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Assanis, Dennis N.
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Design and Modeling of a Novel Internal Combustion Engine with Direct Hydraulic Power Take-off

SAE International Journal of Alternative Powertrains

Clemson University-Zoran Filipi
Stony Brook University-Aristotelis Babajimopoulos, Dennis N. Assanis
  • Journal Article
  • 2013-01-1733
Published 2013-04-08 by SAE International in United States
This paper introduces a Hydraulic Linear Engine (HLE) concept and describes a model to simulate instantaneous engine behavior. The United States Environmental Protection Agency has developed an HLE prototype as an evolution of their previous six-cylinder, four-stroke, free-piston engine (FPE) hardware. The HLE design extracts work hydraulically, in a fashion identical to the initial FPE, and is intended for use in a series hydraulic hybrid vehicle. Unlike the FPE, however, the HLE utilizes a crank for improved timing control and increased robustness. Preliminary experimental results show significant speed fluctuations and cylinder imbalance that require careful controls design. This paper also introduces a model of the HLE that exhibits similar behavior, making it an indispensible tool for controls design. Further, the model's behavior is evaluated over a range of operating conditions currently unobtainable by the experimental setup.
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The Effects of CO, H2, and C3H6 on the SCR Reactions of an Fe Zeolite SCR Catalyst

University of Kansas-Christopher Depcik
University of Michigan-Michael Andrew Smith, John Hoard, Stani Bohac, Dennis N. Assanis
Published 2013-04-08 by SAE International in United States
Selective Catalytic Reduction (SCR) catalysts used in Lean NOx Trap (LNT) - SCR exhaust aftertreatment systems typically encounter alternating oxidizing and reducing environments. Reducing conditions occur when diesel fuel is injected upstream of a reformer catalyst, generating high concentrations of hydrogen (H₂), carbon monoxide (CO), and hydrocarbons to deNOx the LNT. In this study, the functionality of an iron (Fe) zeolite SCR catalyst is explored with a bench top reactor during steady-state and cyclic transient SCR operation.Experiments to characterize the effect of an LNT deNOx event on SCR operation show that adding H₂ or CO only slightly changes SCR behavior with the primary contribution being an enhancement of nitrogen dioxide (NO₂) decomposition into nitric oxide (NO). Exposure of the catalyst to C₃H₆ (a surrogate for an actual exhaust HC mixture) leads to a significant decrease in NOx reduction capabilities of the catalyst. A degradation mechanism is proposed to account for the decrease in NOx conversion efficiency, highlighted by reactions between NO₂ and C₃H₆ to make NO at a rate of similar order of magnitude as…
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Optical and Infrared In-Situ Measurements of EGR Cooler Fouling

Ford Motor Co.-Daniel J. Styles, Mehdi Abarham, Eric W. Curtis
Stony Brook Univ.-Dennis N. Assanis
Published 2013-04-08 by SAE International in United States
The use of exhaust gas recirculation (EGR) in internal combustion engines has significant impacts on combustion and emissions. EGR can be used to reduce in-cylinder NOx production, reduce emitted particulate matter, and enable advanced forms of combustion. To maximize the benefits of EGR, the exhaust gases are often cooled with on-engine liquid to gas heat exchangers. A common problem with this approach is the build-up of a fouling layer inside the heat exchanger due to thermophoresis and condensation, reducing the effectiveness of the heat exchanger in lowering gas temperatures.Literature has shown the effectiveness to initially drop rapidly and then approach steady state after a variable amount of time. The asymptotic behavior of the effectiveness has not been well explained. A range of theories have been proposed including fouling layer removal, changing fouling layer properties, and cessation of thermophoresis. In an effort to investigate this phenomenon, an EGR cooler visualization rig has been constructed. This rig incorporates an optically and infrared transparent access window, allowing for measurement of key deposit layer variables in-situ. These variables coupled…
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A Visualization Test Setup for Investigation of Water-Deposit Interaction in a Surrogate Rectangular Cooler Exposed to Diesel Exhaust Flow

