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Dive into the research topics where William F. Northrop is active.

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Featured researches published by William F. Northrop.


Aerosol Science and Technology | 2011

Condensational Growth of Particulate Matter from Partially Premixed Low Temperature Combustion of Biodiesel in a Compression Ignition Engine

William F. Northrop; Praveen V. Madathil; Stanislav V. Bohac; Dennis N. Assanis

Condensational growth is not typically assumed to be significant compared with adsorption for conversion of unburned hydrocarbons in the exhaust of diesel engines to the particulate phase. However, when partially premixed low temperature combustion (LTC) modes designed to simultaneously reduce soot and NO X emissions are implemented, unburned hydrocarbon (UHC) concentrations in the exhaust are an order of magnitude higher than for conventional combustion modes, increasing the likelihood of gas to particle conversion by condensation. In this work, two LTC operating conditions are compared with conventional diesel combustion using a multi-cylinder direct-injection diesel engine using low-sulfur fuel, a soy-based biodiesel and a 50% by volume biodiesel blend. Gaseous emissions of unburned hydrocarbons were measured and particulate samples were taken using a partial-flow dilution tunnel. Gravimetric analysis of the collected filters, Soxhlet extraction of particulate and speciation using GC-FID was performed for all operating conditions. Elemental carbon (EC) emissions were measured using a thermal optical analyzer and particle size distribution was analyzed using a differential mobility spectrometer. For increasing biodiesel concentration in the fuel, mass emissions of both EC and UHC decreased for all combustion modes compared with petroleum diesel. However, for biodiesel use in LTC modes of operation, particulate mass significantly increased following exhaust dilution. Low vapor pressure methyl esters found in the exhaust of biodiesel LTC increases heterogeneous condensation onto soot particles in the exhaust compared with unburned species from petroleum diesel fuel operation. A model estimating this condensation mechanism accurately predicts the experimental findings of increased mass of particulate for biodiesel operation.


Journal of Engineering for Gas Turbines and Power-transactions of The Asme | 2011

Comparison of Filter Smoke Number and Elemental Carbon Mass From Partially Premixed Low Temperature Combustion in a Direct-Injection Diesel Engine

William F. Northrop; Stanislav V. Bohac; Jo Yu Chin; Dennis N. Assanis

Partially premixed low temperature combustion (LTC) is an established advanced engine strategy that enables the simultaneous reduction of soot and NOX emissions in diesel engines. Measuring extremely low levels of soot emissions achievable with LTC modes using a filter smoke meter requires large sample volumes and repeated measurements to achieve the desired data precision and accuracy. Even taking such measures, doubt exists as to whether filter smoke number (FSN) accurately represents the actual smoke emissions emitted from such low soot conditions. The use of alternative fuels such as biodiesel also compounds efforts to accurately report soot emissions since the reflectivity of high levels of organic matter found on the particulate matter collected may result in erroneous readings from the optical detector. Using FSN, it is desired to report mass emissions of soot using empirical correlations derived for use with petroleum diesel fuels and conventional modes of combustion. The work presented in this paper compares the experimental results of well known formulae for calculating mass of soot using FSN and elemental carbon mass using thermal optical analysis (TOA) over a range of operating conditions and fuels from a four cylinder direct injection passenger car diesel engine. The data show that the mass of soot emitted by the engine can be accurately predicted with the smoke meter method utilizing a 3000 ml sample volume over a range of FSN from 0.02 to 1.5. Soot mass exhaust concentration calculated from FSN using the best of the literature expressions and that from the TOA taken over all conditions correlated linearly with a slope of 0.99 and R2 value of 0.94. A primary implication of the work is that the level of confidence in reporting soot mass based on FSN for low soot formation regimes like LTC is improved for both petroleum diesel and biodiesel fuels.Copyright


Journal of Engineering for Gas Turbines and Power-transactions of The Asme | 2014

Dual-Fuel Diesel Engine Combustion With Hydrogen, Gasoline, and Ethanol as Fumigants: Effect of Diesel Injection Timing

