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2010-10-25
Journal Article
2010-01-2204
Yue Ma, Ho Teng, Marina Thelliez
Lithium-ion (Li-ion) batteries are becoming widely used high-energy sources and a replacement of the Nickel Metal Hydride batteries in electric vehicles (EV), hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV). Because of their light weight and high energy density, Li-ion cells can significantly reduce the weight and volume of the battery packs for EVs, HEVs and PHEVs. Some materials in the Li-ion cells have low thermal stabilities and they may become thermally unstable when their working temperature becomes higher than the upper limit of allowed operating temperature range. Thus, the cell working temperature has a significant impact on the life of Li-ion batteries. A proper control of the cell working temperature is crucial to the safety of the battery system and improving the battery life. This paper outlines an approach for the thermal analysis of Li-ion battery cells and modules.
2011-04-12
Technical Paper
2011-01-0668
Yue Ma, Ho Teng
Lithium ion batteries can be developed for vehicle applications from high power specification to high energy specification. Thermal response of a battery cell is the main factor to be considered for battery selection in the design of an electrified vehicle because some materials in the cells have low thermal stability and they may become thermally unstable when their working temperature becomes higher than the upper limit of allowed operating range. In this paper the thermal characteristics of different sizes and forms of commercially available batteries is investigated through electro-thermal analysis. The relation between cell capacity and cell internal resistance is also studied. The authors find that certain criteria can be defined for battery selection for electric vehicles, hybrid electric vehicles and plug-in hybrid electric vehicles. These criteria can be served as design guidelines for battery development for vehicle applications.
2010-04-12
Technical Paper
2010-01-0730
Ho Teng, Matthew Barnard
Physicochemical characteristics of the soot deposits in a fouled EGR cooler are studied in this paper. It is found that a three-layer model for the soot deposited in the EGR cooler may well describe the behavior of the depositing process: a dense base layer with micro pores (≺ 5 nm), a randomly packed intermediate layer with meso pores (5-50 nm) and a loose surface layer with macro pores (≻ 50 nm). The surface layer is thick and highly porous, formed by mechanical interlocking of the agglomerated primary soot particles or soot clusters. The soot particles in the surface layer may be removed by a high shear EGR flow. Condensates in the deposit, especially water, can have a significant influence on the structure of the deposit. Capillary forces on the wetted soot particles could be comparable to the contact forces holding the particles together. It is found that the hydroscopicity of the soot particles vary with their content of soluble organic fraction (SOF).
2010-04-12
Technical Paper
2010-01-0804
Ho Teng
The passenger cabin heating and cooling has a considerable impact on the fuel economy for buses, especially during the waiting period. This problem becomes more significant for the hybrid buses for which the impact of the auxiliary load on the fuel economy is almost twice that on the conventional buses. A second-law analysis conducted in this study indicates that a heat-driven AC system has higher energy utilization efficiency than the conventional AC system. On the basis of this analysis, a concept waste-heat-driven absorptive aqua-ammonia heat pump system is proposed and analyzed. Results of the analysis show that the heat-driven system can reduce the engine auxiliary load significantly because it eliminates the conventional AC compressor. In the AC mode, its energy utilization efficiency can be up to 50%. In the heating mode, the effective efficiency for heating can be up to 100%.
2011-04-12
Journal Article
2011-01-1149
Ho Teng
In this paper, a thermodynamic model is discussed for a single cylinder diesel engine with its intake and exhaust systems simulating a turbo-charged V8 diesel engine. Following criteria are used in determination of the gas exchange systems of the single cylinder engine (SCE): 1) the level of pressure fluctuations in the intake and exhaust systems should be within the lower and upper bounds of those simulated by the thermodynamic model for the V8 engine and patterns of the pressure waves should be similar; 2) the intake and exhaust flows should be reasonably close to those of the V8 engine; 3) the cylinder pressures during the combustion and gas exchange should be reasonably close to those of the V8 engine under the same conditions for the valve timing, fuel injection, rate of heat release and in-cylinder heat transfer. The thermodynamic model for the SCE is developed using the 1D engine thermodynamic simulation tool AVL BOOST.
