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441.
J. Abraham 《International Journal of Automotive Technology》2011,12(5):721-732
Under light-load conditions in early-injection stratified-charge compression-ignition (SCCI) engines, excessive premixing
can lead to undesirable levels of unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions. Optimal stratification can
reduce these emissions. In this work, the effects of changes in swirl, injection pressure, injector hole-size and number of
holes, injection timing, and piston geometry on stratification are computationally investigated. It is shown that these parameters
affect the stratification through their influence on the rate of spray penetration, drop vaporization, and fuel/air mixing.
The outcome is characterized by examining the evolution of the spatial distribution of the fuel vapor in the chamber and its
mass-based distribution function. All other parameters remaining the same, decreasing drop size leads to faster vaporization
and richer mixtures. Increasing penetration leads to greater spreading and leaner mixtures. Increasing spray included-angle
leads to greater spreading and leaner mixtures. Increasing injection pressure leads to increased mixing and leaner mixtures.
Increasing injector hole-size leads to richer mixtures at lighter loads because the duration of injection is reduced and the
fuel is confined closer to the axis. Increasing swirl leads to faster breakup of the head-vortex and confinement of the fuel
closer to the axis, and hence richer mixture. 相似文献
442.
In an HLA (hydraulic lash adjuster) piston engine, “pump up” can occur when a valve is opened by the HLA when it should be
closed. HLA pump up is more frequently encountered with exhaust valves than with intake valves. When HLA pump up in occurs
in the exhaust valve, exhaust gas from the exhaust manifold enters the cylinder on the intake stroke, and fresh air-fuel mixture
exits through the exhaust manifold on the compression stroke and is burned in the catalyst, causing partial burning, misfire,
catalyst melting and power drop. HLA pump up occurs when the force on the valve from the HLA is higher than the force on the
HLA from the valve. HLA pump up is related to design parameters, such as oil pressure, rocker ratio, spring load, spring surge,
and both intake and exhaust valve timing. In this study, valve lift and load on a roller finger follower were measured at
varying engine firing conditions to evaluate HLA pump up. The results indicated that effective measures to reduce HLA pump
up include a higher rocker ratio, a lower oil supply pressure to the HLA, a higher spring installation load and a lower spring
surge. 相似文献
443.
Gerotor pumps are widely used in the automotive industry for engine oil lubrication, due to their high volumetric efficiency
and smooth pumping action. In many cases, the lubricating oil from the sump is mixed with contaminants, such as dust and tiny
solid particles, or becomes thickened, due to aging. These problems will lead to critical situations, such as increased noise,
enhanced wear and erosion, and poor lubrication of the engine. These critical situations were studied by conducting a detailed
CFD integrated investigation on a gerotor pump’s performance at different operating conditions in three phases, and the results
are presented in this paper. In first phase, a CFD model of a gerotor pump was developed with a dynamic mesh for the rotary
movement of both the inner and outer rotors. The effects on pump flow rate of important parameters, such as rotor speed, fluid
viscosity and number of ports, were simulated using non-contaminated oil at room temperature and an elevated temperature of
140oC. The relationship between flow rate and pressure at different rotor speeds was predicted and validated with test data
for further parametric study. The pressure ripples at different time steps were measured at different angular positions of
the rotors to examine the model accuracy. It was found that the flow rate increased and pressure pulsation, as well as flow
recirculation, was reduced when ports were added to the cover plate. A suction pipe with a strainer was added for the second
phase to capture the undesired changes in flow behavior, such as cavitation, which is caused by negative suction at the inlet
region of pump. A suitable size for the inlet suction pipe for this pump was chosen after performing tests to characterize
the flow behavior with single and double ports. Next, the relationship between pressure drop and strainer porosity was determined
using different porosity values for the strainers. In the final phase, oil with different concentrations of solids was simulated
to measure the effect of solid particles on flow rates and pressure losses. It was observed that the intensity of the recirculation
was reduced at the suction end at the higher concentration of 0.04%, due to particle inertial effects. It was also found that
particle size distribution affected the overall efficiency and pressure head of the pump. 相似文献
444.
Breakup modeling of a liquid jet in cross flow 总被引:3,自引:0,他引:3
K. -S. Im K. -C. Lin M. -C. Lai M. S. Chon 《International Journal of Automotive Technology》2011,12(4):489-496
We propose a novel breakup model to simulate the catastrophic breakup regime in a supersonic cross flow. A developed model
has been extended from an existing Kelvin-Helmholtz/Rayleigh-Taylor (K-H/R-T) hybrid model. A new mass reduction rate equation,
which has critical effects on overall spray structure, is successfully adopted, and the breakup length, which is an important
parameter in existing model, is replaced by the breakup initiation time. Measured data from the supersonic wind tunnel with
a dimension of 762×152×127 mm was employed to validate the newly developed breakup model. A nonaerated injector with an orifice
diameter of 0.5 mm is used to inject water into a supersonic flow prescribed by the momentum flux ratio of the liquid jet
to free stream air, q
0
. The conservation-element and solution-element (CE/SE) method, a novel numerical framework for the general conservation law,
is applied to simulate the supersonic compressible flow. The spray penetration height and average droplet size along with
a spray penetration axis are quantitatively compared with data. The shock train flow structures induced by the presence of
a liquid jet are further discussed. 相似文献
445.
