When allocation “back out” agreements can become “lose out” agreements

Experimental and numerical investigation on inner flow and spray characteristics of elliptical GDI injectors with large aspect ratio

<div class="htmlview paragraph">The tightening legislation in the on-road heavy-duty diesel area means that pollution control systems will soon be widely introduced on such engines. A number of different aftertreatment systems are currently being considered to meet the incoming legislation, including Diesel Particulate Filters (DPF), Diesel Oxidation Catalysts (DOC) and Selective Catalytic Reduction (SCR) systems.</div> <div class="htmlview paragraph">Relatively little is known about the interactions between lubricant-derived species and such aftertreatment systems. This paper describes the results of an experimental program carried out to investigate these interactions within DPF, DOC and SCR systems on a state-of-the-art 9 litre engine.</div> <div class="htmlview paragraph">The influence of lubricant composition and lube oil ash level was investigated on the different catalyst systems. In order to reduce costs and to speed up testing, test oil was dosed into the fuel. Tests without dosing lubricant into the fuel were also run.</div> <div class="htmlview paragraph">Driving distances of up to 115,000 km (based on oil consumption) were simulated in these experiments. Following such treatments, no significant change in the activity of the CR-DPF oxidation catalyst, Diesel Oxidation Catalysts or SCR catalysts were observed. In each case, the distribution of oil-derived species was studied as a function of distance down the catalyst. It was found that the Ca, Zn and P were generally present in higher concentrations at the front of the catalyst, decreasing down the unit. In contrast, sulfur is distributed evenly throughout the length of each catalyst. This is because sulfur can be deposited from the gas phase and is more mobile on the catalyst surface.</div> <div class="htmlview paragraph">Interestingly, when doping high ash oil into the fuel it was found that the back pressure of the DPF system increased rapidly. This is particularly important since it is known that used engine oil is sometimes poured back into the fuel tank for disposal. These results imply that this practice may strongly affect the efficiency of DPF devices.</div> <div class="htmlview paragraph">This rapid increase in back pressure is a consequence of doping the fuel with the high ash oil, since operation of the engine with the high ash oil without doping, or with a low ash oil with doping, resulted in only a gradual increase in back pressure. In addition, the distribution of the ash in the filter was strongly affected when doping the high ash oil into the fuel, in that the ash was uniformly distributed down the length of the filter. In the other experiments carried out here, and in measurements of field-aged filters, the ash thickness increases with distance into the filter. These observations reveal that care needs to be taken when doping oil into the fuel to accelerate the observation of oil-derived effects in DPF systems.</div>

Equal channel angular pressing (ECAP) is one of the most promising processes to fabricate ultra-fine grained materials. The material deformation is affected by die geometry, material behavior, friction and back pressure. The optimum back pressure for 1100Al during ECAP was studied. The effect of back pressure on deformation behavior, effective strain and deformation load were analyzed by using finite element software. The results show that the corner gap between the billet and the die in the external part of the deformation zone decreases and even disappears with the increase of back pressure, which can produce more uniform and larger strain in the billet. The deformation load enhances with the increase of back pressure. From the simulation results, it can be found out that the optimum back pressure for 1100Al pressed in the die of Φ=90° is about 30MPa.

Hydrous ethanol application in engines can not only improve combustion and reduce emissions but also save energy consumption in the production process, which is a potential alternative fuel for engines. However, little research has been conducted on the influences of hydrous ethanol, gasoline, and hydrous ethanol–gasoline blends on spray characteristics, especially the phenomenon of flash boiling. In this investigation, the spray characteristics of hydrous ethanol and gasoline have been conducted using a constant volume chamber system, and the spray characteristics of hydrous ethanol–gasoline blends have been simulated using validated models. The results show that hydrous ethanol fuel is more likely to enter a flash-boiling state in comparison with gasoline. In addition, the spray penetration of hydrous ethanol is higher than that of gasoline, which increases by 10% approximately under the same temperature. Moreover, the spray cone angle of test fuels is between 32 deg and 43 deg and decreases with the increase of back pressure in trend. Besides, the spray projection area of hydrous ethanol and gasoline decreases significantly with the increase of back pressure. In terms of simulation, the spray penetration of E10w, E20w, E50w, and E85w fuels decreases with the increase of back pressure.

