compressor would also promote downsizing by increasing torque at low revs, especially in smaller-sized supercharged engines.

Exceptionally Low Emissions

"To achieve exceptionally low emission levels Bosch has developed gasoline direct injection with exclusively homogenous mixture formation for exhaust gas treatment using commercial three-way catalytic converters.

"This allows current gasoline engines to meet the much tougher U.S. emission regulations which will be introduced in future," Leonhard states. "Both engine manufacturers and their suppliers are currently investigating 'jet-directed combustion' as a further development of stratified charge gasoline direct injection. It will make gasoline engines even cleaner and more fuel efficient, because the fuel will be even more efficiently burnt than before. Special injection valves necessary for the new combustion process are being developed."