Bosch developing series production water injection system for SI engines to reduce fuel consumption and improve performance
Bosch is developing a water injection (WI) system for spark ignition engines in partnership with a pilot customer, said Dr. Rolf Bulander, member of the board of management of Robert Bosch GmbH and chairman of the Mobility Solutions business sector, in his talk on powertrain optimization at the Vienna Motor Symposium. The port water injection system comprises a water pump; a water rail; and injectors which have been designed to handle the specific challenges arising as a result of operation with water.
Dr. Bulander said that a WI system can enable up to a 4% improvement in NEDC fuel consumption by cooling the charge to minimize/avoid fuel enrichment; mitigate knocking (premature denotation); and enable an increased compression ratio. A port-injection WI system is low complexity and highly effective, he noted.
Increasing the compression ratio is one means of improving the efficiency of an engine; this, however, also increases the charge temperature and eventually leads to knocking. Thus the compression ratio of a spark ignition engine end up being a compromise between part-load efficiency and performance and efficiency at full-load conditions, he noted.
Current production engines typically retard ignition timing at high loads to avoid knocking. This, however, leads to a loss in fuel efficiency, reduced engine power, and increased exhaust-gas temperatures. Water injection (WI) can mitigate these drawbacks, if not remedy them completely, he said.
The use of water injection reduces fuel consumption at high loads and low rpm, and reduces or avoids of fuel enrichment and lower exhaust-gas temperatures at high loads and high rpm.
Both effects result in lower CO2 emissions in real driving conditions. The first effect also reduces CO2 under the conditions of the future WLTC test cycle.
Moreover, this reduced knock tendency can also be utilized to increase engine compression, which has additional benefits at part load. It also results in lower fuel consumption and reduced CO2 emissions in the areas relevant for the NEDC and WLTC.
WI can also be used to increase torque. The additional cooling of air makes a bigger charge possible, and thus greater torque.
Other optimization technologies. Dr. Bulander also touched on other powertrain optimization technologies, specifically direct injection at 350 bar, which improves mixture formation and reduces particulate emissions; further optimized turbochargers; the electronic clutch system (eCS) developed for manual transmissions; a 48-volt boost recuperation system; and electrification.