Pressure in diesel engines

Joern Ebberg

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Why higher injection pressure saves fuel and also increases performance and torque

Outlook:"Over the next decade, the vast majority of diesel engines will manage with injection pressures of around 2,000 bar. Although 3,000 bar is not unrealistic, it will be limited to racing cars and high-performance diesel engines."
(Dr. Markus Heyn, President of the Diesel Systems division at Robert Bosch GmbH)

Common-rail diesel:The CRS3-25 common-rail system features Bosch's first piezo injector for passenger vehicles that works with an injection pressure of 2,500 bar. With their higher injection pressure, the new piezo models from Bosch are at the technological vanguard. The optimized fuel injection system atomizes the fuel more finely, improving combustion. Lower consumption is just one advantage of this technology.

By way of comparison:The pressure generated by a common-rail system is roughly equivalent to the pressure a 2,000-kilogram rhinoceros would exert standing on a fingernail. The compressed fuel is then finely dispersed at the speed of a supersonic jet.

Enhanced performance:A higher injection pressure generates greater specific power and increases torque. This is why increasing an engine's injection pressure makes it more powerful: the time available for combustion is extremely limited as soon as an engine is running at full load and high engine speed. This means the fuel must be injected into the engine very quickly at high pressure in order to achieve optimum power yield.

Turbo:The more air there is in the combustion chamber, the higher the injection pressure must be. A large amount of fuel has to be introduced within a short space of time to achieve a combustible air-fuel mixture. Multiple turbocharged engines – particularly bi-turbo and tri-turbo models – benefit from injection pressures in excess of 2,000 bar.

Emissions:A higher injection pressure is a key factor in reducing an engine's untreated emissions. Indeed, in compact-class vehicles it can often even help to avoid the need for exhaust gas treatment. The greater the injection pressure, the more finely both the injector and injection nozzle can be constructed. This improves atomization and results in a better air-fuel mixture, meaning that optimum combustion is achieved and no soot can form.

Systems competence:A higher injection pressure requires more than just a re-engineered injector. With its comprehensive diesel systems competence, Bosch is able to assemble a finely tuned system comprising not only the control unit, but also the fuel pump, the common-rail system and the injector.

Development of injection pressure – Bosch began with 100 bar

up to 100 bar
Goal at the start of development in 1922

over 100 bar
First series-production inline injection pump
(MAN truck, 1927)

300 bar
VE distributor injection pump (VW Golf D, 1975)

900 bar
Axial-piston pump (Audi 100 TDI, 1989)

1,500 – 1,750 bar
VP 44 radial-piston pump
(Opel Vectra, Audi A6 2.5 TDI, 1996; BMW 320d, 1998)

1,350 bar
Common rail (Alfa-Romeo 156 2.4 JTD, 1997)

2,050 bar
Unit injector system (VW Passat TDI, 1998)

over 2,000 bar
Common rail with piezo injector
(first deployed in the Audi A6 3.0 TDI, 2003/4)

2,500 bar
CRS3-25 common-rail system (available in series-production vehicles as of 2014)

Mobility Solutions is the largest Bosch Group business sector. It generated sales of 46.8 billion euros in 2019, and thus contributed 60 percent of total sales from operations. This makes the Bosch Group one of the leading automotive suppliers. The Mobility Solutions business sector pursues a vision of mobility that is safe, sustainable, and exciting, and combines the group’s expertise in the domains of personalization, automation, electrification, and connectivity. For its customers, the outcome is integrated mobility solutions. The business sector’s main areas of activity are injection technology and powertrain peripherals for internal-combustion engines, diverse solutions for powertrain electrification, vehicle safety systems, driver-assistance and automated functions, technology for user-friendly infotainment as well as vehicle-to-vehicle and vehicle-to-infrastructure communication, repair-shop concepts, and technology and services for the automotive aftermarket. Bosch is synonymous with important automotive innovations, such as electronic engine management, the ESP anti-skid system, and common-rail diesel technology.

The Bosch Group is a leading global supplier of technology and services. It employs roughly 400,000 associates worldwide (as of December 31, 2019). The company generated sales of 77.7 billion euros in 2019. Its operations are divided into four business sectors: Mobility Solutions, Industrial Technology, Consumer Goods, and Energy and Building Technology. As a leading IoT provider, Bosch offers innovative solutions for smart homes, Industry 4.0, and connected mobility. Bosch is pursuing a vision of mobility that is sustainable, safe, and exciting. It uses its expertise in sensor technology, software, and services, as well as its own IoT cloud, to offer its customers connected, cross-domain solutions from a single source. The Bosch Group’s strategic objective is to facilitate connected living with products and solutions that either contain artificial intelligence (AI) or have been developed or manufactured with its help. Bosch improves quality of life worldwide with products and services that are innovative and spark enthusiasm. In short, Bosch creates technology that is “Invented for life.” The Bosch Group comprises Robert Bosch GmbH and its roughly 440 subsidiary and regional companies in 60 countries. Including sales and service partners, Bosch’s global manufacturing, engineering, and sales network covers nearly every country in the world. The basis for the company’s future growth is its innovative strength. Bosch employs some 72,600 associates in research and development at 126 locations across the globe, as well as roughly 30,000 software engineers.

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