In the past decade, reports such as the National Academies' "Engineering in K-12 Education: Understanding the Status and Improving the Prospects" (2009) have discussed the importance of - and challenges of - effectively incorporating engineering concepts into the K-12 curriculum. Multiple reports have echoed and further elaborated on the need to effectively and authentically introduce engineering within K-12; not just to address a perpetual shortage of engineers, but to increase technological literacy within the U.S.The NSF-funded initiative Engineering for US All (E4USA): A National Pilot Program for High School Engineering Course and Database curriculum was intentionally designed `for us all;' in other words, the design is meant to be inclusive and to engage in an examination and exploration of `engineering'. The intent behind the `for us all' curriculum is to emphasize the idea of thinking like an engineer, rather than simply to develop more engineers. Therefore, the focus is not on `how to become an engineer' but `what is an engineer' and `who is an engineer'.This paper will discuss the design of the first iteration of the curriculum. The initial design was based on the First Year Engineering Classification Scheme, used to classify all possible content found in first-year, multidisciplinary Introduction to Engineering courses in general-admit (non direct-admit) engineering programs. The curriculum provides progressively larger engineering design experiences relating to student fields of interest and real-world problems. Course objectives are broken into four major threads. Each of these threads is woven through seven modules. The threads are: Discovering Engineering, Engineering in Society, Engineering Professional Skills, and Engineering Design.The paper will describe the design and details of the initial implementation of the E4USA curriculum, focusing on the features that make this course suitable `for all.'

Small closely-coupled post injections of fuel in diesel engines are known to reduce engine-out soot emissions, but the relative roles of various underlying in-cylinder mechanisms have not been established. Furthermore, the efficacy of soot reduction is not universal, and depends in unclear ways on operating conditions and injection schedule, among other factors. Consequently, designing engine hardware and operating strategies to fully realize the potential of post-injections is limited by this lack of understanding. Following previous work, several different post-injection schedules are investigated using a single-cylinder 2.34 L heavy-duty optical engine equipped with a Delphi DFI 1.5 light-duty injector. In this configuration, adding a closely-coupled post injection with sufficiently short injection duration can increase the load without increasing soot emissions. With increasing post-injection duration, the plateau in soot emissions eventually turns upward until the post-injection increases engine-out soot above that for a single-injection strategy at the same load and main injection timing. To gain more insight into in-cylinder processes affecting soot with post-injections, a new optical diagnostic technique is utilized. Diffused back-illumination imaging (DBI) of soot extinction has previously been used in a high-pressure constant volume vessel, but has not yet been reported in the literature for heavy-duty engines. The DBI setup developed for this experiment enables quantitative 2-dimensional (2D) line-of-sight optical thickness (KL) measurements from soot extinction with a temporal resolution of 42 kHz. The high temporal resolution and relatively large field of view (FoV) quantifies the evolution of in-cylinder soot for roughly the downstream half of one diesel jet of the multi-hole injector throughout each cycle. The DBI imaging reveals that at these operating conditions, when the post injection is sufficiently short, the majority of the soot in the post injection is oxidized, thus allowing for increased load with similar soot emissions compared to a single-injection condition. A transient increase in that occurs after the end of injection (the entrainment wave) is a candidate explanation for the observed completeness of post-injection soot oxidation. Additionally, semi-quantitative comparisons of soot KL and natural luminosity (NL) trends reveal decreasing KL accompanied by increasing NL. This observation is consistent with an increase in post-injection soot temperature after the end of the post injection, which may further aid oxidation. (Less)

