Effect of engine operating conditions on the size of primary particles composing diesel soot agglomerates (original) (raw)
Related papers
An experimental investigation of soot particle size inside the combustion chamber of a diesel engine
Energy Conversion and Management, 1989
The knowledge of soot particle size distribution inside the combustion chamber of diesel engines is important for both radiation heat transfer calculations and soot release inside the combustion chamber. However, little information is known about the rates of soot formation and oxidation. The aim of this investigation is to gain more information about the range of soot particle sizes available inside the combustion chamber. The results show that the size of soot particles varies from 94 to 1000 A and that soot particles have almost spherical shapes. The results also show that soot agglomerates have no definite size and shape; some have spherical shape, others have a bead-like or chain-structure shapes.
2011
We report the first in situ size-resolved density measurements of particles produced by premixed charge compression ignition (PCCI) combustion and compare these with conventional diesel exhaust particles. The effective densities (F eff) of sizeclassified particles were determined by measurements with a differential mobility analyzer (DMA) and an aerosol particle mass analyzer (APM). Particle inherent densities (F i) were calculated using an expression for particle mass given by idealized aggregate (IA) theory, transmission electron microscopy (TEM) measurements of primary particle diameter (d pp), and a comparison of the measured number of particles in each size class with that predicted by a proposed DMA-APM response function for aggregates. The F eff of PCCI and conventional diesel particles were similar over a range of diameters characteristic of their number-size distributions. The F eff were 0.89, 0.58, and 0.51 g/cm 3 for conventional diesel and 0.90, 0.62, and 0.42 g/cm 3 for PCCI particles with 50, 100, and 150 nm electrical mobility diameters (d m), respectively. The error associated with F eff was about one percent of each measurement. The lowest F eff were observed for exhaust gas recirculation (EGR) levels somewhat lower than that required for PCCI operation. The F i of 50 and 100 nm conventional diesel particles were 1.22 (0.14 and 1.77 (0.29 g/cm 3 , which is in good agreement with previously reported values. PCCI F i for these size classes did not differ significantly (1.27 (0.16 and 2.10 (0.20 g/cm 3), suggesting like amounts of adsorbed liquid hydrocarbons. In addition, for 150 nm particles, the PCCI and conventional F i were the same (2.20 (0.34 g/cm 3). Given the close density values, we expect that particulate emissions control with diesel particulate filters (DPFs) would not be adversely affected by PCCI particle physical properties.
Combustion and Flame, 2006
Particulate emissions at the exhaust of a diesel engine were systematically investigated at different engine loads and speeds by rapid thermophoretic sampling followed by direct transmission electron microscope (TEM) visualization. Spherule and aggregate size distributions, aggregate fractal dimensions and prefactors, and particle volume fractions were comprehensively characterized using this novel technique, which provided new, accurate, and relevant data on diesel particulates compared to the abundant past studies involving questionable mobility sizing measurements. In contrast to the narrow (Gaussian) distributions of spherule sizes, there were broad variations in aggregate sizes that were approximated by a lognormal probability function with a geometric standard deviation of about 1.8. Mean spherule diameters were in the range 20-35 nm, and mean aggregate gyration diameters of 0.16-0.35 µm were always smaller than the PM2.5 standard. Average sizes of both spherules and aggregates mostly increased with the relative engine load or overall equivalence ratio, which disagreed with the trends and correlations suggested by a recent study. Independent of engine operating condition, aggregate fractal dimension was 1.77 ± 0.14, a nearly universal property that contradicted with the broad range of past values reported for diesel engines based on mobility-based experiments. The aggregate fractal prefactor, which was also necessary to fully characterize the morphology of diesel soot, was found to be 1.9 ± 0.5. In addition to this new contribution, sampling/TEM experiments were also implemented for the first time in a diesel engine to estimate particle volume fractions, which were crucial for the determination of available specific surface areas. The present method was more accurate than the laser attenuation method for the relatively low particle volume fractions of 0.001-0.1 ppm emitted by the diesel engine considered here.
Engineering and Technology Journal, 2019
Understanding the size and morphological properties of particulate matter (PM) is essential to improve analysis of the process of PM formation in diesel engines. These will help to reduce undesirable environmental impact and health effects. A scanning mobility particle sizer (SMPS) and thermal gravimetric analysis (TGA) were used to study the changes in size characteristics of PM/soot and soot reactivity. Furthermore, improve the oxidation of soot particles in diesel engines is necessary under the range of different fuel combustions. Oxygenated fuels (e.g., ethanol blend, E10 and butanol blend, B16) were used in this experimental study to show how insignificant changes in morphological characteristics and activity of PM. The oxidation and activation energy of PM was achieved at the lower temperature from the combustion of oxygenated fuels compared with diesel fuel combustion. Besides, it was found that both the size of soot particulate and the number of primary particles are reduced with increasing the oxygen content in oxygenated fuels than the diesel fuel. The shape of primary soot particle for PM is a bit more spherical in the case of diesel fuel than to the oxygenated fuels.
