An RKDG finite element method for the one-dimensional inviscid compressible gas dynamics equations in a Lagrangian coordinate

In this paper,Runge-Kutta Discontinuous Galerkin（RKDG） finite element method is presented to solve the onedimensional inviscid compressible gas dynamic equations in a Lagrangian coordinate.The equations are discretized by the DG method in space and the temporal discretization is accomplished by the total variation diminishing Runge-Kutta method.A limiter based on the characteristic field decomposition is applied to maintain stability and non-oscillatory property of the RKDG method.For multi-medium fluid simulation,the two cells adjacent to the interface are treated differently from other cells.At first,a linear Riemann solver is applied to calculate the numerical ？ux at the interface.Numerical examples show that there is some oscillation in the vicinity of the interface.Then a nonlinear Riemann solver based on the characteristic formulation of the equation and the discontinuity relations is adopted to calculate the numerical ？ux at the interface,which suppresses the oscillation successfully.Several single-medium and multi-medium fluid examples are given to demonstrate the reliability and efficiency of the algorithm.

Numerical model of compressible gas flow in soil pollution control

Based on the theory of fluid dynamics in porous media, a numerical model of gas flow in unsaturated zone is developed with the consideration of gas density change due to variation of air pressure. This model is characterized of its wider range of availability. The accuracy of this numerical model is analyzed through comparison with modeling results by previous model with presumption of little pressure variation and the validity of this numerical model is shown. Thus it provides basis for the designing and management of landfill gas control system or soil vapor extraction system in soil pollution control.

Revaluating coal permeability-gas pressure relation under various gas pressure differential conditions

Identifying changes in coal permeability with gas pressure and accurately codifying mean efective stresses in laboratory samples are crucial in predicting gas-fow behavior in coal reservoirs. Traditionally, coal permeability to gas is assessed using the steady-state method, where the equivalent gas pressure in the coal is indexed to the average of upstream and downstream pressures of the coal, while ignoring the nonlinear gas pressure gradient along the gas fow path. For the fow of a compressible gas, the traditional method consistently underestimates the length/volume-averaged pressure and overestimates mean efective stress. The higher the pressure diferential within the sample, the greater the error between the true mean pressure for a compressible fuid and that assumed as the average between upstream and downstream pressures under typical reservoir conditions. A correction coefcient for the compressible fuid pressure asymptotes to approximately 1.3%, representing that the error in mean pressure and efective stress can be on the order of approximately 30%, particularly for highly pressure-sensitive permeabilities and compressibilities, further amplifying errors in evaluated reservoir properties. We utilized this volume-averaged pressure and efective stress to correct permeability and compressibility data reported in the literature. Both the corrected initial permeability and the corrected pore compressibility were found to be smaller than the uncorrected values, due to the underestimation of the true mean fuid pressure, resulting in an overestimation of reservoir permeability if not corrected. The correction coefcient for the initial permeability ranges from 0.6 to 0.1 (reservoir values are only approximately 40% to 90% of laboratory values), while the correction coefcient for pore compressibility remains at approximately 0.75 (reservoir values are only approximately 25% of laboratory value). Errors between the uncorrected and corrected parameters are quantifed under various factors, such as confning pressure, gas sorption, and temperature. By analyzing the evolutions of the initial permeability and pore compressibility, the coupling mechanisms of mechanical compression, adsorption swelling, and thermal expansion on the pore structure of the coal can be interpreted. These fndings can provide insights that are useful for assessing the sensitivity of coal permeability to gas pressure as truly representative of reservoir conditions.

Utilization of compressed natural gas for the production of carbon nanotubes

The present work aims at utilizing compressed natural gas （CNG） as carbon source for the synthesis of carbon nanotubes （CNTs） over CoO-MoO/Al2O3 catalyst via catalytic chemical vapor deposition （CCVD） method. The as-produced carbonaceous product was characterized by thermal gravimetric analyzer （TGA）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and Raman spectroscopy. The experimental finding shows that CNTs were successfully produced from CNG while carbon nanofibers （CNFs） were formed as the side products. In addition, the catalytic activity and lifetime were found sustained and prolonged, as compared with using high purity methane as carbon source. The present study suggests an alternative route which can effectively produce CNTs and CNFs using low cost CNG.

