A study is presented ofthe influence ofusing mixtures of natural gas andhydrogenin different fractions (0, 25, 50, 75, 100%) on thecombustion velocity and cycle-to-cycle var- iations in a spark ignition engine. The experimental facility consists of a single-cylinder spark ignition engine. Theengine rotational speeds are 1000, 1750 and 2500 rpm. Fuel/air equivalence ratio was kept constant equal to 0.7 during the experiments. A two-zone thermodynamic combustion diagnosis model, based on solving the mass and energy conservation equations, is used to analyze the experimentally obtained pressure com- bustion chamber intheengine. The two-zone model considers a spherical flame front centred at the spark plug, and solves the intersection ofthe flame front with the piston, cylinder head and cylinder wall, in order to provide the values ofthe flame radius corre- sponding to the burned mass volume andthe surfaces for heat to the piston and walls. An automatic procedure based on genetic algorithms is used to determine the optimum pa- rameters needed for combustion diagnosis: Angular positioning and pressure offset ofthe pressure register, dynamic compression ratio, and heat transfer coefficients. The paper focuses on usingthe values ofthe burning velocity computed from the pressure register and especially on the analysis ofthe cycle to cycle variation inthe natural gas/hydrogen fuelled engine, quantified through the standard deviation andthe coefficient of variation ofthe burning speed. Increasing thehydrogen content inthe mixture with natural gas in- creases its burning velocity. This effect is linear with hydrogen fraction, except for very high values ofthe fraction, when theeffectofhydrogen dominates combustion. Addi- tionally, andof practical importance, increasing thehydrogen fraction reduces the relative dispersion ofcombustion. This effectofhydrogen addition on reducing combustion vari- ability is evident from 25% hydrogen content.
million tons for optimistic scenarios inthe year 2030 . The reduction of emissions is considered to be more a matter ofengine design than fuel technology. The adverse effects ofthe general degradation ofcombustionperformancein kerosene for over 25 years cause emissions andengine life span to be in need of consideration, and this has led to a rapid demand for new and alternative fuel . These rapid changes bring a serious effectin creating global carbon neutrality, where in this case, improvements in carbon engine outputs alone will not work. Adaptation and current work with new ‘alternative energy’ with zero carbon distributions will help to reduce air pollution that directly impacts the atmosphere . Alternative energy in commercial aviation can be defined as using biojet fuel, gas to liquid, andhydrogen cells. The use of battery andhydrogen cells addresses some issues such as weight limitation, and thus it will not be discussed in this paper. Similarly, GTL or gas to liquid will not be considered in this article as it has an adverse feedback on the environment .
This paper shows the results ofan investigation carried out to assess the application of different fuels produced by blending diesel fuel with methyl ester obtained from mixture of 75% (v/v) sunflower oil and 25% (v/v) used cooking oil on a Kubota agricultural indirect injection diesel engine, natural aspirated, and with a rated horsepower of 19.7 kW. Seven fuels, namely diesel fuel; 90:10, 80:20, 70:30, 50:50, 25:75 and 0:100 (%v/v) blends were prepared and tested for theperformanceofthe diesel enginein accordance with the standardised OECD test code 2. The test results showed that theperformanceoftheengine was satisfactory without a significant reduction inpower output and torque with blends smaller than 50%. Fuel consumptions with biodiesel were higher than that when fuelled with diesel but differences were not very marked up to 30% blends. As the reduction oftheengine thermal efficiency was less than the corresponding reduction in heating value ofthe different biodiesel blends, the latter resulted in a more complete combustionin comparison with diesel fuel. The oxides of nitrogen (NO x ) emissions were found to be reduced as the biodiesel concentration increase,
The results also show the high potential ofhydrogen fueled buses to reduce GHG emis- sions. However, if electrolysis with the average carbon foot print ofthe today’s Argentine grid is used, thehydrogen fueled bus platforms have no greenhouse gas emission edge over CB. But assuming 2025’s composition ofpower generation sources, the GHG emission reduc- tion using electrolysis is higher than using a SMR. Scenario four has shown the potential ofhydrogen fueled buses using renewable energy source inthe production of electricity. Further- more, scenario four has shown, looking at GHG emissions, that the efficiency becomes less important when the amount of renewable energy sources inthepower generation production increase. Using 100% renewable energy sources, the efficiency benefit do not lead to benefits inthe avoidance of GHG emissions.
