Single-Fuel Concept (SFC) describes the desire to operate diesel engines using JP-8 as the only fuel in the US military due to mostly logistic reasons. However, there is a lack of a fundamental database on the combustion characteristics of JP-8 compared to those studies that have been done for diesel combustion. In this current study, several kinetic models are used to look into flame properties including ignition behavior, fuel properties including evaporation characteristics, and species evolution such as soot precursor, acetylene. Several surrogates for JP-8 fuel including tetradecane, n-dodecane and a mixture of 77 vol-% n-dodecane and 23 vol-% m-xylene are selected in the model using a detailed chemical kinetic mechanism with 330 species and 1957 reactions. Included in the model are growth mechanisms of Polycyclic Aromatic Hydrocarbon (PAH), which are known to be important for soot formation. Studies are performed to describe the fundamental combustion characteristics of JP-8 surrogates under spray diesel conditions. Numerical models used include closed reactor simulation, Two-Stage Lagrangian (TSL) model, and Computational Fluid Dynamics (CFD) simulation. Simulation conditions include temperatures range of 1000-1400 K and injection pressures of 1100 bar, and ambient density of 14.8 kg/m3. Experiment was performed with limited number of runs to compare with the result from simulation. Vapor penetration from CFD simulation currently under predicts the values from experiments.

Reflective writing, as a reflection and communication tool, may help engineers frame their experiences with technical and professional challenges, thus possibly broadening their mindset. We conjecture that it is possible to gauge the broadening of mindset quantitatively. To this end, we have deployed a before- and after- style reflective writing activity in a graduate seminar course. The reflection prompts were developed based on the Entrepreneurial Mindset framework. This framework is a curious, connected, and value-creating way of thinking which fosters problem-solving, critical thinking, etc. These are important dimensions to prepare engineers for the future. We apply hypothesis testing to conduct a quantitative metadiscourse marker analysis of students’ reflections before and after weekly seminars to measure change in students’ mindset. Our analysis framework is applicable to assessing broadening of mindset ranging from individual students in a given semester to separate groups of students over multiple semesters for a longitudinal study.

This extended abstract proposes using the capabilities of open-source large language models (Lillis) to assess rhetorical moves in the executive summaries delivered by students enrolled in a Mechanical Engineering Capstone Senior Design course at a North American public STEM university. Our brief discussion surrounds the national and institutional contextualization of a capstone course, the current state of affairs and drawbacks of the executive summary assessment method, using an LLM to overcome these drawbacks, its potential benefits, and future work.

Extensive studies have been completed for diesel engine high pressure injection on spray and combustion characteristics with diesel fuel. However the US military’s objective is to use JP-8 as a replacement to diesel fuel, which has limited spray and combustion information available. The differences between JP-8 and diesel in terms of fuel properties translate to differing spray and combustion characteristics. To fulfill the Single-Fuel Concept of the military and incorporate JP-8 fuels, knowledge of the fuels spray, vaporization, and combustion behavior is imperative for determining fuel impact on performance. This work quantifies vaporizing spray characteristics of vapor penetration and vaporizing liquid length using high speed imaging methods of combined Mie-scatter and Schlieren in a constant volume combustion vessel. Studies are undertaken at a constant injection pressure of 700 bar, at temperatures of 800, 946, and 1150 K at a density of 24.1 kg/m 3 . Tetradecane is used as a vaporizing single component surrogate for JP-8, with results compared to spray characteristics of JP-8 and diesel available in the literature. Tetradecane is chosen as a surrogate since prior experimental work using heptamethylonone (HMN) as a surrogate showed HMN does not match JP-8 liquid length trends, especially at low density conditions. Although the boiling point of HMN (240°C) matches the 90% distillation point of JP-8, a higher boiling point fuel (tetradecane at 252°C) may provide a better match to vaporization characteristics of JP-8. Results from this study provide an understanding of spray and vaporization characteristics of tetradecane as a surrogate for JP-8.

