A Dual - Reductant HC LNC Approach to Commercial Vehicle Tier 4 Final Solutions 2011-01-2203
Stringent global emissions legislations demand effective NOx reduction strategies for both the engine as well as the aftertreatment. Diesel applications have previously applied Lean NOx Catalysts (LNCs) [1, 2], but their reduction efficiency and longevity have been far less than that of the competing ammonia-based SCR systems, such as urea . A catalyst has been developed to significantly reduce NOx emissions, approaching 60% with ULSD and exceeding 95% with E85. Both thermal and sulfur aging are applied, as well as on-engine aging, illustrating resilient performance to accommodate necessary life requirements. A robust system is developed to introduce both ULSD from the vehicle's tank as well as E85 (up to 85% ethanol with the balance being gasoline) from a moderately sized supplemental tank, enabling extended mileage service intervals to replenish the reductant, as compared with urea, particularly when coupled with an engine-out based NOx reduction technology, such as EGR. The highly efficient E85 is applied when engine-out NOx conditions are at their highest, and in other less polluting regions the ULSD is leveraged for moderate reductions, ensuring Not-to-Exceed (NTE) requirements are achieved, of course. Results illustrate the ability to extend reductant refill intervals, while keeping the E85 reductant tank volume to less than that necessary with urea. Additional benefits of E85 in the system design are described, including improved evaporation, deposit avoidance, simplified freeze-thaw strategies, and existing reductant infrastructure and availability. Low temperature management is accommodated through the integration of a thermal regenerator, which provides heat necessary for DPF regeneration as well as catalyst activation and desulfation. Temperature sensitivities of the catalyst are compared, evaluating fuel and reductant consumption effects, particularly as engine-out NOx concentrations and exhaust temperatures change. In conclusion, the system is applied to a Tier 3 off-road tractor, demonstrating not only Tier 4 Final compliance, but significant additional reductions.