RF researchers have demonstrated that soot formation indiesel fuel jets can be avoided with the use of very small

orifices on fuel injector tips. The research, sponsored by DOE’sOffice of FreedomCAR and Vehicle Technologies in cooperationwith automotive and heavy-duty diesel engine manufacturers,was motivated by the need to reduce engine soot and nitrogenoxide (NOx) emissions.

Lyle Pickett and DennisSiebers investigated the effectsof injector tip orifice diameteron diesel combustion andemissions formation processesat the CRF. An electronicallycontrolled common rail dieselfuel injector was fitted withsingle-orifice, mini-sac typeinjector tips with various sizeorifice diameters. The diam-eters considered rangedfrom 180 µm—the typicalsize used on current heavy-duty diesel fuel injectors—to “micro-orifices” as smallas 50 µm.

The soot formationprocesses in these single,isolated fuel jets were studiedin experimental conditionssimulating the mixing-controlled phase of diesel com-bustion, the phase where sootformation rates are the highest.The researchers used reducedambient oxygen concentrationto simulate the use of exhaustgas recirculation (EGR) inengines, allowing them toinvestigate conditions whereengine-out NOx emissions arelow, but particulate matteremissions are typicallymost problematic.

Using planar laser-induced incandescence (PLII), Pickett andSiebers found that soot levels decreased with decreasing orificediameter. With a 50 µm orifice, no soot was detected despite muchhigher camera gain, as shown by the PLII images in Figure 1.

The decrease in soot that occurs within a fuel jet with adecreasing orifice diameter results from an increase in fuel-air

mixing prior to the initialcombustion zone in a fuel jet(i.e., upstream of the lift-offlength). Soot disappearedwhen fuel-air mixing up-stream of the lift-off lengthresulted in a cross-sectionalaverage equivalence ratio atthe lift-off length,φ (H),with a value less thanapproximately two (see the

values ofφ (H) in Figure 1).This trend of no soot withina fuel jet forφ (H) less thantwo held over a wide rangeof operating conditions considered.

Additional experimentswere performed with ambientoxygen concentrationsreduced to as low as 10%while other experimentalconditions remained thesame. Even with oxygen

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COMBUSTION RESEARCH FACILITY NEWS 1

Soot Formation Avoided Through Use of Micro-Orifice Fuel Injectors

C

Figure 1. Composite-average PLII images for four different injector tip orifice

diameters. PLII images were obtained by passing a laser sheet from the side through

the centerline of the fuel jet during mixing-controlled diesel combustion. Measured

lift-off lengths are indicated on the PLII images by the vertical dashed lines. The

ambient gas temperature and density were 1000 K and 14.8 kg/m3, the injector orifice

pressure drop was 138 MPa,and the ambient oxygen concentration was 21%. (Continued on page 6)

Micro-orifices,together with fuel-air mixing inthe fuel jet priorto combustion,eliminate sootwithin the fuel jets.

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S Sandia National Laboratories July/August 2003 Volume 25, No. 4

Laser-Based,Active-Illumination Technologies Show Greater SensitivityThan Passive Methods for Airborne Detection of Gas Pipeline Leaks

ndustry interest in the ability to detectleaks from gas transmission pipelines

from aboard an aircraft has prompted Sandiaresearchers to explore the possibility ofextending the range of remote gas detectionusing backscatter absorption gas imaging, orBAGI (CRF News, July/August 2000).Since the sensitivity of BAGI declines withstandoff distance, researchers explored thepossibility of using passive methods, whichrely on detecting the thermal transferbetween the gas and its surroundings.

In a recent theoretical and experimentalanalysis, a CRF team led by Tom Reichardtfound that laser-based active illuminationtechnologies have greater sensitivity thanthermal-based passive methods for remotelydetecting methane at distances up to 600 m(see Figure 1). Since the aircraft would beflown at an altitude of approximately 200 m,the laser-based approach would provide sig-nificantly improved sensitivity over thethermal approaches for this application,according to the team’s findings.

The findings resulted from a thoroughcomparison of the relative merits of thetwo approaches, sponsored by theNational Energy Technology Laboratory(Morgantown, WV). The team, which alsoincluded Sandians Sanjay Devdas, TomKulp and Wayne Einfeld, predicted leakconcentrations and geometries, calculateddetection sensitivities for the two approachesand experimentally confirmed performance predictions. For thermal detection, theyexamined the signal source term, measuringtemperature differences between the groundand air that would drive the thermal transferand define the detection limit.

