Aftertreatment Architecture and Control Methodologies for Future Light Duty Diesel Emission Regulations

Paper #:
  • 2017-01-0911

  • 2017-03-28
Light duty emission certification levels such as Tier 2 Bin 2 (equivalent of Tier 3 Bin 30) are 70% and 88% lower in NOx and HC respectively from current Tier 2 Bin 5 level. For light duty chassis certified automotive applications, the weighting factor of the cold portion of the FTP-75 (federal transient procedure) cycle is 43% of the overall emissions certification value. NOx and HC emissions must be mitigated at much lower exhaust temperatures as compared to diesel aftertreatment systems currently in production. In this work, a novel aftertreatment architecture to improve low temperature NOx and HC conversion efficiency is proposed. This system consists of a diesel cold start concept (dCSC™) catalyst and selective catalytic reduction catalyst on filter (SCRF®) close coupled to the engine for faster warm up. Additionally, a flow-through SCR catalyst is located downstream of the SCR on DPF catalyst. The diesel cold start concept catalyst not only functions as an oxidation catalyst but also passively adsorbs NOx and HC at low temperatures. The diesel cold start concept catalyst desorbs NOx and oxidizes the adsorbed HC at higher temperatures mitigating the low temperature emissions. Low temperature NOx reduction is further improved by utilizing a gaseous ammonia dosing system with capability to dose at both SCR on DPF catalyst upstream and downstream locations. Dual ammonia injection system enables high NOx reduction during high temperature operation (e.g. regeneration of filter) and helps reduce parasitic ammonia oxidation on SCR on DPF catalyst. This is accomplished by relying more on the downstream SCR catalyst for NOx reduction which would be operating at a lower temperature than SCR on DPF catalyst. The dosing controller determines the appropriate dosing location to maximize the system NOx reduction and minimize NH3 oxidation on SCR on DPF catalyst. This paper discusses the approach utilized to achieve T2B5 followed by T2B2 emission compliance, highlighting the necessity of the diesel cold start concept catalyst for lowered tail pipe NOx & HC targets. The aftertreatment systems were evaluated on a chassis dynamometer for FTP-75 and highway fuel economy (HFET) cycles. The dual dosing control strategy achieved similar NOx reduction and lower NH3 consumption as compared to dosing upstream of the SCR on DPF catalyst upstream. Dual dosing controls strategy reduced ammonia consumption by 10% and 25% for FTP-75 and HFET cycles respectively as compared to single dosing controls.
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