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Sarvi A.,Abo Akademi University | Lyyranen J.,VTT Technical Research Center of Finland | Jokiniemi J.,VTT Technical Research Center of Finland | Jokiniemi J.,Aerosol and Particle Technology Laboratory | Zevenhoven R.,Abo Akademi University
Fuel Processing Technology | Year: 2011

This paper addresses particulate matter (PM) size distributions in large-scale diesel engine exhaust. The test engines were multivariable large-scale turbo-charged, after-cooled medium speed (~ 500 rpm, ~ 1 MW power per cylinder) direct injection diesel engines. Emissions measurements were carried out while burning heavy fuel (HFO) and light fuel (LFO) oils. Test modes for investigation were propulsion mode (marine) and generator mode (power plant), with load varying from 25 to 100%. PM was measured using a gravimetric impactor with four impactor stages plus a filter, classifying particles between 0.005 and 2.5 μm (aerodynamic diameter). The results show that HFO firing produces significantly higher PM emissions (more than factor of ~three on mass bases for high load operation) compared to LFO, especially for particles smaller than 0.5 μm. This is mainly due to higher ash-forming elements and sulphur content of HFO. For HFO, the fraction of the finest particles increases with load, more strongly for generator mode than for propulsion mode, with generator mode giving ~ 50% higher PM emissions than propulsion mode. With LFO firing, the largest amount of fine PM was emitted at the lowest load, for propulsion mode being lower and almost independent of load at higher loads, while for generator mode a steady decrease in emissions with increasing load is seen for all PM size classes measured. © 2011 Elsevier B.V. All rights reserved.

Nakamura K.,Ibiden Co. | Vlachos N.,Aerosol and Particle Technology Laboratory | Konstandopoulos A.,CERTH CPERI | Iwata H.,Ibiden Co. | Kazushige O.,Ibiden Co.
SAE Technical Papers | Year: 2012

Nowadays diesel particulate filters (DPFs) with catalyst coatings have assumed one of the most significant roles for road vehicle emission control. DPFs made of re-crystallized SiC (SiC-DPFs) have guaranteed the soot filtration efficiency for the current regulation. In order to further enhance their filtration efficiency, even though a higher porosity and larger pore size must be adopted for sufficient catalyst coating capacity, we developed the concept of a filtration layer on the DPF inlet channel walls and researched its performance both theoretically and experimentally. First of all, models of the new filtration layer, closely resembling the real one made in the laboratory, were digitally reconstructed and soot deposition simulations were conducted. According to the results, the pore size of the filtration layer providing the target filtration efficiency is found to be between the characteristic soot particle size (of order 100 nm) and the nominal DPF wall pore size (of order 10 μm). Additionally, it is shown that the optimum spatial distribution of filtration layer thickness along DPF length should be matched to the filtration velocity distribution. Finally we experimentally verified the performances of SiC-DPF with filtration layer by engine bench tests. We found that very high filtration efficiency is attained while it is shown that the concept presented can bring 3 significant advantages through its use: a high initial filtration efficiency of 97 % in spite of a higher porosity SiC-DPF wall, an 18 % decrease of transient pressure drop at 4 g/L soot mass in DPF without increased initial pressure drop due to a deep-bedding of soot, and a repeatability of transient pressure drop after several loading-regeneration cycles. Copyright © 2012 SAE International.

Melas A.D.,European Commission - Joint Research Center Ispra | Melas A.D.,Aristotle University of Thessaloniki | Isella L.,European Commission | Konstandopoulos A.G.,Aristotle University of Thessaloniki | And 2 more authors.
Journal of Colloid and Interface Science | Year: 2014

The relationship between geometric and dynamic properties of fractal-like aggregates is studied in the continuum mass and momentum-transfer regimes. The synthetic aggregates were generated by a cluster-cluster aggregation algorithm. The analysis of their morphological features suggests that the fractal dimension is a descriptor of a cluster's large-scale structure, whereas the fractal prefactor is a local-structure indicator. For a constant fractal dimension, the prefactor becomes also an indicator of a cluster's shape anisotropy. The hydrodynamic radius of orientationally averaged aggregates was calculated via molecule-aggregate collision rates determined from the solution of a Laplace equation. An empirical expression that relates the aggregate hydrodynamic radius to its radius of gyration and the number of primary particles is proposed. The suggested expression depends only on geometrical quantities, being independent of statistical (ensemble-averaged) properties like the fractal dimension and prefactor. Hydrodynamic radius predictions for a variety of fractal-like aggregates are in very good agreement with predictions of other methods and literature values. Aggregate dynamic shape factors and DLCA individual monomer hydrodynamic shielding factors are also calculated. © 2013 Elsevier Inc.

Konstandopoulos A.G.,Aerosol and Particle Technology Laboratory | Kostoglou M.,Aerosol and Particle Technology Laboratory
SAE Technical Papers | Year: 2010

In the present work we derive analytical solutions for the problem of convection, diffusion and chemical reaction in wall-flow monoliths. The advantage of having analytical instead of numerical treatments is clear as the analytical solutions not only can be exploited to bring full scale simulations of diesel particulate filters to the real time domain, but also they enable efficient implementations on computationally limited engine control units (ECUs) for on-board management and control of emission control systems. The presentation describes the mathematical problem formulation, the governing dimensionless parameters and the corresponding assumptions. Then the analytical solution is derived and several asymptotic (for limiting values of the parameters) and approximating solutions are developed, corresponding to different physical situations. Reactant distributions in the filter are presented and discussed for several values of the parameters. The conclusion is that the classic single channel model for DPF simulation can for all practical conditions accommodate diffusive phenomena with no added computational cost and without significantly altering the structure of existing code implementations. Copyright © 2010 SAE International.

Lee K.S.,Aerosol and Particle Technology Laboratory | Jung J.H.,Korea Institute of Science and Technology | Keel S.I.,Environmental Systems Research Division | Yun J.H.,Environmental Systems Research Division | And 2 more authors.
Science of the Total Environment | Year: 2012

The oxy-fuel combustion system is a promising technology to control CO 2 and NO X emissions. Furthermore, sulfation reaction mechanism under CO 2-rich atmospheric condition in a furnace may lead to in-furnace desulfurization. In the present study, we evaluated characteristics of calcium carbonate (CaCO 3) sorbent particles under different atmospheric conditions. To examine the physical/chemical characteristics of CaCO 3, which is used as a sorbent particle for in-furnace desulfurization in the oxy-fuel combustion system, they were injected into high temperature drop tube furnace (DTF). Experiments were conducted at varying temperatures, residence times, and atmospheric conditions in a reactor. To evaluate the aerosolizing characteristics of the CaCO 3 sorbent particle, changes in the size distribution and total particle concentration between the DTF inlet and outlet were measured. Structural changes (e.g., porosity, grain size, and morphology) of the calcined sorbent particles were estimated by BET/BJH, XRD, and SEM analyses. It was shown that sorbent particles rapidly calcined and sintered in the air atmosphere, whereas calcination was delayed in the CO 2 atmosphere due to the higher CO 2 partial pressure. Instead, the sintering effect was dominant in the CO 2 atmosphere early in the reaction. Based on the SEM images, it was shown that the reactions of sorbent particles could be explained as a grain-subgrain structure model in both the air and CO 2 atmospheres. © 2012.

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