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Natural gas distributed energy supply system (DES) can realize the cascade and efficient use of energy, which is an important way to solve the current global energy crisis. Different operating strategies will affect the operation of the device, which in turn affects the overall performance of the system. The DES model was constructed by Modelica taking the distributed energy station of a factory in Shanghai as an example. The annual dynamic simulation of DES under three operation strategies - follow electricity load (FEL) 、 follow thermal load (FTL) and follow hybrid load (FHL) was carried out. The results showed that the annual operating costs of the three strategies could be saved by 7.4%, 7.8% and 6.9% respectively, and the comprehensive utilization rates of energy were 76%, 74% and 72% respectively.

Constructing navigation condition of oil supply vessels is of vital importance to both the research on the main engine and the safety of navigation. This paper carries out in-depth research and analysis based on the half-year shipping data derived from Hai Gong You 31, the oil supply vessel of Shanghai Chimbusco Marine Bunker Co., Ltd. After classifying 3946 pieces of shipping data, and there are 119 valid sequences. As for 13 characteristic parameters ,which include time, distance, average acceleration ,etc., they are eigenvalues of kinematics sequences ,and there are principal component analysis and contribution rate analysis relevant to them. Instead of original eigenvalues, three principal components whose contribution ratios are the highest and the accumulative one is around 85% are selected to be analyzed then. By means of between-groups linkage, this paper calculates the distance among clusters ,and the nearest two clusters are regarded as a new cluster. Afterward, calculations and combinations are made over and over till there is only one cluster. Eventually, the navigation condition of oil supply vessels is successfully formed, that is the one with a total length of 9240s.

The relationship between lifted flames and burner head temperature of partially premixed gas burners supplied by various natural gas sources was investigated, and the application of AGA(American Gas Association) lifting limit for Chinese domestic gas burners was studied. Results showed that lifted flames became more seriously with the burner head temperature decreasing, also with the increase of lift height of flames, it would lead to reduce the burner head temperature, eventually the burner head would reach the thermal equilibrium state which maintained stable flames and temperature. The lifting limit curve of partially premixed gas burners was only one under the same gas source, and it only depended on the burner structures and gas source characteristics, but nothing to do with the burner head temperature. The gas source with lower Wobbe index and calorific value made the burner appearing lifted flame more easily. Comparing with the experiment results and AGA lifting index prediction, it suggested that the limits of AGA lifting index IL≤ 1.10 should be change into IL≤ 1.05 using in China. Keywords: Partially premixed gas burners, Lifted flames, Natural gas, AGA lifting index

The porous media combustion technology is an effective solution to stable combustion and clean utilization of low heating value gas. For observing the combustion characteristics of porous media burners under various back pressures, investigating flame stability and figuring out the distribution laws of combustion gas flow and resistance loss, so as to achieve an optimized design and efficient operation of the devices, a bench of foamed ceramics porous media combustion devices was thus set up to test the cold-state resistance and hot-state combustion characteristic of burners in working conditions without back pressures and with two different back pressures. The following results are achieved from this experimental study. (1) The strong thermal reflux of porous media can preheat the premixed air effectively, so the flame can be kept stable easily, the combustion equivalent ratio of porous media burners is lower than that of traditional burners, and its pollutant content of flue gas is much lower than the national standard value. (2) The friction coefficient of foamed ceramics decreases with the increase of air flow rate, and its decreasing rate slows down gradually. (3) When the flow rate of air is low, viscosity is the dominant flow resistance, and the friction coefficient is in an inverse relation with the flow rate. (4) As the flow rate of air increases, inertia is the dominant flow resistance, and the friction coefficient is mainly influenced by the roughness and cracks of foamed ceramics. (5) After the introduction of secondary air, the minimum equivalent ratio of porous media burners gets much lower and its range of equivalent ratio is much larger than that of traditional burners.

