Stuart Daw

Stuart Daw
Oak Ridge National Laboratory | ORNL · Energy and Transportation Science Division

About

232
Publications
36,508
Reads
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4,539
Citations
Citations since 2016
15 Research Items
1926 Citations
2016201720182019202020212022050100150200250300
2016201720182019202020212022050100150200250300
2016201720182019202020212022050100150200250300
2016201720182019202020212022050100150200250300
Additional affiliations
April 1979 - present
Oak Ridge National Laboratory
Position
  • UT-Battelle Corporate Fellow

Publications

Publications (232)
Article
We report results from a multiscale computational modeling study of biomass fast pyrolysis in an experimental laboratory reactor that combined the hydrodynamics predicted by a two-fluid model (TFM) with predictions from a finite element model (FEM) of heat and mass transfer and chemical reactions within biomass particles. The experimental pyrolyzer...
Article
We present statistical analyses for highly resolved, short and long-time-scale experimental measurements of magnetic flotsam tracer particle motion in bubbling air-fluidized beds of Geldart Group B particles. The observed axial tracer trajectories appear to exhibit Weibull distributions over both short and long time scales and suggest possible anal...
Article
In this study, the results from laboratory measurements of the devolatilization kinetics of switchgrass in a rapidly heated fixed bed reactor flushed with argon and operated at constant temperatures between 600 and 800 °C was reported. Results indicate that switchgrass decomposes in two sequential stages during pyrolysis: stage I involves the evapo...
Article
Full-text available
We summarize a global kinetic model for a commercial automotive Lean NOx Trap (LNT) catalyst derived from laboratory flow reactor measurements at Oak Ridge National Laboratory (ORNL). The experimental measurements were made according to a modified version of a publicly shared protocol developed for characterizing the dynamic responses of LNT cataly...
Article
We report results from a numerical study of multi-time-scale bistable dynamics for CO oxidation on a catalytic surface in a flowing, well-mixed gas stream. The problem is posed in terms of surface and gas-phase sub-models that dynamically interact in the presence of stochastic perturbations reflecting the impact of molecular-scale fluctuations on t...
Article
The nanostructure of diesel particulates has been shown to impact its oxidation rate and burnout trajectory. Additionally, this nanostructure can evolve during the oxidation process, furthering its influence on the burnout process. For this study, exhaust particulates were generated on a light-duty diesel engine with conventional diesel fuel, biodi...
Article
We report results from a computational study of the transition from bubbling to slugging in a laboratory-scale fluidized-bed reactor with Geldart Group B glass particles. For simulating the three-dimensional fluidized-bed hydrodynamics, we employ MFiX, a widely studied multi-phase flow simulation tool, that uses a two-fluid Eulerian-Eulerian approx...
Article
We present a computationally efficient, one-dimensional simulation methodology for biomass particle heating under conditions typical of fast pyrolysis. Our methodology is based on identifying the rate limiting geometric and structural factors for conductive heat transport in realistic biomass particles. Comparisons of transient temperature trends p...
Article
Full-text available
The NO2 oxidation kinetics and burning mode for diesel particulate from light-duty and medium-duty engines fueled with either ultra low sulfur diesel or soy methyl ester biodiesel blends have been investigated and are shown to be significantly different from oxidation by O2. Oxidation kinetics were measured using a flow-through packed bed microreac...
Article
We propose a wavelet-based scheme that encodes the essential dynamics of discrete microscale surface reactions in a form that can be coupled with continuum macroscale flow simulations with high computational efficiency. This makes it possible to simulate the dynamic behavior of reactor-scale heterogeneous catalysis without requiring detailed concur...
Article
The compatibility of notable infrastructure elastomers and plastics with DME and its blends with diesel fuel were examined using solubility analysis. The elastomer materials were fluorocarbon, acrylonitrile butadiene rubber (NBR), styrene butadiene (SBR), neoprene, polyurethane and silicone. Plastic materials included polyphenylene sulfide (PPS), p...
Article
We report results from computational simulations of an experimental, lab-scale bubbling bed biomass pyrolysis reactor that include a distributed activation energy model (DAEM) for the kinetics. In this study, we utilized multiphase computational fluid dynamics (CFD) to account for the turbulent hydrodynam-ics, and this was combined with the DAEM ki...
Article
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The fuel economy and emissions of conventional and hybrid buses equipped with emissions aftertreatment were evaluated via computational simulation for six representative city bus drive cycles. Both series and parallel configurations for the hybrid case were studied. The simulation results indicated that series hybrid buses have the greatest overall...