EFFECTS OF COOLED EXTERNAL EXHAUST GAS RECIRCULATION ON DIESEL HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE

The effects of cooled external exhaust gas recirculation （EGR） on the combustion and emission performance of diesel fuel homogeneous charge compression ignition （HCCI） are studied. Homogeneous mixture is formed by injecting fuel in-cylinder in the negative valve overlap （NVO） period. So, the HCCI combustion which has low NOx and smoke emission is achieved. Cooled external EGR can delay the start of combustion effectively, which is very useful for high cetane fuel （diesel） HCCI, because these fuels can easily self-ignition, which makes the start of combustion more early. External EGR can avoid the knock combustion of HCCI at high load which means that the EGR can expand the high load limit. HCCI maintains low smoke emission at various EGR rate and various load compared with conventional diesel engine because there is no fuel-rich area in cylinder.

Effect of gas compressibility on the characteristics of a synthetic jet flow

Numerical simulations are performed to investigate the effects of gas compressibility on the synthetic jet flow. A slot synthetic jet and a circular orifice synthetic jet are simulated assuming 2D and axis-symmetric behavior. The velocity of orifice, frequency response and the compressibility are studied through simulation. The numerical results are validated against existing experimental and analytical data, and good agreement are obtained, Gas compressibility effects on the synthetic jet flow are discussed. In conclusion, for the two kinds of different synthetic jets studied in this paper, the critical values of Mach number are 0. 082 and 0. 033.

A unified theory for gas dynamics and aeroacoustics in viscous compressible flows.Part I.Unbounded fluid

This paper presents a deep reflection on the advective wave equations for velocity vector and dilatation discovered in the past decade.We show that these equations can form the theoretical basis of modern gas dynamics,because they dominate not only various complex viscous and heat-conducting gas flows but also their associated longitudinal waves,including aero-generated sound.Current aeroacoustics theory has been developing in a manner quite independently of gas dynamics;it is based on the advective wave equations for thermodynamic variables,say the exact Phillips equation of relative disturbance pressure as a representative one.However,these equations do not cover the fluid flow that generates and propagates sound waves.In using them,one has to assume simplified base-flow models,which we argue is the main theoretical obstacle to identifying sound source and achieving effective noise control.Instead,we show that the Phillips equation and alike is nothing but the first integral of the dilatation equation that also governs the longitudinal part of the flow field.Therefore,we conclude that modern aeroacoustics should merge back into the general unsteady gas dynamics as a special branch of it,with dilatation of multiple sources being a new additional and sharper sound variable.

Integration Possibility of Urban Public Bus System and Cable Car in Maribor

Combination of a bus system and cable car system can reduce the overall congestion of traffic in urban areas, where surrounding hills or mountains hold larger settlements or tourist and recreational infrastructure. With this kind of integration number of individual car trips can be significantly reduced. In this paper, the authors present an analysis of the pilot project implementation, which was held in Maribor. The authors conducted a limited test trial of two means of transportation, combining them into a single operating transport offer for inhabitants and tourists. Combined transport option proved to be a good starting point for reduction of traffic and parking congestion during winter tourist season and beyond. Method used in the research, in order to gain actual potential of integrating two systems and improving public transport offer, was establishment and implementation of the pilot project in Maribor during January 2011. Data was gathered through interviews of two interest groups. The first covered the users who were brought to the foothills of Pohorje＇s ski center by bus. The second covered the cable car users that were traveling to the top of Pohorje. For a limited time period, a trial principle of a single ticket was established, which gave ski-pass holders free bus ride on bus line No. 6. With the aim of reducing CO2, test drives of hybrid bus and compressed natural gas bus were conducted alongside many promotional activities with which users were informed of importance of environmentally friendly mobility options.

Numerical study of CNG engine combustion using CFD with detailed chemical kinetics

A three dimensional model which considers the effects of turbulence and detailed chemi cal kinetics is built to simulate the combustion process of engine fueled by compressed nature gas （CNG）. The model is accomplished by integrating CFD software KIVA3V and chemical kinetic soft- ware CHEMKINII. Meanwhile, a turbulence combustion model which is suitable for describing the reaction rate under the coupled simulation is developed to balance the effects of turbulence and de tailed chemical kinetics. To reduce the computation time, subsequent development of the simulation code is realized, which enables the simulation code to have the function of parallel computing and run on parallel computing facility based on message passing interface （MPI）. The coupled software is used to simulate the combustion process of spark ignition CNG engine. The results show that sim ulation data have a good consistency with experimental results and parallel computing has good effi ciency and accelerate ratio.

