Development of Steady State NO ₂ :NOX Control via an Independent Nitric Decomposition System for the Exhaust Composition Transient Operation Laboratory

Southwest Research Institute (SwRI) utilizes the burner-based Exhaust Composition Transient Operation Laboratory^TM (ECTO-Lab) to accurately simulate transient engines and replicate real exhaust that is produced by light and heavy-duty engines for aftertreatment aging and evaluations. This system can generate and dose NO_X over transient cycles from a range of 20 ppm to 1200 ppm where the NO_X is generated by the in-situ decomposition and combustion of a fuel-bound, nitrogen containing compound. During the combustion and decomposition of the nitrogen containing compound over 95 % of the NO_X generated is in the form of NO. To authentically simulate exhaust gases, it is necessary to account for the distribution of the NO to the NO₂. Since previous work has established that the decomposition of nitric acid can be utilized as a method to generate NO₂, the objective of this project was to develop control of NO and NO₂ within SwRI’s ECTO-Lab through the decomposition of nitric acid. In addition to this, a system was built capable of generating NO₂ and NO independently of the ECTO-Lab via nitric acid decomposition. It was determined that NO₂:NO_X control can be achieved by varying the proprietary fuel-bound, nitrogen containing compound flow rate and nitric acid flow rate. Total NO_X control was approximately ± 20 ppm when total NO_X was 1000 ppm, and the gas phase HNO₃ concentration was maintained below 3 ppm for all operating points. The maximum NO₂:NO_X ratio achieved was 90 %, and the minimum was 2%. This proves that when utilizing the HNO₃ decomposition system, the ECTO-Lab systems have the capability of controlling the NO₂:NO_X distribution at steady-state.