Characterization of exhaust particulates from diesel engine
Atmospheric Environment, 2005
Engine exhaust particulates undergo different processes in the ambient environment such as agglomeration, coagulation, surface condensation, adsorption, and oxidation before evolving as mature particles. Conventional CI engines emit a significant mass/ number of particulates due to heterogeneous combustion. However this problem can be resolved by using an advanced combustion technology named as Homogeneous Charge Compression Ignition (HCCI), which has potential to substantially reduce particulates and NOx simultaneously and deliver efficiencies comparable to conventional CI combustion. In the present study involving homogeneous mixture of diesel and air, an electrically heated diesel vaporizer was developed. Experiments were performed at different relative air-fuel ratios and EGR levels. Enrichment of the mixture increases the peak in-cylinder temperature, which was effectively controlled by EGR under leaner HCCI conditions. A partial flow dilution tunnel was used to collect particulate samples for trace metal content and Benzene Soluble Organic Fraction (BSOF), which is considered to be a marker of toxicity. This analysis showed that the trace metals detected were comparatively lower in HCCI particles. Trace metal concentration increased with application of EGR in the HCCI engine. BSOF content of the HCCI particulates increased when the mixture becomes leaner as well as with increasing EGR. Physical characterization of particulates was also carried out using engine exhaust particle sizer (EEPS), which measures the particle size-number distribution for the nano-particles in the exhaust. The particles collected on the filter paper were also analyzed for morphology using scanning electron microscopy (SEM).
Review of Particle Size Distribution Measurements of Engine Exhaust Before 1985
Real-time measurement of the size distribution of particles in engine exhaust emissions is used by engine manufacturers to optimize engines with regard to emissions, by automotive suppliers to develop efficient exhaust aftertreatment systems, and by scientists and legislators to assess the effect of engine exhaust on air quality and possible adverse health effects. Few measurements of the size distribution of engine exhaust particles were made before 1970. One reason for this was the lack of suitable measuring instruments. Many early measurements required an electron microscope. In addition, representative samples of airborne particles for electron microscopy were difficult to obtain and required long sampling periods. Researchers also were required to manually view at least 1,000 particle images to obtain a single size distribution. Another difficulty was that researchers had to observe two dimensions of a 3-dimensional object to assign a single size to a nonspherical aggregate, a ...
Soot Particle Evolution and Transport in a Direct Injection Diesel Engine
Jurnal Teknologi, 2015
Particle-based in-cylinder soot distribution study is becoming more important as the rules and regulations pertaining to particulate emission of diesel-powered vehicles have been increasingly more stringent. This paper focuses on the investigation of soot size evolution and its distribution and transport inside an engine cylinder. The overall process of soot formation includes soot nucleation, surface growth, oxidation, coagulation and agglomeration. The present study considers only soot surface growth, oxidation and coagulation to predict the in-cylinder soot particle size. The soot surface growth model was based on Hiroyasu’s soot formation model while soot oxidation was referred to Nagle & Strickland-Constable’s soot oxidation model. Coagulation rate was defined using Smoluchowski’s equation with constant proposed by Wersborg. From this study, it is demonstrated that soot particles with relatively larger size are gathered in the centre of the cylinder while smaller soot particles...
Metal Particle Emissions in the Exhaust Stream of Diesel Engines: An Electron Microscope Study
Environmental Science & Technology, 2013
Scanning electron microscopy and transmission electron microscopy were applied to investigate the morphology, mode of occurrence and chemical composition of metal particles (diesel ash) in the exhaust stream of a small truck outfitted with a typical after-treatment system (a diesel oxidation catalyst (DOC) and a downstream diesel particulate filter (DPF)). Ash consists of Ca-Zn-P-Mg-S-Na-Al-K-phases (lube-oil related), Fe, Cr, Ni, Sn, Pb, Sn (engine wear), and Pd (DOC coating). Soot agglomerates of variable sizes (<0.5−5 μm) are abundant upstream of the DPF and are ash-free or contain notably little attached ash. Post-DPF soot agglomerates are very few, typically large (>1−5 μm, exceptionally 13 μm), rarely <0.5 μm, and contain abundant ash carried mostly from inside the DPF. The ash that reaches the atmosphere also occurs as separate aggregates ca. 0.2−2 μm in size consisting of sintered primary phases, ca. 20−400 nm large. Insoluble particles of these sizes may harm the respiratory and cardiovascular systems. The DPF probably promotes breakout of large soot agglomerates (mostly ashbearing) by favoring sintering. Noble metals detached from the DOC coating may reach the ambient air. Finally, very few agglomerates of Fe−oxide nanoparticles form newly from engine wear and escape into the atmosphere.
Journal of Liquid Chromatography & Related Technologies, 2007
Soot particles emitted from a light duty (LD) Volkswagen diesel engine running at different operating points (speed and torque levels) are analyzed for mean size determination using a laser-based three Wavelength Extinction Method (3-WEM). For this reason, collected soot samples are suspended using an appropriate sample preparation technique with optimized conditions of sonication as it revealed its effect on the soot mean particle size measured by 3-WEM. An online Scanning Mobility Particle Analyzer (SMPS) is also used to measure soot emission at identical engine operating points. Size values obtained from SMPS are lower than those of suspended soot samples obtained from 3-WEM. The size discrepancies are mainly related to the required sample preparation procedure employed for 3-WEM measurements. The engine operating points affect, differently, the size measurements obtained from SMPS and 3-WEM. Sedimentation Field-Flow Fractionation (SdFFF) is used for density determination of soot samples based on size measurements of fractions collected at peak maxima
Journal of Aerosol Science, 2002
The objective of this study is to develop a physical model that accurately accounts for the nucleation, coagulation, and condensation processes in the formation of particulate matter (PM) inside the exhaust plume of the diesel-fueled vehicles. The PM concentration has been predicted based on the fuel sulfur content, fuel-to-air ratio, exhaust ow rate, and the ambient conditions. It was predicted that the critical nucleus diameter of the particles decreased by approximately 30% and the number concentration increased by a factor of 6 with the increase in relative humidity from 10% to 90% for a fuel with 50 ppm sulfur content. The parametric studies suggested that the condensation e ects are very important near the stack. Ignoring the contribution from condensation term decreased PM count median diameter from 52 to 10 nm. A fair agreement is observed between the numerically predicted PM size distribution and concentration and the experimentally measured values.