2011-04-12
Technical Paper
2011-01-1337
Talus Park, Ho Teng, Gary L. Hunter, Bryan van der Velde, Jeffrey Klaver
A Rankine cycle system with ethanol as the working fluid was developed to investigate the fuel economy benefit of recovering waste heat from a 10.8-liter heavy-duty (HD) truck diesel engine. Recovering rejected heat from a primary engine with a secondary bottoming cycle is a proven concept for improving the overall efficiency of the thermodynamic process. However, the application of waste heat recovery (WHR) technology to the HD diesel engine has proven to be challenging due to cost, complexity, packaging and control during transient operation. This paper discusses the methods and technical innovations required to achieve reliable high performance operation of the WHR system. The control techniques for maintaining optimum energy recovery while protecting the system components and working fluid are described. The experimental results are presented and demonstrate that 3-5% fuel saving is achievable by utilizing this technology.
2011-09-13
Journal Article
2011-01-2249
Ho Teng, Yue Ma, Kim Yeow, Marina Thelliez
Ideal operation temperatures for Li-ion batteries fall in a narrow range from 20°C to 40°C. If the cell operation temperatures are too high, active materials in the cells may become thermally unstable. If the temperatures are too low, the resistance to lithium-ion transport in the cells may become very high, limiting the electrochemical reactions. Good battery thermal management is crucial to both the battery performance and life. Characteristics of various battery thermal management systems are reviewed. Analyses show that the advantages of direct and indirect air cooling systems are their simplicity and capability of cooling the cells in a battery pack at ambient temperatures up to 40°C. However, the disadvantages are their poor control of the cell-to-cell differential temperatures in the pack and their capability to dissipate high cell generations.
2011-09-13
Journal Article
2011-01-2248
Ho Teng, Yue Ma, Kim Yeow, Marina Thelliez
The temperature distribution is studied theoretically in a battery module stacked with 12 high-power Li-ion pouch cells. The module is cooled indirectly with ambient air through aluminum heat-sink plates or cooling plates sandwiched between each pair of cells in the module. Each of the cooling plates has an extended cooling fin exposed in the cooling air channel. The cell temperatures can be controlled by changing the air temperature and/or the heat transfer coefficient on the cooling fin surfaces by regulating the air flow rate. It is found that due to the high thermal conductivity and thermal diffusivity of the cooling plates, heat transfer of the cooling plate governs the cell temperature distribution by spreading the cell heat over the entire cell surface. Influence of thermal from the cooling fins is also simulated.
2011-04-12
Technical Paper
2011-01-0311
Ho Teng, Jeffrey Klaver, Talus Park, Gary L. Hunter, Bryan van der Velde
Waste heat recovery (WHR) has been recognized as a promising technology to achieve the fuel economy and green house gas reduction goals for future heavy-duty (HD) truck diesel engines. A Rankine cycle system with ethanol as the working fluid was developed at AVL Powertrain Engineering, Inc. to investigate the fuel economy benefit from recovering waste heat from a 10.8L HD truck diesel engine. Thermodynamic analysis on this WHR system demonstrated that 5% fuel saving could be achievable. The fuel economy benefit can be further improved by optimizing the design of the WHR system components and through better utilization of the available engine waste heat. Although the WHR system was designed for a stand-alone system for the laboratory testing, all the heat exchangers were sized such that their heat transfer areas are equivalent to compact heat exchangers suitable for installation on a HD truck diesel engine.
2000-03-06
Technical Paper
2000-01-0687
James C. McCandless, Ho Teng, Jeffrey B. Schneyer
A variable-displacement, 275-bar dimethyl-ether pump for a common-rail injection system has been developed successfully. The pump is an inlet-throttled, wobble-plate-actuated, multi-plunger system. Results of the pump tests/simulations show that the pump can deliver fuel according to the engine requirement at different speeds due to its variable-displacement feature, which is obtained by controlling the discharge phase angle via the two-phase filling characteristic of the pump. Although the pump is designed for dimethyl ether, its concept is general and thus may be applied to the common-rail systems for other fuels.
