京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22552号 / エネ博第403号 / 新制||エネ||77(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)教授 石山 拓二, 教授 川那辺 洋, 教授 今谷 勝次 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

Decades of research on compression ignition engines have led to a highly efficient combustion cycle in contemporary diesel engines. Nonetheless, the combustion process is being studied perpetually to meet both current and future emission regulations. One of the most influential parameters that impacts the combustion quality, is the fuel spray evolution during injection, and subsequent fuel-air mixture formation inside the engine cylinder. The spray evolution has been investigated to a high level of detail, and the highly complex processes of mixture formation and combustion are well-documented for diesel engines. Most of these investigations are limited to studying either research-grade injectors, or brand new production injectors. Injectors in real-world diesel engines, i.e. normal passenger cars and trucks that are used on a daily basis, are however subject to deposit formation at the tip of the injector nozzle. These deposits have the potential of altering the internal nozzle flow and fuel spray pattern, which in turn degrades combustion quality and increases engine emissions. In the work presented in this thesis the spray evolution of production injectors has been studied over a wide range of injector conditions. Common rail light-duty injectors with a usage history of up to 90 000 miles were acquired from the UK commuter car parc, and several brand new injectors were studied for comparison purposes. It is shown that the spray pattern of the injected fuel changes over the lifetime of the injector. For used injectors a reduced penetration rate was observed in the transient regime of fuel injection, during needle lift. The reduced penetration rate was often accompanied by anomalous radial expansions. Although the magnitude of the effects varied from injector to injector, the highest mileage injectors tended to produce the strongest spray deviations. For several high-mileage injectors the end of injection appeared retarded with respect to new injectors. Expulsions of liquid ligaments and droplets after the end of injection were observed from all injectors, irrespective of the mileage of the injector.

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The Sandwich Plate System (SPS) is created by bonding two steel plates together with an elastomer core that is injected into a cavity formed by the steel plates and perimeter bars. The result is a stiffer and lighter panel that can be used for plate-like structures such as bridge decks, stadium risers or ship decks. For more versatility, the effects of welding post-injection to the SPS panels were investigated. Three post-injection welded joints were tested to determine fatigue resistance and the effects of cyclic loading on the localized debonding of the heat affected zone at the post-injection welded joint of a SPS bridge deck. Seven panels containing one of three post-injection weld configurations were investigated. Each panel was fatigue tested to ten million cycles or until failure, by applying remote bending to the post-injection welded joint. Experimental deflections and strains were compared to finite element analyses. Fatigue-life predictions were made using code based S-N curves, and a relatively new mesh-insensitive structural stress method with a master S-N curve approach. The post-injection welded joint demonstrated good fatigue resistance to recommended AASHTO loading when shims were used under the middle support to offset the camber in the SPS panels. It was also found that stresses caused by draw down of the camber had an adverse affect on the post-injection welded joint and greatly reduced its fatigue resistance. / Master of Science