A New Electrically Heated Mixer (EHM) for Efficient SCR of NOx in Low Load Cycles

New regulations by the California Air Resources Board (CARB) demand a stringent 0.02 g/hp-hr tailpipe NOx limit by the year 2027, requiring Selective Catalytic Reduction (SCR) catalysts to provide high NOx conversions even at low (below 200°C) exhaust temperatures. This work describes utilizing an Electrically Heated Mixer System (EHM system) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) catalyst followed by a conventional aftertreatment (AT) system containing DOC, DPF, and SCR, enabling high NOx conversions meeting CARB’s NOx emission target. The AT catalysts were hydrothermally aged to Full Useful Life. Conventional unheated Diesel Exhaust Fluid (DEF) was injected upstream of both the LO-SCR and primary downstream SCR. The EHM system allowed for DEF to be injected as low as 130°C upstream of the LO-SCR, whereas, in previous studies, unheated DEF was injected at 180°C or dosed at 130°C with heated DEF. The combination of unheated DEF, EHM system, LO-SCR, and downstream SCR enabled the needed increase in NOx efficiency in low exhaust temperatures, which was observed in drive cycles such as in cold-FTP, LLC, and World Harmonized Transient Cycle (WHTC). There were several-fold reductions in tailpipe NOx using this configuration compared to its baseline: 3.3-fold reduction in FTP, 22-fold in Low Load Cycle (LLC), 38-fold in Beverage Cycle, 8-fold in “Stay Hot” Cycle, and 10-fold in WHTC. Finally, it is shown that the EHM system can heat the exhaust gas, such as during a cold start, without needing additional heating hardware integrated into the system. These results were observed without performing changes in the engine base calibration.

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A Multi-Function, Heated Mixer for Rapid Heat-up, Low-Temperature Ammonia Demand, Deposit Prevention and to Meet Ultra-Low NOx Regulations

Masoudi¹,

Poliakov²,

Noorfeshan³

2023

SAE Technical Paper Series

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<div class="section abstract"><div class="htmlview paragraph">Selective Catalytic Reduction (SCR) operation depends strongly on both heat and ammonia availability (stored or incoming). These requirements make high efficiency SCR challenging in lower temperature cycles where SCR is relatively cold, and Diesel Exhaust Fluid (DEF) injection is largely absent due to deposit risks. Examples include low temperature cycles such as low-idling, stop-and-go or low-load cycles such as city driving or local delivery cycles.</div><div class="htmlview paragraph">An Electrically Heated Mixer/ EHM™ is utilized to address these challenges in a single component. EHM simultaneously provides heat for rapid SCR heat-up during the cold phase or in other low-temperature operations, steady or transient. Second, its heating mechanism makes deposit risks nearly non-existent. Third, EHM enables DEF injection at 130 °C, markedly enhancing the low temperature SCR impact. It is shown that these capabilities collectively make EHM a promising pathway for meeting ultra-stringent NOx targets including California 2027 (0.02 gr/hp.hr). Via rapidly heating the SCR catalyst during cold-start, EHM enables substantially lowering the cold-phase NOx. For instance, it is shown this lowers the cold FTP and cold WHTC NOx emission by 2 – 2.5 fold and in Low-Load Cycle by 22-fold.</div><div class="htmlview paragraph">EHM also allows DEF injection in low exhaust temperatures such as in 70 - 80 °C, for instance for rapidly filling the SCR catalyst with ammonia, if needed.</div><div class="htmlview paragraph">Unlike adding other exhaust flow heating devices where an additional component is ultimately integrated in the aftertreatment architecture, EHM is a mixer, already present in emission control systems. These flexibilities, along with its lower cost and ease in fitting, make EHM an enabling pathway for Diesel emission control systems meeting very low NOx regulations.</div></div>

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A New Electrically Heated Mixer (EHM) for Efficient SCR of NOx in Low Load Cycles

Cited by 4 publications

References 7 publications

Effects of different EHC on times on gaseous, particulate pollutants and energy consumption of PNA + DOC + SDPF system under low temperature and WHTC conditions

Effects of different EHC on times on gaseous, particulate pollutants and energy consumption of PNA + DOC + SDPF system under low temperature and WHTC conditions

Meeting future NOX emission regulations by adding an electrically heated mixer

A Multi-Function, Heated Mixer for Rapid Heat-up, Low-Temperature Ammonia Demand, Deposit Prevention and to Meet Ultra-Low NOx Regulations

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