2005-04-11
Technical Paper
2005-01-0909
Ho Teng, James C. McCandless
This paper discusses the performance of the radial plunger pump used in the contemporary diesel common-rail fuel systems for rail-pressure supply. On the ground of the pump mechanism, the transient flow, drive torque, and efficiency of the pump are analyzed for various operation conditions. The analysis shows that the number of plungers and utilization of the pump capacity govern fluctuations in the pump discharge. The pump flow can be characterized by a discharge function which applies to both full- and part-capacity pump flows. At the full pump capacity, the discharge fluctuation is determined solely by the number of plungers: a pump with an odd number of plungers has more ripples and lower amplitudes in its discharge than a pump with an even number of plungers does. A pump operates at a part capacity has more fluctuations in the discharge than when at the full capacity.
2005-04-11
Technical Paper
2005-01-1723
Ho Teng, James C. McCandless
A comparative study of characteristics of diesel fuel and dimethyl ether sprays was conducted on the basis of momentum conservation. The analysis reveals that the DME spray in the diesel combustion system may not develop as well as that of diesel fuel at high engine loads and speeds due primarily to the following reasons. (1) Because 42% more fuel volume must be injected into the engine to reach the diesel-fuel equivalent and because the DME injection pressure is lower than that of diesel fuel, longer injection duration for DME is needed even if with the enlarged orifice diameters.
2012-04-16
Technical Paper
2012-01-0119
Kim Yeow, Ho Teng, Marina Thelliez, Eugene Tan
The battery packs for plug-in hybrid electrical vehicle (PHEV) applications are relatively small in the charge depleting (CD) mode but fairly large in the charge sustaining (CS) mode for their duties in comparison to the battery packs for hybrid electrical vehicle (HEV) applications. Thus, the heaviest battery thermal load for a PHEV pack is encountered at the end of the CD mode. Because the cells in PHEV battery packs are generally larger than those in the HEV packs in both capacity and size, control of the maximum cell temperature and the maximum differential cell temperature for the cells in a PHEV pack with high packing efficiency is a challenge for the cooling system design. The maximum cell temperatures locate in the areas near the terminal tabs where the current densities are highest.
2013-04-08
Technical Paper
2013-01-0234
Kim F. Yeow, Ho Teng
For lithium-ion battery systems assembled with high-capacity, high-power pouch cells, the cells are commonly cooled with thin aluminum cooling plates in contact with the cells. The cooling plates extract the cell heat and dissipate it to a cooling medium (air or liquid). During the pack utilizations with high-pulse currents, large temperature gradients along the cell surfaces can be encountered as a result of non-uniform distributions of the ohmic heat generated in the cells. The non-uniform cell temperature distributions can be significant for large-size cells. Maximum cell temperatures typically occur near the cell terminal tabs as a result of the ohmic heat of the terminal tabs and connecting busbars and the high local current densities. In this study, a new cooling plate is proposed for improving the uniformity in temperature distributions for the cells with large capacities.
2012-09-24
Journal Article
2012-01-2017
Ho Teng, Kim Yeow
Battery packs for plug-in hybrid electrical vehicle (PHEV) applications can be characterized as high-capacity and high-power packs. For PHEV battery packs, their power and electrical-energy capacities are determined by the range of the electrical-energy-driven operation and the required vehicle drive power. PHEV packs often employ high-power lithium-ion (Li-ion) pouch cells with large cell capacity in order to achieve high packing efficiency. Lithium-ion battery packs for PHEV applications generally have a 96SnP configuration, where S is for cells in series, P is for cells in parallel, and n = 1, 2 or 3. Two PHEV battery packs with 355V nominal voltage and 25-kWh nominal energy capacity are studied. The first pack is assembled with 96 70Ah high-power Li-ion pouch cells in 96S1P configuration. The second pack is assembled with 192 35Ah high-power Li-ion pouch cells in 96S2P configuration.