One strategy to reduce soot formation in compression-ignition engines is extending the ignition delay to provide more time for mixing. However, vapor-fuel concentration measurements have shown that near-injector mixtures become too lean to achieve complete combustion, leading to a relative increase in unburned hydrocarbon emissions. One potential contributor to over-leaning is an "entrainment wave,"which is a transient increase in local entrainment after the end of injection. Although an entrainment wave can be predicted by a one-dimensional (1D) free-jet model, no previous measurements at diesel injection conditions have demonstrated conclusively its existence, nor has its magnitude been verified. Using particle image velocimetry (PIV) in the ambient gases, we measure entrained gas velocity through a diesel jet boundary before, during, and after the injection. The entrainment calculation depends on the definition of the jet boundary, here newly proposed based on the minimum of the radial coordinate and the radial velocity (r upsilon(r\)). Unlike previous formulations, the method is robust even in the presence of axial flow gradients in the ambient gases. Prior to the end of injection, the measured entrainment rates that agree well with non-reacting steady gas-jet behavior, as well as with the 1D free-jet model. After end of injection, the local entrainment rate temporarily increases by a factor of 2, which is similar to the factor 2.5 increase predicted by the 1D model. However, the entrainment wave is more broadly distributed in the experimental data, likely due to confinement and/or other real-jet processes absent in the 1D model.

Reactivity Controlled Compression Ignition (RCCI) is an approach to increase engine efficiency and lower engine-out emissions by using in-cylinder stratification of fuels with differing reactivity (i.e., autoignition characteristics) to control combustion phasing. Stratification can be altered by varying the injection timing of the high-reactivity fuel, causing transitions across multiple regimes of combustion. When injection is sufficiently early, combustion approaches a highly-premixed autoignition regime, and when it is sufficiently late it approaches more mixing-controlled, diesel-like conditions. Engine performance, emissions, and control authority over combustion phasing with injection timing are most favorable in between, within the RCCI regime. To study charge preparation phenomena that dictate regime transitions, two different optical diagnostics are applied in a single-cylinder heavy-duty optical engine, and conventional engine diagnostics are applied in a multi-cylinder, light-duty all-metal engine. Both engines are operated with iso-octane and n-heptane as the low-and high-reactivity fuels, respectively. The iso-octane fuel fraction delivers 80% of the total fuel energy, the global equivalence ratio is 0.35, and no exhaust gas recirculation is used. In the optical engine, single-shot, band-pass infrared (IR) imaging of emission near 3.3 microns measures thermal C-H stretch-band emission of hot fuel vapor and intermediate combustion products, providing qualitative information about the fuel-vapor distribution and ignition locations during low-temperature heat release. Additionally, high-speed 7.2 kHz visible-light imaging of natural luminosity, optimized to detect chemiluminescence, indicates the spatial and temporal evolution of high-temperature heat release and combustion. Similar combustion regimes are observed for both engine platforms, allowing an opportunity for optical engine data to provide insight into fundamental phenomena affecting regime ranges and transitions in production engines. Key findings from imaging diagnostics indicate that at the late-injection limit of RCCI control authority, low-temperature ignition occurs when clearly identifiable jet structures are still intact, and during high-temperature combustion there is prevalent and persistent soot incandescence representative of locally mixing-limited (i.e., fuel-rich) combustion. At the early-injection limit of RCCI control, observed stratification during low-temperature ignition is subtle; however, high-temperature combustion still occurs sequentially from the bowl rim radially inwards.

This paper presents new measurements of liquid and liftoff lengths, vapor penetration, and ignition delay using the Engine Combustion Network (ECN) 'Spray B' injector in a 2.34 L skip-fired heavy-duty optical engine. The data from the Spray B injector, having three 90-micron holes, are compared with previously existing constant-volume vessel data using both the Spray B injector as well as the ECN Spray A injector, which has a single 90-micron axial hole. The new data were acquired using Mie scattering, OH* chemiluminescence imaging, schlieren imaging, and incylinder pressure measurements. This paper presents data from estimated isentropic-core top-dead-center conditions with ambient densities of 15.2 and 22.8 kg/m(3), temperatures of 800, 900, and 1000 K, and for both non-reacting (0% and 7.5% O-2) and reacting (13, 15, and 21% O-2) injections of n-dodecane at fuel-rail pressures of 500, 1000, and 1500 bar. Particular attention is given to the data analysis process during transient injection, and boundary condition uncertainty. In addition to the hole of interest (#3), measurements from all three Spray B holes demonstrate that the hole-to-hole variations are small, but may indicate that the influence of internal sac flows, as well as orifice geometry, are important. In addition to the ensemble-averaged data presented here, the full dataset including cycle-to-cycle variability has also been published to an online-database available at https://ecn.sandia.gov for computer model validation. A companion paper makes a preliminary comparison of these data to Reynolds-averaged Navier Stokes solutions using Lib-ICE to simulate Spray B with a sector mesh.

