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Wiebe functions, analytical equations that estimate the fuel mass fraction burned (MFB) during combustion, have been effective at describing spark-ignition (SI) engine combustion using gasoline fuels. This study explores if the same methodology can be extended for SI combustion with syngas, a gaseous fuel mixture composed of H2, CO, and CO2, and anode-off gas; the latter is an exhaust gas mixture emitted from the anode of a Solid Oxide Fuel Cell, containing H2, CO, H2O, and CO2. For this study, anode off-gas is treated as a syngas fuel diluted with CO2 and vaporized water. Combustion experiments were run on a single-cylinder, research engine using syngas and anode-off gas as fuels. One single Wiebe function and three double Wiebe functions were fitted and compared with the MFB profile calculated from the experimental data. It was determined that the SI combustion process of both the syngas and the anode-off gas could be estimated using a governing Wiebe function. While the detailed double Wiebe function had the highest accuracy, a reduced double Wiebe function is capable of achieving comparable accuracy. On the other hand, a single Wiebe function is not able to fully capture the combustion process of a SI engine using syngas and anode off-gas.

In the first quarter of 2020, SARs-CoV-2 (COVID-19) infections began to grow at an alarming rate despite drastic measures to reduce infection rates. Severe COVID-19 cases required mechanical ventilation, resulting in ventilator shortages worldwide. To address the ventilator shortages, the authors developed the CoreVent 2020, an emergency-use ventilator for adult patients that was designed, built, and tested in ten days. The CoreVent 2020 is a pressure-cycled, time-limited ventilator with a breath-assist mode that operates on standard pressurized oxygen and medical air. It provides adjustable peak inspiratory pressure (PIP) and positive end-expiratory pressure (PEEP). A medical-grade commercially available breathing circuit is used to minimize non-medical component requirements. The CoreVent 2020 was fabricated in-house at Stony Brook University Hospital and tested on three mechanical lung simulators in which the operating modes and alarm features were demonstrated. Animal studies were also performed in both normal breathing mode and breath-assisted modes. Arterial blood gas measurements confirmed that the ventilator provided satisfactory ventilation for the test subjects. The COVID-19 pandemic presented unique constraints on the design and innovation process not normally encountered in typical practice. Design decisions such as component choice, delivery time, and ease of high-volume, rapid manufacturing influenced all aspects of the design process. This aspect of the design/innovation process is also discussed, as well as an introductory discussion on how training and simulations can be developed so that innovation can occur efficiently in future crises situations.

Solid oxide fuel cells (SOFCs) have been deployed in hybrid decentralized energy systems, in which they are directly coupled to internal combustion engines (ICEs). Prior research indicated that the anode tailgas exiting the SOFC stack should be additionally exploited due to its high energy value, with typical ICE operation favoring hybridization due to matching thermodynamic conditions during operation. Consequently, extensive research has been performed, in which engines are positioned downstream the SOFC subsystem, operating in several modes of combustion, with the most prevalent being homogeneous compression ignition (HCCI) and spark ignition (SI). Experiments were performed in a 3-cylinder ICE operating in the latter modus operandi, where the anode tailgas was assimilated by mixing syngas (H2: 33.9%, CO: 15.6%, CO2: 50.5%) with three different water vapor flowrates in the engine’s intake. While increased vapor content significantly undermined engine performance, brake thermal efficiency (BTE) surpassed 34% in the best case scenario, which outperformed the majority of engines operating under similar operating conditions, as determined from the conducted literature review. Nevertheless, the best performing application was identified operating under HCCI, in which diesel reformates assimilating SOFC anode tailgas, fueled a heavy duty ICE (17:1), and gross indicated thermal efficiency ([Formula: see text]) of 48.8% was achieved, with the same engine exhibiting identical performance when operating in reactivity-controlled compression ignition (RCCI). Overall, emissions in terms of NOx and CO were minimal, especially in SI engines, while unburned hydrocarbons (UHC) were non-existent due to the absence of hydrocarbons in the assessed reformates.