2015-03-30
Technical Paper
2015-01-0084
Xuwei Luo, Ho Teng, Tingjun Hu, Ruigang Miao, Liming Cao
Abstract Turbocharged gasoline direct injection (TGDI) engines can achieve a very high level of brake mean effective pressure and thus the engines can be downsized. The biggest challenge in developing highly-boosted TGDI engines may be how to mitigate the pre-ignition (PI) triggered severe engine knocks at high loads and low engine speeds. Since magnitudes of cylinder pressure fluctuations during aforementioned engine knocks reach those for peak firing pressures in normal combustion, they are characterized as super knocks. It is widely believed that the root cause for super knocks is the oil particles entering the engine cylinder, which pre-ignite the cylinder mixture in late of the compression stroke. It is neither possible nor practical to completely eliminate the oil particles from the engine cylinder; a reasonable approach to mitigate super knocks is to weaken the conditions favoring super knocks.
2009-10-06
Technical Paper
2009-01-2913
Ho Teng, Gerhard Regner
The fuel saving benefit is analyzed for a class-8 truck diesel engine equipped with a WHR system, which recovers the waste heat from the EGR. With this EGR-WHR system, the composite fuel savings over the ESC 13-mode test is up to 5%. The fuel economy benefit can be further improved if the charge air cooling is also integrated in the Rankine cycle loop. The influence of working fluid properties on the WHR efficiency is studied by operating the Rankine cycle with two different working fluids, R245fa and ethanol. The two working fluids are compared in the temperature-entropy and enthalpy-entropy diagrams for both subcritical and supercritical cycles. For R245fa, the subcritical cycle shows advantages over the supercritical cycle. For ethanol, the supercritical cycle has better performance than the subcritical cycle. The comparison indicates that ethanol can be an alternative for R245fa.
2009-11-02
Journal Article
2009-01-2671
Ho Teng, Gerhard Regner
Characteristics of soot deposits in the EGR cooler were studied, on basis of which a comprehensive model for soot particle depositions was developed. It was found that the soot deposit may be divided into three characteristic layers: a quasi-crystal base layer formed by nano-particles, an intermediate layer of denser packing of soot particles with meso pores, and a highly porous top layer formed by mechanical interlocking of soot particles. The cooler performance is affected significantly by the top layer of the deposit. Because of their weak contact energy, particles in the top layer and intermediate layers may be removed by the shear force under high EGR flows. The contact energy for the particles in the base layer is much stronger than that in the surface and intermediate layers. The base layer may be removed only with physicochemical methods.
2007-04-16
Technical Paper
2007-01-0543
Ho Teng, Gerhard Regner, Chris Cowland
In Part I of this paper, the organic Rankine cycle for waste heat recovery (ORC-WHR) from the heavy-duty diesel truck engines was discussed. This work is Part II of the paper. The efficiency of the ORC-WHR system varies considerably with thermodynamic properties of the working fluid. In this work, characteristics of candidate working fluids are discussed on the basis of the thermodynamic theory. The discussion covers inorganic and organic fluids for both pure fluids and binary-mixture fluids. On the basis of the characteristics of the working fluids, the thermal efficiency for the ORC-WHR system is analyzed. Discussions and conclusions of this paper are helpful in selecting proper working fluids for the ORC-WHR system and determining a proper temperature range for system operations.
2007-04-16
Technical Paper
2007-01-0537
Ho Teng, Gerhard Regner, Chris Cowland
Waste heat from a heavy-duty truck diesel engine is analyzed employing the first and second law of thermodynamics. A hybrid energy system is proposed, with the diesel cycle being hybridized with an organic Rankine cycle for waste heat recovery (ORC-WHR). The charge air cooler and EGR cooler(s) are integrated in the ORC loop as pre-heaters and the ORC working fluid serves as the coolant for these coolers. A supercritical reciprocating Rankine engine is proposed, which avoids using the high-cost evaporator and is easier for the system packaging. It is demonstrated in a case study that up to 20 % of waste heat from the heavy-duty diesel engine may be recovered by the supercritical ORC-WHR system, making the efficiency for the hybrid energy system be ≥ 50%. Discussion on working fluids for the WHR-ORC system is covered in Part II of this paper.