Pioneering Laser-Based Leak DetectionFor the past decade, Sandia’s Remote

Sensing Group has pioneered thedevelopment of these laser-based, activeillumination leak detection systems.These systems transmit light that isabsorbed by the gas to be detected. Thetransmitted light is then reflected bysurfaces behind the gas, and collectedby the instrument’s receiving optics(see Figure 2). These laser-based instru-ments have been limited to relativelyshort distances appropriate for ground-portable systems (5-20 m).

Because the range of active illuminationmethods were limited, Sandia researchersconsidered passive methods to detect gasleaks. Such methods allow a nearly unlim-ited range with a simple instrumentalconfiguration but rely upon a thermal fluxbetween the gas plume and the ground’s sur-face. However, for the distances needed forairborne deployment, experimental and

modeling results indicate that active illumi-nation methods maintain greater sensitivityin detecting the leaking gas, without havingto rely on a thermal flux (see Figure 1).

Future work on this project involvesthe design and construction of a laser-based instrument that demonstrates theperformance requirements suitable forairborne remote sensing of pipeline leaks.

I

Figure 1. Experimentally confirmed modeling shows that a laser-based approach demonstrates superior

sensitivity over a thermal approach at the ranges required for low flying aircraft.

Figure 2. Sensing of gas plume by infrared radiation can be based on thermal exchange between the

gas and the background, or illumination with an external source (e.g., laser radiation).

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COMBUSTION RESEARCH FACILITY NEWS 3

PeoplePeople

Frank Behrendt (left), vice dean of the School of ProcessSciences and Engineering at Berlin University of Technology,visited the Combustion Research Facility for three weeks inFebruary 2003. A long time CRF collaborator, Behrendt workedwith Sandian Bob Gallagher (right) to explore the possibility ofinitiating interactions between his Berlin research group andthe CRF in the area of biomass combustion with particularemphasis on diagnostics development.

Berlin University of TechnologyProfessor Visits the CRF

The DOE annual Advanced Combustion Engine R&Daward for best project from 2002 was presented toDennis Siebers (right) and Lyle Pickett (left) of Sandia,and Brian Higgins of California Polytechnic StateUniversity at this year’s merit/peer review meeting.They received the award for providing fundamentalnew insight into the effects of diesel engine parameterson soot formation processes in diesel fuel sprays. Themerit/peer review meeting for the DOE Office ofFreedomCAR and Vehicle Technologies’ CIDI(Compression-Ignition, Direction-Injection) EngineCombustion, Emission Control, and Fuels R&DProgram was held May 13–15 at Argonne NationalLaboratory. Seven engine combustion research projectsout of 28 projects reviewed were from Sandia. Thereview panel was composed of representatives fromvarious universities and sectors of the automotive andheavy-duty engine industries.

Sandians Receive DOECombustion Engine R&D Award

Sandians Tom Settersten and Brian Patterson (right) are working withvisiting researchers Sukesh Roy (left) of Innovative ScientificSolutions, James Gord of Air Force Research Laboratory and RobertLucht of Purdue University in the CRF’s Picosecond DiagnosticsLaboratory. The researchers are investigating two-color, two-photon,laser-induced polarization spectroscopy of atomic hydrogen usingsingle-mode picosecond laser pulses.

Sandians Work with Researchers

New DOE Office Holds First Peer Review Many Sandians attended the first peer review meeting under the new DOE Office of Hydrogen, Fuel Cells & InfrastructureTechnologies, held May 19–22 at the Claremont Hotel in Berkeley, Calif. The meeting attracted 550 attendees, making it one ofthe largest peer review meetings held by DOE. Sandians giving presentations included Karl Gross on gas separations, Andy Lutzon power park systems analysis, Peter Van Blarigan on free-piston internal combustion engines and Bob Schefer on hydrogen-fueled gas turbines.

4 COMBUSTION RESEARCH FACILITY NEWS

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esearchers at the CRF have teamedwith eight other institutions to

create a knowledge management systemon the Web that will allow scientists invarious disciplines to collaborativelydevelop and share chemical information.This pilot project, called the Collaboratoryfor Multi-scale Chemical Science (CMCS),differs from earlier research projects inthat it is dedicated to producing aproduction-quality service.