OSEK OS (Offene Systeme und deren Schnittstellen für die Elektronik in Kraftfahrzeugen Operating System) is an open, real-time
operating system standard for ECU software in vehicles. Because it was originally designed to be used in an extremely resource-constrained
environment, an OSEK-compliant operating system must incur low processing overhead and memory usage. Unfortunately, as OSEK
OS has evolved over time, it now specifies nontrivial kernel features along with multiple conformance classes and application
modes. This may lead to unwanted dynamic resource usage in a system using OSEK OS unless the standard is carefully interpreted
and designed into an OSEK OS implementation. In this paper, we analyzed the various kernel features of OSEK OS and their interactions
to identify areas in the standard that warrant further resource usage optimization. In particular, we attempted to reduce
the run-time memory footprint. Based on our analyses, we present two kernel mechanisms: (1) stack sharing among tasks and
(2) light-weight ready queue handling specialized for OSEK OS conformance classes. We also offer implementation methods for
the proposed mechanisms by extending OIL and associated tools. Finally, we show the effectiveness of the proposed mechanisms
via extensive experiments. Our mechanisms allow OSEK-based systems to use only 36% of the memory requirements of conventional
OSEK-based systems on average. 相似文献
446.
Model referenced adaptive control to compensate slip-stick transition during clutch engagement 总被引:1,自引:0,他引:1
Clutches are widely used in various vehicle powertrains. The engagement process of a friction clutch has three phases, i.e.,
open, slipping, and sticking. Transitions between different phases introduce a discontinuity to the powertrain dynamics, which
has been neglected in previous research. A model referenced adaptive controller (MRAC), based on Popov hyper-stability criterion,
is designed to compensate the discontinuity. MRAC adjusts the frictional torque along with the errors of the state variables
compared with those of a referenced model. The designed MRAC is applied to a clutch in a bus. Simulation and experimental
results under fast and slow startup cases show that MRAC can simultaneously reduce vehicle jerk and frictional dissipation
when compared with the conventional controller. 相似文献
447.
不同加载方式的斜齿轮接触分析 总被引:2,自引:1,他引:1
尹长城 《湖北汽车工业学院学报》2011,25(2):28-31,42
以一对相互啮合的渐开线斜齿轮为研究对象,通过APDL语言生成参数化几何模型,研究映射网格划分方式并建立了斜齿轮接触的有限元模型,基于非线性接触算法在不同加载方式下对齿轮啮合齿面的接触应力进行了分析,将仿真与赫兹计算结果进行了比较,讨论了不同加载方式对接触应力的影响. 相似文献
448.
Jinggao Li I. Kim S. Lee S. Han C. Lee S. Cheon W. Lee K. An G. Cho J. Hwang D. Mun 《Journal of Marine Science and Technology》2011,16(1):76-83
In the shipbuilding industry, different computer-aided design (CAD) systems are used for different design domains, structure, and outfitting. We need to exchange data among different CAD systems such as Tribon, AutoCAD, Intergraph or PDMS to complete the whole design and production process. There are two approaches to data exchange. One is direct translation; the other is indirect translation, which is based on a neutral format. If we use a neutral format, the data specification is open to the public and the design model can be used by other CAD systems, including next-generation CAD systems. In this paper, we propose an indirect method that uses ISO 10303 (STandard for the Exchange of Product model data) AP227 and ISO 15926 to define neutral formats. A separate ShapeDB is constructed to manage the geometry information, referenced to the catalogue data defined by ISO 15926. An experimental implementation for data exchange between Tribon and PDMS is described. 相似文献
449.
Experimental assessment of the ultimate strength of a box girder subjected to severe corrosion 总被引:1,自引:0,他引:1
The objective of this paper is to describe the experimental assessment of the ultimate strength of a severely corroded box girder subjected to a uniform bending moment resulting from four-point loading. Three box girders that could simulate the behaviour of midship sections have been deteriorated in corrosive seawater environment to simulate different levels of corrosion degradation of ageing ship structures. During the deterioration process, various parameters have been controlled and the total weight lost was registered. Corroded plate thicknesses have been measured in 212 points and a statistical analysis has been performed. The resulting corrosion wastage has been fitted by a non-linear time variant degradation model. The experimental results of the ultimate strength test of a severely corroded box girder subjected to a four-point loading have been analysed. The load-displacement and moment-curvature relationship is discussed, different failure modes are identified, and the strain gauges readings are analysed. 相似文献
450.
Dean A. JonesJulie L. Farkas Orr BernsteinChad E. Davis Adam TurkMark A. Turnquist Linda K. NozickBrian Levine Carmen G. RawlsScott D. Ostrowski William Sawaya 《Research in Transportation Economics》2011,32(1):3-14
International containerized freight movement is a vital part of the supply chain for many companies, and a critical element of moving consumer goods to points of retail sale within the U.S. Containerized imports also present a clear security concern (e.g., terrorists attempting to ship “dirty bombs,” chemical, biological or even nuclear weapons, into the U.S. in a shipping container). The goal of the research presented here is to create a modeling tool for analyzing flows of U.S. imports and exports of containerized freight, and the potential changes in those flows under a variety of conditions (e.g., port disruptions, extensive security-related delays, etc.). Our focus is on movements through maritime container ports, and not overland movements between the U.S. and Canada or Mexico.The network model, referred to as the System for Import/Export Routing and Recovery Analysis (SIERRA), represents container movements between the U.S. and 46 other countries that account for the vast majority of U.S. imports and exports. The SIERRA model is a network equilibrium model that predicts flows between foreign countries and North American ports, the total volumes handled (import and export) by each port, the modal volumes (truck and rail) moving domestically into and out of each port, and volumes between each port and a set of transportation analysis zones within the U.S. 相似文献