Jay K. Martin

Development of a concept inventory for fluid mechanics

Concept inventories are assessment tools designed to determine the degree to which students understand the concepts of a subject and to identify the misconceptions that students hold. The results of a concept inventory can be used to change the methods of instruction to overcome student misconceptions. A cooperative effort between mechanical engineering faculty at the Universities of Wisconsin-Madison and Illinois, Champaign-Urbana has been directed toward development of a fluid mechanics concept inventory (FMCI). Fluid mechanics typically follows thermodynamics in the sequence of courses in thermal sciences, involves both the mechanics and dynamics of fluids, and builds on basic physics and Newtonian mechanics. This paper describes the process used for development of the FMCI, the details of how we determined the content, and examples of actual content of the instrument itself.

Characteristics of Homogeneous Charge Compression Ignition (HCCI) Engine Operation for Variations in Compression Ratio, Speed, and Intake Temperature While Using n-Butane as a Fuel

In this paper, some basic properties of homogeneous charge compression ignition operation are reported. The effect of inlet temperature, compression ratio and engine speed on the homogeneous charge compression ignition (HCCI) operating ranges were evaluated in a CFR engine using n-butane as a fuel. The minimum and maximum loads for HCCI operation were determined using criteria of coefficient of variation of the indicated mean effective pressure and the derivative of in-cylinder pressure, respectively. Exhaust emissions, particularly hydrocarbons, were measured using a Fourier transform infrared spectrometer. The concentration of intermediate hydrocarbon species rapidly decreased as the magnitude of the energy release increased. Hydrocarbon emission at the maximum HCCI load mainly consists of the fuel itself, which is probably emitted from colder areas in the combustion chamber Finally, the relationship between IMEPCOV and ISFC is discussed.

Droplet sizes and velocities in a transient diesel fuel spray

Abstract : Simultaneous droplet sizes and velocities were obtained for a transient diesel fuel spray in a quiescent chamber at atmospheric temperature and pressure. Instantaneous injection pressure, needle lift, and rate of injection were also measured, allowing calculation of the instantaneous nozzle discharge coefficient. Short-exposure still photographs were obtained at various chamber pressure and densities to further investigate this spray. Correlations between droplet size and velocity were determined at each crank angle to observe the detailed nature of the transient events occurring in this transient diesel fuel spray. As expected, peak mean and rms velocities are observed in the center of the spray. Measured average velocities are consistent with a calculated value, using the discharge coefficient for the nozzle and the known rate of fuel injection. The spray was nearly symmetric, with higher velocities occurring near the injector tip, and the radial dependence of velocity consistent with that observed from the spray photographs. Factors observed to effect the droplet size and velocity distributions and history include pump speed, fuel quantity delivered, and needle lift. Reprints. (aw)

Physical Mechanisms for Atomization of a Jet Spray: A Comparison of Models and Experiments

Because combustion in direct injection engines is strongly influenced by the details of the fuel spray in thes engines, the authors have begun a broad research effort of jet breakup experiments and modelling of these high pressure sprays. The main objective of this effort is to better understand fuel injection from the study of the spray-jet breakup process and the associated fuel-oxidant mixing. The focus of this paper is the development of specific models for atomization of the spray-jet. These models are then compared to each other and to preliminary data from the spray-jet breakup experiments. Initial results indicate that KIVA with this proposed spray model shows good agreement with low pressure data (69 MPa) but underestimates spray penetration for higher pressures (104 MPa).

Assistive technology: Impact on education, employment, and independence of individuals with physical disabilities

The purpose of this manuscript is to discuss how assistive technology impacts individuals with disabilities in relation to their education, employment, and ability to live independently. Appropriately selected and utilized assistive technology is imperative for individuals to approach an even par with their non-disabled peers. This paper specifically addresses a number of key questions: How important is assistive technology (AT) to the success of individuals with disabilities in education, employment, and achieving independence? If AT is important, in what ways is it important? What essential need(s) are met by the use of AT in education, employment, and independence? What remain as unresolved issues and questions regarding the use of AT by individuals with disabilities as they pursue postsecondary education, meaningful careers, and living independently? This review notes that AT is a foundational support that produces multiple and life-altering benefits. While we know much about the impact of AT on the lives of individuals with disabilities, many unanswered issues and questions remain.

Burn modes and prior-cycle effects on cyclic variations in lean-burn spark-ignition engine combustion

Cyclic variation is examined by: (1) conditional grouping and heat-release analysis to reveal different modes of combustion, (2) considering the order in which the burn modes occur to establish prior-cycle effects and (3) comparing the measured variation in IMEP with data generated by simple models. Results show that several burn modes may exist, particularly under fuel-lean conditions. Prior-cycle effects also become more obvious as the air-fuel ratio is increased. Finally, comparisons with data generated by simple models show that the nature of cyclic variation may range from completely stochastic to a superposition of a non-chaotic deterministic process on a stochastic process

Heat-transfer predictions and experiments in a motored engine

In the first part of this study, a one-dimensional code was used to compare predictions from six different two-equation turbulence models. It is shown that the application of the traditional K-E models to the viscous-dominated region of the boundary layer can produce errors in both the calculated heat flux and surface friction. A low-Reynolds-number model does hot appear to predict similar non-physical effects. A new one-dimensional model, which includes the effect of compression, has been formulated by multiparameter fit to the numerical solution of the energy equation. This model can be used in place of the law-of-the-wall to calculate the surface heat flux. The experiments were performed in a specially-instrumented engine, allowing optical access to the clearance volume . Measurements of heat flux, swirl velocities, and momentum boundary layer thickness were made for different engine speeds. Comparison of the model predictions with the results from the experiment showed good agreement.

An Optical Sensor for Spark-Ignition Engine Combustion Analysis and Control

An in-cylinder optical sensor has been developed and tested for use in spark-ignition engine combustion analysis and control. This sensor measures the luminous emission in the near infrared region. Results of these tests show good correlation between the measured luminosity and traditional combustion parameters, such as location and magnitude of maximum cylinder pressure, and location and magnitude of maximum heat release. These results are discussed in this paper.

Tools for assessing conceptual understanding in the engineering sciences

One of the hindrances to reform in science, technology, engineering and mathematics (STEM) education is the absence of good assessment instruments that can measure the value added to student learning by new ways of teaching important material. The well-known Force Concept Inventory (FCI) assessment instrument is a good model of an instrument that can be used to check on students understanding of basic concepts in a discipline. This panel session paper discusses work in progress by the panel members and their co-developers to construct FCI-like Concept Inventories in each of the disciplines of thermodynamics, systems and signals, strength of materials, electromagnetics, circuits, materials, fluid mechanics, and transport processes.

Comparison Between Air-Assisted and Single-Fluid Pressure Atomizers for Direct-Injection SI Engines Via Spatial and Temporal Mass Flux Measurements

Abstract : Two distinct atomization strategies are contrasted through the measurement of time and spatially dependent mass flux. The two systems investigated include a pressure atomizer (6.9 MPa opening pressure) and an air assist atomizer. Both systems have potential for use in direct injection spark ignition engines. The mass flux data presented were obtained using a spray patternator that was developed to allow phased sampling of the spray. The temporal mass related history of the spray was reconstructed as volume versus time plots and interpolated mass flux contour plots. Results indicate substantial differences in the distribution of both mass and mass flux in space and time for the two injection systems. For example, the pressure atomizer at high mass delivery rates produced a spray that collapsed into a dispersed cylindrical shape while at low rates, generated a hollow cone structure. In addition, the air-assist device discharges 87% of its injected volume within the first of three poppet oscillations while producing a wide hollow cone structure.