Mark L. Stewart

A semi-implicit lattice method for simulating flow

We propose a new semi-implicit lattice numerical method for modeling fluid flow that depends only on local primitive variable information (density, pressure, velocity) and not on relaxed upstream distribution function values. This method has the potential for reducing parallel processor communication and permitting larger time steps than the lattice-Boltzmann method. Several benchmark problems are solved to demonstrate the accuracy of the method.

Detailed characterization of particulate matter emitted by lean-burn gasoline direct injection engine

This study presents detailed characterization of the chemical and physical properties of particulate matter emitted by a 2.0-L BMW lean-burn turbocharged gasoline direct injection engine operated under a number of combustion strategies that include lean homogeneous, lean stratified, stoichiometric, and fuel-rich conditions. We characterized particulate matter number concentrations, size distributions, and the size, mass, compositions, and effective density of fractal and compact individual exhaust particles. For the fractal particles, these measurements yielded fractal dimension, average diameter of primary spherules, and number of spherules, void fraction, and dynamic shape factors as function of particle size. Overall, the particulate matter properties were shown to vary significantly with engine operation condition. Lean stratified operation yielded the most diesel-like size distribution and the largest particulate matter number and mass concentrations, with nearly all particles being fractal agglomerates composed of elemental carbon with small amounts of ash and organics. In contrast, stoichiometric operation yielded a larger fraction of ash particles, especially at low speed and low load. Three distinct forms of ash particles were observed, with their fractions strongly dependent on engine operating conditions: sub-50 nm ash particles, abundant at low speed and low load, ash-containing fractal particles, and large compact ash particles that significantly contribute to particulate matter mass loadings.

Optimizing the Advanced Ceramic Material for Diesel Particulate Filter Applications

This paper describes the application of pore-scale filtration simulations to the ‘Advanced Ceramic Material’ (ACM) developed by Dow Automotive for use in advanced diesel particulate filters. The application required the generation of a three dimensional substrate geometry to provide the boundary conditions for the flow model. An innovative stochastic modeling technique was applied matching chord length distribution and the porosity profile of the material. Additional experimental validation was provided by the single channel experimental apparatus. Results show that the stochastic reconstruction techniques provide flexibility and appropriate accuracy for the modeling efforts. Early optimization efforts imply that needle length may provide a mechanism for adjusting performance of the ACM for DPF applications. New techniques have been developed to visualize soot deposition in both traditional and new DPF substrate materials. Loading experiments have been conducted on a variety of single channel DPF substrates to develop a deeper understanding of soot penetration, soot deposition characteristics, and to confirm modeling results.

Evolution of deep-bed filtration of engine exhaust particulates with trapped mass

Size-resolved particle mass and number concentrations were obtained from different operating conditions using a spark-ignition direct-injection engine and a heavy-duty diesel engine. Particle mass versus mobility diameter results obtained for the engines showed weak dependence on the operating condition. The particle mass–mobility data enabled the use of an integrated particle size distribution method to estimate the particulate matter mass concentration in the exhaust stream. Average mass concentrations determined with the integrated particle size distribution method were 77 − 32 + 47 % of the gravimetric measurements performed using Teflon filters. Despite the relatively low elemental carbon fraction (∼0.4 to 0.7), the integrated particle size distribution mass for stoichiometric spark-ignition direct-injection exhaust was 83% ± 38 % of the gravimetric measurement. Exhaust from the spark-ignition direct-injection engine was also used to perform wall-scale filtration experiments on identical cordierite filter samples with properties representative of diesel particulate filters. The filters were sequentially loaded with particulate matter from four spark-ignition direct-injection engine operating conditions, in order of increasing particulate matter mass concentration. Simultaneous particle size distribution measurements upstream and downstream of the filter sample were used to evaluate filter performance evolution and the instantaneous trapped mass within the filter for two different filter face velocities. The filtration experiments focused on the filter wall loading stage where the estimated trapped mass was < 0.3 g/m2. The evolution of filtration performance at a fixed filtration velocity was found to only be sensitive to the trapped mass, despite using particulate matter from different operating conditions. Higher filtration velocity resulted in a more rapid shift of the most penetrating particle size toward smaller mobility diameters.

EMSL Pore Scale Modeling Challenge/Workshop

Report covers the background for the workshop, objectives, important research directions, necessary capabilities and overall recommendations.

Coating Distribution in a Commercial SCR Filter

A commercial SCR filter, deployed in the USA in 2015, was sectioned and examined using techniques including mercury porosimetry, electron microscopy, and micro-X-ray computed tomography. The catalyst washcoat was found to be consistent with Cu/SSZ-13, possibly including some zirconia and alumina. Three distinct regions were observed with respect to catalyst loading and location. A region at the inlet end of the filter, comprising 15 to 21% of the total effective filter length, was relatively lightly coated. Most of the catalyst present in this region was observed inside the porous filter walls, and the catalyst concentration was generally greater near the upstream filter wall surfaces. Moving axially down the monolith toward the outlet, a second region comprising 14 to 20% of the total effective filter length was more heavily coated, with catalyst present throughout the thickness of the porous filter walls, as well as coatings on both the upstream and downstream filter wall surfaces. The final region at the outlet end of the monolith, which accounted for 65 to 70% of the filter length, had an intermediate catalyst loading. Most of the catalyst here was again observed inside the porous filter wall. Concentrations in this region were higher near the downstream filter wall surfaces. Detailed models of multi-functional aftertreatment devices, such as the one examined here, have included representations of catalyst distribution within the filter bricks and indicate that catalyst distribution may have an impact on flow distribution, soot loading patterns, local concentrations, and ultimately conversion efficiency. Previous work has also shown that catalyst distribution across the thickness of an exhaust filter wall can have significant impacts on backpressure during soot loading.

Uranium Oxide Aerosol Transport in Porous Graphite

The objective of this paper is to investigate the transport of uranium oxide particles that may be present in carbon dioxide (CO2) gas coolant, into the graphite blocks of gas-cooled, graphite moderated reactors. The transport of uranium oxide in the coolant system, and subsequent deposition of this material in the graphite, of such reactors is of interest because it has the potential to influence the application of the Graphite Isotope Ratio Method (GIRM). The GIRM is a technology that has been developed to validate the declared operation of graphite moderated reactors. GIRM exploits isotopic ratio changes that occur in the impurity elements present in the graphite to infer cumulative exposure and hence the reactor’s lifetime cumulative plutonium production. Reference Gesh, et. al., for a more complete discussion on the GIRM technology.