Gasoline compression ignition (GCI) is a promising combustion technology that could help alleviate the projected demand for diesel in commercial transport while providing a pathway to achieve upcoming CO 2 and criteria pollutant regulations for heavy-duty engines. However, relatively high (i.e., diesel-like) injection pressures are needed to enable GCI across the entire load range while maintaining soot emissions benefits and managing heat release rates. There have only been a limited number of previous studies investigating the spray characteristics of light distillates with high-pressure direct-injection hardware under charge gas conditions relevant to heavy-duty applications. The current work aims to address this issue while providing experimental data needed for calibrating spray models used in simulation-led design activities. The non-reacting spray characteristics of two gasoline-like fuels relevant to GCI were studied and compared to ultra-low-sulfur diesel (ULSD). These fuels shared similar physical properties and were thus differentiated based on their research octane number (RON). Although RON60 and RON92 had different reactivities, it was hypothesized that they would exhibit similar non-reacting spray characteristics due to their physical similarities. Experiments were conducted in an optically accessible, constant volume combustion chamber using a single-hole injector representing high-pressure, common-rail fuel systems. Shadowgraph and Mie-scattering techniques were employed to measure the spray dispersion angles and penetration lengths under both non-vaporizing and vaporizing conditions. Gasoline-like fuels exhibited similar or larger non-vaporizing dispersion angle compared to ULSD. All fuels followed a typical correlation based on air-to-fuel density ratio indicating that liquid density is the main governing fuel parameter. Injection pressure had a negligible effect on the dispersion angle. Gasoline-like fuels had slower non-vaporizing penetration rates compared to ULSD, primarily due to their larger dispersion angles. As evidenced by the collapse of data onto a non-dimensional penetration correlation over a wide range of test conditions, all fuels conformed to the expected physical theory governing non-vaporizing sprays. There was no significant trend in the vaporizing dispersion angle with respect to fuel type which remained relatively constant across the entire charge gas temperature range of 800–1200 K. There was also no discernable difference in vapor penetration among the fuels or across charge temperature. The liquid length of gasoline-like fuels was much shorter than ULSD and exhibited no dependence on charge temperature at a given charge gas pressure. This behavior was attributed to gasoline being limited by interphase transport as opposed to mixing or air entrainment rates during its evaporation process. RON92 had a larger non-vaporizing dispersion angle but similar penetration compared to RON60. Although this seems to violate the original similarity hypothesis for these fuels, the analysis was made difficult due to the use of different injector builds for the experiments. However, RON92 did show a slightly larger vapor dispersion angle than RON60 and ULSD. This observation was attributed to nuanced volatility differences between the gasoline-like fuels and indicates that vapor dispersion angle likely relies on a more complex correlation beyond that of only air-to-fuel density ratio. Finally, RON92 showed the same quantitative liquid length and insensitivity to charge gas temperature as RON60.

Hands-on lab experiences are essential for enabling students to be successful engineers, especially those who identify as kinesthetic learners. This case study describes how a Mechanical Engineering Practice course sequence was redesigned during the COVID-19 emergency transition to remote learning and examines how students responded to these changes. The remote course included videos of Graduate Teaching Assistants conducting data acquisition phases of the practice session to replace hands-on experiments. To understand student perspectives and performance, researchers reviewed approximately 400 reflective essays from Spring 2020, and compared assignment submissions between Fall 2019 and Spring 2020. Results suggest that some students perceived the loss of hands-on activities as detrimental to their learning and it was not comparable to face-to-face counterparts. Furthermore, students felt forced to develop self-directed learning skills. However, in contrast to student comments in reflective essays, comparisons of assignment submissions suggested that students in Spring 2020 did not receive lower grades or have a reduced demonstration of conceptual knowledge obtained in the course.

Introduction: The COVID-19 pandemic brought unprecedented challenges to universities when instruction had to shift entirely online. Universities were quick to survey their students about those challenges, and education researchers are now focused on building more effective online experiences based on student feedback. About the case: The loss of in-person instruction was difficult for engineering students in practice-based courses as they lost the courses' hands-on aspect, which is essential for reinforcing theoretical concepts. They also lost the support provided through daily interactions with their peers and instructors. Situating the case: Students in a required four-course practice-based mechanical engineering sequence shared their perspectives via reflective portfolio essays on how shifting to online instruction affected their ability to participate in their learning communities and negotiate meaningful learning experiences. Methods/approach: Through thematic analysis of the reflective essays, we applied the lens of communities of practice to put the students' responses into context. Results/discussion: The students' concerns varied depending on their position in the course sequence and the course; however, most students felt that the loss of in-person interaction was most detrimental and disruptive in the transition to online instruction and yielded communication and teaming issues. Implications and conclusions: Five implications arose from the results of this study, including recognizing the unique challenges of online learning in practice-based courses, instructing students in virtual communication tools, exercising empathy, being mindful of cognitive load, and researching self-directed learners in online environments. In addition, faculty should consider the importance of students' communities of practice and build opportunities to maintain and strengthen the bonds of those communities within their courses, both online and face to face. They should also add more opportunities for virtual interaction early in the curriculum to build digital communication skills, which will undoubtedly be required in their careers.

