Tier 4 High Efficiency SCR for Agricultural Applications 2012-01-1087
This paper describes the evolution in diesel engine SCR
technology used on tractors ≻130 kW. Details on the SCR technology
evolution from Tier 3 to Tier 4 interim are disclosed. Furthermore,
this paper demonstrates how state-of-the-art SCR technology can
make a non-EGR diesel engine meet Tier 4 final emission limits
without using particulate filtration.
Initially, it was assumed that Tier 4 aftertreatment systems
would use aftertreatment for NOx and PM, combined with an advanced
combustion concept and EGR. However, with this solution, one can
expect disadvantages such as: cost, complexity, high heat
rejection, large space claim and less than optimal fuel efficiency.
Furthermore, active PM filter regeneration is challenging and can
be hazardous in certain agricultural applications.
A Tier 4 final engine without PM filtration would require a SCR
aftertreatment system with NOx conversion efficiencies in the range
of 90-97% on all relevant conditions for the entire life of the
engine. With this approach, the base engine technology needs
limited alterations from Tier 4 interim. This allows retention of
engine robustness, fuel economy and heat rejection.
The feasibility of such a SCR system is demonstrated by means of
CFD results, engine dyno data and field test results. This
information is used to describe the evolution in SCR aftertreatment
mixer design, packaging, NOx reduction performance and deposit
formation. Furthermore, an outline is given on how an improved
integration of the engine with the aftertreatment can enhance the
total system performance (e.g., thermal management, variable raw