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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.

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.

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.

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.

On the basis of the molecular thermodynamics for fluids, the thermodynamic properties of DME are developed for pressure p ≤ 500 bar and temperature T ≤ 200 °C, which covers pressures and temperatures that a DME fuel system for the CI-engine application would experience. The properties cover subcooled, two-phase, and superheated/supercritical regions, including p-v-T properties, enthalpy, entropy, latent heat, heat capacity, speed of sound in vapor, liquid and two-phase mixtures, bulk modulus, and surface tension. A volume-cubic equation of state for DME also is developed, which allows calculating the DME density at any given pressure and temperature analytically. All the properties are given in equations as well as in charts. For convenience in two-phase-flow applications, e.g., design of the fuel tank and cavitation analysis, the saturated properties are also given in tables, listed in both pressure and temperature up to the critical point.

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.

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.

The performance and life of Li-ion battery packs for electric vehicle (EV), hybrid electrical vehicle (HEV), and plug-in hybrid electrical vehicle (PHEV) applications are influenced significantly by battery operation temperatures. Thermal management of a battery pack is one of the main factors to be considered in the pack design, especially for those with indirect air or indirect liquid cooling since the cooling medium is not in contact with the battery cells. In this paper, thermal behavior of Li-ion pouch cells in a battery system for PHEV applications is studied. The battery system is cooled indirectly with liquid through aluminum cooling fins in contact with each cell and a liquid cooled cold plate for each module in the battery pack. The aluminum cooling fins function as a thermal bridge between the cells and the cold plate. Cell temperature distributions are simulated using a finite element analysis approach under cell utilizations corresponding to PHEV applications.

Thermal behavior of a lithium-ion (Li-ion) battery module for hybrid electrical vehicle (HEV) applications is analyzed in this study. The module is stacked with 12 high-power pouch Li-ion battery cells. The cells are cooled indirectly with air through aluminum fins sandwiched between each two cells in the module, and each of the cooling fins has an extended cooling surface exposed in the cooling air flow channel. The cell temperatures are analyzed using a quasi-dimensional model under both the transient module load in a user-defined cycle for the battery system utilizations and an equivalent continuous load in the cycle. The cell thermal behavior is evaluated with the volume averaged cell temperature and the cell heat transfer is characterized with resistances for all thermal links in the heat transfer path from the cell to the cooling air. Simulations results are compared with measurements. Good agreement is observed between the simulated and measured cell temperatures.

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.

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.

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.

The relationship between fuel dilution of the crankcase oil and low-speed pre-ignition (LSPI) was studied experimentally with a highly-boosted 1.8L turbocharged gasoline direct injection (TGDI) engine fueled with RON93 gasoline. It was found that properties of oil particles entered the engine cylinder were affected significantly by fuel dilution. The gasoline content in the oil represents those with long carbon chain or heavy species in gasoline, with much lower boiling points and auto ignition temperatures than those for the undiluted engine oil. Thus, dilution of the engine oil by these gasoline species lowers the volatility and the minimum auto ignition temperature of the engine oil. With 15% fuel content in the oil, the flash point and the fire point of the SAE 5W30 oil dropped from 245 °C to 90 °C and from 265 °C to 150 °C, respectively.

This paper reports an experimental investigation on the influence of the crankcase oil properties on the engine combustion in the low-speed pre-ignition (LSPI) zone. The investigation was conducted on a highly boosted 1.5L TGDI engine operated at the low-speed-end maximum torque, at which LSPI events were observed most frequently. Six different engine oils were tested, covering SAE 0W-20, 0W-30, 0W-40, 5W-20, 5W-30 and 5W-40. In order to evaluate the evaporative characteristics of the crankcase oil, for each of the selected engine oils, the tests were conducted at two different coolant temperatures, 90°C and 105°C. Because SAE 5W-30 was the base oil for the engine under study, for this particular oil, the investigation was extended to the impact of different levels of the mixture enrichment.

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.

Turbocharged gasoline direct injection (TGDI) engines often have a flat torque curve with the maximum torque covering a wide range of engine speeds. Increasing the high-speed-end torque for a TGDI engine provides better acceleration performance to the vehicle powered by the engine. However, it also requires more fuel deliveries and thus longer injection durations at high engine speeds, for which the multiple fuel injections per cycle may not be possible. In this study, results are reported of an experimental investigation of impact of fuel injection on dilution of the crankcase oil for a highly-boosted TGDI engine. It was found in the tests that the high-speed-end torque for the TGDI engine had a significant influence on fuel dilution: longer injection durations resulted in impingement of large liquid fuel drops on the piston top, leading to a considerable level of fuel dilution.

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.

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.

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.

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.