Background: Cerium oxide (CeO2) nanoparticles used as a diesel fuel additive can be emitted into the ambient air leading to human inhalation. Although biological studies have shown CeO2 nanoparticles can cause adverse health effects, the extent of the biodistribution of CeO2 nanoparticles through inhalation has not been well characterized. Furthermore, freshly emitted CeO2 nanoparticles can undergo an aging process by interaction with other ambient airborne pollutants that may influence the biodistribution after inhalation. Therefore, understanding the pharmacokinetic of newly-generated and atmospherically-aged CeO2 nanoparticles is needed to assess the risks to human health.Methods: A novel experimental system was designed to integrate the generation, aging, and inhalation exposure of Sprague Dawley rats to combustion-generated CeO2 nanoparticles (25 and 90 nm bimodal distribution). Aging was done in a chamber representing typical ambient urban air conditions with UV lights. Following a single 4-hour nose-only exposure to freshly emitted or aged CeO2 for 15 min, 24 h, and 7 days, ICP-MS detection of Ce in the blood, lungs, gastrointestinal tract, liver, spleen, kidneys, heart, brain, olfactory bulb, urine, and feces were analyzed with a mass balance approach to gain an overarching understanding of the distribution. A physiologically based pharmacokinetic (PBPK) model that includes mucociliary clearance, phagocytosis, and entry into the systemic circulation by alveolar wall penetration was developed to predict the biodistribution kinetic of the inhaled CeO2 nanoparticles.Results: Cerium was predominantly recovered in the lungs and feces, with extrapulmonary organs contributing less than 4 % to the recovery rate at 24 h post exposure. No significant differences in biodistribution patterns were found between fresh and aged CeO2 nanoparticles. The PBPK model predicted the biodistribution well and identified phagocytizing cells in the pulmonary region accountable for most of the nanoparticles not eliminated by feces.Conclusions: The biodistribution of fresh and aged CeO2 nanoparticles followed the same patterns, with the highest amounts recovered in the feces and lungs. The slow decrease of nanoparticle concentrations in the lungs can be explained by clearance to the gastrointestinal tract and then to the feces. The PBPK model successfully predicted the kinetic of CeO2 nanoparticles in various organs measured in this study and suggested most of the nanoparticles were captured by phagocytizing cells.

Non-conventional operating conditions and fuels in diesel engines can produce longer ignition delays compared to conventional diesel combustion. If those extended delays are longer than the injection duration, the ignition and combustion progress can be significantly influenced by the transient following the end of injection (EOI), and especially by the modification of the mixture field. The objective of this paper is to assess how those long ignition delays, obtained by injecting at low in-cylinder temperatures (e.g., 760-800K), are affected by EOI. Two multi-hole diesel fuel injectors with either six 0.20mm orifices or seven 0.14mm orifices have been used in a 2.34L single-cylinder optical diesel engine. We consider a range of ambient top dead center (TDC) temperatures at the start of injection from 760-1000K as well as a range of injection durations from 0.5ms to 3.1ms. Ignition delays are computed through the analysis of both cylinder pressure and chemiluminescence imaging. A simplified one-dimensional (1-d) model of the diesel jet, able to match the behavior of a transient injection and entrainment processes, is used to estimate the ensemble-averaged mixture fraction fields during the injection event and at the ignition kernel locations.At TDC temperatures of 850K or higher, the injection duration is longer than ignition delay, and thus EOI has no effect on ignition delay. At TDC temperatures of 800K or lower, for short injection durations (<1.3ms), ignition occurs after EOI and ignition delay decreases with decreasing injection duration is observed. In addition, the 1-d spray model predicts a decrease of the mixture fraction at ignition kernels with decreasing ignition delay. This is in contrast to the expected trend of increasing kinetic time with decreasing mixture fraction for well-mixed reactors. This suggests that mixture fraction alone is not the first-order parameter influencing the timing and position of ignition sites. The history of the ignition kernel(s) and/or of the scalar dissipation may also need to be considered.