Ammonia and Hydrogen are attractive alternative fuels for a zero-carbon combustion solution that can rapidly decarbonize the transportation industry. Understanding the chemical behavior and combustion characteristics of these fuels individually, as well as blended together, is pivotal to ensuring their widespread adoption and utilization. Furthermore, in the era of computer-aided engineering, it is critical to evaluate our ability to computationally model the chemical reactivity of these two fuels and validate predictions of experimentally observed phenomena using multi-dimensional simulations. In this study, ammonia/hydrogen chemical kinetics mechanisms available from the research literature are investigated through 0-D, 1-D, and 3-D simulations. The 0-D and 1-D simulations were carried out to understand the ignition delay and laminar flame speeds, respectively, at different operating pressures and temperatures. 3-D simulations were also performed to test the fuels’ behavior in a closed volume combustion chamber. The multi-dimensional computational results were compared against optically measured experimental data available in recent publications. Specifically, a comparison of unstretched flame speeds determined from stretched flame speeds of post-processed computational results is made. Lean and rich combustion limits have been computationally evaluated as well. Lastly, observed physical buoyancy effects were reproducible in a quiescent computational environment leading to increased confidence in using the evaluated chemical kinetics mechanisms for high-fidelity reciprocating piston engine computational research and development.

Partial fuel stratification (PFS) is a low temperature combustion strategy that can alleviate high heat release rates of traditional low temperature combustion strategies by introducing compositional stratification in the combustion chamber using a split fuel injection strategy. In this study, a three-dimensional computational fluid dynamics (CFD) model with large eddy simulations and reduced detailed chemistry was used to model partial fuel stratification at three different stratified conditions. The double direct injection strategy injects 80% of the total fuel mass at −300 CAD aTDC and the remaining 20% of the fuel mass is injected at three different timings of −160, −50, −35 CAD to create low, medium, and high levels of compositional stratification, respectively. The PFS simulations were validated using experiments performed at Sandia National Laboratories on a single-cylinder research engine that operates on RD5-87, a research-grade E10 gasoline. The objective of this study is to compare the performance of three different reduced chemical kinetic mechanisms, namely SKM1, SKM2, and SKM3, at the three compositional stratification levels and identify the most suitable mechanism to reproduce the experimental data. Zero-dimensional chemical kinetic simulations were also performed to further understand differences in performance of the three reduced chemical kinetic mechanisms to explain variations in CFD derived heat release profiles. The modeling results indicate that SKM3 is the most suitable mechanism for partial fuel stratification modeling of research-grade gasoline. The results also show that the autoignition event progresses from the richer to the leaner compositional regions in the combustion chamber. Notably, the leaner regions that have less mass per unit volume, can contribute disproportionately more toward heat release as there are more cells at leaner equivalence ratio ranges. Overall, this study illuminates the underlying compositional stratification phenomena that control the heat release process in PFS combustion.

Solid oxide fuel cell – internal combustion engine (SOFC-ICE) hybrid systems are an attractive solution for electricity generation. The system can achieve up to 70% theoretical electric power conversion efficiency through energy cascading enabled by utilizing the anode off-gas from the SOFC as the fuel source for the ICE. Experimental investigations were conducted with a single cylinder Cooperative Fuel Research (CFR) engine by altering fuel-air equivalence ratio (ϕ), and compression ratio (CR) to study the engine load, combustion characteristics, and emissions levels of dry SOFC anode off-gas consisting of 33.9% H2, 15.6% CO, and 50.5% CO2. The combustion efficiency of the anode off-gas was directly evaluated by measuring the engine-out CO emissions. The highest net-indicated fuel conversion efficiency of 31.3% occurred at ϕ = 0.90 and CR = 13:1. These results demonstrate that the anode off-gas can be successfully oxidized using a spark ignition combustion mode. The fuel conversion efficiency of the anode tail gas is expected to further increase in a more modern engine architecture that can achieve increased burn rates in comparison to the CFR engine. NOx emissions from the combustion of anode off-gas were minimal as the cylinder peak temperatures never exceeded 1800 K. This experimental study ultimately demonstrates the viability of an ICE to operate using an anode off-gas, thus creating a complementary role for an ICE to be paired with a SOFC in a hybrid power generation plant.

Reactivity controlled compression ignition (RCCI) combustion has previously been proposed as a method to achieve high fuel conversion efficiency and reduce engine emissions. A single-fuel RCCI combustion strategy can have decreased fuel system complexity by using a reformate fuel for port fuel injection and the parent fuel (diesel) for direct injection. This paper presents a one-dimensional computational model of a compression ignition engine with single-fuel RCCI. A Wiebe function is used to predict the combustion process by representing the mass fraction burned (MFB) on a crank angle resolved basis. One single-Wiebe function (SWF) and two double-Wiebe functions(DWFs) were fitted to experimentally derive MFB data using the least-square method. The fitted results were compared with MFBs calculated from experimental data to verify the accuracy. The SWF did not fully capture the MFB curve with high fidelity while the detailed DWF captured the MFB curve within a root mean square error of 1.4%. The reduced double-Wiebe function (RDWF) also resulted in a predicted combustion profile with similar accuracy. Hence, the RDWF was used in a GT-power thermodynamic study to understand the effects of the low-temperature heat release (LTHR) fraction and combustion phasing on combustion characteristics. At optimum phasing of 5–10 crank angle degree after the top dead center, increasing the LTHR fraction from 20% to 60% resulted in the fuel conversion efficiency increasing from 39.5% to 41.1%, thus suggesting that the reformate fuel-based RCCI strategy is viable to unlock improved combustion performance.

