Number Geometric Mean Diameter Research Articles

Effect of isopropanol and n-pentanol addition in diesel on the combustion and emission of a common rail diesel engine under pilot plus main injection strategy

In this study, isopropanol and n-pentanol are blended in diesel with 20% ratio by volume, named D80IP20 and D80NP20. Their combustion and emission performances were compared with diesel on a four cylinder common rail diesel engine under pilot plus main injection strategy. The pilot injection duration decreases and the main injection duration increases with engine loads. For test fuels, the starts of pilot and main injection and the durations of pilot injection are remained unchanged in each engine operation. D80IP20 has the longest ignition delay due to the lowest cetane number and the shortest combustion duration due to the highest fuel oxygen. However, the peak combustion temperature of D80IP20 is lower than that of D80NP20 under double injection strategy. Compared to diesel, both D80IP20 and D80NP20 obviously reduce the particle number concentrations (PNCs) and the particle volume concentrations (PVCs), while increase the NOx emissions. D80IP20 has the lowest PNCs and PVCs and its number geometric mean diameter (NGMD) and volume geometric mean diameter (VGMD) are the lowest among the three fuels. D80IP20 has higher NOx emission than diesel, but lower than D80NP20 due to lower PCT. Further, D80IP20 with 10% EGR can achieve the simultaneous reduction for NOx emission and PNCs at low and high loads compared to diesel without EGR. Results indicate that blending isopropanol in diesel has better effects in combustion improvement and emission control and is more suitable than n-pentanol under pilot plus main injection strategy.

Particle fluxes over forests: Analyses of flux methods and functional dependencies

Particle number fluxes at two forests are computed using data from condensation particle counters and both the eddy covariance (EC) and relaxed eddy accumulation (REA) methods applied offline, post data collection. The results indicate that a 30‐min integration period for flux calculation frequently applied for other scalars is also appropriate for particle number fluxes. Half‐hour average particle number fluxes computed using REA and EC are statistically indistinguishable. Less than 1% of all fluxes derived using EC and REA differ by more than the mutual uncertainty bounds, and the average ratio of fluxes computed using the two approaches is 1.00 ± 0.01. This finding tends to support assertions that, for the size of particles under study (with diameters <100 nm), the assumption of similarity with heat transfer is likely robust. Data from both sites indicate higher particle deposition velocities (vd) for particle ensembles with lower number geometric mean diameter (GMD), for GMD of 10 to 100 nm, although the decrease with increasing GMD is less marked than is predicted by the deposition models such as that of Slinn. The relationships between median and mean vd conditionally sampled by GMD are well described by power law fits. Particle vd exhibits a linear dependence on friction velocity for the range of conditions studied and also enhancement under unstable conditions. Similarities between average particle vd conditionally sampled by number GMD, friction velocity, and stability from the two forest sites point to the generalizability of the empirical fits derived herein.

Size-resolved particle deposition velocities of sub-100 nm diameter particles over a forest

Despite their importance to accurate prediction of the particle ensemble and associated impacts, few empirical studies have attempted to quantify the dependence of deposition velocities ( v d) on friction velocity ( u *) and particle diameter for sub-100 nm particles. Data from a pilot study conducted over a Beech forest in Denmark are used here in to test an indirect method of assessing these dependencies where particle fluxes derived using eddy covariance are conditionally sampled based on parameters of the particle size distribution. The data indicate strongly bi-directional fluxes, with almost 1 3 of all 1 2 -h periods exhibiting upwards fluxes particularly during particle formation events. Vertical velocities for particle ensembles with number geometric mean diameter (GMD) of 20–30, 30–40, 40–50, 50–60 and 60–70 nm have an approximately equal magnitude during deposition and emission periods which may imply that surface uptake does not strongly limit deposition rates of these particles. The results also indicate a marked size dependence of v d. During deposition periods the median v d for particle ensembles with a number GMD of 20–30 nm is 4.5 mm s −1 and decreases to 1.5 mm s −1 for particle ensembles with a GMD of 60–70 nm. The median v d for periods when the GMD was approximately 55 nm is 2.7 mm s −1 and the mean is 4.2 mm s −1, which agrees well with the mean v d of 4.3 mm s −1 for 50 nm particles over a Scots Pine forest at Hyytiälä in central Finland. Also, as in the data from Hyytiälä, the v d for GMD of 50–60 nm increases markedly with u * from 1 to 1.8 mm s −1 at u *<0.4 m s −1, to 7.5 mm s −1 at u *>1 m s −1.