The relationship between the three-dimensional vortex structures and flow-separation zones generated by a shock wave/boundary-layer interaction within a low-aspect-ratio duct was studied using stereoscopic particle imaging velocimetry measurements. In this configuration, the interaction of the incident shock with all walls was important in controlling the flowfield; the three interactions coupled to produce a strongly distorted flowfield. Conditional sampling was used to construct the local probability of reverse flow maps, and thus quantify the distribution of regions of intermittent separation on both bottom-walls and side-walls. The latter regions were found to be significantly larger and more likely to separate than the former. Thus, it was concluded that the sidewall and corner flow interactions dominate in this configuration. A triple decomposition of motion was used to construct a three-dimensional representation of the vortex features generated by the interaction. The results indicated that the flowfield was dominated by three vortex systems: 1) the vortex associated with the sidewall swept-shock interaction; 2) a complex, possibly branched, vortex pair induced on the bottom wall; and 3) a vortex pair induced by the flow at the corner, which coupled the two interactions. The role of the three vortex systems on the onset of flow separation was also explored and discussed.

The continuous production of an aerosol of CeO2 nanoparticles is valuable for nanoparticle aging and inhalation exposure studies, compared with other synthesis processes that require subsequent handling and preparation of the aerosol which can alter nanoparticle properties. This paper describes a new method for producing CeO2 nanoparticles and a novel facility where a combustion synthesis system was integrated in-line with an atmospheric ultraviolet (UV) aging chamber and an inhalation exposure system. Poly-disperse CeO2 nanoparticles were continuously produced to demonstrate the capability of the integrated nanoparticle synthesis and delivery system. The CeO2 nanoparticles were products of combustion of cerium acetate hydrate, a solid-phase precursor, with gas-phase hydrogen, oxygen, and nitrogen reactants. Results for particle size, concentration, crystal structure, and morphology are presented for the CeO2 nanoparticles produced in this study with and without UV exposure in the aging chamber. The setup successfully demonstrated the capability to maintain a steady CeO2 particle number concentration throughout four hours of operation with ~90% of the particles less than 200nm in size, corresponding to a mass concentration of approximately 500μg/m3. The CeO2 nanoparticle morphology (including primary particle size and aggregate size) and crystalline phase showed minimal sensitivity to UV aging in the ambient urban environment used in the study. The results indicate other species co-produced in diesel fuel systems (where CeO2 nanoparticles are used as a fuel additive) or found in the urban atmosphere may be required to affect the aging of CeO2 nanoparticles observed in previous studies.

Extensive prior art within the Engine Combustion Network (ECN) using a Bosch single axial-hole injector called ‘Spray A’ in constant-volume vessels has provided a solid foundation from which to evaluate modeling tools relevant to spray combustion. In this paper, a new experiment using a Bosch three-hole nozzle called ‘Spray B’ mounted in a 2.34 L heavy-duty optical engine is compared to sector-mesh engine simulations. Two different approaches are employed to model combustion: the ‘well-mixed model’ considers every cell as a homogeneous reactor and employs multi-zone chemistry to reduce the computational time. The ‘flamelet’ approach represents combustion by an ensemble of laminar diffusion flames evolving in the mixture fraction space and can resolve the influence of mixing, or ‘turbulence-chemistry interactions,’ through the influence of the scalar dissipation rate on combustion. Both combustion methodologies are implemented in the Lib-ICE code which is an unsteady Reynolds-averaged Navier-Stokes solver with k-ɛ turbulence closure based on OpenFOAM® technology. Liquid length and vapor penetration predictions generally fall within the experimental measurement uncertainty at 7.5% O2, 900 K, and 15.2 kg/m3. Flame liftoff length, cylinder pressure, apparent heat release rate, and ignition delay time from the two computations are compared to experiments under single parametric variation of ambient density 15.2 kg/m3 and 22.8 kg/m3, temperatures of 800, 900, and 1000 K, at 13, 15 and 21% Oxygen and injection pressure of 500, 1000, and 1500 bar. Both models generally provide apparent heat release rate maxima to within the uncertainty. The flamelet model better predicts the sensitivity of lift-off length while the well-mixed model better predicts ignition delay.