Article
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We present fuel savings estimates resulting from the combined implementation of multiple advanced energy management technologies in both conventional and parallel hybrid Class 8 diesel trucks. The energy management technologies considered here have been specifically targeted by the 21st Century Truck Partnership (21 CTP) between the U.S. Department...
Article
We report results from computational simulations of an experimental, lab-scale bubbling bed biomass pyrolysis reactor that include a distributed activation energy model (DAEM) for the kinetics. In this study, we utilized multiphase computational fluid dynamics (CFD) to account for the turbulent hydrodynamics, and this was combined with the DAEM kin...
Article
Full-text available
Comparisons are reported on the simulated fuel economy for parallel, series, and dual-mode hybrid electric long-haul trucks, in addition to a conventional powertrain configuration, powered by a commercial 2010-compliant 15-L diesel engine over a freeway-dominated heavy-duty truck driving cycle. The driving cycle was obtained by measurement during n...
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Results from computational simulations of fuel economy and engine-out emissions are presented for light-duty conventional and hybrid vehicles powered by conventional and high-efficiency combustion engines, including use of port fuel-injected, lean gasoline direct injection, reactivity controlled compression ignition, and conventional diesel combust...
Article
We review developments in the understanding of cycle–to–cycle variability in internal combustion engines, with a focus on spark-ignited and premixed combustion conditions. Much of the research on cyclic variability has focused on stochastic aspects, that is, features that can be modeled as inherently random with no short–term predictability. In som...
Article
Spark-ignited internal combustion engines have evolved considerably in recent years in response to increasingly stringent regulations for emissions and fuel economy. One new advanced engine strategy ustilizes high levels of exhaust gas recirculation (EGR) to reduce combustion temperatures, thereby increasing thermodynamic efficiency and reducing ni...
Article
An investigation of the impact of rail pressure and biodiesel fueling on exhaust particulate agglomerate morphology and primary particle (soot) nanostructure was conducted with a common-rail turbocharged direct injection diesel engine. The engine was operated at steady state on a dynamometer running at moderate speed with both low (30%) and medium–...
Conference Paper
In collaboration with a major automotive manufacturer, we are using computational simulations of in-cylinder combustion to understand the multi-scale nonlinear physics of the dilute stability limit. Because some key features of dilute combustion can take thousands of successive cycles to develop, the computation time involved in using complex model...
Conference Paper
Bubbling fluidized bed reactors are widely used for fast pyrolysis of biomass. Whether one is concerned primarily with interpreting laboratory pyrolysis reactor data or evaluating the potential performance of pilot or commercial scale reactors for liquid fuels production, it is important to be able to accurately relate the spatial mixing characteri...
Article
We propose a physically motivated random walk model to describe the spatial and temporal mixing of a single biomass particle in a bubbling fluidized bed. The model parameters are estimated from measurements of a magnetically tagged simulated biomass particle in a laboratory fluidized bed. We demonstrate that Monte Carlo simulations using the model...
Article
Full-text available
We present simulated fuel economy and emissions of city transit buses powered by conventional diesel engines and diesel-hybrid electric powertrains of varying size. Six representative city drive cycles were included in the study. In addition, we included previously published aftertreatment device models for control of CO, HC, NOx, and particulate m...
Article
Full-text available
Two hybrid powertrain configurations, including parallel and series hybrids, were simulated for fuel economy, component energy loss, and emissions control in Class 8 trucks over both city and highway driving conditions. A comprehensive set of component models describing engine fuel consumption, emissions control, battery energy, and accessory power...
Article
Full-text available
Fuel injection into the negative valve overlap (NVO) period is a common method for controlling combustion phasing in homogeneous charge compression ignition (HCCI) and other forms of advanced combustion. When fuel is injected into O2-deficient NVO conditions, a portion of the fuel can be converted to products containing significant levels of H2 and...
Article
An inorganic membrane water recovery concept is evaluated as a method to recover water from the exhaust of an internal combustion engine. Integrating the system on board a vehicle would create a self-sustaining water supply that would make engine water injection technologies "consumer transparent." In laboratory experiments, water recovery from hum...
Article
We report observations of changes in the microstructure of soot from an experimental light-duty diesel engine, produced with varying levels of biodiesel fuel blending. Based on these changes, we propose a hypothesis for how these changes relate to in-cylinder combustion chemistry. Our hypothesis centers on the assumption that fullerenic lamellar st...
