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Thermodynamic Analysis and Comparison of the K6 Cycle

University of Wisconsin, Madison-Matthew D. Carlson, Timothy A. Shedd
Kashmerick Engine Systems LLC-Gerald E. Kashmerick
Published 2011-11-08 by Society of Automotive Engineers of Japan in Japan
International concerns over small engine efficiency and emissions characteristics have lead to several efforts to develop improved internal combustion engine cycles, including investigation of Homogeneous Charge Compression Ignition (HCCI) and Premixed Charge Compression Ignition (PCCI) modifications to classic combustion cycles. Kashmerick Engine Systems LLC. has proposed a K6 cycle that moves the combustion process to an external continuous-combustion chamber to decrease the rate of combustion and allow optimization of the combustion chamber and piston-cylinder as a compression and expansion device separately to improve efficiency and reduce emissions. This paper describes 0-dimension modeling of both an air-standard dual-cycle model and an air-standard K6 cycle model in Engineering Equation Solver (EES) to compare the ideal performance of the two cycles. The dual-cycle is also correlated to a small engine currently in production to estimate typical compression and expansion efficiencies, which are then used with the K6 cycle model to estimate real-world performance. This work suggests that the K6 cycle may offer improvements over a dual-cycle for several air fuel ratios, and yields a useful tool to aid…
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Effects of Fuel Physical Properties on Diesel Engine Combustion using Diesel and Bio-diesel Fuels

SAE International Journal of Fuels and Lubricants

University of Wisconsin, Madison-Youngchul Ra, Rolf D. Reitz
Oak Ridge National Laboratory-Joanna McFarlane, C. Stuart Daw
  • Journal Article
  • 2008-01-1379
Published 2008-04-14 by SAE International in United States
A computational study using multi-dimensional CFD modeling was performed to investigate the effects of physical properties on diesel engine combustion characteristics with bio-diesel fuels. Properties of typical bio-diesel fuels that were either calculated or measured are used in the study and the simulation results are compared with those of conventional diesel fuels. The sensitivity of the computational results to individual physical properties is also investigated, and the results provide information about the desirable characteristics of the blended fuels. The properties considered in the study include liquid density, vapor pressure, surface tension, liquid viscosity, liquid thermal conductivity, liquid specific heat, latent heat, vapor specific heat, vapor diffusion coefficient, vapor viscosity and vapor thermal conductivity. The results show significant effects of the fuel physical properties on ignition delay and burning rates at various engine operating conditions. It is seen that there is no single physical property that dominates differences of ignition delay between diesel and bio-diesel fuels. However, among the 11 properties considered in the study, the simulation results were found to be most sensitive to the…
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Development and Validation of a Reduced Reaction Mechanism for Biodiesel-Fueled Engine Simulations

SAE International Journal of Fuels and Lubricants

University of Wisconsin, Madison-Jessica L. Brakora, Youngchul Ra, Rolf D. Reitz
Oak Ridge National Laboratory-Joanna McFarlane, C. Stuart Daw
  • Journal Article
  • 2008-01-1378
Published 2008-04-14 by SAE International in United States
In the present study a reduced chemical reaction mechanism for biodiesel surrogate fuel was developed and validated for multi-dimensional engine combustion simulations. An existing detailed methyl butanoate mechanism that contained 264 species and 1219 reactions was chosen to represent the oxygenated portion of the fuel. The reduction process included flux analysis, ignition sensitivity analysis, and optimization of reaction rate constants under constant volume conditions. The current reduced mechanism consists of 41 species and 150 reactions and gives predictions in excellent agreement with those of the comprehensive mechanism.In order to validate the mechanism under biodiesel-fueled engine conditions, it was combined with another skeletal mechanism for n-heptane oxidation. This combined reaction mechanism can be used to adjust the energy content of the fuel, and account for diesel/biodiesel blend engine simulations. The combined mechanism, ERC-bio, contains 53 species and 156 reactions. Biodiesel-fueled engine operation was successfully simulated using the ERC-bio mechanism.
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Physical Properties of Bio-Diesel and Implications for Use of Bio-Diesel in Diesel Engines