A methodology is presented for studying the influence ofusing alternative fuels on the cycle-to-cycle variations of a spark ignition engine which has been fuelled with mixtures of natural gas andhydrogenin different proportions (0e100%). The experimental facility consists of a single-cylindrical spark ignition engine coupled to an asynchronous machine with a constant engine rotation speed of 1500 rpm. A thermodynamic combustion diag- nostic model based on genetic algorithms is used to evaluate thecombustion chamber pressure data experimentally obtained inthe mentioned engine. The model is used to make the pressure diagnosis of series of 830 consecutive engine cycles automatically, with a high grade of objectivity ofthecombustion analysis, since the relevant adjustment pa- rameters (i.e. pressure offset, effective compression ratio, top dead center angular position, heat transfer coefficients) are calculated by the genetic algorithm. Results indicate that thecombustion process is dominated by the turbulence inside thecombustion chamber (generated during intake and compression), showing little dependency ofcombustion variation on the mixture composition. This becomes more evident when relevant com- bustion variables are plotted versus the Mass Fraction Burned of each mixture. The only exception is the case of 100% hydrogen, due to the inherent higher laminar speed ofhydrogen that causes combustion acceleration and thus turbulence generation.
thepowerand efficiency decrease in both cases (k = 1 and k = − 1). It is interesting that the minimum value for the relaxation time at √ τ = α/β is observed for the case k = 1. On the other hand, the efficiency is constant (case k = 1), and is a decreasing function (case k = −1) ofthe ratio β/α, whereas the stability, in both cases, declines as α/β → 0 or β/α → 0. Physically, the limits β/α → 0 and α/β → 0 correspond to reversible absorption of heat and reversible release of heat, respectively. Our local analysis reveals that in these limits, for the cases k = 1 and k = −1, any small perturbation intheinternal temperature (y inthe case of absorption and x inthe case of release) decays very slowly—in fact, the time to return to the steady-state temperature is infinity. For this reason the system loses its stability. At the same time, the temperature (x inthe case of absorption and y inthe case of release) decays almost instantaneously.
In this project would be explained the principal modifications to aninternalcombustionengine with a turbocharged, taking into account the way a four-stroke engine works as shown on the Figure 1. Four-Stroke Engine Cycle. It all stars at the admission ofthe air to the cylinders, this step is called “Intake” in which air comes inandthe fuel is injected, in this step there are different aspects to be modified, you can increase the amount of air that enter in to the chamber, you can also increment the amount of fuel that enter in to the chamber or you can decrease the temperature ofthe air coming in, to have air with a higher density.
In this article a comparative study of some performance characteristics and parameters ofaninternalcombustionengine operating with gasoline and with natural gas is presented. The software of calculation of chemical equilibrium Stanjan ® , for the determination ofthe composition ofcombustion products andthe calculation ofthe flame temperatures, is implemented. For the calculation of other performance parameters, like the indicated mean effective pressure, the simulation of a motor is carried out by means of software Engine Simulation Program ® . The analysis and interpretation ofthe results are established and conclusions in relation to the advantages and disadvantages ofthe conversion of a gasoline motor to natural gas, are planted from the thermodynamic perspective.
The government’s internal control system consists of five elements, namely : control environment (a condition in government agencies to build awareness of all the personnel ofthe importance of controlling an organization in carrying out activities under his responsibility thus increasing the effectiveness ofinternal controls through enforcement of integrity and ethical values, commitment to competence, leadership conducive, the establishment ofan organizational structure that fits the needs, delegation of authority and appropriateresponsibility, and developing and implementing sound policies on human resource development), Risk assessment (assessment of possible situations that threaten the achievement ofthe goals and objectives of government agencies whose activities include the identification, analysis, and manage the risks that are relevant to the process or organizational activities), Control activities (control activities are necessary action to address the risk andthe implementation and execution of policies and procedures to ensure that the risk prevention has been effectively implemented), Information and communication (Information is data that has been processed to be used for decision making inthe context of implementation of tasks and functions of government agencies, while communication is the process of delivering a message or information using a particular symbol or emblem either directly or indirectly to obtain feedback), and Monitoring (process of assessing theperformance quality ofinternal control systems and processes that provide confidence that the findings of audits and other evaluations soon followed.)