Whereas there are case reports of laparoscopy in patients with ventriculoperitoneal shunts, there are no studies assessing the potential failure of shunt valves with the increased intra-abdominal pressure of laparoscopy. This study aims to assess this factor. An in vitro model was used to assess the potential for retrograde failure of ventriculoperitoneal shunt valves in a commonly used shunt. Nine shunts were subjected to graded increases in back pressure and observed for retrograde valve leak. None of the shunts tested showed any signs of leak associated with the increased back pressure. However, disruption of shunt seals was noted in seven of the nine shunts, occurring at the minimal pressure of 80 mmHg. There appears to be minimal risk of retrograde failure of the valve system in the ventriculoperitoneal shunt tested. However, tests on different types of ventriculoperitoneal shunts would be needed to confirm these results if laparoscopy is to be considered safe in patients with ventriculoperitoneal shunts in situ.

Petroleum fuel consign has been lessening at a very high proportion. Almost all automobiles depend upon an IC engine driven by petroleum fuels. As much as the number of automobiles is developing in this modern world, it is obligated to reduce fuel expenditure. One of the ways to do this is to diminish the car's drag. Among a manifold process of reducing drag, using Vortex Generators is one. Delta-shaped vortex generators are used at the rear trunk of the range rover, where the flow separates. K-epsilon turbulent model in ANSYS-Fluent 19.2 software is used to imitate the airflows. This work observed the number and spacing between successive vortex generators based on comparing drag coefficient values. The contours of static pressure and velocity magnitude were also observed for each model. When the vortex generators were attached, the pressure coefficients at the rear trunk began to increase, confirming the increment in back pressure. Hence, the increase in back pressure indicates a reduction in the drag coefficient. It has been found that a combination of 7 vortex generators is the optimum solution. The devices work better at a higher velocity than the lower velocity without affecting vehicle stability. The vortex - 4 model's drag coefficient was found to be significantly lower than that of the standard model vehicle, which is 0.42877. The Base Model of Range Rover (2020) is my sense of humor, the highest drag coefficient. So vortex generators are commonly used on automobile vehicles to prevent downstream flow separation and improve their overall performance by reducing drag.

Objectives In wells which are producing on intermittent gas lift (IGL), the injected gas cannot sweep the entire liquid volume to the surface from the bottom of the tubing as there is continuously some fluid falling back in the tubing. The fallback can be described as the difference between the volume of the slug at the start of the gas injection and the volume of the actual produced slug at the surface. This fallback of liquid happens due to the fact that the gas has a tendency to flow through the liquid slug and letting the liquid to fall. The intensity of the liquid fallback increases more when there is increase in back pressure at wellhead. In order to minimize this liquid falling back in wells on intermittent gas lift, the sweeping pipe bend technology has been used in the various onshore fields operated by ONGC which has resulted in substantial gains and has been brought out in the paper. Process Gas break through and fallback are affected by three factors including the development of the gas bubble, the velocity of the slug flowing upward in the tubing, and wellhead restrictions caused due to presence of many 90-degree bends. To prevent gas breakthrough and to optimize the liquid fallback to minimum 5-7 % per 1000 feet of lift, it is recommended to maintain 1000 feet/min of minimum velocity of slug. Slower is the velocity of the slug which is moving up in the tubing, the longer time it takes for the gas to break through the liquid. At 1000 feet/min velocity, the wellhead restrictions can result in fallback losses due to breakthrough of gas in the well. In general, the flow path through the Christmas tree into the flowline is rather tortuous, moving first through a tee to the wing valve, then through other 90-degree ells before finally reaching the flowline. These restrictions further result in slowdown of the velocity of the slug thus resulting in more liquid to fallback and subsequently in significant production losses. Results In order to overcome the aforementioned problem and to reduce fallback in an intermittent gas lift well, sweeping pipe bend technology was considered and in the first phase implemented in 5 identified wells of different fields of ONGC Assets. With the help of sweeping pipe bend, the flow pattern becomes streamlined and number of 90-degree bends reduces or eliminates resulting in substantial reduction in the back pressure thus reducing the fall back. The implementation of the technology has resulted in an average liquid gain of 20.3% per well. Various guidelines for successful application of sweeping pipe bend have also been brought out in the paper. Additive Information 650 candidate wells operating on intermittent gas lift have been identified for the implementation of Sweeping Pipe Bends. As per the analysis, the implementation of Sweeping Pipe Bend is likely to result in a liquid gain of about 1000 m3/day from these wells.