With the rise in wood stove use in recent years, a number of experimental research efforts have been undertaken with the objective of developing cleaner, and more efficient stove designs. However, numerical modeling of stoves is still in its nascent years, thus making it imperative to start adapting more mature computational techniques, established in other combustion-based applications (e.g., combustion engines), to wood stoves. This study focuses on a critical review of the state-of-the-art in wood combustion modeling techniques and on providing recommendations for needed enhancements. In order to develop an optimum conceptual numerical model for wood stoves, the basic processes inside the stove are broken down and isolated into generic computational domains: surface reactions, gas reactions, and the fluid domain. Then state-of-the-art numerical efforts for wood stove and similar applications are broken down in a similar manner to highlight points of strength and possible improvements. Finally, based on the comparison between the different models, an improved modeling approach is proposed as a road map for future research efforts to achieve a higher fidelity wood stove numerical model., 14 pages, 10 figures, 1 table

Urban intersections, merging roadways, roundabouts, and speed reduction zones along with the driver responses to various disturbances are the primary sources of bottlenecks in corridors that contribute to traffic congestion. The implementation of connected and automated technologies can enable a novel computational framework for real-time control aimed at optimizing energy consumption and travel time. In this paper, we propose a decentralized energy-efficient optimal control framework for two adjacent intersections. We derive a closed-form analytical solution that includes interior boundary conditions and evaluate the effectiveness of the solution through simulation. Fuel consumption and travel time are significantly reduced compared to the baseline scenario designed with conventional fixed time signalized intersections.

Recent modifications to the University of Michigan rapid compression facility (UM RCF) were made to allow direct imaging of flame/autoignition interactions using compression to initiate autoignition chemistry and a spark plug to initiate simultaneous flame development. The experimental data in this study quantify the effects of spark-initiated flame propagation on autoignition of iso-octane/O2/inert gas mixtures at well-defined initial conditions. The work leveraged the controlled environment of the UM RCF, in which temperature, pressure, and composition are nominally uniform and well-known at the end of compression. Flame initiation by the spark plasma, flame propagation, and autoignition were monitored using high-speed optical imaging of chemiluminescence and in situ pressure time histories. End-of-compression temperatures from TEOC = 942–1012 K were considered, while the end-of-compression pressures were nominally constant within the range of PEOC = 7.8–9.5 atm. The fuel-to-O2 molar equivalence ratio was varied from ϕ = 0.20–0.99 and dilution, defined as the molar ratio of inert gases to O2 in the reactant mixture, was varied from inert:O2 = 3.76–7.47 to determine the effects on flame/autoignition interactions as well as to identify the lean flammability limit of the mixtures as a function of dilution. Flame propagation is generally expected to decrease autoignition delay times by compression heating the unburned portion of the mixture. The effect of flame propagation was maximized in these experiments by igniting the mixtures early during the autoignition process. Later spark timings had small to negligible effect on the autoignition delay time. Dilution had significant effect on the lean flammability limits, increasing from a lean limit of ϕ = 0.35 at air levels of dilution to ϕ = 0.65 at inert:O2 dilution of 7.5. The flammability limit was well correlated with the theoretical adiabatic flame temperature of each experiment. The propagation rates of flames successfully initiated by the spark plasma were determined from the imaging data and were ∼1 to 12 m/s. The magnitude of the propagation rates and the effect on the time integrated temperature scaled with the energy content of the mixtures as indicated by the theoretical adiabatic flame temperature.