In this paper, we reflect on current notions of engineering practice by examining some of the motives for engineered solutions to the problem of climate change. We draw on fields such as science and technology studies, the philosophy of technology, and environmental ethics to highlight how dominant notions of apoliticism and ahistoricity are ingrained in contemporary engineering practice. We argue that a solely technological response to climate change does not question the social, political, and cultural tenet of infinite material growth, one of the root causes of climate change. In response to the contemporary engineering practice, we define an activist engineer as someone who not only can provide specific engineered solutions, but who also steps back from their work and tackles the question, What is the real problem and does this problem "require" an engineering intervention? Solving complex problems like climate change requires radical cultural change, and a significant obstacle is educating engineers about how to conceive of and create "authentic alternatives," that is, solutions that differ from the paradigm of "technologically improving" our way out of problems. As a means to realize radically new solutions, we investigate how engineers might (re)deploy the concept of praxis, which raises awareness in engineers of the inherent politics of technological design. Praxis empowers engineers with a more comprehensive understanding of problems, and thus transforms technologies, when appropriate, into more socially just and ecologically sensitive interventions. Most importantly, praxis also raises a radical alternative rarely considered-not "engineering a solution." Activist engineering offers a contrasting method to contemporary engineering practice and leads toward social justice and ecological protection through problem solving by asking not, How will we technologize our way out of the problems we face? but instead, What really needs to be done?.

Reliable prediction of spray penetration and spray break-up is required to achieve increases in fuel efficiency and reduction of emissions in diesel engines. Of particular interest is the early transient-flow regime. In the current work, diesel fuel spray development was studied using high-speed imaging of a high-pressure diesel common-rail fuel injector mounted in a spherical constant volume combustion chamber. The fuel injector nozzle had four holes aligned on a radial plane with diameters of 90, 110, 130, and 150 mu m. Fuel was injected into a room temperature T = 298 K (+/- 1.5%), nitrogen environment at chamber densities of 17.5, 24.2, and 32.7 kg/m(3) (+/- 3%) and for fuel-rail pressures of 1000, 1500, and 2000 bar (+/- 1.5%). High-speed images of the backlit fuel injection were captured at 100,000 frames per second. Image processing algorithms were used to determine fuel spray penetration distance and maximum penetration rate as a function of time. The early time history of the spray penetration was not sensitive to orifice size, orifice location or chamber density at the conditions studied. However, fuel injection pressure significantly affected the spray-tip penetration and time to spray break-up. The experimental results for maximum penetration rate and transition time were compared with various quasi-one-dimensional fuel-spray models. The experimental data indicated a power law relationship for the spray-tip penetration at early times in the spray development, which is consistent with recent recommendations. However, the experimental results for time to spray break up departed from the model predictions at most of the conditions studied, with the model significantly under-predicting the time for spray transition. Furthermore, the spray penetration data showed significant fluctuations in the spray geometry at early times. A fuel spray-tip tracking algorithm was developed and the results showed the maximum penetration distance did not occur along the spray center-line during the transient period of injection and the results quantified the angular location of the maximum penetration distance. These data provide valuable new insights into transient fuel spray behavior and will guide the development of the next generation of spray theory and models. (C) 2013 Elsevier Ltd. All rights reserved.