Wei Fang; Bin Huang; David B. Kittelson; William F. Northrop

Premixed compression ignition (CI) combustion has attracted increasing research effort recently due to its potential to achieve both high thermal efficiency and low emissions. Dual-fuel strategies for enabling premixed CI have been a focus using a low reactivity fumigant and direct diesel injection to control ignition. Alternative fuels like hydrogen and ethanol have been used as fumigants in the past but typically with diesel injection systems that did not allow the same degree of control or mixing enabled by modern common rail systems. In this work we experimentally investigated hydrogen, ethanol and gasoline as fumigants and examined three levels of fumigant energy fraction (FEF) using gasoline over a large direct diesel injection timing range with a single cylinder diesel engine. It was found that the operable diesel injection timing range at constant FEF was dependent on the fumigant’s propensity for autoignition. Peak indicated gross cycle efficiency occurred with advanced diesel injection timing and aligned well with combustion phasing near TDC as we found in an earlier work. The use of hydrogen as a fumigant resulted in very low HC emissions compared with ethanol and gasoline, establishing that they mainly result from incomplete combustion of the fumigated fuel. Hydrogen emissions were independent of diesel injection timing and HC emissions were strongly linked to combustion phasing, giving further indication that squish and crevice flows are responsible for partially burned species from fumigation combustion.Copyright


Journal of Energy Resources Technology-transactions of The Asme | 2014

An Experimental Investigation of Reactivity-Controlled Compression Ignition Combustion in a Single-Cylinder Diesel Engine Using Hydrous Ethanol

Wei Fang; Junhua Fang; David B. Kittelson; William F. Northrop

Dual-fuel reactivity-controlled compression ignition (RCCI) combustion using port injection of a less reactive fuel and early-cycle direct injection (DI) of a more reactive fuel has been shown to yield both high thermal efficiency and low NOX and soot emissions over a wide engine operating range. Conventional and alternative fuels such as gasoline, natural gas, and E85 as the lower reactivity fuel in RCCI have been studied by many researchers; however, published experimental investigations of hydrous ethanol use in RCCI are scarce. Making greater use of hydrous ethanol in internal combustion engines has the potential to dramatically improve the economics and life cycle carbon dioxide emissions of using bioethanol. In this work, an experimental investigation was conducted using 150 proof hydrous ethanol as the low reactivity fuel and commercially available diesel as the high reactivity fuel in an RCCI combustion mode at various load conditions. A modified single-cylinder diesel engine was used for the experiments. Based on previous studies on RCCI combustion by other researchers, early-cycle split-injection strategy of diesel fuel was used to create an in-cylinder fuel reactivity distribution to maintain high thermal efficiency and low NOX and soot emissions. At each load condition, timing and mass fraction of the first diesel injection was held constant, while timing of the second diesel injection was swept over a range where stable combustion could be maintained. Since hydrous ethanol is highly resistant to auto-ignition and has large heat of vaporization, intake air heating was needed to obtain stable operations of the engine. The study shows that 150 proof hydrous ethanol can be used as the low reactivity fuel in RCCI through 8.6 bar indicated mean effective pressure (IMEP) and with ethanol energy fraction up to 75% while achieving simultaneously low levels of NOX and soot emissions. With increasing engine load, less intake heating is needed and exhaust gas recirculation (EGR) is required to maintain low NOX emissions.


International Journal of Engine Research | 2007

Deactivation of a diesel oxidation catalyst due to exhaust species from rich premixed compression ignition combustion in a light-duty diesel engine

William F. Northrop; Timothy J. Jacobs; Dionissios N. Assanis; Stanislav V. Bohac

