1,721,001 research outputs found
Definition and Validation of a Zero-Dimensional IC Engine Model for Assessing the Performance of Different Methane-Hydrogen Mixtures
Full text linkTo decarbonize the maritime transport sector, a solution inspired by the automotive industry involves using a solid oxide fuel cell (SOFC) in conjunction with an internal combustion engine. For optimal emission efficiency, the internal combustion engine is fueled with a primary fuel, typically methane already on board for feeding the SOFC, plus anode off-gases from SOFC, which are a mixture of variable composition of hydrogen, carbon dioxide, and carbon monoxide. To assess the performance of the integrated system (SOFC+ICE) and subsequently search for an optimal set-up, it is useful to use a zero-dimensional model of each component of the system. Particularly, the internal combustion engine model must balance speed of execution with flexibility in terms of fuel composition, engine dimensions, and other relevant parameters. In this study, an engine model originally developed for gasoline-fueled ICE, is adapted for variable methane-hydrogen mixtures. The model is validated against experimental data measured on an engine operating with similar mixture compositions and available in the literature
The anharmonic force field of (cis)-1-chloro-2-fluoroethylene
No full textA comprehensive anharmonic vibrational analysis of cis-1-chloro-2-fluoroethylene and its isotopomers has been performed on the basis of a complete ab initio quartic force field constructed by means of second-order Moller-Plesset perturbation theory (MP2) and the coupled-cluster singles and doubles approach, augmented for structural optimization and harmonic force field by a contribution of connected triple excitations (CCSD(T)). The theoretical force field was scaled by global least-squares fitting to all spectroscopic data and parameters experimentally determined for this molecule. This final force field, employing standard perturbation theory, yields a complete set of spectroscopic molecular constants providing a critical assessment of experimental rotational and centrifugal distortion constants, fundamentals, overtones, and combination bands determined over many years. Effects of Fermi and Darling-Dennison resonances were included by matrix diagonalization
Thermal Efficiency Enhancement for Future Rightsized Boosted GDI Engines - Effectiveness of the Operation Point Strategies Depending on the Engine Type
Full text linkInternal combustion engines are the primary transportation mover for today society and they will likely continue to be for decades to come. Hybridization is the most common solution to reduce the petrol-fuels consumption and to respect the new raw emission limits. The gasoline engines designed for running together with an electric motor need to have a very high thermal efficiency because they must work at high loads, where engine thermal efficiency is close to the maximum one. Therefore, the technical solutions bringing to thermal efficiency enhancement were adopted on HVs (Hybrid Vehicles) prior to conventional vehicles. In these days, these solutions are going to be adopted on conventional vehicles too. The purpose of this work was to trace development guidelines useful for engine designers, based on the target power and focused on the maximization of the engine thermal efficiency, following the engine rightsizing concept. The originality of the present work stands in the comparison of the effectiveness of the most common strategies adopted today between two types of engine. The chosen engines for this study were modern boosted GDI engines, in line with the current automotive market, designed by CAD at the University of Bologna. 3D CFD computations of non-reacting flows were carried out by means Fire Code 2020 by AVL. The paper aimed to numerically investigate the rightsizing concept depending on the target level of power: two levels of power were chosen, 290 kW and 120 kW respectively, typical the former one of a high-power engine, the last one of an engine more devoted to efficiency purposes. The two engine bores were selected based on the common automotive solutions depending on the target power: 84 mm for the high-power engine, 75 mm for the other engine. Once fixed the bore value and pursuing the maximization of the thermal efficiency, a study on the possible geometries was performed, searching for the best stroke-to-bore ratio S/B: the long stroke engine design finds its limit in the maximum average piston speed, depending on the engine regime at maximum power. Then, the study was moved to the compression ratio increase and the adoption of over-expanded cycles, both aimed to increase the thermal efficiency. For solving the knocking issues arising from the adoption of increased compression ratio, the water injection strategy was analyzed too. Finally, some considerations were deduced on the effectiveness in applying the over-expanded cycles to the two different types of engine: the critical point to be solved is if the applicability and thus the effectiveness of the over-expanded cycles depend on the engine type
PWI and DWI Systems in Modern GDI Engines: Optimization and Comparison Part I: Non-Reacting Flow Analysis
Full text linkCurrently engine designers are focusing their attention on the improvement of the engine efficiency, led by the reduction of in-cylinder temperature and the adoption of stoichiometric combustion in the full range of the engine operation map. The most demanding points are those close to full power: water injection is thought to help in fulfilling this goal, thus contributing towards more efficient engines. To perform a rapid optimization of the main parameters involved by the water injection process, it is necessary to have reliable CFD methodologies capable of capturing the most important phenomena. In the present work, a methodological approach based on the CFD simulation of non-reacting flows of S.I. GDI turbocharged engines under water injection operation is pursued using AVL Fire code v. 2020. Port Water Injection (PWI) and Direct Water Injection (DWI) have been tested for the same baseline engine configuration and they have been run at full power condition, at the same rated power engine speed by varying: i) the injection