The first goal of this work was to determine the relative importance of two regions of flow separation that are caused by a shock wave boundary layer interaction (SBLI) in a rectangular duct. Separation occurs on both the bottom wall and the sidewall; the areas of these two separated regions were measured and compared. The location where separation first begins was also estimated. Most previous studies of SBLI have focused only on a single wall and have ignored interactions where walls meet at corners. A challenging problem that arose was how to best measure separation of 3-D flow that is sufficiently unsteady that the separation has become intermittent. This required that the probability of separation be measured. Two methods were applied to stereo-PIV velocity data in a SBLI occuring at a rectangular corner region of a Mach 2.75 wind tunnel. Method 1 is called the “h-criterion” and Method 2 is called the AVT (Axial velocity threshold) criterion. These methods are used to detect separation regions and provide a separation map at the interaction region. The importance of the side-wall separation regions versus the centerline separation is clearly evident from the results hence presented.

This paper shows through a comparative case study that many contemporary engineers working on a technological response to climate change—biofuel production—continue to be guided by traditional ethical and historical principles of efficiency and growth in spite of the uniqueness of climate change as a problem unbounded globally in space and time. The comparative case study reveals that in the past environmental issues like water scarcity were viewed as deficiencies of nature. In contrast, the development of biofuels as an engineering response to climate change shows that environmental and ecological issues today are viewed as deficiencies of technologies. Yet, just like large dams on rivers had (and continue to have) negative socioecological outcomes, political economy and political ecology research show biofuel development has socially unjust and ecologically degrading outcomes. Many engineers continue to separate the “technical” from the “political” aspects of engineering work, resulting in lost opportunities to reshape the technological development paradigm. While every technology has some negative impacts, engineers, as socioecological experimentalists, must account for these outcomes in their work to mitigate them. Encouragingly, the engineers interviewed for this paper (along the authors of this paper, who are all engineers) believe that problems like climate change are too narrowly defined, and that the problem-solving capabilities of engineers would lead to more favorable outcomes if problems were more broadly defined to incorporate concerns of social justice and ecological holism, and if we are given legitimacy and agency in proposing alternative, radical, and paradigm-changing solutions to problems like climate change.

The interaction between two separated flow regions was studied for the fundamental problem of a shock wave-boundary layer interaction (SBLI) within a rectangular inlet. One motivation is that the inlet of an engine on a supersonic aircraft may contain separation zones on the sidewalls and the bottom wall; if one region separates first it can alter the flow on the other wall and lead to engine unstart. In our work an oblique shock wave was generated by a wedge suspended from the upper wall of a Mach 2.75 wind tunnel. Stereo particle image velocimetry (PIV) measurements were recorded in 25 planes that include all three possible orthogonal orientations. The lateral velocity and vorticity measurements help to explain the underlying flow structure and these quantities were not measured previously for this problem. It is concluded that the sidewall and bottom wall separation zones interact due to an underlying flow structure that is similar to the two types of 3-D separation patterns previously described by Tobak & Peake (Annu. Rev. Fluid Mech., vol. 14, 1982, pp. 61-85). Separation first occurs at an upstream location where the shock interacts with the sidewall. Lateral velocities direct flow toward the centreline to cause separation on the bottom wall. This causes significant curvature of the shock wave, so that even the region near the tunnel centreline cannot be explained by conventional 2-D concepts. A number of critical points (saddle points, nodes, focus points) were identified. Results are consistent with the general ideas of Burton & Babinsky (J. Fluid Mech., vol. 707, 2012, pp. 287-306) and help to provide details of how the sidewalls redistribute the adverse pressure gradient in space.