Spearheaded by Sandians Larry Rahnand David Leahy, the goal of CMCS is toenhance chemical science research byfacilitating rapid sharing of validatedinformation through a new environmentdesigned to assist development of multi-scale research projects. To accomplishthis, CMCS is developing a data-centric,adaptive informatics infrastructure thatwill provide researchers with a centralizedinformation source, easily accessedthrough a Web-based portal. It works bypublicly deploying an integrated set of keycollaboration tools and chemistry-specificapplications, data resources and services.This CMCS service becomes a problem-solving environment for scientists to sharedata and collaborate in diverse, geographi-cally distributed teams.

Testing CMCS CapabilitiesCMCS is piloting this new infrastructure

among a multidisciplinary team of chemicalscientists who are working to advancecombustion science. The team is in theprocess of testing the capabilities of CMCSby using it to analyze and research differentphysical scales in various combustionproblems. The use of the CMCS serviceby these scientists will prove that theCMCS project has initiated and facilitatedcollaboration. While this pilot collaboratoryis focused on combustion, the underlyingadaptive informatics infrastructure is broadlyapplicable to many other research areas, andhas already received attention from otherresearchers in a variety of disciplines.

The adaptive informatics infrastructureuses a “portal” as the Web interface. Theinfrastructure takes advantage of a varietyof open-source information technologies toshare data, metadata and project informa-tion within groups and across communities.The portal, which can easily be enhanced

and customized through the inclusion ofnew “portlets,” includes real-time collabo-ration capabilities, search and notificationtools, and a pedigree browser.

Using CMCSFigure 1 shows how CMCS users interact

primarily with the top layer: the CMCSportal and chemistry applications. Thesechemistry applications can appear withinthe portal or can provide their own userinterfaces that interact directly with theunderlying data store. The portal providesa straightforward way for data resourcesto be associated with automatic data trans-lators. These translations are beneficialboth for providing useful views forinspection of data and to transform datainto application-ready input formats.

The capacity to record and display datapedigree (metadata) is at the heart of the

CMCS project and a key capability forenabling new approaches to science. Itallows researchers to categorize and tracescientific data across disciplines andscales and to identify both the origins andthe context of scientific data. The metadataprovides the handles for the CMCS datasearch engine. Researchers have developeda pedigree browser that provides aconvenient visualization of pedigree data.This pedigree view can easily be traversedfrom dataset to dataset using embeddedlinks in the pedigree.

Pilot Project Facilitates Knowledge Sharing,Chemical Science Research

R

Figure 1. Architecture of the CMCS Data Service and portal: The large rectangle represents the

Shared Data Repository. Contributors can use this to share chemistry data either privately or in

groups. The Scientific Annotation Middleware wraps the repository, providing automatic ways to

annotate data with pedigree information and performing translations of data to any format (ASCII,

HTML, etc.). The yellow rectangle represents the CMCS portal, an easy-to-use Web interface that

provides data searching, browsing and sharing capabilities. The portal has group management tools

including discussion forums. Chemistry applications can connect from users’ computers to the data

store, or can be embedded in the portal for easy Web access.

The CRF News is published bimonthly by theCombustion Research Facility, Sandia NationalLaboratories, Livermore, California, 94551-0969.

Director: William J. McLean, Mail Stop 9054

Editors: Julie Hall, email: jchall@sandia.gov

Natalie Cherry

Graphic Artist: Daniel Strong

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COMBUSTION RESEARCH FACILITY NEWS 5

n computational fluid dynamics,researchers have worked to be able to

computationally analyze and track theunsteady features of combustion. Currentmethods for tracking and computing theunsteady features place a mesh-basednumerical “cover” over the features.However, this process poses its own prob-lems, for meshes must be adaptable toaccount for the constantly changing fea-tures of the elements. If the mesh cannotadapt, essential flow features would bemissed, causing the numerical results tobe inaccurate.

Several automatic mesh-generationapproaches are available, but they focus onadaptivity with respect to numerical solu-tion, or on mesh geometry modification.None have yet proposed a general frame-work that could cover all variability withmesh adaptation.

About two dozen researchers workingon issues of mesh adaptation gathered atthe CRF Jan. 16–17 for the Workshop onMesh Quality and Dynamic Meshing(WMQDM). Organized by PhilippePébay, the workshop gathered researcherstogether to develop the general frame-work needed to account for the manydifferent variables associated with mesh adaptation. The proceedings of the workshop can be found athttp://www.ca.sandia.gov/CRF/mqdm.