pressure; ii) the injection timing (water injection phasing has significant effect on the water evaporation rate and on its impact on walls); iii) the normalized water injected mass on the stoichiometric fuel mass. The main results have been checked in terms of evaporation rate, cooling temperature, and efficiency, also considering the mixture quality and the fluid-dynamics aspects, in particular the possible degeneration of the turbulence level during the water injection process. The main aim of these simulations is to maximize water injection benefits and minimize possible disadvantage, such as primarily oil dilution and incomplete water evaporation to reduce water tank volume and refilling frequency. Water injection has demonstrated to allow to adopt higher compression ratio with limited penalties on performance. Therefore, for pursuing the target of improving the engine efficiency over the whole engine map and maintaining good performance level, the geometric compression ratio of the baseline engine has been increased. The adopted CFD methodology has shown to be able to capture the thermodynamic effects of water injection
Millimeter-wave and infrared spectrum of brc15n: Equilibrium structure of cyanogen bromide
No full textThe rotational spectra of 79Br12C15N and 81Br12C15N in the low-lying 01 10, 1000, 0200, and 0220 vibrational states have been observed in the millimeter-wave region, and the ν3 fundamental band of both 14N- and 15N-containing species has been recorded from 2125 to 2215 cm-1 with a diode laser spectrometer. A very precise equilibrium structure has been calculated for cyanogen bromide using the obtained data together with those already known for the normal isotopomers. The ground state rotational spectra of 79Br13C15N and 81Br13C15N have been also observed, so that r0, rs, and rm structures could be evaluated from the ground state moments of inertia of eight different isotopic species. © 1995 Academic Press, Inc
Nuclear quadrupole tensors for Cl-35 and Cl-37 in cis-1-chloro-2-fluoroethylene obtained by detection of perturbation-allowed Delta J=2 and Delta J=3 transitions
No full textThe nuclear quadrupole hyperfine structure in rotational transitions of cis-1-chloro-2-fluoroethylene was measured for both Cl-35 and Cl-37 containing isotopomers in the millimeter-wave region. Near degeneracies of the 9(3,7) and 10(2,9) levels of (ClHC)-Cl-35=CFH and of the 19(9,10/11) and 17(10,7/8) levels of (ClHC)-Cl-37=CFH cause strong perturbations of the hyperfine patterns and give rise to perturbation-allowed DeltaJ = 2 and DeltaJ = 3 transitions. Lamb-dip measurements of such perturbed hyperfine patterns and of forbidden DeltaJ = +2 and perturbation-enhanced DeltaJ = 0 transitions of (ClHC)-Cl-35=CFH provided an accurate determination of chi (ab), the off-diagonal element of the inertial nuclear quadrupole tensor. For (ClHC)-Cl-37=CFH, chi (ab) was determined for the first time thanks to the observation of perturbed hyperfine patterns and of forbidden DeltaJ = +3 and DeltaJ = -2 transitions. Additional measurements of hyperfine structures led to improved values for the diagonal elements of the chi tensor of both Cl-35 and Cl-37. Moreover, the complete inertial nuclear quadrupole tensor was evaluated from the field gradient at the chlorine nucleus computed by using the Multi-Configuration Self-Consistent Field (MCSCF) approach and employing basis sets of triple-zeta quality: very good agreement with the experiment was obtained. (C) 2000 Academic Press
Hyperfine structure of J = 1 ← 0 transition of 13CO
No full textAs outlined by Klapper et al., highly accurate rotational transition frequencies of 12C16O and also of the rare isotopomers of CO are desirable because this molecule has a great importance not only as a secondary calibration standard, covering the millimeter region up to the far infrared, but also in the atmospheric and astrophysical chemistry
Numerical study towards smoke-less and NOx-less HSDI diesel engine combustion
No full textThis paper explores the possibility to extend the lowerature combustion concept developed for low load conditions to medium load conditions of HSDI DI Diesel engines. The aim is to understand which is the limit of conventional Diesel combustion towards smoke-lees and NOx-less conditions. The present research is based on numerical simulations performed by using the Kiva-3 code updated with physical sub-models. The combined influence of EGR cooling and EGR rate on combustion characteristics and emission formation is analyzed. Then, possible improvements to mixture formation are discussed with particularly emphasis on the use of multiple injection. The calculations show that smoke-less conditions by lowerature combustion cannot be achieved at medium load and therefore a great role is played by mixture formation. Simulations have revealed that promoting leaner mixtures during spray combustion with further significant benefits on soot engine-out emissions is difficult to accomplish. Copyright © 2002 Society of Automotive Engineers, Inc
Molecular structure of cis-1-chloro-2-fluoroethylene from ab initio calculations and microwave spectroscopy
No full textThe molecular structure of cis-1-chloro-2-fluoroethylene has been investigated both theoretically and experimentally. As far as ab initio computations are concerned, the equilibrium geometry has been evaluated using the coupled-cluster approach [CCSD(T)] and basis sets of triple and quadruple zeta quality. Accurate results are presented. A recommended equilibrium geometry, obtained by adding ad hoc corrections, is also given. The centimetre and millimetre-wave spectra of the following 8 isotopomers have been observed: (CDCl)-Cl-35=CHF, (CDCl)-Cl-37=CHF, (CHCl)-Cl-35=CDF, (CHCl)-Cl-37=CDF, (CDCl)-Cl-35-CDF, (CDCl)-Cl-37-CDF, (CHCl)-C-13-Cl-35-CHF, (CHCl)-Cl-35=(CHF)-C-13. Ground state rotational and quartic centrifugal distortion constants and diagonal elements of the nuclear quadrupole tensor (for both Cl-35 and Cl-37) have been accurately determined. The structure of cis-1-chloro-2-fluoroethylene has been experimentally determined for the first time by isotopic substitution, employing three independent methods. A comparison between the experimental and theoretical geometry is also presented
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