Partially premixed combustion strategies for compression-ignition engines reduce soot formation in part by extending the ignition delay to provide more time for mixing before combustion. However, vapor-fuel concentration measurements have shown that near-injector mixtures become too lean to achieve complete combustion, leading to an increase in unburned hydrocarbon emissions compared to conventional diesel combustion. One potential cause of the over-leaning is an “entrainment wave,” which is a transient increase in local entrainment after the end of injection that has been predicted by a one-dimensional (1D) free-jet model. No previous measurements at diesel injection conditions have demonstrated conclusively that this entrainment wave exists, nor has its magnitude been verified. Using particle image velocimetry (PIV) in the ambient gases, we measure entrained gas flows through a diesel jet boundary before and after the end of injection. The entrainment calculation depends on the definition of the jet boundary, and we propose a definition for this boundary based on the local minimum in the product of the radial coordinate and the radial velocity ( ). We demonstrate that the method is robust for calculating entrainment in the presence of axial flow gradients in the ambient gases outside the jet. Prior to the end of injection, the measured portions of the quasi-steady jet exhibit steady entrainment rates that agree well with typical non-reacting gas-jet behavior, as well as with the 1D free-jet model. After end of injection, the local entrainment rate temporarily increases by as much as a factor of two, which is similar to the factor of 2.5 peak increase predicted by the 1D model. However, the entrainment wave is more broadly distributed in the experimental data, likely due to jet confinement or other real-jet processes absent in the 1D model. Corresponding author: weeagle@sandia.gov ILASS Americas 26th Annual Conference on Liquid Atomization and Spray Systems, Portland, OR, May 2014 Introduction Turbulent jets are useful for many practical applications where mass and/or momentum need to be transferred rapidly between fluids. For the case of incompressible, non-reacting jets, a measured increase in jet mass flow must arise from induction, or ‘entrainment,’ of the surrounding fluid into the jet. Since entrainment must occur dynamically, we are interested in what variables control the transient local ‘entrainment rate.’ A brute-force numerical solution to the fully coupled Navier-stokes equations could provide a prediction of the locally-driven time-dependent process of entrainment, but these solutions are only practical for limited domain sizes. On the other hand, the widespread use of turbulent jets and the similarity of different jets across a wide range of flow scales demonstrate both a need and plausibility of a simplified treatment. From a fundamental perspective, we would like to predict entrainment along the jet boundary, that is, directly at the interface between the jet and the ambient fluid, and so predict the mixing state throughout the jet (Nickels & Perry, 1996). However, we are impeded by two major issues. One is a diversity of possible definitions for the jet boundary, particularly in the case of a transient injection. The second is a lack of relevant entrainment measurements for developing jets, or in the case of a steady jet, accurate measurements of local entrainment in the near field. On dimensional grounds, for an axisymmetric jet, the total entrained mass flow ̇ ( ) [ ⁄ ] depends on only four global variables: the jet’s initial velocity, diameter, fluid density and viscosity ( ( ) ) Individual variation in these parameters can be assessed through the jet Reynolds number, ⁄ . For large values of Re, a free-jet develops ‘self-similar’ behavior some distance downstream of an initial ‘transition’ region, and the mixing rate also becomes independent of viscosity (Curtet and Ricou, 1964). In this region, the total entrained flow ̇ , increases linearly. The simplest assumption that satisfies ‘selfsimilar’ development is a linear jet boundary (e.g. for an axisymmetric-cone), and a constant value (typically 0.32) of the local entrainment rate (Ricou and Spalding, 1960). Different entrainment rate constants for ‘self-similar’ development of submerged (no-coflow), co-flow, and counter-flowing jets, can be found in textbooks on the subject of turbulent jets (for example, Abramovich, 1963). To understand mixing and combustion of fuel and air in direct-injection diesel engines, knowledge of the local entrainment becomes critical. Combustion optimization requires properly designing an injection strategy that achieves a desired local mixing state. Locally rich regions contribute to smoke (carbonaceous soot) and other smog emissions (nitrogen oxides) (O’Connor & Musculus, 2013). Non-conventional diesel combustion strategies like partially premixed combustion aim to increase mixing before combustion to reduce