Performance and regulated gaseous emissions of a Euro 6 diesel vehicle with Lean NOx Trap at different ambient conditions: Sensitivity to the type of fuel

Abstract

Three advanced biofuels, namely HVO (Hydrotreated Vegetable Oil), a glycerol-derived biofuel (Mo·bio) and biodiesel from oil industry wastes, were tested in a Euro 6 diesel vehicle equipped with a Lean NOx Trap under the worldwide harmonized light-duty vehicles test cycle (WLTC) at warm (24 °C) and cold (−7 °C) ambient temperature. HVO was tested pure, biodiesel was used both pure and blended at 20% (v/v) with a reference diesel fuel and Mo·bio was also blended with the diesel fuel at the same ratio. In order to analyse the sensitivity of the gaseous emissions and the aftertreatment efficiency to the type of fuel, emissions were measured upstream and downstream of the aftertreatment system and fuel-associated effects were isolated from those of the engine operating conditions (EGR rate, injection strategy and equivalence ratio). The energy consumption was not very different between fuels, although HVO led to a higher engine efficiency while biodiesel behaved oppositely at the low speed phase. Regarding NOx emissions, no differences were found between fuels while cold temperature led to higher NOx because of the lower EGR rate and the use of only high pressure EGR. Biodiesel and Mo·bio improved CO and THC engine-out emissions at warm temperature, but these compounds were deteriorated at low ambient conditions because of the poorer viscosity and volatility of these fuels. The DOC efficiency was higher for CO than for THC excepting the low speed phase, for which deposition of high molecular weight hydrocarbons could mask the results. The LNT efficiency was lower at cold conditions because of the high NOx engine-out emissions. Differences between fuels were only observed in the case of the DOC and during the engine warm-up period.