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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.

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 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.

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.

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.

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.

In this study, thermal runaway of a 3-cell Li-ion battery module is analyzed using a 3D finite-element-analysis (FEA) method. The module is stacked with three 70Ah lithium-nickel-manganese-cobalt (NMC) pouch cells and indirectly cooled with a liquid-cooled cold plate. Thermal runaway of the module is assumed to be triggered by the instantaneous increase of the middle cell temperature due to an abusive condition. The self-heating rate for the runaway cell is modeled on the basis of Accelerating Rate Calorimetry (ARC) test data. Thermal runaway of the battery module is simulated with and without cooling from the cold plate; with the latter representing a failed cooling system. Simulation results reveal that a minimum of 165°C for the middle cell is needed to trigger thermal runaway of the 3-cell module for cases with and without cold plate cooling.

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.

Good understanding of fuel sprays in the engine cylinder is crucial to optimizing the operation of direct injection gasoline engines. In this paper, a detailed analysis is conducted on direct gasoline injection sprays from a multi-hole injector. Penetrations and angles of the sprays are characterized with a homogeneous model for the fuel spray. The drop size distributions in the sprays are analyzed using an empirical distribution model. Predicted spray penetrations, spray angles, and drop size distributions under three different injection pressures are compared with the measurements for injection pressures = 40, 100 and 150 bar and good agreements are observed. Transient evaporation rates are also studied for fuel drops in an environment simulating the cylinder condition during the intake stroke of a direct injection gasoline engine.

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.

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.

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.

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.