Investigation of vehicle exhaust sub-23 nm particle emissions

Abstract

A solid particle number limit was applied to the European legislation for diesel vehicles in 2011. Extension to gasoline direct injection vehicles raised concerns because many studies found particles below the lower size limit of the method (23 nm). Here we investigated experimentally the feasibility of lowering this size. A nano condensation nucleus counter system (nCNC) (d 50% D 1.3 nm) was used in parallel with condensation particle counters (CPCs) (d 50% D 3 nm, 10 nm and 23 nm) at various sampling systems based on ejector or rotating disk diluters and having thermal pre-treatment systems consisting of evaporation tubes or catalytic strippers. An engine exhaust particle sizer (EEPS) measured the particle size distributions. Depending on the losses and thermal pre-treatment of the sampling system, differences of up to 150% could be seen on the final detected particle concentrations when including the particles smaller than 23 nm in diameter. A volatile artefact as particles with diameters below 10 nm was at times observed during the cold start measurements of a 2-stroke moped. The diesel vehicles equipped with the Diesel Particulate Filter (DPF) had a low solid sub-23 nm particles fraction (<20%), the gasoline with direct injection vehicles had higher (35-50%), the gasoline vehicles with port fuel injection and the two mopeds (two and four-stroke) had the majority of particles below 23 nm. The size distributions peaked at 60-80 nm for the DPF equipped vehicles, at 40-90 nm for the gasoline vehicles with a separate nucleation mode peak at approximately 10 nm sometimes. Mopeds peaked at sizes below 50 nm when their aerosol was thermally pre-treated.

Particle Number Measurements Directly from the Tailpipe for Type Approval of Heavy-Duty Engines

“…Even though the overestimation seems small (+5%), the small change of the cut-off size in combination with the different penetration of the system compared to the others can result in high differences when many small particles exist. The calibration discrepancies have been discussed in the literature for both thermal pre-treatment systems [16] and condensation particle counters [22,41] and will not be repeated here.…”

“…The losses should be similar for all systems examined, thus the conclusions should be the same even correcting separately for the losses below 30 nm. If losses would be taken into account, the results of the 10-23 nm levels would need a correction of approximately 1.7, as explained elsewhere [16,27]. Figure 2 summarises the results of the tests where the length of the heated line to the "Golden" system TP(CS) varied between 0.5 and 4 m. The tests were conducted with three engines.…”

“…While the agreement is excellent for the first regenerating cycle, high differences are seen for the third one. The most likely explanation is that volatile particles re-nucleated downstream of the evaporation tube (volatile artefact) [16]. The TP(CS) had PCRF 2000, while the PD(ET) only 100.…”

“…In Europe there is the intention to decrease the 50% detection efficiency of the CPC from 23 nm to 10 nm [9]. The reason is that high concentrations of particles below 23 nm have been found for light-duty vehicles [15][16][17], but also for heavy-duty ones [18]. Measuring from lower sizes poses the risk of falsely measuring volatile particles that go through the evaporation tube or are re-nucleated downstream of the evaporation tube (i.e., volatile artefact) [19].…”

Assessment of air management strategies on particulate number and size distributions from a 2-stroke compression-ignition engine operating with gasoline Partially Premixed Combustion concept

“…ISFC corr is calculated according to Equation (15) multiplying the ISFC measured in the single-cylinder engine with a factor that considers the effective power demanded by the supercharger (P weff,sc ) that would be taken from the indicated power (P wind ) delivered to the crankshaft. = · + weff,sc (15) In order to provide a fast approximation of ISFC corr if all air loop devices were present, the effective power required by the supercharger is estimated by resolving simple mass and energy balances on the turbine, compressor and supercharger, considering the experimentally measured data (temperature, pressure and mass ow rates) as inputs for the calculation. The following assumptions were made to simplify the calculation:…”