A dynamic model for a PZT actuated valveless micropump is presented in this work. The model couples PZT actuation with fluid flow in a flow chamber. Extended Bernoulli equation is used to describe flow dynamics in the inlet and outlet of the micropump. The dependence of the output pressure and flow rate on pump parameters is discussed. For low frequency actuation, the flow rate and back pressure increase as the PZT membrane thickness increases. The flow rate also increases for larger nozzle neck. The back pressure increases as the nozzle neck enlarges, reaches a maximum at about 80 microns, and then decreases when the nozzle neck keeps increasing. Such dependence becomes insignificant for nozzle neck larger than 200 microns. This model also predicts that the neck length has little influence on the back pressure and flow rate.

Uniformity of plasma etching and deposition processes critically depends on the wafer temperature and its spatial variation across the wafer. The goal of this work is to use mathematical modeling to investigate the key factors that determine the wafer temperature and its radial uniformity during plasma etching. Toward this end, a mathematical model of energy transport in and out of a Si wafer in a plasma etching reactor that employs a substrate platen with a He back side cooling arrangement was developed. The possibility of wafer bowing due to high He back side pressure was considered and the effects of ion bombardment flux uniformity, He back side pressure, and different wafer clamping arrangements were studied. While an increase in He back side pressure increases the rate of heat transfer from the wafer to the electrode, excessive He pressure causes the wafer to bow. Bowing increases the electrode‐wafer gap, decreases the heat transfer rate, and adversely affects the temperature uniformity. These effects are most pronounced for large diameter wafers (>200 mm) and are predicted to be very important in the processing of 300 and 400 mm substrates. The manner in which the wafer is clamped to the cooled electrode is another key factor that determines the heat transport at the wafer edge and the radial temperature profile across the wafer. The uniformity of the wafer temperature depends on the heat transport at the wafer edges. Poor thermal contact at the wafer edge leads to a high but uniform wafer temperature; on the other hand, if a good thermal contact is made at the wafer edge, the average temperature is lower but less uniform. Model predictions compared well with the available experimental data.

The increase in hydrogen back pressure unexpectedly enhances the overall dehydrogenation reaction rate of the 4LiBH(4) + YH(3) composite significantly. Also, argon back pressure has a similar influence on the composite. Gas back pressure seems to enhance the dehydrogenation reaction by kinetically suppressing the formation of the diborane by-product.

