Tier 4 High Efficiency SCR for Agricultural Applications

This paper describes the evolution in diesel engine SCR technology used on tractors > 130kW. 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 emissions).