Lean NO x trap supplemental energy savings with a long breathing strategy

Abstract

Current and upcoming diesel engine emission regulations in the USA and in Europe stipulate significant reductions of nitrogen oxide emissions. To satisfy these emission regulations and to maintain high fuel efficiency, energy efficient diesel after-treatment to remove nitrogen oxides is required. In this study, a long breathing (long adsorption) strategy was investigated for the reduction of supplemental energy consumption of a diesel lean nitrogen oxide trap. The long breathing strategy would be enabled by moderate exhaust gas recirculation to reduce the engine-out nitrogen oxide levels. With reduced feed gas nitrogen oxide levels, the adsorption time of the lean nitrogen oxide trap could be extended, leading to less frequent fuel-rich regeneration of the lean nitrogen oxide trap. Proof of concept studies were undertaken on a diesel engine to demonstrate the enabling of the long breathing lean nitrogen oxide trap strategy, while further tests were undertaken on a flow bench set-up to demonstrate the potential energy savings with the long breathing lean nitrogen oxide trap strategy. The test results indicated that, at the selected operating conditions, the long breathing strategy could be enabled by reducing the engine-out nitrogen oxide from 110 ppm to 50 ppm via moderate exhaust gas recirculation. The flow bench test results indicated that the adsorption time of the lean nitrogen oxide trap increased exponentially when the feed gas nitrogen oxide level was reduced. The longer adsorption led to supplemental energy savings in excess of 60% when the feed gas nitrogen oxide level was reduced from 110 ppm to 50 ppm. Furthermore, it was calculated that the long breathing lean nitrogen oxide trap strategy enabled a higher overall indicated efficiency of 36.4% compared to 35.9% with a conventional lean nitrogen oxide trap strategy.