Mixture Preparation and Combustion of CNG Low-Pressure Compound Direct Injection Spark-Ignited Engines

A set of compressed natural gas (CNG) multi-point direct injection system of spark-ignited engines and the corresponding measurement and data acquisition systems were developed in this paper. Based on different injection modes, the mixture formation and combustion of CNG low-pressure direct injection (LPDI) engines were studied under varying factors such as air/ fuel ratio, injection timing. Meanwhile, three-dimensional simulations were adopted to explain the mixture formation mechanisms of CNG low-pressure compound direct injection (LPCDI) mode. On the basis of test results and simulation of the mixture homogeneous degree, the conception of injection window was proposed, and the LPCDI mode was proved to be more beneficial to the mixture concentration stratification formation in cylinder under lean-burning conditions, which resulted in effective combustion and stability.

Polycyclic Aromatic Hydrocarbons in Water: A Review of the Sources, Properties, Exposure Pathways, Bionetwork and Strategies for Remediation

Polycyclic aromatic hydrocarbons (PAHs) are by-products arising from incomplete combustion. These organic chemicals substances are found almost everywhere and pose a risk to human health because of their potentially hazardous nature and bioavailability in the environment as determined by several regulatory agencies such as US Environmental Protection Agency (US-EPA), US Department of Health and Human Services (DHHS), International Agency for Research on Cancer (IARC) and the National Agency for Food and Drug Administration and Control (NAFDAC). The paper is aimed at studying polycyclic aromatic hydrocarbons in water. The possible sources, chemistry, risk and remediation strategies for polycyclic aromatic hydrocarbons in water have been considered. Studies have shown that exposure to PAHs at levels above the maximum contaminant level for relatively short periods will cause damage to the red blood cells leading to anaemia;suppressed immune system. Long-term exposure to Benzo(a)pyrene at levels above the maximum contaminant level has the potential to cause developmental and reproductive defects as well as cancer. US-EPA, IARC and DHHS has sets a maximum contaminant level (MCL) for benzo(a)pyrene, the most carcinogenic PAH, at 0.0002 mg/L, 0.0001 mg/L for benz(a)anthracene, 0.0002 mg/L for benzo(b)fluoranthene, benzo(k)fluoranthene, and chrysene. 0.0003 mg/L and 0.0004 mg/L have been set for dibenz(a,h)anthracene and indeno (1,2,3-c,d)pyrene respectively. Sustained barn on smoking in public places and burning of word, use of concretes in road construction as against the traditional surfacing of roads using coal tar as well as cars running on compressed natural gas (CNG) or liquefied petroleum gas (LPG) can form part of the preventive strategies.

Performance,combustion,and emission characteristics of on a diesel engine fuelled with hydrogen compressed natural gas and Kusum seed biodiesel

Renewable fuels have many advantages over fossil fuels because they are biodegradable and sustainable,and help mitigate social and environmental problems.The objective of the present study is to evaluate the performance,combustion,and emission characteristics of a compression–ignition engine using hydrogen compressed natural gas(HCNG)-enriched Kusum seed biodiesel blend(KSOBD20).The flow rate of HCNG was set at 5 L/min,10 L/min,and 15 L/min,and the injection pressure was varied in the range of 180 bar to 240 bar.Brake thermal efficiency(BTE)and brake-specific fuel consumption(BSFC)were improved when HCNG was added to the KSOBD20.Combustion characteristics,namely,cylinder pressure(CP)and net heat release rate(NHRR),were also improved.Emissions of carbon monoxide(CO),hydrocarbons(HC),and smoke were also reduced,with the exception of nitrogen oxides(NO_(x)).The higher injection pressure(240 bar)had a positive effect on the operating characteristics.At an injection pressure of 240 bar,for KSOB20+15 L/min HCNG,the highest BTE and the lowest BSFC were found to be 32.09%and 0.227 kg/kWh,respectively.Also,the CP and NHRR were 69.34 bar and 66.04 J/°.CO,HC,and smoke levels were finally reduced to 0.013%,47×10^(-6)and 9%,respectively,with NO_(x)levels at 1623×10^(-6).For optimum results in terms of engine characteristics,the fuel combination KSOBD20+15 L/min HCNG at FIP 240 bar is recommended.

