Fuel consumption and aftertreatment thermal management synergy in compression ignition engines at variable altitude and ambient temperature

New regulations applied to the transportation sector are widening the operation range where the pollutant emissions are evaluated. Besides ambient temperature, the driving altitude is also considered to reduce the gap between regulated and real-life emissions. The altitude effect on the engine performance is usually overcome by acting on the turbocharger control. The traditional strategy assumes to keep (or even to increase) the boost pressure, that is, compressor pressure ratio increase, as the altitude is increased to offset the ambient density reduction, followed by the reduction of the exhaust gas recirculation to reach the targeted engine torque. However, this is done at the expense of an increase on fuel consumption and emissions. This work remarks experimentally the importance of a detailed understanding of the effects of the boost pressure and low-pressure exhaust gas recirculation (LP-EGR) settings when the engine runs low partial loads at different altitudes, accounting for extreme warm and cold ambient temperatures. The experimental results allow defining and justifying clear guidelines for an optimal engine calibration. Opposite to traditional strategies, a proper calibration of the boost pressure and LP-EGR enables reductions in specific fuel consumption along with the gas temperature increase at the exhaust aftertreatment system.