A generalized scheme for analysis of multifarious commercially used mufflers

Commercial automotive mufflers are often too complex to be broken into a cascade of one-dimensional elements with predetermined transfer matrices. The one-dimensional (1-D) scheme presented in this paper is based on an algorithm that uses user-friendly visual volume elements along with the theory of transfer matrix based muffler analysis. This work attempts to exploit the speed of the one-dimensional analysis with the flexibility, generality and user-friendliness of three-dimensional analysis using geometric modeling. A code based on the developed algorithm has been employed to demonstrate the generality of the proposed method in analyzing commercial mufflers by considering three very diverse classes of mufflers with different kinds of combinations of reactive, perforated and absorptive elements. Though the examples used in the paper are not very complex for they are meant to be just representative cases of certain classes of mufflers, yet the algorithm can handle a large domain of commercial mufflers of high degree of complexity. Results from the present algorithm have been validated through comparisons with both the analytical (plane wave based) and the more general, three-dimensional FEM based results. The forte of the proposed method is its power to construct the system matrix consistent with the boundary conditions from the geometrical model to evaluate the four-pole parameters of the entire muffler and thence its transmission loss, etc. Thus, the algorithm can be used in conjunction with the transfer matrix based muffler programs to analyze the entire exhaust system of an automobile.     

HFC134a与HFO1234yf用于汽车空调的理论分析

对HFC134a和HFO1234yf应用于汽车空调进行了理论分析,研究表明:HFC134a的排气温度明显高于HFO1234yf,HFC134a的排气温度随着蒸发温度的升高而降低,HFO1234yf的排气温度随着蒸发温度的升高而升高;HFC134a与HFO1234yf的单位制冷量都是随着蒸发温度的升高而增大,但HFC134a的单位制冷量明显高于HFO1234yf,其平均高于HFO1234yf约34.9kW/kg;HFO1234yf压缩机输入功率明显高于HFC134a;HFC134a的系统COP高于HFO1234yf的系统COP,且二者都是随着蒸发温度的升高而升高,蒸发温度为-10℃时,其系统COP分别为3.739和3.493,蒸发温度为18℃时,其系统COP分别为9.6和9.36。     

Modelling Asymmetric Unemployment Dynamics: The Logarithmic-Harmonic Potential Approach

Asymmetric behaviour has been documented in unemployment rates which increase quickly in recessions but decline relatively slowly during expansions. To model such asymmetric dynamics, this paper provides a rigorous derivation of the asymmetric mean-reverting fundamental dynamics governing the unemployment rate based on a model of a simple labour supply and demand (fundamental) relationship, and shows that the fundamental dynamics is a unique choice following the Rayleigh process. By analogy, such a fundamental can be considered as a one-dimensional overdamped Brownian particle moving in a logarithmic–harmonic potential well, and a simple prototype of stochastic heat engines. The solution of the model equation illustrates that the unemployment rate rises faster with more flattened potential well of the fundamental, more ample labour supply, and less anchored expectation of the unemployment rate, suggesting asymmetric unemployment rate dynamics in recessions and expansions. We perform explicit calibration of both the unemployment rate and fundamental dynamics, confirming the validity of our model for the fundamental dynamics.     

I.C.E. Net and Lost Power Estimation During Free Run-Up and Coast-Down

The measurement of torque-speed characteristic curve for an internalcombustion engine (I.C.E.) gives fundamental information about its overallworking conditions. In this work a very simple and effective method ispresented and verified through tests on several spark I.C.E. It consists ofa detection of spark pulses with a current clamp and of a data processingprocedure that provides the torque-speed curve in real time. The mainadvantage of this method is that it provides an easy and economical way tocheck operating conditions of an engine without any particular setup.Results are presented for three engines for which manufacturers data areavailable.     

On Gear Modelling in Multistage Rotary Vane Engines

A discussion of the dynamics of a multistage rotary vane engine is given in terms of a simplified model for combustion driving torques, power dissipation, and torque transmission. Torque transmission is effected by conjugate gear pairs attached to each unit of the engine. An argument for the design of such pairs is presented so that unwanted torque fluctuations in a flywheel attached to a member of the pair can be significantly attenuated. It is suggested that a variant of simple Cosserat dynamics offers a useful modelling tool for discussing the complex interaction between interacting gear teeth. A quasi-stationary analysis is used to place bounds of a particular choice of conjugate gear coupling in the presence of such interactions. It is concluded that a multistage rotary vane engine with at least two units can be usefully coupled to a single flywheel via a well-defined conjugate gear system that attenuates unwanted torque fluctuations over a broad range of rotary speeds.     

Assessment of environmental contamination risk by Pt, Rh and Pd from automobile catalyst

The main active components of present-day car catalysts are the noble metals Pt, Pd and Rh, belonging to the platinum group elements (PGEs). It is recognized that these elements are being spread into the environment to an as-yet incompletely known extent, mainly due to surface abrasion of the catalyst during car operation. These new pollutants have motivated extensive research on PGE determination. Our work is planned to ascertain the health and ecosystem risks of these PGEs emitted through a series of interrelated objectives that address the pathway of these elements from the catalyst to the different environmental compartments. Combined studies of catalyst surface abrasion and exhaust fumes analysis, the monitoring of Pt, Pd and Rh in airborne particles and road dust sediments and bioaccumulation studies in aquatic organisms, plants and urine enable a realistic assessment of the risk that this release represents for man and environment. In this work some previous results are presented.     

Spectrophotometric determination of sulphate in automotive fuel ethanol by sequential injection analysis using dimethylsulphonazo(III) reaction

A sensitive SIA method was developed for sulphate determination in automotive fuel ethanol. This method was based on the reaction of sulphate with barium-dimethylsulphonazo(III) leading to a decrease on the magnitude of analytical signal monitored at 665 nm. Alcohol fuel samples were previously burned up to avoid matrix effects for sulphate determinations. Binary sampling and stop-flow strategies were used to increase the sensitivity of the method. The optimization of analytical parameter was performed by response surface method using Box-Behnker and central composite designs. The proposed sequential flow procedure permits to determine up to 10.0 mg SO₄²⁻ l⁻¹ with R.S.D. <2.5% and limit of detection of 0.27 mg l⁻¹. The method has been successfully applied for sulphate determination in automotive fuel alcohol and the results agreed with the reference volumetric method. In the optimized condition the SIA system carried out 27 samples per hour.     

A Model for Evaluating and Determining the Most Appropriate Polymer Matrix Type for Natural Fiber Composites

The process of determining the proper polymer matrix type, using a wide range of criteria, to form a natural fiber–reinforced polymer composite is still not established enough. This work introduces, for the first time, a model to select the proper polymer matrix type for natural fibers to enhance the sustainability of the automotive industry. The model was developed to rank different polymers and to determine their relative merits considering 20 different criteria simultaneously, including different physical, mechanical, chemical, environmental, and technical criteria. This work can support establishing a road map for proper selection of polymers in different engineering applications as well as increasing the reliability of the polymer selection process.