This paper aimed to evaluate the behavior ofan Otto Cycle internalcombustionof a 1.6 L engine measuring its performance by the energy and exergy balance. The energy calculation was developed in a previously set route at a constant speed of 50 km/h and 90 km/h. It was determined, that the analysis ofthe energy and exergy balance contributes to recognize theperformanceofaninternalcombustion after the experimentation based on observation, measurement, methods of induction, deduction and synthesis. Also, it was resolved that theengine has an average energy efficiency of 27.57 % for a speed of 50 km/h, while the total exergy flow ofthe system is 22 %. Therefore, there is no significant difference with the efficiency results at 90 km/h.
The basic intuition that one must recall inthe measurement of a plant productive efficiency from DEA estimation is the following: consider a set of plants that use different combinations of inputs to produce one unit of a homogeneous output (electricity fits concept). If every plant is producing efficiently, all are in best practice isoquant. Inthe case that one plant is demanding more inputs in order to produce one unit of output, we are able to say that the plant is inefficient to the best practice isoquant. Data Envelope Analysis (DEA) allows us to calculate a measure of plant technical efficiency. In particular, DEA uses a sequence of linear programs to construct a transformation frontier to compute efficiency measures relative to this reference technology. Inefficiency is measured as the ratio ofthe radial distance from the origin to the combination of input usage inan input space andthe radial distance from the origin to the frontier, which is a isoquant made up ofthe input combinations ofthe remaining group of firms which are considered efficient (i.e. pair wise input - one output inan Cartesian plane). This ratio will take a value between zero and one. If a plant has an efficiency score of 1, one says that is technically efficient. If the score is less than 1 then the plant is inefficient. For instance if plant B has a score 0.8 and plant A has a score of 1, then plant B is 20% inefficient relative to the production frontier. That is if plant B uses its inputs as plant A, then she would increase its output in 20%. The above measurement is called as non-parametric input-oriented efficiency scores. 13
The analysis performed inthe previous sections suggests that theeffectofthe BRF/MRP merger was in general favorable to the Argentine hamburger consumers, since it induced a price decrease and a quantity increase (especially for the brands manufactured by BRF). This result, however, is not due to a reduction inthe degree of unilateral market power that the merging company had inthe Argentine hamburger market. Quite the contrary, that degree of market power seemed to have increased due to the merger. Nevertheless, the BRF/MRP transaction seems to have induced an important cost reduction that was partially passed through consumers, probably influenced by the fact that other hamburger producers (e.g., Swift, Paladini, etc.) may have increased their productive efficiency levels as well.
This article reports the initial findings ofan MA in Applied Linguistics on theeffect collaborative and individual strategic planning have on performanceofan oral task by young learners of English as an L2 in Brazil. Strategic planning (Ellis, 2003, 2005) is an important concept within the task-based approach (TBA), as this condition may trigger metacognitive processes.Yet, only a few studies have had young learners of English as participants in strategic planning research. The participants, teenage learners,enrolled inthe second year of a public high school in Florianópolis (Brazil), performed two monological oral tasks under two different planning conditions: (a) collaborative, and (b) individual. The oral messages sent using WhatsApp were analysed in terms of accuracy, fluency and outcome (pragmatic). In addition, the participants filled in post-task questionnaires after theperformanceof each task, aiming at unveiling their perception on the conditions and tasks. In this paper, data from the pilot study as well as some preliminary results were analysed. In spite ofthe absence of statistically significant results for accuracy and fluency, results indicated a trend supporting the collaborative work condition. While, the qualitative data showed strong support for the collaborative planning condition. These initial findings, in general, support the use of L2 oral tasks involving strategic planning inthe public school context.
