The loading of a diesel particulate filters (DPFs) entails the need of trap regeneration by particulate combustion, whose efficiency and frequency are somehow affected by the way soot is deposited along the channels. Great efforts are thus spent to improve the understanding of the filtration process of DPFs, aimed at obtaining a deeper insight into the relationship between engine performance and filter loading so as to take advantage of this insight for DPF design and optimization purposes. Small lab-scale 300 cpsi DPF samples were loaded downstream the Diesel oxidation catalyst (DOC) in an ad hoc designed reactor capable of hosting five samples with part of the entire flow produced by an automotive diesel engine at the 2500 9 8 BMEP operating condition, selected to be representative as one of the critical engine points of the New European Driving Cycle (NEDC). Soot layer thickness was estimated by means of Field emission scanning electron microscope (FESEM) observations after sample sectioning at progressive locations, obtained through a procedure defined not to affect the distribution of the soot inside the filter and to enable estimation of the actual soot thickness along the channel length. This is a pre-requisite to get suitable data for the validation of the DPF models required for trap design and optimisation.
The particle number and size distribution are important aspects to qualify diesel engine emissions, considering that new limits, in term of particle number, are expected for Euro 6 regulations. In this scenario it is important to study particulate matter (PM) emissions, not only during engine normal operating mode, but also during diesel particulate filter (DPF) regeneration processes. The aim of this work is therefore to analyze PM emissions throughout the whole exhaust system of a small displacement Euro 5 common rail automotive diesel engine, during both normal operating conditions and DPF regeneration mode. Because the test engine was equipped with a close-coupled after-treatment system, featuring a Diesel Oxidation Catalyst (DOC) and a DPF integrated in a single canning, the exhaust gas was sampled at the engine outlet, at the DOC outlet, and at the DPF outlet to fully characterize the PM emissions throughout the exhaust line. After a two-stage dilution, the sampled gas was analyzed by means of a TSI 3080 SMPS, in the range 6 to 225 nm range. The particle number and size distribution were evaluated at part load, both under normal operating conditions and at DPF regeneration mode, to highlight the impact of the different combustion processes on the PM characteristics. Finally, the particle number and size distribution at the engine outlet were also evaluated while fueling the engine with neat fatty acid methyl ester (FAME) to evaluate the impact of alternative fuels on PM characteristics during normal operating conditions. The results have shown that, under normal operating conditions, the engine and DOC outlet particle number and mass size distributions appear to be very similar, while the DPF exhibits high values of filtration efficiency on a particle number basis, even in the nanoparticle range. Regeneration mode caused a particle number increase of 1 order of magnitude, with a substantial shift of the number distribution peaks toward larger diameters. The particle number across the DOC showed a remarkable reduction for particles larger than 40 nm, with a reduction of 1 order of magnitude in their concentrations. Finally, fueling the engine with FAME leads to remarkable reductions in terms of particle number and mass (up to 80% and 90%, respectively) under normal operating mode conditions.
Experimental work has been carried out on a small displacement Euro 5 automotive diesel engine fueled alternatively with ultralow sulfur diesel (ULSD) and with two blends (30% vol) of ULSD, with two different fatty acid methyl esters (FAME) obtained from rapeseed methyl ester (RME) and jatropha methyl ester (JME). The engine-out particulate matter (PM) emissions have been characterized in terms of number and mass size distributions; measurements were performed under different engine operating conditions that are representative of the New European Driving Cycle (NEDC), including cold start of the engine. No significant differences were detected in the particle numbers (PN) for the different fuels under steady-state operating conditions, while a moderate reduction in particle mass size distribution was observed for the biofuel blends. The effects on PN emissions due to shifts in the engine operating points on the calibration maps, caused by the different fuel characteristics, have been shown to be significantly larger than the effects due to the different combustion characteristics of the biofuel blends, thus highlighting the need for a specific adjustment of the engine calibration.
The effects of using a B30 blend of ultra low sulphur diesel and two different Fatty Acid Methyl Esters (FAME) obtained from both Rapeseed Methyl Ester (RME) and Jatropha Methyl Ester (JME) in a Euro 5 small displacement passenger car diesel engine on both full load performance and part load emissions have been evaluated in this paper.In particular the effects on engine torque were firstly analyzed, for both a standard ECU calibration (i.e. without any special tuning for the different fuel characteristics) and for a specifically adjusted ECU calibration obtained by properly increasing the injected fuel quantities to compensate for the lower LHV of the B30: with the latter, the same torque levels measured under diesel operation could be observed with the B30 blend too, with lower smoke levels, thus highlighting the potential for maintaining the same level of performance while achieving substantial emissions benefits.Moreover, the effects of the two different 30% vol. blends on brake specific fuel consumption and on engine-out exhaust emissions (CO 2 , CO, HC, NO x and smoke) were also evaluated at 6 different part load operating conditions, representative of the New European Driving Cycle.Both standard engine calibration (change of the accelerator pedal position) and specifically adjusted engine calibration (adjustment of the energizing time of main injection) were evaluated for part load operating conditions, highlighting a 4% average rise of fuel consumption, on a mass basis, at same fuel conversion efficiency and CO 2 emissions. A noticeable increase of CO and HC emissions at low load could also be noticed, along with a significant NO x emissions decrease when using a specifically adjusted engine calibration, and a considerable smoke emission reduction.
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