In China, it has become a more common practice to introduce natural gases from different sources into the same distribution system to improve supply security and reliability. Variable gas constituents may cause a negative impact on the performance of domestic gas appliances. This paper aims to study the CO emission of a Chinese gas cooker under different constituents of natural gas. A typical Chinese gas cooker with two burners, each of which has a nominal heat input of 3.8 kW, was selected. One of the burners was modified to a forced-mixed mode to replace primary air injection. Within operational ranges corresponding to the permissible Wobbe index—namely, primary air coefficients and heat inputs—the equivalence between original gas and the CH4/C3H8/N2 three-component mixture in terms of CO emission was experimentally validated. Then, different three-component mixtures were input into the other unmodified burner, which operates under injected primary air, to investigate how the CO emission changed with different gas constituents. It was found that the CO emission of a natural gas and a CH4/C3H8/N2 three-component mixture, in terms of CO emission, were equivalent. The combination of the two indexes, W and PN, can describe the CO emission from a gas cooker accurately. By means of a three-component mixture, the empirical formula, which can correlate CO and the gas property parameters, was proposed. A set of equal-CO lines was revealed for a given initial primary air adjustment. Finally, a feasible approach to manage gas quality management in China was put forward, and the conclusion can help control the CO emission of gas cookers and improve indoor air quality.

Scientific analyses and the provision of practical ways of improving the hydraulic reliability of urban high-pressure gas networks are essential for the safe and stable supply of natural gas by a supplier. A reasonable estimation of the actual obtainable flow for each consumer in the event of a failure is key to the quantitative analysis of hydraulic reliability, which is not an easy task for a loop network. Based on an analysis of the hydraulic characteristics of a loop network, this paper discusses the limitations of existing methods and presents a feasible method for determining the actual nodal flow in a high-pressure gas network loop. This method adopts a process whereby the hydraulic regimes are first analysed according to the designed nodal flow. Next, the nodal pressures are checked, and the actual nodal flow is gradually rectified. Finally, the hydraulic regimes are repeatedly analysed according to the rectified flow until each nodal pressure and each nodal flow satisfy the nodal pressure equations. Moreover, a detailed procedure for a hydraulic reliability analysis of a loop network is presented, and its feasibility is confirmed with an example. The example results show that the network system hydraulic reliability is only 0.879 using the proposed method when pipe 2 fails, whereas the reliability would become 1.0 if using the existing method. The factors affecting the reliability are discussed exhaustively from the aspects of the network system and the consumer, and a number of measures are suggested for improving the hydraulic reliability.

This paper presents theoretical and experiment analysis of a hybrid residential hot water (HRHW) supplying system with domestic solar water heater (DSWH) and gas instantaneous water heater (GIWH) in shanghai. Mathematical model of the system has been established and its validity was tested by experiments. Economic analysis has been conducted for the HRHW system and traditional gas water heater systems through simulation along with Shanghai weather condition considering the influence of different minimum temperature rise (MTR) of GIWH. The economic comparison results show that the HRHW supplying system has greater economic benefits than gas water heater with a payback period of 7.2 years, and minimum temperature rise (MRT) of GIWH has low impacts on the supplementary gas consumption for the case in shanghai. For other region, operation of the HRHW system needs precise simulation according to the local meteorological conditions.

The economic benefit gained from a combined cooling heating and power (CCHP) system depends on many factors. It is essential to optimize the system configuration and operational scheme as early in the design stage as possible. In this paper, a sizing optimization model (SOM) focused on the minimum annual total cost ( ATC ) and an operational optimization model (OOM) focused on the minimum annual energy charge ( AEC ) were established. The former was used to determine the optimal capacity of a CCHP system, whereas the latter was used to provide the optimal schemes. Both the SOM and OOM contain large numbers of hourly linear programming (LP) models, and the solution processes of both models proved to be quite time-consuming when the conventional iterative method was used. In this study, a piecewise elimination method was proposed for hourly LP models, and a graphical method in which the iteration was converted to an algebraic matrix was introduced to greatly improve the computational efficiency. The results demonstrated that the calculation time was reduced from 84.496 s for the conventional solution to 0.017 s for the graphical method in the OOM. The CCHP system SOM contains an OOM, and the calculation time was only 0.41 s when using the graphical method, whereas the conventional iterative method took 2367 s. The impact of gas price upon the optimal operational schemes and the equipment capacity was discussed for a building application in Shanghai. The improved efficiency of the calculation method could be helpful to compare different schemes and to perform sensitivity analyses.

