Fuel economy, NOx emissions and lean NOx trap efficiency: Lessons from current driving cycles

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 NOx emissions on a diesel passenger car equipped with a lean NOx 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 NOx, keeping high aftertreatment performance was crucial. For this, low engine-out NOx emissions were four times more important than exhaust temperature or flow rate.