Spark-assisted homogeneous charge compression ignition (HCCI) combustion may be a method to improve the operation of HCCI engines. In the current study, the impact of spark assist on the fundamental properties of ignition and combustion was investigated in a single cylinder, optically-accessible research engine. Early port fuel injection and air preheating were used with indolene fuel in the study. The effects of a range of air preheat ( Tin = 256–281 °C), fuel/air equivalence ratio (ϕ = 0.38–0.62) and spark assist timing (10°−90° before top dead centre) conditions on maximum in-cylinder pressure and timing, cycle variability, indicated mean effective pressure (IMEP) and heat release rate were investigated. Additionally, high-speed imaging was used to capture the piston-view ignition and combustion events during spark-assisted and unassisted HCCI operation. Methods were developed and applied to the imaging sequences to quantify the physical characteristics (e.g. location of autoignition sites) and the rate of propagation of the reaction fronts formed during spark-assisted and unassisted HCCI operation. The imaging data show that autoignition sites appear with increasing frequency as air preheat temperature is increased. The addition of spark assist led to the formation of reaction fronts at all conditions that propagated outward from the spark electrode at average speeds between 1.9 and 4.3 m/s. The imaging data indicate the effects of spark assist are due to compression heating of the unburned gases by the propagating reaction fronts which also leads to more consistent location of autoignition. Comparison of the imaging and engine data show the initial formation of the reaction fronts are not significant sources of heat release. While the engine data show that spark assist can affect phasing, heat release rate, IMEP and engine stability at the marginal HCCI operating conditions studied, the results also indicate spark assist has a narrow temperature range where the changes will be significant compared to the effects of the inherent thermal stratification of the HCCI fuel/air charge.

A technique which uses trained neural nets to model the compressor in the context of a turbocharged diesel engine simulation is introduced. This technique replaces the usual interpolation of compressor maps with the evaluation of a smooth mathematical function. Following presentation of the methodology, the proposed neural net technique is validated against data from a truck type, 6-cylinder 14-liter diesel engine. Furthermore, with the introduction of an additional parameter, the proposed neural net can be trained to simulate an entire family of compressors. As a demonstration, a family of compressors of different sizes is represented with a single neural net model which is subsequently used for matching calculations with intercooled and nonintercooled engine configurations at different speeds. This novel approach readily allows for evaluation of various options within a wide range of possible compressor configurations prior to prototype production. It can also be used to represent the variable geometry machine regardless of the method used to vary compressor characteristics. Hence, it is a powerful design tool for selection of the best compressor for a given diesel engine system and for broader system optimization studies.

A flexible model for computing one-dimensional, unsteady manifold gas dynamics in single-cylinder spark-ignition and diesel engines has been developed. The numerical method applies an explicit, finite volume formulation and a shock-capturing total variation diminishing scheme. The numerical model has been validated against the method of characteristics for valve flows without combustion prior to coupling with combustion engine simulations. The coupling of the gas-dynamics model with single-cylinder, spark-ignition and diesel engine modules is accomplished using the graphical MATLAB-SIMULINK environment. Comparisons between predictions of the coupled model and measurements shows good agreement for both spark ignition and diesel engines. Parametric studies demonstrating the effect of varying the intake runner length on the volumetric efficiency of a diesel engine illustrate the model use.

A non-linear, transient, single-cylinder diesel engine simulation has been developed for predictions of instantaneous engine speed and torque. The foundation of our model is a physically based, thermodynamic, steady-state diesel engine simulation (Assanis, D. N., and Heywood, J. B., 1986, “Development and Use of a Computer Simulation of the Turbocompounded Diesel System for Engine Performance and Component Heat Transfer Studies,” SAE Paper 860329), which has been comprehensively validated for various engine designs. The transient extension of the parent model represents the diesel engine as a non-linear, dynamic system. The instantaneous crank-shaft speed is determined from the solution of the engine-external load dynamics equation, where the engine torque is tracked on a crank-angle basis. Validation of the transient model during rapid engine acceleration shows that both the cyclic fluctuations in the instantaneous crank-shaft speed line and the overall engine response are in good agreement with experimental measurements. Predictions of single-cylinder engine starting reveals the importance of selecting the proper value of the engine moment of inertia in order to control the amplitude of angular velocity fluctuations and ensure stable engine operation. It is further shown that the variation in the inertial forces on the reciprocating components with speed has a dramatic impact on the instantaneous torque profile, and consequently on angular velocity fluctuations.

A thermodynamic simulation is used to study the effects of oxygen-enriched intake air on the performance and nitrogen oxide (NO) emissions of a locomotive diesel engine. The parasitic power of the air separation membrane required to supply the oxygen-enriched air is also estimated. For a given constraint on peak cylinder pressure, the gross and net power output of an engine operating under different levels of oxygen enrichment are compared with those obtained when a high-boost turbocharged engine is used. A 4 percent increase in peak cylinder pressure can result in an increase in net engine power of approximately 10 percent when intake air with an oxygen content of 28 percent by volume is used and fuel injection timing is retarded by 4 degrees. When the engine is turbocharged to a higher inlet boost, the same increase in peak cylinder pressure can improve power by only 4 percent. If part of the significantly higher exhaust enthalpies available as a result of oxygen enrichment is recovered, the power requirements of the air separator membrane can be met, resulting in substantial net power improvements. Oxygen enrichment with its attendant higher combustion temperatures, reduces emissions of particulates and visible smoke but increases NO emissions (by up to three times at 26 percent oxygen content). Therefore, exhaust gas after-treatment and heat recovery would be required if the full potential of oxygen enrichment for improving the performance of locomotive diesel engines is to be realized.