In this paper, the flame stability of partially premixed combustion for pipeline natural gas (PNG) and liquefied natural gas (LNG) interchangeability was investigated. A wide range of primary air ratio was considered and the characteristics of yellow flame and lifted flame were emphasized. The effect of gas flame speed (Sn), flame inner core height (h), gas flow rate (Lg), air flow rate (La), port thermal intensity (qp) and burner head temperature were discussed. Experiments showed that flame speed and flame inner cone height were mainly affected by gas components and lifted flame was influenced by flame speed and burner head temperature. When gases were interchanged, the flame speed and lifted flame could not be simply predicted by Wobbe index. When gas wobbe index increased, more chances yellow flame would appear and the gases with similar wobbe indexes have similar performance of yellow flame characteristics.

Almost all of finished household biogas plants in China incorporated medium-temperature fermentation and no auxiliary heating were integrated. Accordingly the production efficiency was quite poor due to lack of reasonable thermal support. Meanwhile solar-collector became more and more popular accompanied with decreasing cost resulting from mass production. A solar-assisted biogas system was put forward and experimentally investigated in this paper. The initiative was to combine popularly-available house biogas plant with solar-collector at a reasonable cost, therefore to maintain year-round operation of biogas plant and to produce enough amount of biogas in winter for daily use. The recorded data in a pilot project revealed that additional electricity consumed accounted to only 7.2% of biogas produced, suggesting an economically feasible approach.

Stray current corrosion (SCC) is the most severe form of electrochemical corrosion to buried metallic structure. With the development of rail transportation and gas industry, the SCC of buried gas pipelines is becoming more serious in china. In this paper, principle and characteristic of Stray Current (SC) resulting from rail transit system were introduced. Presently available SC testing methods, equipment, and determination standards in china were summarized. For an underground gas pipeline located in the neighboring area and parallel to the rail transit in Shanghai, pipe-to-soil potential, potential gradient of soil, current within pipeline were measured during different operation time of rail transit with a self-made SC monitoring system based upon virtual instrument. Result shows that pipe-to-soil potential fluctuation of the tested gas pipeline is 200 mV, current within pipeline and potential gradient of soil is 100 mA, and 62 mV/m respectively, which is consistent with the operation of rail transit, serious corrosion of the buried gas pipeline may occur. Through theoretical Analysis, several protective measures were introduced.

In China, the imported Liquefied Natural Gas (LNG) has been steadily increased in past years, with its constituents different from those of traditional pipeline natural gases (PNG) to various extents. In this paper several natural gases to be delivered to Guangdong provinces in China were selected as test gases to measure performance response of 17 sets of domestic gas cookers. Heat input rating, CO and NO x emission, and thermal efficiency was measured according to related national standards. American Gas Association indexes and Weaver indexes were used to predict combustion stability and emission under different gas constituents. Experiment results were compared with prediction to analyze the applicability of the two well-established indexes systems. It was concluded that Wobbe Index can predict heat input rating quite accurately, and CO and NO x emissions can be remained with reasonable limits for the changing constituents discussed. For combustion stability prediction, judgment criteria should be adjusted as follows: Weaver lifting index from J L ≥ 0.64 to J L ≥ 0.95, Weaver incomplete combustion index from J I ≤ 0.05 to J I ≤ 0.04, and AGA lifting index from I L ≤ 1.10 to I L ≤ 1.05.