2006-04-03
Technical Paper
2006-01-0053
Ho Teng, James C. McCandless
Emissions from CI engines fueled with dimethyl ether (DME) were discussed in this paper. Thanks to its high content of fuel oxygen, DME combustion is virtually soot free. This characteristic of DME combustion indicates that the particulate filter will not be needed in the aftertreatment system for engines fueled with DME. NOx emissions from a CI engine fueled with DME can meet the US 2007 regulation with a high EGR rate. Because 49% more fuel mass must be delivered in each DME injection than the corresponding diesel-fuel injection, and the DME injection pressure is lower than 500 bar under the current fuel-system technology, the DME injection duration is generally longer than that of diesel-fuel injection. This is unfavorable to further NOx reduction. A multiple-injection strategy with timing for the primary injection determined by the cylinder temperature was proposed.
2006-10-16
Technical Paper
2006-01-3238
Gerhard Regner, Ho Teng, Peter Van Wieren, Jae In Park, Soo Youl Park, Dae Joon Yeom
On the basis of the newly-developed fractal combustion model, the engine-thermodynamic-cycle simulations were conducted with the 1D engine-cycle-simulation program AVL-BOOST for a passenger-car SI engine with a fully-variable valve train. Results of the simulations showed a good agreement with measurements for both full and part load at various engine speeds. On the basis of the thermodynamic model for the engine, the valve event optimization was carried out for both full and part load with a partial factorial DoE plan consisting of various valve event durations and timings. For each of the selected cases, an independent optimization for the ignition timing was performed to determine the minimum BSFC under a constraint on specified knock criteria. Satisfactory results for the valve event optimization were achieved.
2006-10-16
Technical Paper
2006-01-3324
Ho Teng, Gerhard Regner
A new fuel injection strategy is proposed for DME engines. Under this strategy, a pre-injection up to 40% demand is conducted after intake valves closing. Due to high volatility of DME, a lean homogeneous mixture can be formed during the compression stroke. Near TDC, a pilot injection is conducted. Combined fuel mass for the pre-injection and pilot injection is under the lean combustion limit of DME. Thus, the mixture is enriched and combustion can take place only in the neighborhood of sprays of the pilot injection. The main injection is conducted after TDC. Because only about half of the demand needs to be injected and DME evaporates almost immediately, combustion duration for the main injection plus the unburnt fuel in the cylinder should not be long because a large portion of the fuel has been premixed with air. With a high EGR rate and proper timing for the main injection, low temperature combustion could be realized.
2006-10-31
Technical Paper
2006-01-3522
Ho Teng, Gerhard Regner, Chris Cowland
A supercritical organic Rankine cycle (ORC) system for recovery of waste heat from heavy-duty diesel engines is proposed. In this system, an organic, medium-boiling-point fluid is selected as the working fluid, which also serves as the coolant for the charge air cooler and the EGR coolers. Because the exhaust temperature can be as high as 650 °C during the DPF regeneration, an exhaust cooler is included in the system to recover some of the high level exhaust energy. In the present ORC system, the expansion work is conducted by a uniflow reciprocating expander, which simplifies the waste-heat-recovery (WHR) system significantly. This reciprocating Rankine engine is more appropriate for on-road-vehicle applications where the condition for waste heat is variable. The energy level of waste heat from a heavy-duty diesel engine is evaluated by the analyses of the first and second law of thermodynamics.
2001-03-05
Technical Paper
2001-01-0154
Ho Teng, James C. McCandless, Jeffrey B. Schneyer
This paper analyzed chemical and thermophysical properties of dimethyl ether (DME) as an alternative fuel for compression-ignition engines. On the basis of the chemical structure of DME and the molecular thermodynamics of fluids, equations have been developed for most of the DME thermophysical properties that would influence the fuel-system performance. These equations are easy to use and accurate in the pressure and temperature ranges for CI engine applications. The paper also pointed out that the DME spray in the engine cylinder would differ significantly from that of diesel fuel due to the thermodynamic characteristics of DME. The DME spray pattern will affect the mixing and combustion processes in the engine cylinder, which, in turn, will influence emissions from combustion.