This study presents two new methods to rapidly analyze the ignition and combustion events recorded during in-cylinder high-speed imaging of homogeneous charge compression ignition (HCCI) and spark-assisted (SA) HCCI engine operation. Two categories of ignition have been observed during HCCI and SA HCCI: auto-ignition of parcels of fuel/air and ignition and propagation of reaction fronts. In this work, two methods of image analysis are developed which accommodate differences in the ignition and propagation events for the two categories. The methods are described by application to high speed imaging data acquired from an optically accessible engine operated in HCCI and SA HCCI modes using indolene fuel. Using method I, the projected area of reaction is identified in each frame, and a circle with a characteristic radius that yields the equivalent area is defined. The rate of area expansion is used to define the speed of reaction. Using method II, an edge-finding algorithm is used to identify the location of well-defined reaction fronts. The maximum dimensions of the reaction front in an x-y coordinate frame are measured. The projected area based on the average of these maximum dimensions is then determined. The change in the characteristic radius of the projected area is defined as the average propagation speed for the reaction front. The two analytical methods are applied to typical HCCI and SA HCCI image sequences. Outcomes of the image analysis indicate propagation speeds are typically between 2–5 m/s prior to volumetric ignition. Volumetric ignition is identified by propagation speeds greater than 20 m/s. The imaging data also identify times when reaction quenching occurred after spark ignition as times when negative propagation speeds are observed. When applied to the same imaging sequence, the two methods yield consistent results for propagation speeds; however, the method based on edge-finding exhibits larger variance.Copyright © 2010 by ASME

High-speed imaging combined with the optical access provided by a research engine offer the ability to directly image and compare ignition and combustion phenomena of various fuels. Such data provide valuable insight into the physical and chemical mechanisms important in each system. In this study, crank-angle resolved imaging data were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using gasoline, indolene, and iso-octane. Lean operating limits were the focus of the study with the primary objective of identifying different modes of reaction front initiation and propagation for each fuel. HCCI combustion was initiated and maintained over a range of lean conditions for various fuels, from 0.69 to 0.27. The time-resolved imaging and pressure data show that high rates of heat release in HCCI combustion correlate temporally to simultaneous, intense volumetric blue emission. Lower rates of heat release are characteristic of spatially resolved blue emission. Gasoline supported leaner HCCI operation than indolene. Iso-octane showed a dramatic transition into misfire. Similar regions of preferential ignition were identified for each of the fuels considered using the imaging data. DOI: 10.1115/1.2898720

High-speed imaging combined with the optical access provided by a single-cylinder research engine offer the ability to directly study ignition and combustion phenomena. Such data provide valuable insight into the physical and chemical mechanisms important in advanced engine combustion strategies. In this study, crank-angle resolved chemiluminescence imaging data both orthogonal to and along the piston axis were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using indolene. This preliminary study focused on identifying how multi-axis imaging can contribute to understanding the effects of spark-assist on HCCI performance. Operating conditions of advanced spark ignition timing for extending the lean limits of bulk charge compression ignition were used. The experiments were performed at a fixed equivalence ratio of φ = 0.56, with fixed intake conditions (wide open throttle with air preheat). The multi-axis imaging provides a clear indication of the propagation of a reaction front from the spark kernel. The combination of orthogonal and axial views may provide valuable information spatially resolving volumetric heat release, thereby providing an indication of the fractional energy release due to the spark assist compared to the energy released by auto-ignition.Copyright © 2007 by ASME

High-speed imaging combined with the optical access provided by a research engine offer the ability to directly image and compare ignition and combustion phenomena of various fuels. Such data provide valuable insight into the physical and chemical mechanisms important in each system. In this study, crank-angle resolved imaging data were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using gasoline, indolene, and iso-octane. Lean operating limits were the focus of the study with the primary objective of identifying different modes of reaction front initiation and propagation for each fuel. HCCI combustion was initiated and maintained over a range of lean conditions for various fuels, from φ = 0.77 to 0.27. The time-resolved imaging and pressure data show high rates of heat release in HCCI combustion correlate temporally to simultaneous, intense volumetric blue emission. Lower rates of heat release are characteristic of spatially-resolved blue emission. Gasoline supported leaner HCCI operation than indolene. Iso-octane showed a dramatic transition into misfire. Similar regions of preferential ignition were identified for each of the fuels considered using the imaging data.Copyright © 2006 by ASME