Ceramsite is widely used in the construction industry, insulation works and oil industry in China, and the manufacture equipment is mainly industrial kiln. In this paper, energy consumption analysis had been carried out through experimental test of a Ceramsite kiln in Henan province. Results showed that the discharge temperature of Ceramsite was about 1393K, and the waste heat accounted for 22.1% of the total energy consumption. A structure of cyclone preheater which recovered waste heat of the high temperature Ceramsite by blast cooling was designed. Then, using Fluent software, performance of the unit was simulated. The minimum temperature that Ceramsite could reach, heat dissipating capacity of Ceramsite, temperature at air outlet, wall temperature of the unit and pressure loss were analyzed. Performance of the designed unit under different inlet velocity was analyzed as well.

A hybrid air-conditioning system that combines an engine-driven chiller with desiccant dehumidification was configured and experimentally tested to provide reliable data for energy consumption and operation cost. The engine performance and the desiccant wheel performance were measured and a numeric model previously set up for dehumidification capacity prediction was validated. For a reference building, the results based upon measured data show that under present electricity/gas price ratio, more than 40% of operation cost can be saved by the hybrid system.

With intensified energy restructure in China, energy efficiency of various industrial furnaces and kilns fired by natural gas draws attentions of more and more researchers. In this article, a field test was performed for shuttle kiln popular in ceramics and refractory manufacture industry. The thermal efficiency, main heat loss, and the energy-saving potential were evaluated, and the defects of the existing kilns and improvement measure were clarified. The results show that the overall efficiency was only 13%–15%, if measured in terms of the entire heating period. The energy loss of flue gas accounted up to 50%; the effectiveness of air preheater was as low as only 30%; large amount of cold air infiltration was observed at the venting exit at the bottom of the kiln. The burner controls and gas flow within furnace remain to be optimized.

The purpose of this research is to analyze influence of energy equation on gas pipeline transient simulation. The paper briefly presents current models for gas pipeline simulation, and analyzes their characteristics, applicable conditions, and solution methods. Calculation errors are analyzed by applying one model considering energy equation and the other neglecting to simulate a gas pipeline in service. The example results show the average relative error between the two models is lower than 1.32%, which indicates the neglect of energy equation can satisfy general gas pipeline design. However, the maximum relative error is 4.40%, especially the maximum absolute error of temperature is 12.14K, which indicates energy equation could not be neglected if some pipeline simulation condition needing higher accuracy. Finally, influence of energy equation on simulation result is evaluated and some conclusions are drawn.

Biogas interchangeability was proposed in view of the variation in component contents of biogas and investigated theoretically and experimentally. It was found that all predictions of “C” index, “I” indices and Weaver indices have very similar interchangeability limits, but the reliability requires further study. Calculated and experimental results showed that only a small range of gas contents with regard to the variations of biogas contents could meet requirements of interchangeability, and the variations give rise to the issues of biogas interchangeability. Studies suggest that it is necessary to promote research on biogas interchangeability systematically according to China's national conditions. 2 Development of Studies on Biogas Interchangeability and Judgment Methods

Interchangeabilities of biogas (BG) and liquefied petroleum gas (LPG) mixed gases according to American Gas Association (AGA) Bulletin 36 and Weaver indices were investigated. BG-LPG mixed fuels were defined so as to have a Wobbe index (WI) nearly equivalent to those of natural gas (NG). The qualities of BG and LPG used are considered by varying the CH 4 and C 3 H 8 percentage in the BG and LPG composition, respectively. It was found that BG-LPG mixed gases can not be used as interchangeable gases for natural gas and can not be applied to gas appliances for natural gas directly because of yellow-tipping and incomplete combustion. However, natural gas can be substituted for BG-LPG mixed gas completely and can be applied to gas appliances for BG-LPG mixed gas without any modification. On the other hand, BG-LPG mixed gases show interchangeability with itself without any unstable flame on gas appliances regardless of the components concentration variation.