SI Engine Fueled with Gasoline, CNG and CNG-HHO Blend: Comparative Evaluation of Performance, Emission and Lubrication Oil Deterioration

Hydroxy gas (HHO) is one of the potential alternative fuels for spark ignition (SI) engine,notably due to simultaneous increase in engine performance and reduction in exhaust emissions.However,impact of HHO gas on lubrication oil for longer periods of engine operation has not yet been studied.Current study focuses on investigation of the effect of gasoline,CNG and CNG-HHO blend on lubrication oil deterioration along with engine performance and emissions in SI engine.HHO unit produces HHO gas at 4.72 L/min by using 6 g/L of KOH in the aqueous solution.CNG was supplied to the test engine at a pressure of 0.11 MPa using an electronically controlled solenoid valve.Engine tests were carried out at different speeds at 80%open throttle condition and various performance parameters such as brake power (BP),brake specific fuel consumption(BSFC),brake thermal efficiency (BTE),exhaust gas temperature and exhaust emissions (HC,CO_(2),CO and NO_(x))were investigated.In addition,various lubrication oil samples were extracted over 120 h of engine running while topping for drain out volume and samples were analyzed as per ASTM standards.CNG-HHO blend exhibited better performance i.e.,15.4%increase in average BP in comparison to CNG,however,15.1%decrease was observed when compared to gasoline.CNG-HHO outperformed gasoline and CNG in the case of HC,CO_(2),CO and brake specific fuel consumption (31.1%decrease in comparison to gasoline).On the other hand,CNG-HHO produced higher average NO_(x) (12.9%) when compared to CNG only.Furthermore,lubrication oil condition(kinematic viscosity,water contents,flash point and total base number (TBN)),wear debris (Iron (Fe),Aluminum(Al),Copper (Cu),Chromium (Cr)) and additives depletion (Zinc (Zn),Calcium (Ca)) presented a significant degradation in the case of CNG-HHO blend as compared to gasoline and CNG.Lubrication oil analyses illustrated 19.6%,12.8%and 14.2%decrease in average viscosity,flash point and TBN for CNG-HHO blend respectively.However,average water contents,Fe,Al and Cu mass concentration appeared 2.7%,25×10^(-6),19×10^(-6),and 22×10^(-6) in lubrication oil for CNG-HHO respectively.

Catalytic performance of a Pt-Rh/CeO_2-ZrO_2-La_2O_3-Nd_2O_3 three-way compress nature gas catalyst prepared by a modified double-solvent method

A Pt-Rh three-way catalyst（M-DS） supported on CeO_2-ZrO_2-La_2O_3-Nd_2O_3 and its analogous supported catalyst（DS） were developed via a modified double-solvent method and conventional double-solvent method, respectively. The as-prepared catalysts were characterized by N_2 adsorption-desorption, X-ray diffraction（XRD）, CO-chemisorption, X-ray photoelectron spectroscopy（XPS） and hydrogen temperature-programmed reduction（H_2-TPR）. The preformed Pt nanoparticles generated using ethanol as a reducing agent on M-DS presented enhanced Pt dispersion regardless of aging treatment as confirmed by XRD and CO-chemisorption measurements. The textural properties and reduction ability of M-DS were maintained to a large extent after aging treatment. This result was consistent with those of the N_2 adsorption-desorption and H_2-TPR, respectively. Meanwhile, the XPS analysis demonstrated that higher Pt^0 species and larger Ce^（3＋） concentration could be obtained for M-DS. In the conversion of a simulated compressed natural gas（CNG） vehicle exhaust, both fresh and aged M-DS showed a significant enhancement in the activity and N_2-selectivity. Particularly, the complete conversion temperature（T_（90）） of CH_4 over the aged M-DS catalyst was 65 oC lower than that over the aged catalyst by conventional double-solvent method.

Gaseous emissions from compressed natural gas buses in urban road and highway tests in China

The natural gas vehicle market is rapidly developing throughout the world, and the majority of such vehicles operate on compressed natural gas （CNG）. However, most studies on the emission characteristics of CNG vehicles rely on laboratory chassis dynamometer measurements, which do not accurately represent actual road driving conditions. To further investigate the emission characteristics of CNG vehicles, two CNG city buses and two CNG coaches were tested on public urban roads and highway sections. Our results show that when speeds of 0-10 km/hr were increased to 10-20 km/hr, the CO2, CO, nitrogen oxide （NOx）, and total hydrocarbon （THC） emission factors decreased by （71.6 ± 4.3）%, （65.6 ± 9.5）%, （64.9± 9.2）% and （67.8 ± 0.3）%, respectively. In this study, The Beijing city buses with stricter emission standards （Euro IV） did not have lower emission factors than the Chongqing coaches with Euro II emission standards. Both the higher emission factors at 0-10 km/hr speeds and the higher percentage of driving in the low-speed regime during the entire road cycle may have contributed to the higher CO2 and CO emission factors of these city buses. Additionally, compared with the emission factors produced in the urban road tests, the CO emission factors of the CNG buses in highway tests decreased the most （by 83.2%）, followed by the THC emission factors, which decreased by 67.1%.