Conference Paper
Full-text available
Fuel injection into the negative valve overlap (NVO) period is a common method for controlling combustion phasing in homogeneous charge compression ignition (HCCI) as well as other forms of advanced combustion. During this event, at least a portion of the fuel hydrocarbons can be converted to products containing significant levels of H2 and CO, as...
Article
Full-text available
This study reports measurements of the oxygen reactivity of diesel engine particulates generated with a range of conventional and biodiesel fuel blends. Particulate samples were collected from a modern light-duty diesel engine and then devolatilized at 650 °C under argon. Reaction rates of the remaining fixed carbon component with oxygen were measu...
Article
Full-text available
We compare simulated fuel economy and emissions for both conventional and hybrid class 8 heavy-duty diesel trucks operating over multiple urban and highway driving cycles. Both light and heavy freight loads were considered, and all simulations included full aftertreatment for NOx and particulate emissions controls. The aftertreatment components inc...
Article
We summarize results from comparative simulations of hybrid electric vehicles with either stoichiometric gasoline or diesel engines. Our simulations utilize previously published models of transient engine-out emissions and models of aftertreatment devices for both stoichiometric and lean exhaust. Fuel consumption and emissions were estimated for co...
Article
Urea-selective catalytic reduction (SCR) catalysts are the leading aftertreatment technology for diesel engines, but there are major challenges associated with meeting future NOx emission standards, especially under transient drive cycle conditions that include large swings in exhaust temperatures. Here we present a simplified, transient, one-dimen...
Article
Full-text available
We report results from urban drive cycle simulations of a light-duty conventional vehicle and a similar hybrid electric vehicle, both of which are equipped with diesel engines capable of operating in either conventional diesel combustion mode or in premixed charge compression ignition mode. Both simulated vehicles include lean exhaust after-treatme...
Article
We report experimental observations of the dynamic behavior of single, magnetically tagged 3–4 mm particles varying in density from 0.55 g/cm3 to 1.2 g/cm3 as they migrate freely in a bubbling air-fluidized bed of 177–250 μm glass beads of 2.5 g/cm3 density over a range of air flows. The densities of the tracer particles (made by imbedding small ma...
Article
Full-text available
We present results from a computational study of the potential for using low-cost sorbent materials to trap the emissions of hydrocarbons and nitrogen oxides temporally during cold-start periods in hybrid electric vehicles and plug-in hybrid electric vehicles operating over transient driving cycles. The hydrocarbon adsorption behavior of a candidat...
Article
In this study we model the effects of 23 different fuels on First and Second Law thermodynamic efficiency of an adiabatic internal combustion engine. First Law efficiency is calculated using lower heating value (LHV) while Second Law efficiency is calculated with exergy, which represents the inherent chemical energy available to produce propulsion....
Article
Our previously developed microkinetic model for lean NOx trap (LNT) storage and regeneration has been updated to address some longstanding issues, in particular the formation of N2O during the regeneration phase at low temperatures. To this finalized mechanism has been added a relatively simple (12-step) scheme that accounts semi-quantitatively for...
Article
Full-text available
We utilize physically-based models for diesel exhaust catalytic oxidation and urea-based selective catalytic NOx reduction to study their impact on drive cycle performance of hypothetical light-duty diesel powered hybrid vehicles. The models have been implemented as highly flexible SIMULINK block modules that can be used to study multiple engine-af...
Article
We summarize results from an investigation of the spatiotemporal distribution of NOâ storage and intermediate gas species in determining the performance of a fully formulated, Ba-based, lean NOâ trap catalyst under lean/rich cycling conditions. By experimentally resolving spatiotemporal profiles of gas composition, we found that stored NOâ was sign...
Conference Paper
Results from a visual observation of bubbling laboratory beds combined with magnetic particle tracking to measure detailed mixing and segregation patterns for simulated biomass particles are presented. Neodymium magnets embedded in wooden spherical and cylindrical particles and externally positioned magnetic field detectors are used to continuously...
Article
Full-text available
This paper presents details and results of hybrid and plug-in hybrid electric passenger vehicle (HEV and PHEV) simulations that account for the interaction of thermal transients from drive cycle demands and engine start/stop events with aftertreatment devices and their associated fuel penalties. The simulations were conducted using the Powertrain S...
Article
We study selected examples of previously published cyclic heat-release measurements from a single-cylinder gasoline engine as stepwise valve timing adjustments were made to shift from spark ignited (SI) combustion to homogeneous charge compression ignition (HCCI). Wavelet analysis of the time series, combined with conventional statistics and multif...