Stray current corrosion (SCC) is one of the most severe forms of electrochemical corrosion. In the paper, the mechanism and character of stray current from DC electric traction systems and its influence upon buried pipe were briefly introduced. The stray current testing methods and testing equipments were reviewed. A new system for monitoring the stray current, based upon virtual instrument, was put forward. The proposed system has some advantages such as real-time display, frequency control, and automatic data storage. The pipe-soil potentials of a gas pipeline, located in the neighboring area and parallel to the rail transit powered by a DC source in Shanghai, were tested by means of proposed system. Actual results show that stray current corrosion of underground gas pipeline is existed, some protective measures must be done to eliminate the corrosion, and the feasibility of the system has been proved.

the reason and character of stray current from DC electric traction systems and its influence upon buried pipe were briefly introduced in the paper. The traditional measurements and monitoring methods in subway for stray current were discussed. A new system for monitoring the stray current, based upon virtual instrument, was put forward. The proposed system has some advantages such as automatic and continuous monitoring of stray current. The pipe-soil potentials of a gas pipeline, located in the neighboring area and parallel to the rail transit powered by a DC source in Shanghai, were tested by means of proposed system. The actual results prove the feasibility of the system.

A quasi dimensional model for a four-stroke spark ignition natural gas engine was developed using Modelica. Three different kinds of heat transfer models were evaluated and compared in Modelica in order to determine suitable heat transfer correlation for the natural gas engine simulation. Three important parameters of the natural gas engine, including compression ratio, spark timing and combustion duration, were investigated to optimize the design and work of the natural gas engine. The model was validated against measured data from a natural gas engine which was conversed from a gasoline engine by retrofitting fuel intake system. The results show: correlation proposed by Woshni led to a better matching with experimental data than those by Hohenberg and Eichelberg. Good agreement was observed between the simulated engine performance and measured data. Modelica, featured with “re-usable” and “object-oriented”, would be efficient for the theoretical design and the optimum work of natural gas engine.

A quasi-dimensional spark ignition (SI) engine cycle model is used to predict the combustion and exhaust emissions of a gas engine driven generator for the cases of using biogas and liquefied petroleum gas (LPG)-biogas blends. Two different thermodynamic regions consisting of unburned gases and burned gases that are separated by the flame front are considered. Liquefied petroleum gas (0%, 5% and 15%) was added to the biogas and was simulated as the fuel of SI engine. The results suggest that: There is an increase in cylinder pressure and temperature with the addition of LPG in biogas. Comparisons show that if LPG fueled SI engines are operated at the same conditions with those of biogas fueled SI engine, the mole fractions of CO and NO predicted for LPG-biogas blends are higher than those for biogas and the effects on the engine structural elements are not promising.

Since the physical and chemical characteristics of biogas, some problems will occur in its applications in engine. The biogas engine and its performance parameters analysis is regarded as research object, the biogas engine model library was built based on the object-oriented language Modelica. The effect of compression ratio, ignition advance angle and the combustion duration on the performance of biogas engine was analyzed through simulation study. The optimization of operating parameters and design parameters of biogas engine was performed. Natural gas (33%, 67% and 100%) and liquefied petroleum gas (5%, 10% and 15%) were added to the biogas and were simulated as the fuel of SI engine. The effects of natural gas/liquefied petroleum gas-biogas blends on the performance of spark-ignition engine used for electricity production were numerical investigated. The results suggest that: There is an improvement in brake thermal efficiency and brake power with the addition of natural gas/liquefied petroleum gas in biogas. The feature of reusable and object-oriented of Modelica will enhance the modeling and simulation of biogas engine performance greatly not only in accuracy but simulation efficiency, this would be efficient for the theoretical design and the optimum work of the biogas fuelled engine.