2001-03-05
Technical Paper
2001-01-0652
James C. McCandless, Ho Teng, Jeffrey B. Schneyer
A novel fuel tank for storing liquid dimethyl ether (DME) has been developed. This fuel tank was made of cast aluminum with a water capacity of 40 liters. It contains two fluids: liquid DME and a vapor-liquid mixture of propane. A diaphragm separates the two fluids. The propane in the tank is a pressurizing fluid that pressurizes DME into a subcooled-liquid state; and, it also functions as a driving fluid that pumps the liquid DME from the tank to the injection pump using its vapor pressure. These features characterize the tank as a thermodynamic pump. Several hundred hours of tank tests at various temperatures have been conducted. Results of tank filling-discharge cycles simulating those in vehicle applications demonstrated that the concept of the two-fluid thermodynamic pump works and that the tank design is successful.
2003-03-03
Technical Paper
2003-01-0759
Ho Teng, James C. McCandless, Jeffrey B. Schneyer
Compression ignition delay of DME is studied theoretically. Physical phenomena that would influence the ignition delay, characteristics of the DME spray and evaporation of DME droplets in the spray, are analyzed. It is found that the short ignition delay of DME revealed in engine tests is due largely to the short physical delay of DME: The evaporation rate of DME droplets is about twice that of diesel-fuel droplets at the same cylinder condition and, the stoichiometric mixture in a DME spray can be established immediately - in comparison, the stoichiometric mixture in a diesel-fuel spray cannot be established before temperatures of diesel-fuel droplets become higher than 225 °C. The high droplet evaporation rate of DME is also responsible for the irregular boundary and tip of the DME spray as observed by many investigators. On the basis of experimental data reported in the literature, cetane number of DME is estimated to be 68.
2002-03-04
Technical Paper
2002-01-0862
Ho Teng, James C. McCandless, Jeffrey B. Schneyer
In this paper, dependence of liquid-DME viscosity on temperature and pressure was studied theoretically. It was found that in the saturated-liquid state, the DME viscosity is 0.37 cSt at - 40 ° C and it drops to 0.17 cSt when temperature increases to 80 ° C. In the subcooled-liquid state, viscosity varies linearly with pressure at a given temperature; at 20 ° C, viscosity of the subcooled liquid is 0.23 cSt at 5.3 bar and it increases to 0.33 cSt at 500 bar. The predicted liquid-DME viscosity and its pressure dependence agree with those obtained by measurement. Lubricity of liquid DME also was studied. Polar-headed, long-chain alcohols and fatty acids with chain length of C15 ∼ C22 were found to be candidates of lubricity additives for DME. Castor oil (chemically, it is basically a C18 fatty acid) was found to be a good additive for improving the DME lubricity.
2010-10-05
Journal Article
2010-01-1928
Ho Teng
Fuel economy is critical for heavy-duty line haul applications. As fuel prices rise and impending fuel economy regulations are implemented, new ways to improve heavy-vehicle fuel economy will be in high demand. AVL Powertrain Engineering has undertaken a research and development project to demonstrate the feasibility of a Rankine Cycle Waste Heat Recovery (WHR) system. The goals of the project were to reduce the overall engine heat rejection, specific emissions and fuel consumption (CO₂ emissions) of heavy-duty diesel engines by converting heat that is typically wasted to the exhaust stack and through the EGR cooler to useable mechanical energy. A detailed thermodynamic analysis was conducted which laid the groundwork for working fluid selection and proper sizing of the WHR components. Based on the system specifications, a prototype WHR system was designed and built. The performance of the system was evaluated on a 10.8-liter heavy-duty on-highway diesel engine.
2010-10-05
Journal Article
2010-01-1948
Ho Teng
The performance of an EGR cooler is influenced significantly by particulate fouling in the cooler. As a result of fouling, a highly porous soot deposit layer is formed in the EGR cooler. This deposit layer not only causes a decrease in the cooler effectiveness but also an increase in the EGR pressure drop over the cooler. Increasing the EGR cooler pressure drop reduces the driving force for the EGR flow under a given differential pressure across the engine. Thus, the EGR cooler fouling has a big impact on the control of the engine-out NO emissions. In this paper, a semi-empirical model is developed for predicting pressure drops of fouled EGR coolers. Based on this model and the particulate fouling model developed previously by the author, the process is analyzed for the pressure drop increase with building up of the soot deposit in an EGR cooler.
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