The rate of injection profile is a key parameter describing the fuel injection process for diesel injection. It is also an essential input parameter for computational fluid dynamics simulations of spray flows. In the present work, rate of injection profiles of a multi-hole diesel injector were measured using the Zeuch method and the momentum flux method. The rate of injection profiles measured by the momentum flux method had a faster rise in rate of injection during the initial ramp-up phase than with the Zeuch method. The measured rate of injection profiles were applied in three-dimensional computational fluid dynamics simulations of diesel sprays under non-vaporizing and vaporizing conditions with sweeps in injection pressure, bulk charge gas density, and bulk charge gas temperature. Analytical results were compared against experimental data for liquid penetration generated under those conditions. Computational fluid dynamics results with the rate of injection profile measured by the Zeuch method under-predict liquid penetration during the initial ramp-up phase, while computational fluid dynamics results with the rate of injection profiles measured by the momentum flux method showed much better agreement with the experimental data of liquid length and penetration. This suggests that current computational fluid dynamics spray models may be able to more accurately model transient liquid penetration when using the velocity profile developed from momentum flux measurements. Further study is needed to evaluate how computational fluid dynamics predictions of combustion and emissions of affected when using these two rate of injection profiles.

Diesel combustion and emissions is largely spray and mixing controlled. Spray and combustion models enable characterization over a range of conditions to understand optimum combustion strategies. The validity of models depends on the inputs, including the rate of injection profile of the injector. One method to measure the rate of injection is to measure the momentum, where the injected fuel spray is directed onto a force transducer which provides measurements of momentum flux. From this the mass flow rate is calculated. In this study, the impact of impingement distance, the distance from injector nozzle exit to the anvil connected to the force transducer, is characterized over a range of 2 - 12 mm. This characterization includes the impact of the distance on the momentum flux signal in both magnitude and shape. At longer impingement distances, it is hypothesized that a peak in momentum could occur due to increasing velocity of fuel injected as the pintle fully opens. The study is completed at injection pressures of 620 and 2000 bar at 1 bar charge gas pressure, for 50 injection events per condition. The data is supplemented with micro-photography images of the first injection event to validate the impingement of the fuel spray on the anvil for complete momentum transfer. Results show no significant influence of impingement distance on peak momentum and a wide range of recommended impingement distances between 4 - 12 mm. At 2 mm impingement distance there is some anomalies in the behavior which is attributed to the gaseous momentum influence of neighboring sprays.

This chapter discusses the various internal combustion engine operating cycles, including the standard two and four-stroke cycle, along with alternative cycles such as over-expanded and split-cycle engines. Additionally, real engine operating strategies are reviewed including spark-ignition and compression-ignition engines. The cycle performances are compared and limitations are addressed. The chapter concludes with a discussion on future trends for internal combustion engine operating cycles.

Multiple-injection has shown significant benefits in the reduction of combustion emissions and soot formation. However, there is a need to understand the secondary flow-induced air–fuel mixture formation and subsequent combustion mechanism under multiple-injection. An experiment was performed by changing the dwell time between the pilot and main injections under the conditions of 23kg/m3 ambient density with 0% O2 (non-combusting) and 15% O2 (combusting) ambient conditions, at an injection pressure of 120MPa. The mass ratios of pilot and main injections in the study were 15/85% and 20/80%. A hybrid shadowgraph and Mie scattering imaging technique in a nearly simultaneous mode along the same line of sight was used to visualize the spray and flame luminosity. Pilot-main spray flame properties including ignition delay, ignition location, and lift-off length were characterized from experimental images. CFD simulation of pilot-main spray combustion was performed under the same experimental conditions to provide additional insights into the combustion process. The air–fuel mixing field and ignition process followed by main injection flame structure are significantly altered at different dwells. The spray-to-flame interaction mechanism model has been established for the development of an optimal multiple-injection scheme for, possibly, low soot formation and emissions.