Bioenergy recovery from landfill gas:A case study in China

Landfill gas(LFG)utilization which means a synergy between environmental protection and bioenergy recovery was investigated in this study.Pressure swing adsorption technology was used in LFG purification,and laboratory experiment,pilot-scale test,and on-site demonstration were carried out in Shenzhen,China.In the laboratory experiment,A-type carbon molecular sieve was selected as the adsorbent by comparison of several other adsorbents.The optimal adsorption pressure and adsorption time were 0.25 MPa and 2 min,respectively,under which the product generation rate was 4.5 m^(3)/h and the methane concentration was above 90%.The process and optimization of the pilot-scale test were also reported in the paper.The product gas was of high quality compared with the National Standard of Compressed Natural Gas as Vehicle Fuel(GB18047-2000),when the air concentration in feed gas was under 10.96%.The demonstration project was composed of a collection system,production system,and utilization system.The drive performance,environmental protection performance,and economic feasibility of the product gas—as alternative fuel in passenger car,truck,and bulldozer—were tested,showing the feasibility technology for LFG utilization.

High temperature deformation behavior and processing map of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders

The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323-1473 Kand strain rate range of 0.001-0.5s^（-1）.The calculated activation energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6kJ/mol based on the constitutive relationship models developed with the Arrhenius-type constitutive model respectively considering the strain rate and deformation temperature.The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution.Meanwhile,the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions.Finally,the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353-1453 Kand the low strain rate of 0.001-0.1s^（-1） was obtained.

Research on Calculation Method of Aerodynamic Parameters of Supersonic Probe Based on Gas Compressibility Factor

The supersonic multi-hole probe is an essential test tool for wind tunnel experiments, which is necessary to develop the basic research of improving the measurement accuracy and expanding the application of the probes.

New 0D/1D Physical Approach for Modelling the Gas Dynamics Behavior Inside the Intake System of an Engine

The competition among carmakers to introduce the most innovative solutions is growing day by day. Since few years, simulation is being used widely in automotive industries. Instead of building costly prototypes and expending fuel for doing tests on a real engine, simulation became a good solution before taking new decisions. Concerning the study of gas dynamics and pressure wave's propagation in the intake system of an internal combustion engine, a precise modelling is needed in order to obtain good results. Unfortunately, the computational time for these simulations is considered as high compared to the real time. The main objective of the new approach presented in this paper, is to reduce simulation time of models in the internal combustion engine simulation code, allowing them to accomplish many engine simulations faster than one-dimensional non-linear approach. A transfer function is defined to link directly the relative pressure and the air mass flow rate. In a second time, the model is included into an internal combustion engine simulation code. The results obtained with this code are compared to experimental ones which are measured on a one-cylinder engine test bench. A good agreement is obtained between the experimental results and the numerical one. The model was improved by adding a transfer function for temperature evolution. The convergence time is then reduced as well as the global simulation time of the model.

Network Modeling and Operation Optimization of Electricity-HCNG-Integrated Energy System

Hydrogen-enriched compressed natural gas(HCNG)has great potential for renewable energy and hydrogen utilization.However,injecting hydrogen into the natural gas network will change original fluid dynamics and complicate compressed gas's physical properties,threatening operational safety of the electricity-HCNG-integrated energy system(E-HCNG-IES).To resolve such problem,this paper investigates effect of HCNG on gas network dynamics and presents an improved HCNG network model,which embodies the influence of blending hydrogen on the pressure drop equation and line pack equation.In addition,an optimal dispatch model for the E-HCNG-IES,considering the“production-storage-blending-transportation-utilization”link of the HCNG supply chain,is also proposed.The dispatch model is converted into a mixed-integer second-order conic programming(MISOCP)problem using the second-order cone(SOC)relaxation and piecewise linearization techniques.An iterative algorithm is proposed based on the convex-concave procedure and bound-tightening method to obtain a tight solution.Finally,the proposed methodology is evaluated through two E-HCNGIES numerical testbeds with different hydrogen volume fractions.Detailed operation analysis reveals that E-HCNG-IES can benefit from economic and environmental improvement with increased hydrogen volume fraction,despite declining energy delivery capacityand line pack flexibility.