Ford Motor Co-Daniel Styles
Univ of Michigan-Mehdi Abarham, Tejas Chafekar, John Hoard, Dennis N. Assanis
Published 2012-04-16 by SAE International in United States
Exhaust gas recirculation (EGR) coolers are commonly used in diesel engines to reduce the temperature of recirculated exhaust gases in order to reduce NOx emissions. The presence of a cool surface in the hot exhaust causes particulate soot deposition as well as hydrocarbon and water condensation. Fouling experienced through deposition of particulate matter and hydrocarbons results in degraded cooler effectiveness and increased pressure drop. In this study, a visualization test setup is designed and constructed so that the effect of water condensation on the deposit formation and growth at various coolant temperatures can be studied. A water-cooled surrogate rectangular channel is employed to represent the EGR cooler. One side of the channel is made of glass for visualization purposes. A medium duty diesel engine is used to generate the exhaust stream. An automated system controls all critical parameters including gas inlet temperature and pressure, coolant temperature, and the exhaust flow rate to correlate laminar, transition, and turbulent flow regimes in the channel. A digital microscope is also utilized to record the deposit formation and water-deposit…
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Understanding the Dynamic Evolution of Cyclic Variability at the Operating Limits of HCCI Engines with Negative Valve Overlap

SAE International Journal of Engines

Robert Bosch LLC-Li Jiang, Hakan Yilmaz
University of Michigan-Erik Hellström, Anna Stefanopoulou, Jiri Vavra, Aristotelis Babajimopoulos, Dennis N. Assanis
  • Journal Article
  • 2012-01-1106
Published 2012-04-16 by SAE International in United States
An experimental study is performed for homogeneous charge compression ignition (HCCI) combustion focusing on late phasing conditions with high cyclic variability (CV) approaching misfire. High CV limits the feasible operating range and the objective is to understand and quantify the dominating effects of the CV in order to enable controls for widening the operating range of HCCI. A combustion analysis method is developed for explaining the dynamic coupling in sequences of combustion cycles where important variables are residual gas temperature, combustion efficiency, heat release during re-compression, and unburned fuel mass. The results show that the unburned fuel mass carries over to the re-compression and to the next cycle creating a coupling between cycles, in addition to the well known temperature coupling, that is essential for understanding and predicting the HCCI behavior at lean conditions with high CV.
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Bridging the Gap between HCCI and SI: Spark-Assisted Compression Ignition

Czech Technical Univ.-Jiri Vavra
Univ. of Michigan-Laura Manofsky, Dennis N. Assanis, Aristotelis Babajimopoulos
Published 2011-04-12 by SAE International in United States
Homogeneous charge compression ignition (HCCI) has received much attention in recent years due to its ability to reduce both fuel consumption and NO emissions compared to normal spark-ignited (SI) combustion. However, due to the limited operating range of HCCI, production feasible engines will need to employ a combination of combustion strategies, such as stoichiometric SI combustion at high loads and leaner burn spark-assisted compression ignition (SACI) and HCCI at intermediate and low loads. The goal of this study was to extend the high load limit of HCCI into the SACI region while maintaining a stoichiometric equivalence ratio. Experiments were conducted on a single-cylinder research engine with fully flexible valve actuation. In-cylinder pressure rise rates and combustion stability were controlled using cooled external EGR, spark assist, and negative valve overlap. Several engine loads within the SACI regime were investigated. Heat release analysis of these points showed a distinct region of flame propagation followed by rapid auto-ignition of the remaining charge. With proper control of the combustion variables, this region of flame propagation became larger as load…
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Evaluation of Diesel Oxidation Catalyst Conversion of Hydrocarbons and Particulate Matter from Premixed Low Temperature Combustion of Biodiesel

SAE International Journal of Engines

Univ of Michigan-Dennis N. Assanis, Stani Bohac
Univ. of Michigan-Ann Arbor-William F. Northrop
  • Journal Article
  • 2011-01-1186
Published 2011-04-12 by SAE International in United States
Premixed low temperature combustion (LTC) in diesel engines simultaneously reduces soot and NOx at the expense of increased hydrocarbon (HC) and CO emissions. The use of biodiesel in the LTC regime has been shown to produce lower HC emissions than petroleum diesel; however, unburned methyl esters from biodiesel are more susceptible to particulate matter (PM) formation following atmospheric dilution due to their low volatility. In this study, the efficacy of a production-type diesel oxidation catalyst (DOC) for the conversion of light hydrocarbons species and heavier, semi-volatile species like those in unburned fuel is examined. Experimental data were taken from a high speed direct-injection diesel engine operating in a mid-load, late injection partially premixed LTC mode on ultra-low sulfur diesel (ULSD) and neat soy-based biodiesel (B100). Gaseous emissions were recorded using a conventional suite of analyzers and individual light HCs were measured using an FT-IR analyzer. PM emissions data were collected from filter samples taken before and after the DOC using gravimetric analysis, Soxhlet extraction with speciation of extracted HCs, and total organic versus elemental carbon…
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Turbocharger Matching for a 4-Cylinder Gasoline HCCI Engine Using a 1D Engine Simulation