Issues in Improving Mesh Quality

Numerical simulations, based on finitevolume (FV) or finite element (FE) methods,require the prior construction of a mesh(TΩ) of the domain of interest (Ω). Thismesh (TΩ) must form a polygonal (2-D) orpolyhedric (3-D) cover of Ω (see Figure 1).However, it becomes much harder to createthis mesh for a nonsimplicial, that is, nonte-trahedral element. In addition, making themesh adaptable for a nonsimplicial elementis even more difficult.

Current mesh generation is inadequatefor anisotropic or unsteady problems. Forexample, some essential features, such asfronts or vortices, within a reduced sub-domain of Ω, require local meshrefinement to improve accuracy. Conversely,zones where the considered variables are

relatively smooth and slow-varyingrequire mesh coarsening in order to saveprocessing time.

Another issue is that the unfolding ofthe physical process itself may cause thegeometry and/or the topology of Ω to bemodified. All of these phenomena vary intime, essentially requiring a new assess-ment of the mesh at each step because thequality of the mesh must be maintained,or the numerical results of the mesh willbe compromised. Not only is maintainingthe quality of the mesh a concern, but inturn, the quality of the mesh affects theability to adapt the mesh, creating aneven greater challenge.

Limitations of Adaptivity Approaches

In recent years, a wide variety ofapproaches have been proposed to dealwith these issues. Recent methods basedon Riemannian metrics take into accountthe “weighted” geometry that resultsfrom numerical error estimates. Thesemethods have been proposed and sucessfullytested in the case of anisotropic adaptivity.Nevertheless, the number of availableresults providing comparisons betweenthese various mesh quality estimates,and in particular how they relate to thesubsequent mesh adaptivity process, isstill very limited.

Workshop Focuses On Need for Improved Mesh Adaptation Ability

I

Figure 1. This Sedov explosion compares the present experimental determination of the HCO+O2 rate

constant to previously published measurements. This is an example of Jean-François Remacle’s (Catholic

University of Louvain,Belgium) work with mesh adaptivity.Remacle presented a remarkable discontinuous

Galerkin scheme combined with dynamic anistotropic mesh adaptation at the workshop.

S Sandia National Laboratories July/August 2003 Volume 25, No. 4

Sandia National LaboratoriesMail Stop 9056P.O. Box 969Livermore, California 94551-0969

http://www.ca.sandia.gov/CRF/TEMP- RETURN SERVICEREQUESTED

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Sandia is a multiprogram laboratoryoperated by Sandia Corporation, aLockheed Martin Company, for theUnited States Department of Energyunder contract DE-AC04-94AL85000

Sandia to Host American Flame ResearchCommittee Symposium

Sandia will host the 2003 AmericanFlame Research Committee Interna-tional Symposium Oct. 16–17. Thesymposium will be held at the CRFand will focus on bridging the gapbetween combustion research andindustrial practice in a more cost-effective manner. Presentations willalso cover research, development andcommercialization of technology forimprovements related to combustion,pollution abatement and energyutilization.

Registration is $350 for members,$450 for nonmembers and is due Sept. 5.

Of interest will be papers identifyingkey combustion research and develop-ment activities that have producedsignificant advances in abatement ofparticulate and toxic combustion by-products; burners, boilers, furnaces,and industrial processes; flaring, incineration or recovery of waste by-products or process off gases; indus-trial energy utilization and reduction ofgreenhouse gas emissions; sensors andcombustion control strategies.

For more information please visithttp://www.ca.sandia.gov/afrc/geninfo.html.

concentrations as low as 10%, nodetectable soot was found when using themicro-orifice. The results indicate that lift-off length increases with decreasingoxygen concentration, allowing moreambient gas entrainment into the fuel jetprior to the lift-off length, the net effectbeing thatφ (H) does not change signifi-cantly with oxygen concentration.

The reduced oxygen concentrationresults are significant because a decreasingoxygen concentration decreases flametemperature, which in turn decreases NOxformation. The lack of soot formation evenat low ambient oxygen concentrationssuggests that soot and NOx could bereduced simultaneously in an enginethrough the use of small orifices and EGR.

Although these single-jet results areuseful in understanding limiting-casebehavior of single-jet mixing and combus-tion during a diesel injection event, theinvestigation did not address the effects ofjet-jet interactions as well as other “real”engine effects. If proven feasible, the useof micro-orifice injectors would likelyrequire a significant redesign of the typical in-cylinder geometry in a dieselengine to promote efficient air utilization.

Soot(Continued from page 1)