University of Wisconsin, Madison-Youngchul Ra, Rolf D. Reitz
Georgia Institute of Technology-Jelani Griffin
Published 2007-10-29 by SAE International in United States
In this study we identify components of a typical biodiesel fuel and estimate both their individual and mixed thermo-physical and transport properties. We then use the estimated mixture properties in computational simulations to gauge the extent to which combustion is modified when biodiesel is substituted for conventional diesel fuel. Our simulation studies included both conventional diesel combustion (DI) and premixed charge compression ignition (PCCI). Preliminary results indicate that biodiesel ignition is significantly delayed due to slower liquid evaporation, with the effects being more pronounced for DI than PCCI. The lower vapor pressure and higher liquid heat capacity of biodiesel are two key contributors to this slower rate of evaporation. Other physical properties are more similar between the two fuels, and their impacts are not clearly evident in the present study. Future studies of diesel combustion sensitivity to both physical and chemical properties of biodiesel are suggested.
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Development of a Hybrid, Auto-Ignition/Flame-Propagation Model and Validation Against Engine Experiments and Flame Liftoff

University of Wisconsin, Madison-Satbir Singh, Rolf D. Reitz
Cummins Inc.-Donald Stanton, Zhichao Tan
Published 2007-04-16 by SAE International in United States
In previous publications, Singh et al. [1, 2] have shown that direct integration of CFD with a detailed chemistry auto-ignition model (KIVA-CHEMKIN) performs reasonably well for predicting combustion, emissions, and flame structure for stratified diesel engine operation. In this publication, it is shown that the same model fails to predict combustion for partially premixed dual-fuel engines. In general, models that account for chemistry alone, greatly under-predict cylinder pressure. This is shown to be due to the inability of such models to simulate a propagating flame, which is the major source of heat release in partially premixed dual-fuel engines, under certain operating conditions.To extend the range of the existing model, a level-set-based, hybrid, auto-ignition/flame-propagation (KIVA-CHEMKIN-G) model is proposed, validated and applied for both stratified diesel engine and partially premixed dual-fuel engine operation. The newly proposed model gives good predictions of trends in cylinder pressure and exhaust NOx emissions for both the engines. Finally, both the KIVA-CHEMKIN and the KIVA-CHEMKIN-G models are validated using available measurements of diesel flame liftoff lengths. The models give good qualitative predictions…
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2-Color Thermometry Experiments and High-Speed Imaging of Multi-Mode Diesel Engine Combustion

Satbir Singh, Rolf D. Reitz, Mark P. B. Musculus
Published 2005-10-24 by SAE International in United States
Although in-cylinder optical diagnostics have provided significant understanding of conventional diesel combustion, most alternative combustion strategies have not yet been explored to the same extent. In an effort to build the knowledge base for alternative low-temperature combustion strategies, this paper presents a comparison of three alternative low-temperature combustion strategies to two high-temperature conventional diesel combustion conditions. The baseline conditions, representative of conventional high-temperature diesel combustion, have either a short or a long ignition delay. The other three conditions are representative of some alternative combustion strategies, employing significant charge-gas dilution along with either early or late fuel injection, or a combination of both (double-injection). These operating conditions are investigated for soot volume fraction, soot temperatures, calculated adiabatic flame temperatures, and soot radiation heat loss through 2-color soot thermometry experiments. The spatial location of in-cylinder soot is imaged using a high-speed CMOS camera, and exhaust-gas NOx is also measured.The soot thermometry and high-speed soot luminosity imaging show that the low-temperature operating conditions have lower in-cylinder soot than the high-temperature conditions. Also, soot is formed upstream in the…
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Numerical Analysis of High-Pressure Fast-Response Common Rail Injector Dynamics

