Advancement in understanding the extreme altitude and ambient temperature impact on diesel engine and aftertreatment performance

Resumen

The increasingly stringent emission standards act as a guide for the development of cleaner vehicles in a context of climate change. The latest European regulations applied to the transportation sector widened the operation range where homologation tests are carried out. The variables of ambient temperature and driving altitude are now extra requirements that must be considered in a way to shorten the gap between those tests and real driving. The understanding of the ambient conditions impact on the engine response becomes fundamental to overcome the drawbacks represented by them, being determinant for the engine response with an extended impact on engine-out emissions. As a consequence of altitude or ambient temperature variation, the exhaust aftertreatment systems (EATS) boundaries are modified, compromising their operation and impacting on tailpipe emissions. In the specific case of Diesel engines, the two most common EATS are the diesel oxidation catalyst (DOC) and the diesel particulate filter (DPF). In this context, this doctoral thesis proposes different approaches to understand the main factors that extreme ambient conditions impose to the engine and to the DOC and DPF operation. An important part of this work consisted of the set up of an experimental test bench equipped with an altitude simulator and of a one-dimensional (1D) thermo-fluid dynamic modelling tool for a wide-ranging analysis. Following low temperature steady state conditions experimental outcomes, CO and HC emission contour maps led to the evaluation of how extreme ambient conditions impact on the DOC light-off and pollutant emissions conversion efficiency. The modelling analysis helped to build guidelines that determine the contribution of the flow properties caused by such conditions. Besides, the effect of applying computational exhaust line thermal insulation solutions on the DOC and engine response is additionally addressed. On the other hand, the variable geometry turbine (VGT) actuation on the DPF regeneration process is performed experimentally. The impact that the boost pressure strategy has on the rate of soot depletion during active regeneration as a function of the driving altitude is considered with the guidance of the modelling tools. The reduction of the regeneration rate in altitude with standard boosting strategies is discussed, leading to the re-evaluation of the VGT actuation for high altitude practices. Finally, the sensitivity of the VGT position and low pressure exhaust gases recirculation (LP-EGR) rate at a vast array of ambient conditions is experimentally analysed for regular engine operation at partial loads. The results led to the engine calibration redefinition based on EATS inlet temperature increase and the reduction of the specific fuel consumption.