SCR or EGR, how hard can it be?

Somewhat surprised I learn that there is still some discussion about weather SCR or EGR is the better choice. When I moved from research to become environmental director at Volvo Bus Corporation, soon two years ago, we just finished the final technology evaluation of the catalytic aftertreatment system that Volvo uses. There were undoubtedly major advantages for the fuel consumption also when the AdBlue use was compensated for, when compared to the most recent EGR technology.

The cost efficiency works out as several percent benefit on the bottom line for the operators. The exact numbers depends, amongst others, on the route and on the driving style. It reaches between 3 and 9% for most customers, when the AdBlue cost is compensated for.

In a recent article in the Danish magazine “Danske Busvognmaend”; Isue 3 March 2008, the last years experiences are summarised (in Danish however). (the article is not available on the homepage)

The new interesting information in this article is that the same engine in the same installation is compared with the two technologies.

The Magazine summarises the properties:

Catalytic exhaust treatment

Selective Catalytic Reduction (SCR)

Exhaust Gas Recirculation technology (EGR)
Fuel consumption decrease relative Euro III

10% better than EGR, while ~5% AdBlue is consumed

Fuel consumption increase relative Euro III


Longer oil change intervals No extra installation
Less technical “stress” because of lower temperature No concern about filling AdBlue


Higher power possible  
Less complicated engine design  


Or as one manufacturer said: “Just add diesel”

“… plenty of it…” I remarked.

About volvobuses

Adjunct Professor of Catalysis at Chalmers University of Technology. Lives in Gothenburg, Sweden, with my wife and three daughters born in 1991, 1994 and 1997. Is a passionate runner.
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