University of Wisconsin, Madison-Song-Charng Kong, Rolf D. Reitz
DIEM - University of Bologna-G.M. Bianchi, S. Falfari, P. Pelloni
Published 2002-03-04 by SAE International in United States
Managing the injection rate profile is a powerful tool to control engine performance and emission levels. In particular, Common Rail (C.R.) injection systems allow an almost completely flexible fuel injection event in DI-diesel engines by permitting a free mapping of the start of injection, injection pressure, rate of injection and, in the near future, multiple injections. This research deals with the development of a network-based numerical tool for understanding operating condition limits of the Common Rail injector. The models simulate the electro-fluid-mechanical behavior of the injector accounting for cavitation in the nozzle holes. Validation against experiments has been performed. The model has been used to provide insight into the operating conditions of the injector and in order to highlight the application to injection system design.
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Advanced Control Techniques For Efficient And Robust Operation Of Advanced Life Support Systems

University of Wisconsin, Madison-W. A. Sethares
NASA Ames Research Center-C. Finn
Published 2001-07-09 by SAE International in United States
This paper examines the structure and performance of three control strategies for a regenerative life support system constrained by mass balance equations. A novel agent-based control strategy derived from economic models of markets is compared to two standard control strategies, proportional feedback and optimal control. The control systems require different amounts of knowledge about the underlying system dynamics, utilize different amounts of information about the current state of the system, and differ in their ability to achieve system-wide performance goals. Simulations illustrate the dynamic behavior of the life support system after it is perturbed away from its equilibrium state or nominal operating point under the three different control strategies. The performance of these strategies is discussed in the context of system-wide performance goals such as efficiency and robustness.
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Cavitation in Two-Dimensional Asymmetric Nozzles

University of Wisconsin, Madison-David P. Schmidt, C. J. Rutland, M. L. Corradini
University of Aachen-P. Roosen, O. Genge
Published 1999-03-01 by SAE International in United States
Diesel fuel spray characteristics are thought to depend on cavitation inside the fuel injector nozzles. These nozzles are very small and the fuel flow is very fast, making experimental observation very difficult. Numerical simulation of the two-phase flow is hindered by the severe density difference between the liquid and vapor as well as the existence of complex free surfaces. Recent experimental and numerical advances are now permitting visual observation of real-scale cavitating flow and two-dimensional simulation of the cavitating flow. In contrast to past work, we have chosen to study asymmetric nozzle flow. Asymmetry is more representative of real injector geometry than symmetric nozzles and may yield more reproducible results.Experimental runs of 1 mm long nozzles were made at upstream pressures up to 120 bar with downstream pressures from 1 to 50 bar. Photographs of planar asymmetric nozzles revealed complex transient structures on the fuel-vapor interface. The nature of these structures depended on both the upstream and downstream pressure. Numerical simulation of selected experimental cases predicted nearly identical vapor location. The numerical simulation also provided…
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Mass-Related Properties of Atomizers for Direct-Injection SI Engines

University of Wisconsin, Madison-Jeffrey A. Hoffman, Farhan Khatri, Jay K. Martin
Mercury Marine, Division of Brunswick Corp.-Sam W. Coates
Published 1998-02-23 by SAE International in United States
Mass-related properties of four atomizers were estimated with the use of a mechanical transient patternator. The properties presented on a temporal and spatial basis are the axial liquid mass flux, liquid fuel to air ratio, and liquid axial velocity. The data are presented in two formats. The first format consists of the mass-related properties that occurred radially between two planes positioned 2.0 cm and 2.25 cm along the atomizer axis. A second format consists of interpolated contour plots of the axial liquid mass flux for all of the spray systems studied.The atomizers used in the study consisted of three liquid-only high-pressure systems and one air-assist system. Two of the liquid-only high-pressure systems and the air - assist system were operated with a volumetric delivery of 20 mm3 per injection while injecting into ambient conditions. A third liquid-only high-pressure system was operated with a delivery of 15 mm3 per injection.Ranges of 0 to 10 for the liquid fuel to air ratios, and 0 to 40 g/cm2/sec for the mass flux were observed. Average axial velocities were…
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