Fuel economy,NO x emissions and lean NO x trap efficiency: Lessons from current driving cycles

Abstract

Transport sector is within a profound changing period, but diesel engines are still called to play a significant role in future supported on their solid share in many regions and superior thermal efficiency compared to spark-ignited engines. This work identifies the parameters that most affect fuel consumption and NO_x emissions on a diesel passenger car equipped with a lean NO_x trap under different driving cycles and ambient temperatures. High average vehicle velocity was beneficial to reduce the fuel consumed per kilometer. The driving dynamics was of little importance, easily counteracted by a higher thermal efficiency, higher engine temperature (because of a longer trip) or/and an efficient gear shifting strategy. Moreover, at low ambient temperature the latter two factors doubled their weight on fuel economy. Regarding tailpipe NO_x, keeping high aftertreatment performance was crucial. For this, low engine-out NO_x emissions were four times more important than exhaust temperature or flow rate.