Article
Full-text available
We propose a cycle-resolved dynamic model for combustion instabilities in spark-ignition engines operating with high levels of exhaust gas recirculation (EGR). We account for the complex combustion response to cycle-to-cycle feedback by utilizing a global probability distribution that describes the pre-spark state of in-cylinder fuel mixing. The pr...
Conference Paper
Full-text available
We describe a two-zone phenomenological model for simulating in-cylinder details in conventional, highdilution, and high-efficiency clean combustion in a diesel engine. Using this model we characterize the differences in these combustion modes in terms of 3D trajectories involving equivalence ratio, flame temperature, and oxygen mass fraction. Thes...
Article
In this article, we review and clarify some of the points made by previous authors(1, 2) regarding chemical looping combustion (CLC). Although much of the recent interest in chemical looping combustion has been associated with carbon sequestration, our primary interest here is its potential to increase the thermodynamic efficiency of converting fue...
Article
Full-text available
A microkinetic chemical reaction mechanism capable of describing both the storage and regeneration processes in a fully formulated lean NO trap (LNT) is presented. The mechanism includes steps occurring on the precious metal, barium oxide (NO storage), and cerium oxide (oxygen storage) sites of the catalyst. The complete reaction set is used in con...
Conference Paper
Introduction Spouted fluidized beds are used extensively for many types of solid-fluid contacting and reaction applications where uniform inter-phase contacting is important. While various commercial applications have been developed, the basic hydrodynamics and mixing patterns are not well characterized. Spouted beds are usually preferred where c...
Article
Full-text available
Diesel particulate samples were collected from a light duty engine operated at a single speed-load point with a range of biodiesel and conventional fuel blends. The oxidation reactivity of the samples was characterized in a laboratory reactor, and BET surface area measurements were made at several points during oxidation of the fixed carbon compone...
Article
Full-text available
A one-dimensional model for simulating lean NOx trap (LNT) performance is developed and validated using both steady state cycling data and transient data from FTP testing cycles. The model consists of the conservation equations for chemical species and energy in the bulk flow, energy of the solid walls, O2 storage and NOx storage (in the form of ni...
Article
We report observations of the nature and spatial distribution of sulfur species on a sulfated Ba-based commercial lean NOx trap (LNT) catalyst. The monolithic catalyst was sulfated in a bench flow reactor during 60/5-s NOx-storage/reduction cycling to achieve a total sulfur loading of 3.4gL−1 of catalyst. Washcoat composition, structure and sulfur...
Article
In this paper we analyze data from previously reported experimental measurements of cycle-to-cycle combustion variations in a lean-fueled, multi-cylinder spark-ignition (SI) engine. We characterize the changes in the observed combustion dynamics with as-fed fuel–air ratio using conventional histograms and statistical moments, and we further charact...
Article
We describe a CHEMKIN-based multi-zone model that simulates the expected combustion variations in a single-cylinder engine fueled with iso-octane as the engine transitions from spark-ignited (SI) combustion to homogenous charge compression ignition (HCCI) combustion. The model includes a 63-species reaction mechanism and mass and energy balances fo...
Article
Full-text available
Many vehicle systems simulations utilize engine maps constructed from steady-state dynamometer measurements to estimate exhaust temperature and emissions as functions of engine speed and load. Unfortunately, steady-state engine behaviour is often significantly different from actual behaviour under transient driving conditions. This is particularly...
Article
A detailed thermodynamic analysis of thermochemical recuperation (TCR) applied to an idealized internal combustion engine with single-stage work extraction is presented. Results for several different fuels are included. For a stoichiometric mixture of methanol and air, TCR can increase the estimated ideal engine second law efficiency by about 3% fo...
Article
Full-text available
Soy methyl ester (SME) biodiesel was volumetrically blended with 2007 certification ultra low sulfur diesel (ULSD) fuel and run in a 1.7L direct-injection common rail diesel engine at one speed-load point (1500rpm, 2.6bar BMEP). Engine fueling rate and injection timing were adjusted to maintain a constant load, while particulate samples were collec...
Article
A heuristic algorithm based on a double Wiebe function is proposed for estimating the relative importance of distinct combustion modes (propagating flame and compression ignition) occurring within individual combustion cycles as an engine is transitioned from conventional spark-ignited (SI) combustion to homogeneous charge compression ignition (HCC...