evolution equations along the trajectories (14)- (16) are expressed for each droplet class with use made ofthe Eulerian differential operator d/dt — d()/dt + v'j • VQ. This continuum formu- lation is often simpler than formulations involving tracking of individual droplets and greatly facili- tates analyses of laminar sprays. However, the continuum description ofthe liquid phase is known to be inadequate for addressing inertial sprays with multiple crossings of droplet trajecto- ries, as occurs, for example, in turbulent flows or inthe presence of recirculating flow regions when the particle size is not small enough. Although for some laminar flow configurations, such as those considered in Sections 6 and 7, introduction of specific modifications to the formulation renders the Eulerian description valid, methods based on Lagrangian descriptions ofthe liquid phase are in general needed inthe presence of droplet cross- ings. A promising alternative approach for tack- ling the crossing of droplet trajectories in inertial sprays, based on field formulations ofthe liquid phase, employs quadrature methods of moments to solve the kinetic spray equation . Despite the significant progress made recently inthe devel- opment of these formulations [46,47], more work remains to be done to warrant full applicability to spray-combustion problems .
Daniel Yupanqui Concha. Patterns and Determinants of Immigrants’ Internal Mobility: An Analysis ofthe Foreign Born inthe Chilean Social Support Registry. Tesis, Magíster en Economía Agraria y Ambiental, Facultad de Agronomía e Ingeniería Forestal. Pontificia Universidad Católica de Chile. Santiago, Chile. 48 pp. This study describes the mobility patterns of foreign immigrants in Chile, beginning with their first location of residence and their later movements to other locations within the country. The study identifies how personal and territorial characteristics interact and correlate with individual location decisions, both when entering the country andin subsequent movements. Using panel data at the individual level from Chilean welfare agencies – the Ficha de Protección Social (FPS) andthe Registro Social de Hogares (RSH) – for the period 2007-2018, an OLS and Logit models was estimated accounting for different aspects ofthe migration decision, the main results are as follows: (1) immigrants have a higher probability of inter-regional movement than native Chileans; (2) employment- related factors (such as the territorial percentage ofthe work force in mining) and income are the main drivers related to residence change; (3) the presence ofthe mining industry is key inthe decision ofthe foreign-born to select their first location of residence in Chile, andin subsequent movements; (4) foreign-born living in Santiago have a higher probability to remain there compared to the native born; (5) among foreign born, women and younger people are more likely to move; and finally (6) that there is a positive though small relationship between internal movements and education.
This paper investigates the impacts of wall heating conditions on heat transfer perform- ace for a rotating channel with one side smooth and one side roughened by 45 degree inclined ribs. Previous experimental and numerical studies for only ribbed wall heated case showed that rotation has significantly negative impact on heat transfer performance. In order to investigate this uncommon behaviour, RANS simulations were conducted un- der three different wall heating conditions in present study: ribbed wall heated, all walls heated and adiabatic conditions. Numerical results show that the uneven wall heating condtions has negligible impact on stationary case, however, it has a large influence on rotational cases, in both the heat transfer andthe fluid field. This is because in rotating cases, uneven heatings result in different buoyancy effects on trailing and leading walls that alter the main flow velocity profile. As a consequence, also secondary flows and heat transfer performance are affected.
The purpose of this study is to compare and examine theperformanceofanengine, using gasoline with 92 octanes (Super), 87 octanes (Extra) and two volume mixtures of these two types of gasoline, the first one had 50% of volume of each type, the second one had a volume value of 70% of Super with 30% of Extra. To evaluate theperformanceoftheengine, a dynamometer was used to obtain the characteristics curves ofpowerand torque, a gas analyzer was used to determine the level of emission of pollutant gases from theengine (CO, CO 2 , HC, y NOx), finally an
This research was made in Cuenca at 2500 meters above sea level (masl), and it studied the influence ofthe use of different types of spark plugs in a spark-ignition engine on the mechanical performanceoftheengine, the pollutant emissions, and fuel consumption. Six types of spark plugs that are available inthe national market are made of differ- ent materials, have different thermal properties, and have different electrode openings. In addition, the mechanical performanceofthe engines and their fuel consumption were evaluated through dynamometer testing. Moreover, the polluting emissions were measured under the static test protocol established by the NTE INEN 2203 and with an 11 km route test in urban areas and on highway based on the New European Driving Cycle. The research showed that a specific spark plug increases 16 % oftheengineperformance due to not only some factors such as less pollution, better cold behavior, lower fuel consumption, but also maintains the torque andpowerofthe vehicle. In addition, this spark plug generates savings on maintenance and annual fuel consumption.