Increasing fuel injection pressure has enabled continuous reduction of diesel emissions while sustaining the high thermal efficiency advantage of diesel engines. Current production diesel injectors operate in the range from 300 to 2000 bar. The ongoing trend for fuel injection systems is to higher injection pressures and smaller nozzle hole diameters for further emissions reduction and fuel efficiency improvements. Fundamental understanding of diesel spray characteristics including liquid penetration and cone angle is imperative to improve model development and facilitate the integration of elevated injection pressure systems into future diesel engines. Studies were conducted in an optically accessible constant volume combustion vessel under nonvaporizing and vaporizing conditions. A 7-hole injector, currently being developed for high injection pressure applications, was studied between 2000 and 3000 bar injection pressures with ultra-low sulfur diesel fuel. The study included two part-load charge density conditions of 7.4 kg/m 3 and 14.7 kg/m 3 along with an elevated density boosted condition of 34.8 kg/m. Diagnostics used included Mie back scatter imaging for liquid phase penetration. Experimental results were compared to spray penetration relationships to extrapolate these relationships to the elevated injection pressure conditions. Thus, an improved understanding of the influence of elevated injection pressure on fundamental spray characteristics was gained. Introduction Diesel combustion and emissions are spray and mixing controlled where the influence of operating parameters, i.e. injection pressure and ambient density, on spray characteristics are significant. One approach to further improve the efficiency of diesel engines is to increase injection pressures with the premise of promoting fuel air mixing [1]. Diesel injection system maximum pressure capabilities have increased from 800 to 2000 bar over the last 10 years, and more recently, higher injection pressures up to 2400 bar have been realized with advanced common rail-systems and smaller nozzles. Injection pressures are likely to increase to 3000 bar by 2015 and 4000 bar by 2020 [2]. Through increases in injection pressure in conjunction with optimized nozzle geometries, designs and other engine advancements, an additional 4% improvement in fuel efficiency may be realized [3]. In addition to the fuel efficiency improvement, exhaust emission standards may be met, with less aftertreatment needed by increasing injection pressures up to 3000 bar levels while simultaneously improving and enhancing nozzle geometry [4]. Based on these trends, an injector was studied in an effort to understand the influence of elevated injection pressures, up to 3000 bar, on spray characteristics under typical engine conditions. Experimental results obtained from Mie back scatter imaging in an optically accessible combustion vessel were quantified and analyzed. In addition, the results were compared to correlations used for predicting penetration and liquid length, to understand their application to elevated injection pressures of 2000 bar and above. Experimental Setup Experimental tests were conducted in the optically accessible constant volume chamber shown in Figure 1. The vessel has an internal volume of approximately 1 liter, six face-ports housing three sapphire windows, a spark plug – dual fan port, a diesel fuel injector port (Figure 1), and one blank port. Additionally, there are eight access ports on the combustion vessel (CV) cube vertices containing a pressure transducer, inlet and exhaust valves, and blanks. Tests are conducted in an inert environment achieved by filling the combustion vessel with * Corresponding Author: jenesbit@mtu.edu ICLASS 2012, 12 th Triennial International Conference on Liquid Atomization and Spray Systems, Heidelberg, Germany, September 2-6, 2012 nitrogen (CV electrically heated to 373 K) or in a zero percent oxygen vaporizing environment (CV electrically heated to 453 K), achieved through the use of a preburn procedure [5-7]. This procedure produces representative diesel engine conditions in the combustion chamber including pressure, temperature, and density. The process involves spark igniting a fuel-lean acetylene, hydrogen, oxygen and nitrogen gaseous mixture which yields a precombustion event and pressure rise, followed by a subsequent cool-down. Pressure is monitored during the cooldown and at the desired pressure (temperature) condition, fuel injection is triggered and combustion of the diesel liquid fuel ensues. Full details on this combustion vessel and its use are provided in [8-10]. Figure 1: Optically accessible combustion vessel with gas panels for mixture creation (left). Internal view of combustion chamber (center) and external view of diesel injector window (right). Images are acquired using a Mie back scattering setup, which enables visualization of the liquid phase diesel spray. The setup includes the high speed camera, a Photron Ultima APX RS, equipped with a 50 mm Nikon Nikkor Lens with a f-stop of 1.4. Illumination is provided by a Cooke SensiFlash flashlamp, reflected off a mirror to provide uniform illumination in the CV. Images are acquired with a 2 μs exposure duration, at varying frame rates depending on image resolution. For inert, non-vaporizing images, the resolution is 512x512 at a 10,000 fps frame rate (0.1 ms interframe time). For vaporizing spray tests, images are at 10,000 fps (0.1 ms interframe time) and 512x512 resolution, or at 30,000 fps (0.033 ms interframe time) and 256x256 resolution. Tests are