Browsing by Subject "Parametric study"
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Item A study to quantitatively analyze cold start emissions for a gasoline direct injection engine(2023-04-12) Hu, Jinghu; Hall, M. J. (Matthew John); Matthews, Ronald D. (Ronald Douglas); Ezekoye, Ofodike A; Yi, Jianwen "James"The gasoline direct injection (GDI) technology is a technology with which the gasoline is directly injected in the cylinder. GDI technology has been gaining popularity among vehicle manufacturers due to multiple advantages it presents compared with the port fuel injection technology, and has been widely implemented in the light-duty passenger vehicles on the US market. One weakness of the GDI engine is the excessive hydrocarbon (HC) emission during the cold start, where the engine speed, cylinder and piston top temperature and engine fuel rail pressure are all far from optimal. Given the more stringent Tier 3 HC emissions regulations enforced by United States Environmental Protection Agency and California Air Resources Board, a detailed research on the GDI engine cold start HC emissions was essential to facilitate the compliance with HC emission standards from the modern GDI engines. A novel experimental system was designed, prototyped and installed. The in-house instrumentation and control system was designed based on the National Instruments hardware and aimed to control the Ford 2.0 L GDI engine and realize the engine cold start using custom engine powertrain parameters. The novel gas collection and analysis system was designed and prototyped to allow a cycle-based emission analysis. The entire study was carried out using three steps. First, the validation experiment was conducted to validate whether the designed system hardware and software operated as desired, and to provide some basic qualitative understanding of the GDI engine cold start profiles. Second, the preliminary quantitative analysis was carried out using both gasoline and iso-pentane as fuel to further understand the contributing factors of the cold start HC emissions for GDI engines. In the final step, a parametric study, multiple parametric sweeps were carried out for various powertrain parameters to identify the quantitative effect of each parameter on the engine power output and emission performances respectively. The initial validation experiment results showed that the designed novel experimental system performed as expected, and that HC emissions actually decreased monotonically among the first five firing cycles of the cold start. The preliminary quantitative analysis revealed that for gasoline-fueled cold starts not all the injected fuel was collected in the exhaust gas. The non-collected fuel was potentially due to fuel wall wetting and piston top impingement, which could be the main reason for the HC emissions. The parametric study found that the main contributing factor of the HC emissions for the very first firing cycle was the injected fuel that did not evaporate in time for combustion but still in time for the emissions. The parametric study also found that the HC emissions increased with injected equivalence ratio. The change in fuel rail pressure had a complicated effect on the HC emissions at the first firing cycle. The increase in injection times, from 2 to 4 injections given the same amount of total injected fuel, did improve the fuel evaporation and combustion status, and led to higher power output and lower HC emissions given the same injected fuel mass. The study showed that the key to mitigate the HC emissions during the GDI engine cold start was improving the fuel evaporation and air-fuel profile, so as to minimize the fuel wall wetting and piston top impingement effect.Item End-region behavior of precast, prestressed concrete I-girders employing 0.7-inch diameter prestressing strands(2016-08-11) Salazar, Jessica Lauren; Bayrak, Oguzhan, 1969-; Hrynyk, TrevorPretensioned concrete girders are currently fabricated using 0.5- or 0.6-in. diameter prestressing strands. In recent years, however, it has become of interest to employ larger-diameter 0.7-in. diameter strands to reduce the number of strands and improve the efficiency of pretensioned concrete members. Such a transition requires a considerable initial investment that needs to be justified based on the benefits obtained. Furthermore, the use of 0.7-in. strands would increase the stresses within the end-region of pretensioned elements, which could lead to undesirable cracking and impact the serviceability of the girders. The work presented in this thesis consists of 1) a comprehensive parametric investigation to evaluate the benefits and limitations of using 0.7-in. strands in pretensioned bridge girders, and 2) a full-scale experimental study to investigate the behavior of pretensioned concrete girders with 0.7-in. strands at the time of prestress transfer. The parametric investigation was accomplished by designing thousands of bridge girders with different span lengths, concrete release strengths, and transverse spacings. The results showed that the most noticeable benefit of 0.7-in. strands over 0.6-in. strands was a reduction of up to 35 percent in the number of strands. However, the difference in the total weight of prestressing steel was insignificant. Increasing the release strength of concrete, at least to 7.5 ksi, was found essential to observe benefits in design aspects other than the number of strands. The experimental investigation involved the fabrication of two Tx46 and two Tx70 specimens at the Ferguson Structural Engineering Laboratory. All specimens employed 0.7-in. strands on a 2- by 2-in. grid and the standard detailing currently used for girders with smaller-diameter strands. The observed crack widths in the specimens upon prestress transfer did not exceed those typically observed in Tx-girders with smaller-diameter strands. Therefore, the use of 0.7-in. strands does not seem to trigger a need to modify the end-region detailing in Tx-girders. However, noticeably greater bursting and spalling forces were observed in the end regions of the specimens compared to the demands predicted by AASHTO LRFD provisions. The measured 24-hour transfer length from the specimens also exceeded estimates by AASHTO LRFD and ACI 318-14 provisions.