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Inside common rail injection

Major changes in emissions requirements means major changes in diesel technology
Tuesday, March 1, 2016 - 09:00
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Automotive industry veterans have witnessed incredible technological change over the past three decades. It all started in the mid-80s with the electronic revolution, which only gained momentum over time and has changed everything we thought we knew about cars. If you’ve made your living in the automotive field that long, hats off to you because you are indeed a resilient and persevering individual!

Alvin Toffler wrote about this dynamic in his book Future Shock, which he published in 1970. Toffler said “the illiterate of the 21st century will not be those who cannot read and write, but those who cannot learn, unlearn and relearn.” Anyone who is still in the automotive game after 30 years has indeed learned, unlearned and relearned many times during their career. Based on Toffler’s definition, an automotive illiterate will have a very short shelf life.

(Photo courtesy of Robert Bosch LLC) Bosch completed the development of HPCR injection for mass production. They went on to release the design for passenger cars in 1997.

Diesel technicians have been experiencing their own private Future Shock in recent years, as major changes in EPA regulations have led to a revolution in diesel engine technology. Diesels were once renowned for noise and black smoke, which endeared them to their fans, but turned the stomachs of the general public. Emissions regulations played a primary role in putting an end to all that, but another significant factor was making the technology more palatable to the non-believer in an effort to increase market share.

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Of course, gasoline engines have been evolving as well, but the big picture is that gasoline and diesel engine technologies are merging. They are using similar electronic controls and onboard diagnostics monitoring, making it easier for drivability technicians to make the transition to diesel service. Higher compression ratios and direct injection are now common among gasoline engines, while diesels are lowering their compression ratios and utilizing fuel systems that seem to have drawn inspiration from their gasoline cousins.

Meeting the latest diesel emission control regulations would not have been possible without a completely new approach in fuel system design. While the earlier hydromechanical systems were certainly reliable, a new level of precision was required that could only be achieved with computer control of individual injectors. Beyond that, injection pressures were going to have to be exponentially higher to achieve atomization and combustion chamber penetration targets. This narrowed the field of possible candidates to a select few, with the eventual winner being high-pressure common rail (HPCR) injection.

(Photo courtesy of Ford Motor Company) The second generation 6.7 liter Power Stroke diesel uses HPCR injection, helping it meet strict EPA emission control regulations.

The way we were

While Rudolf Diesel did the lion’s share of the development work on the engine that bears his name, he was never able to make his design work properly during his lifetime. It wasn’t until Robert Bosch built the first practical injection system that the diesel engine gained credibility.  During the ensuing decades, Bosch’s original pump-line-nozzle design lived on with incremental improvements, enabling the diesel engine to become the workhorse of the industrial world.

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