conducted using ultra-low sulfur diesel fuel. A high pressure (4140 bar) fuel supply system is used to provide the necessary elevated injection pressures. The fuel injector used for this work is the subject of a major development program with demonstrated durability at pressures significantly greater than 3000 bar. The injector used is a 7-hole injector with hole diameters of 0.161 mm and an enclosed angle of 143 degrees. The nozzle needle is low mass and designed to provide fast opening and closing to guarantee maximum spray momentum even with short injection periods. The solenoid injector is driven by a high voltage power supply and switching driver at 42 V, producing an initial peak followed by reduced hold current for the remaining injection duration (electronic trigger), in order to achieve the fastest actuator response whilst maintaining low electrical energy consumption. Control of the fast moving needle is achieved with the next generation, near zero leakage, and fastest response version of Delphi’s established 3-way valve solenoid actuator. The accurate control is achieved by ensuring that the flows, unbalanced forces and hence associated valves are as small as possible. Additional details behind this principle are discussed in [11]. Tests include two levels of injection pressure, charge temperature, and charge density. Injection drive duration (electronic trigger length) is set to provide a 1.7ms injection period. Charge-gas density is the density inside the combustion vessel during the experimental test, used to replicate in-cylinder combustion conditions. This includes part-load cases of lower density (7.4 and 14.7 kg/m 3 ) to represent an engine operating at part-load, and a full load, high density engine operating case of 34.8 kg/m. Image Processing Images are processed to quantify spray parameters as a function of time after start of injection (ASOI, fuel) for each of the spray plumes. For the inert (non-vaporizing) tests the spray penetration is defined as shown in Figure 2, and for the vaporizing sprays tests the desired parameter is liquid length (LL), defined as the fully connected region from the injector tip. As will be observed in some images, there is a detached fuel slug at the leading edge of the spray. This detaching slug is a discontinuous region of liquid, and therefore is not considered in defining the liquid length. Images are read into MATLAB where the post-processing is performed. The images are then subtracted from the background image (Frame 1), and the background subtracted images are rotated in 51.4 degree increments due to a 7-hole injector to align each spray plume exiting the injector horizontally from left to right. A mask is applied to remove adjacent spray plumes and isolate the spray for processing. The spray image is then converted to black and white using a threshold determined based on the image intensity distribution. A boundary is then traced around the thresholded spray (yellow line in figure below), with the leading edge of the boundary being defined as the penetration of the spray or liquid length for the nonvaporizing and vaporizing sprays respectively (magenta circle in image below). This processing is done for each plume of the image frame, and for each frame of the spray movie to determine the temporal variation of spray properties. Results are presented for the median (from the seven plumes) liquid length or penetration, which provides a repreICLASS 2012, 12 th Triennial International Conference on Liquid Atomization and Spray Systems, Heidelberg, Germany, September 2-6, 2012 sentative value of the spray characteristics. The median quasi-steady state liquid length is also defined, which is the mean liquid length over the median liquid length temporal data, from 0.3 to 1.2 ms ASOI. Figure 2: Image processing definitions. Non-vaporizing left and vaporizing right. Yellow line defines traced spray boundary, red circle defines injector tip, magenta circle defines penetration or liquid length. Spray Penetration Correlation Experimentally determined penetration results are compared to the spray penetration correlation of Naber and Siebers [7], presented as Equation (1). This correlation predicts full spray penetration as a function of time ASOI, and will be used to compare to non-vaporizing (T=373K) penetration results. Correlation parameters include inje

An experimental investigation was performed to analyze the effects of EGR rate and turbulence flows on the combustion and flame propagation characteristics of methane (CH_4) - air gaseous mixtures in a constant-volume optically accessible combustion vessel (CV). In this study, combustion pressure data is analyzed in detail for ignition delay and combustion duration, with high-speed schlieren imaging analyzed for flame propagation characteristics. Experimental results showed that the peak combustion pressure decreased as the EGR rate increased. The slope of the pressure rise is lower with a higher EGR rate, resulting in a longer time to reach the maximum pressure compared to 0% EGR. The combustion performance of 20% EGR revealed a near misfire phenomenon, meaning it is difficult for the 20% EGR gas to achieve stable combustion performance under a quiescent condition. The rate of growth of the flame kernel decreased with an increase in EGR, and hence the flame size of 20% EGR case was the smallest at every given time. The influence of turbulent flow on the combustion characteristics showed that the combustion duration was significantly shortened for all EGR rates with compared to the results of quiescent combustion cases.