Naseri, M., Conway, R., Hess, H., Aydin, C. et al., "Development of Emission Control Systems to Enable High NOx Conversion on Heavy Duty Diesel Engines," SAE Technical Paper 2014-01-1525, 2014, doi:10.4271/2014-01-1525.
Selective Catalytic Reduction (SCR) systems have been demonstrated as effective solutions for controlling NOx emissions from Heavy Duty diesel engines. Future HD diesel engines are being designed for higher engine out NOx to improve fuel economy, which will require increasingly higher NOx conversion to meet emission regulations. For future aftertreatment designs, advanced technologies such as SCR coated on filter (SCRF®) and SCR coated on high porous flow through substrates can be utilized to achieve high NOx conversion.In this work, different options were evaluated for achieving high NOx conversion. First, high performance NOx control catalysts were designed by using SCRF unit followed by additional SCR on high porosity substrates. Second, different control strategies were evaluated to understand the effect of reductant dosing strategy and thermal management on NOx conversion. Tests were carried out on a HD engine under transient test cycles. The results indicated that NOx conversion can be significantly improved using the proposed design of SCRF component along with SCR on high porosity substrates. The conversion can be further improved by dosing NH3 rather than urea, especially at low temperatures, when urea cannot be injected. In addition, implementation of thermal management improved the NOx conversion at lower temperature. The results of this work demonstrated that such systems along with improvement in engine control strategy can provide >95% NOx conversion under transient FTP test cycles and will allow diesel engines to meet future emission regulations and fuel economy targets.