Abstract Low-temperature premixed-charge compression ignition (PCI) can significantly reduce both nitric oxide and nitrogen dioxide (NO x ) and particulate matter emissions in compression ignition engines through a range of engine operating conditions. Exhaust hydrocarbons and carbon monoxide can be removed with a diesel oxidation catalyst (DOC). Although PCI normally utilizes a globally fuel-lean mixture, it is independent of equivalence ratio provided that local combustion temperatures are sufficiently low. A more fuel-rich PCI mode of operation could be useful in exhaust after-treatment strategies such as providing carbon monoxide and hydrocarbons for regeneration of a lean NO x trap (LNT). In a previous study, it was found that a rich PCI strategy deactivates a platinum-based DOC within seconds and may allow excessive harmful emissions to be passed into the environment. This study attempts to quantify the effects of different species representative of those found in rich PCI exhaust on a platinum-based DOC in a background of exhaust from an engine operating in a lean PCI regime. Excess carbon monoxide, propane, propylene, and methane were injected in varying concentrations while catalyst outlet temperature, carbon monoxide, and hydrocarbon conversion were measured for a period of 200 s. Of the injected species, it is shown that propylene has the greatest deactivation effect on the catalyst followed by carbon monoxide, both in terms of time and concentration. Propane is found not to deactivate the catalyst even in very globally fuel-rich conditions whereas methane acts as an inert gas over the catalyst in the temperature range of interest. It is concluded from the study that high concentrations of carbon monoxide do not act alone in the poisoning process for the rich PCI condition. The presence of some partial oxidation products such as unsaturated hydrocarbons can also have an adverse effect on DOC performance.


International Journal of Engine Research | 2017

Evolution and current understanding of physicochemical characterization of particulate matter from reactivity controlled compression ignition combustion on a multicylinder light-duty engine

John M. E. Storey; Scott Curran; Samuel A. Lewis; Teresa L Barone; Adam B. Dempsey; Melanie Moses-DeBusk; Reed Hanson; Vitaly Y. Prikhodko; William F. Northrop

Low-temperature compression ignition combustion can result in nearly smokeless combustion, as indicated by a smoke meter or other forms of soot measurement that rely on absorbance due to elemental carbon content. Highly premixed low-temperature combustion modes do not form particulate matter in the traditional pathways seen with conventional diesel combustion. Previous research into reactivity controlled compression ignition particulate matter has shown, despite a near zero smoke number, significant mass can be collected on filter media used for particulate matter certification measurement. In addition, particulate matter size distributions reveal that a fraction of the particles survive heated double-dilution conditions. This study summarizes research completed at Oak Ridge National Laboratory to date on characterizing the nature, chemistry and aftertreatment considerations of reactivity controlled compression ignition particulate matter and presents new research highlighting the importance of injection strategy and fuel composition on reactivity controlled compression ignition particulate matter formation. Particle size measurements and the transmission electron microscopy results do show the presence of soot particles; however, the elemental carbon fraction was, in many cases, within the uncertainty of the thermal–optical measurement. Particulate matter emitted during reactivity controlled compression ignition operation was also collected with a novel sampling technique and analyzed by thermal desorption or pyrolysis gas chromatography mass spectroscopy. Particulate matter speciation results indicated that the high boiling range of diesel hydrocarbons was likely responsible for the particulate matter mass captured on the filter media. To investigate potential fuel chemistry effects, either ethanol or biodiesel were incorporated to assess whether oxygenated fuels may enhance particle emission reduction.


Aerosol Science and Technology | 2016

Volatility characterization of nanoparticles from single and dual-fuel low temperature combustion in compression ignition engines

Glenn Lucachick; Scott Curran; John M. E. Storey; Vitaly Y. Prikhodko; William F. Northrop

ABSTRACT This work explores the volatility of particles produced from two diesel low temperature combustion (LTC) modes proposed for high-efficiency compression ignition engines. It also explores mechanisms of particulate formation and growth upon dilution in the near-tailpipe environment. The number distribution of exhaust particles from low- and mid-load dual-fuel reactivity controlled compression ignition (RCCI) and single-fuel premixed charge compression ignition (PPCI) modes were experimentally studied over a gradient of dilution temperature. Particle volatility of select particle diameters was investigated using volatility tandem differential mobility analysis (V-TDMA). Evaporation rates for exhaust particles were compared with V-TDMA results for candidate pure n-alkanes to identify species with similar volatility characteristics. The results show that LTC particles are mostly comprised of material with volatility similar to engine oil alkanes. V-TDMA results were used as inputs to an aerosol condensation and evaporation model to support the finding that smaller particles in the distribution are comprised of lower volatility material than large particles under primary dilution conditions. Although our results show that saturation levels are high enough to drive condensation of alkanes onto existing particles under the dilution conditions investigated, they are not high enough to allow homogeneous nucleation of these same compounds in the primary exhaust plume. Therefore, we conclude that observed particles from LTC operation must grow from low concentrations of highly nonvolatile compounds present in the exhaust. Copyright