overall in-cylinder stoichiometry, yielding lower emissions of soot and nitrogen oxides; however, improvements in performance and/or reduction in emissions remain limited by the local mixing rate (O’Connor & Musculus, 2013). Another complication in determining the local mixing rate is the transient end of injection. Deceleration of flow at the jet orifice, ( ), has been shown to significantly change jet mixing and entrainment (Boree, Atassi, & Charnay, 1996). Following an orifice flow reduction, experiments indicate a transient increase in entrainment at the jet boundary relative to a steady jet. An increase in local mixing can yield locally fuel-lean mixtures, for which combustion may not proceed to completion, leading to increases in the emission of unburned hydrocarbons and carbon monoxide (Musculus, Miles, & Pickett, 2013). For our engineering application of interest, lessons learned for constant density gaseous jets can be extended to liquid-fuel sprays by accounting for differing densities of ambient and injected fluids. Successful predictions for transient spray penetration and mixing behavior are possible under the condition that entrainment is well predicted (Desantes, Arrègle, López, & Cronhjort, 2006; Iyer & Abraham, 2005; Siebers, 1999). However, as a result of applying a fixed spreading angle, these models enforce a constant local entrainment rate at the jet boundary. Hence, agreement of model predictions with experiments that measure penetration or entrainment requires the spray spreading angle and entrainment rate be known a priori, or tuned empirically. Furthermore, these simple models assume a quiescent and unbounded ambient and this assumption is violated in the case of confined engine combustion chambers. An important advancement in our understanding of jet entrainment and mixing is the predominant role of instantaneous large-scale structures on local mixing and entrainment (Dahm & Dimotakis, 1987; Philip & Marusic, 2012). Unlike an increase in laminar-like diffusion implied by a ‘turbulent diffusivity’ in the Boussinesq approximation, large-scale structure in the flow implies that contact surface and a local mixing rate are coupled. Therefore, two processes control entrainment rate: the large-scale driven local-stretching between fluids (contact surface production) and the rapid mixing occurring at the smallest scales of the flow (contact surface consumption). To understand the entrainment process, we have to understand the dynamics of the jet boundary. Progress may be made on dimensional grounds, if we no longer assume that the stretching of the local jet boundary and the local entrainment rate must be both linear and hence locally constant. Invoking the assumption that axial momentum is only lost due to ambient fluid entrainment (no significant axial pressure gradients), growth of the local entrainment surface is the sole source of momentum transfer. We make a local estimate of the jet surface area, , based on the jet radius, through which the entrainment is occurring. For a given entrainment, the radius should necessarily increase with downstream distance. Likewise, in the case of zero entrainment, should remain constant. For example, consider turbulent selfsimilar flow, where the jet boundary (jet spreading angle) becomes linear (entrainment rate as well) and laminar jet fountains that produce streams of liquid with nearly constant radius. For the dynamic jet boundary case, the local entrainment rate can be functionalized on the basis of the gradient in the local jet boundary radius, . Therefore, a method is desired to accurately determine the jet boundary as an indication of, and a consequence of, entrainment. Unfortunately, as previously mentioned, theoretical determination of a form for the jet boundary remains an open question. We examine different definitions of the jet boundary in the literature for an axisymmetric jet in cylindrical coordinates (r,θ,z) and examine the consequences of integrating the differential volume flux field (rvr) [( ⁄ ) ⁄ ] to see how different definitions of the jet boundary affect the quantification of local jet entrainment (Bisset, Hunt, & Rogers, 2002; Han & Mungal, 2001; Moon, Matsumoto, & Nishida, 2009; Ricou & Spalding, 1960). Although heat release and compressibility are potential sources/sinks of volume flux in the general case, as is momentum loss due to pressure gradients, including drag forces; quantifying these effects remains outside the scope of the current work. Particle-image velocimetry (PIV) and laserDoppler velocimetry (LDV) data have provided insight into entrainment in diesel-like jets including nonvaporizing (Rhim & Farrell, 2000), vaporizing (Kozma & Farrell, 1997; Milano, Brunello, & Coghe, 1991) and confined sprays (Post, Iyer, & Abraham, 2000; Singh, Sundararajan, & Bhaskaran, 2003). Recently, PIV data using 7μs pulse separation in a transient vaporizing diesel jet were analyzed to obtain the velocity field outside the jet a