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Heavy traffic volume makes tailgating a common picture on the road today. Wake interference, particularly in the scenario when a relatively small sedan drives into the wake of a large truck, may raise some serious highway safety concerns. In this paper, the characteristics of the separation bubble of model trucks with various degrees of details are studied. The objective is to find out the impact of truck model details on the characteristics of the wake bubble. Our wind tunnel results revealed that the degree of model detail has a significant effect on the wake bubble; the bubble length increases with model details.

Empirical and analytical investigations are conducted to evaluate the thermal response of exhaust pipe plenums at different levels of exhaust gas recirculation and through a variety of fuel delivery strategies. The effectiveness of different combustion control techniques is evaluated for moderating the engine-out exhaust temperature. Comparison of the external fuel injection with in-cylinder post injection for enabling aftertreatment is provided which indicates the stronger temperature raising potential of the external fuel injection. This research attempts to quantify the thermal response of the exhaust pipe plenums and its effects on the gas temperature at the inlet of the aftertreatment devices. The measurement and modeling of the dynamic thermal response in this research intend to improve the performance of diesel aftertreatment devices.

The exhaust emission and performance characteristics of a 100% biodiesel fuel was evaluated on a single cylinder direct injection diesel engine that had been modified to allow multi-pulse diesel fuel injection at the intake port and independent control of intake heating, exhaust gas recirculation and throttling. Firstly, conventional single-shot direct injection tests were conducted and comparisons made between the use of an ultra-low sulphur diesel fuel and the biodiesel fuel. Secondly, tests for the premixed combustion of neat biodiesel were performed. Exhaust gas recirculation was applied extensively to initiate the low temperature combustion for the conventional in-cylinder single injection operation and to moderate the timing of the homogeneous charge compression ignition for the intake-port sequential injection. Because of the high viscosity and low volatility of the biodiesel, pilot-ignited homogeneous charge compression ignition was used.

The heat rejection process of CO2 air conditioning system takes place in the supercritical region, where pressure is independent of temperature. It has been demonstrated that at any particular ambient temperature, the system efficiency varies nonlinearly with the working pressure. The optimum high pressure was thereby tracked and derived in this study, which corresponds to the best system performance. The system simulation was conducted over typical working pressures. The simulation results suggested that for a specific compressor speed, the gas cooler outlet temperature or the ambient temperature could be used to adjust the high pressure to achieve the maximum COP.

This note focuses on the three fundamental mechanisms behind premixed flame-turbulence interactions that result in progressive acceleration of a spark-ignited flame in a turbulent environment such as that inside a spark-ignition engine cylinder. In addition, as a small step in further advancing our understanding on flame-turbulence interactions, experiments were conducted to quantify the changing turbulence parameters associated with a near-isotropic turbulent free-stream as it approaches a solid sphere in a wind tunnel. It has been observed in some previous studies that when a premixed combustible mixture is ignited in a turbulent environment, the turbulent flame speed / turbulence intensity ratio increases as the flame grows. Depending on the chemical and physical parameters involved, this accelerating turbulent flame may develop into a detonation wave.

Airside heat transfer and fluid flow characteristics of a single array cross flow heat exchanger, made of elliptical tubes, were studied. The heat exchanger, consists of 18 tubes each of 30 cm long with 0.30 minor to major outside axis ratio and equally spaced by 0.61 cm gap, was oriented in a 30 cm by 30 cm test section of a wind tunnel with the major axis parallel to the air flow. Tests were performed with hot water flowing inside the tubes, while cold air flowing across them externally. The mean temperature difference between the approaching air and the surface of the tubes was maintained at roughly 14±2°C. Reynolds number based on the mean free stream air velocity and hydraulic diameter of the elliptical tube was varied from 4500 to 15000, while that based on the mean water velocity inside the tube was altered from 1400 to 7400.

The effects of hydrogen peroxide addition on iso-octane/air Homogeneous Charge Compression Ignition (HCCI) combustion have been investigated analytically. Particular attention was focused on the predications involving homogeneous gas-phase kinetics. Use was made of Peters' iso-octane mechanism in CHEMKIN and convective heat transfer was included in the analyses. This enabled the influences that H2O2 addition has on species concentration and ignition promotion and hence exhaust emissions to be determined. It was found that both CO and NOx emission levels could be ameliorated. The former effect is considered to be a result of the decomposition of H2O2 into OH intermediate species and hence reducing the time to ignition and the onset of combustion.

The effects of turbulence on 60% stoichiometric, premixed methane-air flame propagation were investigated using high speed schlieren video and pressure trace analyses. The mixtures were centrally spark-ignited at 300 K and 101 kPa in a 125 mm cubical chamber. Turbulence was up to 2 m/s intensity with 2 to 8 mm integral scale. With quiescent mixtures, buoyancy convected the slow-burning flame upward onto the upper wall, resulting in dramatic heat loss. With turbulence, the burning rate was enhanced profoundly, though partial flame quenching resulted in cyclic variability at higher turbulence levels. Despite this partial quenching, these ultra-lean flames generally resisted total extinguishment over the conditions tested.

The different roles played by small and large eddies in engine combustion were studied. Experiments compared natural gas combustion in a converted, single cylinder Volvo TD 102 engine and in a 125 mm cubical cell. Turbulence is used to enhance flame growth, ideally giving better efficiency and reduced cyclic variation. Both engine and test cell results showed that flame growth rate correlated best with the level of high frequency, small eddy turbulence. The more effective, small eddy turbulence also tended to lower cyclic variations. Large scales and bulk flows convected the flame relative to cool surfaces and were most important to the initial flame kernel.