symposium on large spatial databases | 2015

Discovering Non-compliant Window Co-Occurrence Patterns: A Summary of Results

Reem Y. Ali; Venkata M. V. Gunturi; Andrew J. Kotz; Shashi Shekhar; William F. Northrop

Given a set of trajectories annotated with measurements of physical variables, the problem of Non-compliant Window Co-occurrence (NWC) pattern discovery aims to determine temporal signatures in the explanatory variables which are highly associated with windows of undesirable behavior in a target variable. NWC discovery is important for societal applications such as eco-friendly transportation (e.g. identifying engine signatures leading to high greenhouse gas emissions). Challenges of designing a scalable algorithm for NWC discovery include the non-monotonicity of popular spatio-temporal statistical interest measures of association such as the cross-K function. This challenge renders the anti-monotone pruning based algorithms (e.g. Apriori) inapplicable. To address this limitation, we propose two novel upper bounds for the cross-K function which help in filtering uninteresting candidate patterns. Using these bounds, we also propose a Multi-Parent Tracking approach (MTNMiner) for mining NWC patterns. A case study with real world engine data demonstrates the ability of the proposed approach to discover patterns which are interesting to engine scientists. Experimental evaluation on real-world data show that MTNMiner results in substantial computational savings over the naive approach.


advances in geographic information systems | 2015

Future connected vehicles: challenges and opportunities for spatio-temporal computing

Reem Y. Ali; Venkata M. V. Gunturi; Shashi Shekhar; Ahmed Eldawy; Mohamed F. Mokbel; Andrew J. Kotz; William F. Northrop

Modern vehicles are increasingly being equipped with rich instrumentation that enables them to collect location aware data on a wide variety of travel related phenomena such as the real-world performance of engines and powertrain, driver preferences, context of the vehicle with respect to others nearby, and--indirectly--traffic on the transportation network itself. Combined with their increased access to the Internet, these connected vehicles are opening up vast opportunities to improve the safety, environmental friendliness, and the overall experience of urban travel. However, significant spatial computing challenges need to be addressed before we can realize the full potential of connected vehicles. This paper presents some of the open research questions under this theme from the perspectives of query processing, data science and data engineering.


Environmental Science & Technology | 2016

Lagrangian Hotspots of In-Use NOX Emissions from Transit Buses

Andrew J. Kotz; David B. Kittelson; William F. Northrop

In-use, spatiotemporal NOX emissions were measured from a conventional powertrain transit bus and a series electric hybrid bus over gradients of route kinetic intensity and ambient temperature. This paper introduces a new method for identifying NOX emissions hotspots along a bus route using high fidelity Lagrangian vehicle data to explore spatial interactions that may influence emissions production. Our study shows that the studied transit buses emit higher than regulated emissions because on-route operation does not accurately represent the range of engine operation tested according to regulatory standards. Using the Lagrangian hotspot detection, we demonstrate that NOX hotspots occurred at bus stops, during cold starts, on inclines, and for accelerations. On the selected routes, bus stops resulted in 3.3 times the route averaged emissions factor in grams/km without significant dependence on bus type or climate. The buses also emitted 2.3 times the route averaged NOX emissions factor at the beginning of each route due to cold selective catalytic reduction aftertreatment temperature. The Lagrangian hotspot detection technique demonstrated here could be employed in future connected vehicles empowered by advances in computational power, data storage capability, and improved sensor technology to optimize emissions as a function of spatial location.

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Isaac W. Ekoto

Sandia National Laboratories

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Benjamin Wolk

Sandia National Laboratories

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Wei Fang

University of Minnesota

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Xuesong Li

University of Minnesota

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