Impact of biodisel on particle emissions and PDF regeneration management in a euro5 automotive diesel engine

Biofuel usage is increasingly expanding thanks to its significant contribution to a well-to-wheel (WTW) reduction of greenhouse gas (GHG) emissions. In addition, stringent emission standards make mandatory the use of Diesel Particulate Filter (DPF) for the particulate emissions control. The different physical properties and chemical composition of biofuels impact the overall engine behaviour. In particular, the PM emissions and the related DPF regeneration strategy are clearly affected by biofuel usage due mainly to its higher oxygen content and lower low heating value (LHV). More specifically, the PM emissions and the related DPF regeneration strategy are clearly affected by biofuel usage due mainly to its higher oxygen content and lower low heating value, respectively. The particle emissions, in fact, are lower mainly because of the higher oxygen content. Subsequently less frequent regenerations are required. On the other hand, as a consequence of the lower LHV of the RME, a larger amount of post - injected fuel is required for the achievement of the right temperature inside the DPF for the oxidation of the soot cake. This could generally result in to a larger oil dilution, a higher smoking and an increment of fuel consumption. Aim of the paper is the characterization of the particle emissions in terms of mass, size and number during the regeneration of a Close Coupled DPF (CCDPF). The measurements were performed at the exhaust of a 2.0l Euro5 CR GM Diesel engine fuelled both with conventional diesel fuel (RF) and Rapeseed Methyl Ester (RME). The investigation was carried out at a steady state engine operating point (2750rpm 12bar BMEP) representative of a typical extraurban driving condition. The regeneration was performed using an actual regeneration strategy adopted in the last generation diesel engine for RF and a modified one for RME. The particulate emissions were characterized by means of a microsoot sensor, for the mass concentration measurement, and a DMS500, for the particle sizing and counting. The results pointed out the benefit of the use of biodiesel on the out DPF particulate emissions and its drawbacks on the management of the regeneration process. In particular, lower particle emissions are observed both during and after the regeneration event. Furthermore, it was observed that the use of RME requires a flexible "management system" that allows the adjustment of the injection strategy according to the fuel properties in order to activate the process and guarantee the complete filter regeneration.