A robust optimization of an automobile valvetrain is presented where the variation of engine performances due to the component dimensional variations is minimized subject to the constraints on mean engine performances. The dimensional variations of valvetrain components are statistically characterized based on the measurements of the actual components. Monte Carlo simulation is used on a neural network model built from an integrated high fidelity valvetrain-engine model, to obtain the mean and standard deviation of horsepower, torque and fuel consumption. Assuming the component production cost is inversely proportional to the coefficient of variation of its dimensions, a multi-objective optimization problem minimizing the variation in engine performances and the total production cost of components is solved by a multi-objective genetic algorithm (MOGA). The comparisons using the newly developed Pareto front quality index (PFQI) indicate that MOGA generates the Pareto fronts of substantially higher quality, than SQP with varying weights on the objectives. The current design of the valvetrain is compared with two alternative designs on the obtained Pareto front, which suggested potential improvements.

The link between manufacturing process and product performance is studied in order to construct analytical, quantifiable criteria for the introduction of new engine technologies and processes. Cost associated with a new process must be balanced against increases in engine performance and thus demand for the particular vehicle. In this work, the effect of the Abrasive Flow Machining (AFM) technique on surface roughness is characterized through measurements of specimens, and a predictive engine simulation is used to quantify performance gains due to the new surface finish. Subsequently, economic cost-benefit analysis is used to evaluate manufacturing decisions based on their impact on firm's profitability. A demonstration study examines the use of AFM for finishing the inner surfaces of intake manifolds for two engines, one installed in a compact car and the other in an SUV.

The macroscopic and microscopic characteristics of flash-boiling spray were experimentally investigated with various optical measurement techniques. The effects of ambient pressure and fuel temperature on flash-boiling characteristics in multi-hole gasoline direct injection injector were analyzed. The analysis was focused on the spray structure and atomization droplet size distributions. In order to increase the understanding of the flash-boiling spray targeting, three injectors with different spray patterns were investigated under strong flash-boiling condition. The results show that ambient pressure and fuel temperature have significant influence on flash boiling. Both lower ambient pressure and higher fuel temperature could accelerate the flash-boiling process. For the macroscopic characteristics, similar influences could be found with the ambient pressure decreased by 0.4 bar and the fuel temperature increased by 10°C. Further, significant difference could be found within cold-jet spray and strong flash-boiling spray, such as the spatial structure. The spray structure always turns from hollow cone into solid when flash boiling occurs. With a higher fuel superheat degree, the spray droplet distribution moves toward smaller sizes and let the larger droplets reduce due to the promotion of atomization. For the strong flash-boiling spray, the Sauter mean diameter has decreased by 50% compared with cold-jet spray. There is a corresponding relationship between collapsed flash-boiling spray target and weighted geometric center of the injector. Spray collapse could be avoided by increasing the plume distance.

<div class="section abstract"><div class="htmlview paragraph">This study introduces the working principle of the two-stage variable compression ratio system, the layout and method of the VCR hydraulic system test. Based on the research and analysis of VCR hydraulic system test, the results shows the average pressure, degree of pressure fluctuation of the VCR conrod supply oil and the temperature of conrod journal are all strongly and positively related to engine speed. The maximum oil pressure fluctuation amplitude at VCR conrod bearing appears at 5500r/min. The temperature at VCR conrod bearing is mainly dominated by the friction between bearing and crankshaft, and its maximum value appears at 6000r/min; Meanwhile, the main contribution of engine load to the temperature is to increase temperature of the whole circle of conrod journal, and also reducing temperature difference of the whole circle. In addition, the state change of VCR hydraulic system under different conditions can reflect the state of engine compression ratio. The results of overall test show that oil pressure fluctuation of the VCR hydraulic system is in normal range, the system has good function and can meet the oil demand of each sub-component under steady and dynamic conditions.</div></div>

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