BorgWarner Inc-Philip Keller, David Roth, Michael Becker
University of Michigan-Prasad Shingne, Dennis N. Assanis, Aristotelis Babajimopoulos
Published 2010-10-25 by SAE International in United States
Naturally aspirated HCCI operation is typically limited to medium load operation (∼ 5 bar net IMEP) by excessive pressure rise rate. Boosting can provide the means to extend the HCCI range to higher loads. Recently, it has been shown that HCCI can achieve loads of up to 16.3 bar of gross IMEP by boosting the intake pressure to more than 3 bar, using externally driven compressors. However, investigating HCCI performance over the entire speed-load range with real turbocharger systems still remains an open topic for research.A 1 - D simulation of a 4 - cylinder 2.0 liter engine model operated in HCCI mode was used to match it with off-the-shelf turbocharger systems. The engine and turbocharger system was simulated to identify maximum load limits over a range of engine speeds. Low exhaust enthalpy due to the low temperatures that are characteristic of HCCI combustion caused increased back-pressure and high pumping losses and demanded the use of a small and more efficient turbocharger. The paper shows that the load range of naturally aspirated HCCI can be…
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Comparison of Different Boosting Strategies for Homogeneous Charge Compression Ignition Engines - A Modeling Study

SAE International Journal of Engines

GM Research and Development-Nicole Wermuth, Paul Najt
Univ. of Michigan-Sotirios Mamalis, Vishnu Nair, Peter Andruskiewicz, Dennis N. Assanis, Aristotelis Babajimopoulos
  • Journal Article
  • 2010-01-0571
Published 2010-04-12 by SAE International in United States
Boosted Homogeneous Charge Compression Ignition (HCCI) has been modeled and has demonstrated the potential to extend the engine's upper load limit. A commercially available engine simulation software (GT-PowerÖ) coupled to the University of Michigan HCCI combustion and heat transfer correlations was used to model a 4-cylinder boosted HCCI engine with three different boosting configurations: turbocharging, supercharging and series turbocharging. The scope of this study is to identify the best boosting approach in order to extend the HCCI engine's operating range. The results of this study are consistent with the literature: Boosting helps increase the HCCI upper load limit, but matching of turbochargers is a problem. In addition, the low exhaust gas enthalpy resulting from HCCI combustion leads to high pressures in the exhaust manifold increasing pumping work. The series turbocharging strategy appears to provide the largest load range extension. Single turbocharging is the most efficient but is limited by increased mass flow rates at increased engine speeds. Supercharging helps avoid the backpressure problem but the mechanical work of the supercharger reduces useful work affecting overall…
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Turbulence Intensity Calculation from Cylinder Pressure Data in a High Degree of Freedom Spark-Ignition Engine

Clemson Univ.-Robert Gary Prucka
Univ. of Michigan-Tae-Kyung Lee, Zoran Filipi, Dennis N. Assanis
Published 2010-04-12 by SAE International in United States
The number of control actuators available on spark-ignition engines is rapidly increasing to meet demand for improved fuel economy and reduced exhaust emissions. The added complexity greatly complicates control strategy development because there can be a wide range of potential actuator settings at each engine operating condition, and map-based actuator calibration becomes challenging as the number of control degrees of freedom expand significantly. Many engine actuators, such as variable valve actuation and flow control valves, directly influence in-cylinder combustion through changes in gas exchange, mixture preparation, and charge motion. The addition of these types of actuators makes it difficult to predict the influences of individual actuator positioning on in-cylinder combustion without substantial experimental complexity. To simplify this experimental task a data processing routine is developed that quickly estimates in-cylinder turbulence intensity in a production-style engine from commonly employed measurements. Calculation of turbulence intensity is described, the data are validated using a quasi-dimensional spark-ignition engine combustion model, and the results are discussed. Results are in good agreement with well-established models for early-combustion conditions, and the new…
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