Coal fired power plants contribute significantly to greenhouse gas emission, notably CO2. A novel method to effectively reduce the amount of CO2 emission is to cofire a high fraction of biomass and coal at oxygen enriched environments. However, this technique has not been demonstrated on a large-scale yet. The objective of this PhD research is to perform a detailed modeling study of combustion of a single biomass particle and to establish reduced models which can be used for describing the main characteristics of pyrolyzing and combusting single biomass particles to be employed in design codes of industrial furnaces. To accomplish the goals of this PhD thesis, the research has been carried out in two main stages. First, the sub-processes involved in the biomass combustion are identified and described with a one-dimensional mathematical model based on conservation of mass, energy and momentum. The model encompasses the kinetics of biomass pyrolysis, homogeneous reactions and heterogeneous char oxidation and gasification reactions, coupled with transient transport equations. Subsequently, this model is implemented in an in-house code and a comprehensive numerical study on pyrolysis and combustion of single biomass particles is conducted. The accuracy of the model is examined by comparing its predictions with several experimental data obtained from the literature on pyrolysis and combustion of various types of single biomass particles. The computer code based on the detailed model allows one to observe time and space evolution of several parameters including biomass and char densities, gaseous species mass fractions, porosity, internal pressure, mass flux of volatiles within the pores of the solid matrix, and temperature. The model is used for simulation of combustion of particles of three common shapes; i.e. slab, cylinder and sphere. The results of the detailed modeling study reveal that the combustion of a single biomass particle at the conditions of industrial furnaces (small particles and high heating conditions) consists of three main sub-processes: preheating, pyrolysis, and char oxidation. Therefore, any simplified/reduced particle model should account for these three processes. In the next stage of the project, simplified models are developed to predict the main characteristics of pyrolyzing and combusting single biomass particles. Initially, the preheating stage is modeled using a time and space integral method, which allows one to convert the partial differential form of the heat transfer equation into an algebraic equation. This treatment is then applied to model the pyrolysis process. Two possible regimes are identified: thermally thin and thermally thick particles. A model is established for both regimes, which consists of a set of algebraic equations. This treatment highly simplifies the pyrolysis model so that it can be used in practical applications, which may involve thousands or even millions of particles. The validation of the simplified preheating and pyrolysis models is carried out using various experiments and the results of the detailed model based on partial differential equations (PDEs). The char particle oxidation and gasification processes as the last stages of the particle combustion process, are modeled using the shrinking core approximation. The accuracy of this model is assessed using the experiments reported in past studies. The model is used to study the dynamics of biomass char combustion at oxy-fuel conditions. The effects of the main process parameters on the maximum particle temperature and burnout time are examined. It is found that oxy-fuel combustion with an oxygen mass fraction of 0.3 and higher may lead to a considerable reduction in particle temperature and burnout time compared to the conventional operating case with air as the gasifying agent. In the last stage of this PhD research, the simplified models of biomass particle pyrolysis and char combustion are combined to establish a reduced model for combustion of a single biomass particle. The accuracy of this simplified combustion model is examined using the measured data available in the literature as well as the results of the detailed model. As a conclusion, the simplified models developed in this thesis for pyrolysis and combustion of single biomass particles are efficient enough to capture the main process parameters, and computationally cheaper than the PDE -based models so that they can be used in the design codes of biomass furnaces.

A single‐phase AC/AC modular multilevel converter (MMC) can interact directly with 25 kV railway grid without a bulky 50 Hz step‐down transformer. This brings in great savings in size and cost. Submodule (SM) voltage balancing of this kind of MMCs remains a major technique issue. This study proposes a voltage‐balancing solution for this scenario which consists of intra‐ and inter‐arm voltage balancing methods. The former combines the advantages of carrier phase‐shifted pulse‐width modulation (PWM) and phase disposition PWM based voltage‐balancing methods. It only uses two proportional regulators, easing the control system significantly. The latter is based on a power channel between the upper and lower arms. It avoids interferences with input/output voltage and current, and gets rid of common mode current component which would be injected into the grid with conventional inter‐arm balancing methods. By assuming perfect voltage‐balancing, a simplified mathematical model is also developed, which reveals more clearly the power conversion relationship. Simulations and experiments verify the proposed voltage‐balancing methods and the mathematical model.

The flight control system design method of wing-in-ground effect aircraft is presented based on robust control theory. With a view to uncertainty of lengthways channels, the simplified mathematical model is constituted for wing-in-ground effect aircraft. According to this simplified model, the lengthways control system is designed. In order to overcome defect of uncertain system, the flight controller of wing-in-ground effect aircraft is designed using robust control theory. Simulation results show that this control method can implement efficiently precision control mission for wing-in-ground effect aircraft as well as preferable robustness.

Mattress is a necessity in everyone’s life. Studies show that the BMI difference is one of the factors affecting the comfort of the mattress. The difference affects the pressure distribution in the contact surface of the mattress. In this study, seven mattresses of different hardness were selected, and pressure distribution test with 72 subjects was carried out to collect the pressure of seven parts of the body. The trend of pressure changing with BMI was got by difference and correlation analysis. It can be concluded that head pressure decreases with the increase of BMI. Back pressure, waist pressure, hip pressure, thigh pressure, calf pressure and whole body pressure increase with the increase of BMI. The research results can provide reference for the mattress design suitable for people with different BMI.

the benefits of exercise and exercise training are numerous, varying from increasing skeletal muscle strength to enhancing cardiovascular and respiratory fitness. These attributes of exercise are key elements to the maintenance of good health and the improvement of athletic performance. But are