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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.

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.

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.

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 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.

A thermo-mechanical fatigue analysis was conducted based on a coupled Finite Element Analysis (FEA) - Computational Fluid Dynamics (CFD) method on the crack failure of the exhaust manifold for an inline 4-cylinder turbo-charged diesel engine under the durability test. In the this analysis, the temperature-dependent material properties were obtained from measurements and the model was calibrated with comparison of the predicted exhaust manifold temperatures with the on-engine measurements under the same engine load condition. Temperature and stress/strain distributions in the exhaust manifold were predicted with the calibrated model. Analysis results showed that the cracks took place at locations with high plastic deformations, suggesting that the cause of the failure be thermo-mechanical fatigue (TMF). Using the equivalent plastic strain (PEEQ) as the indicator for thermal mechanical fatigue, three exhaust manifold design revisions were carried out by CAE analysis.

Although the brake thermal efficiency of the state-of-the-art Atkinson-cycle hybrid engines have reached 41%, such engines typically have a low specific power. The ideal hybrid engines for SUVs should have a high thermal efficiency as well as a high specific power. Jiangling Motors recently developed a 4-cylinder, 1.5L TGDI hybrid Miller engine for powering mid-size SUVs, which has achieved 42% brake thermal efficiency, 19.3-bar BMEP, and 73.3-kW/L specific power. The engine has a high compression ratio, a long stroke, and is equipped with a low-pressure EGR system. It can operate with the stoichiometric mixture on the full engine map, with the help of the water-cooled exhaust manifold and the intelligent thermal management system.

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.

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.

In order to improve low speed torques, turbocharged gasoline direct injection (TGDI) engines often employ scavenging with a help of variable valve timing (VVT) controlled by the cam phasers. Scavenging improves the compressor performance at low flows and boosts low-speed-end torques of the engines. Characteristics of the engine combustion in the scavenging zone were studied with a highly-boosted 1.5L TGDI engine experimentally. It was found that the scavenging zone was associated with the highest blowby rates on the engine map. The blowby recirculation was with heavy oil loading, causing considerable hydrocarbon fouling on the intake ports as well as on the stem and the back of the intake valves after the engine was operated in this zone for a certain period of time. The low-speed pre-ignition (LSPI) events observed in the engine tests fell mainly in the scavenging zone.

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.

The biggest challenge in developing Turbocharged Gasoline Direct Injection (TGDI) engines may be the abnormal combustion phenomenon occurring at low speeds and high loads, known as low-speed pre-ignition (LSPI). LSPI can trigger severe engine knocks with intensities much greater than those of spark knocks and thus characterized as super knocks. In this study, behavior and patterns of LSPI were investigated experimentally with a highly-boosted 1.5L TGDI engine. It was found that LSPI could occur as an isolated event, a couple of events in sequence, or a trail of events. Although occurring randomly among the engine cylinders, LSPI took place frequently when the engine was operated at low speeds and high loads in the zone where scavenging was employed for boosting engine torques at low speeds, typically < 2500 rpm.

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.

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.