The purpose of this paper is to present a study of impact assessment of the traffic-induced vibration on a buried natural gas transmission pipeline. The basic assumption in this study is that the traffic on pipeline-transportation route crossing might have a significant impact on natural gas pipeline structural integrity due to the traffic-induced vibration which propagates from the road surface through the soil and excites the buried natural gas pipeline. The resulting dynamic stress causes pipeline material fatigue loading which consequently may cause pipeline failure with the gas release into the environment exposing the population and the buildings in pipeline vicinity to a significant threat. The experiment on operating buried natural gas pipeline was conducted where measurements were performed on the road surface, the two operating buried natural gas pipelines of external diameter 500 mm and 250 mm and on corresponding casing pipes. The measurement data analysis was performed and the results were used for determination of pipeline lifetime period in the model for theoretical estimation of pipeline lifetime which has been exposed to traffic-induced vibration. The findings of the study in this paper show that the traffic-induced vibration on given buried natural gas pipeline is detectable, however this vibration, compared to the other factors which are influencing pipeline's structural integrity, does not have a significant impact on pipeline lifetime period.
COBISS.SI-ID: 12552987
The paper reports foremost the results of a successful combustion of an innovative lignocellulosic biofuel in a gas turbine. The fuel was processed through liquefaction of lignocellulosic materials with polyhydroxy alcohols in an acid catalyzed reaction. The liquefaction process features: high efficiency, high liquid yields and inexpensive, easily available process equipment. For the purpose of this analysis the following were developed: an experimental gas turbine with internal combustion chamber, a preheated pressurized fuel supply system with swirl-air fuel injector and a heat exchanger to obtain high primary air temperatures. The paper gives results on the emissions of CO, THC, NOx and soot. For the purpose of benchmarking the turbine was also run on diesel fuel. The paper presents analyses of the underlying phenomena with which it aims to provide guidelines for improvements in the fuel processing and in the experimental equipment. It has been shown that direct utilization of this innovative lignocellulosic biofuel gives promising results. Although the CO and THC emissions are higher compared to the benchmark diesel results it has been shown that both emissions decrease with increased turbine inlet temperature and with the increased fuel preheat temperature, due to a very high viscosity of the fuel. It is additionally shown that NOx emissions are low and comparable to those of the diesel fuel, whereas soot emissions are very low for both fuels.
COBISS.SI-ID: 12403483
This paper examines the influence of compressed natural gas, liquefied petroleum gas and gasoline fuel on the exhaust emissions and the fuel consumption of a spark-ignition engine powered passenger car. The vehicle was driven according to the urban driving cycle and extra urban driving cycle speed profiles with the warmed-up engine. Cause and effect based analysis reveals potential for using different fuels to reduce vehicle emission and deficiencies associated with particular fuels. The highest tank to wheel efficiency and the lowest CO2 emission are observed with the natural gas fuelled vehicle, that also featured the highest total hydrocarbon emissions and high NOx emissions because of fast three way catalytic converter aging due the use of the compressed natural gas. Retrofitted liquefied petroleum gas fuel supply systems feature the greatest air-fuel ratio variations that resultin the lowest TtW efficiency and in the highest NOx emissions of the liquefied gas fuelled vehicle.
COBISS.SI-ID: 12154395
No experiment was conducted, yet, to investigate the scale effects on the dynamics of developed cavitating flow with periodical cloud shedding. The present study was motivated by the unclear results obtained from the experiments in a Venturi-type section that was scaled down 10 times for the purpose of measurements by ultra-fast X-ray imaging (Coutier-Delgosha et al. 2009). Cavitation in the original size scale section (Stutz and Reboud in Exp Fluids 23:191-198, 1997, Exp Fluids 29:545-552 2000) always displays unsteady cloud separation. However, when the geometry was scaled down, the cavitation became quasi steady although some oscillations still existed. To investigate this phenomenon more in detail, experiments were conducted in six geometrically similar Venturi test sections where either width or height or both were scaled. Various types of instabilities are obtained, from simple oscillations of the sheet cavity length to large vapor cloud shedding when the size of the test section is increased. It confirms that small scale has a significant influence on cavitation. Especially the height of the test section plays a major role in the dynamics of the re-entrant jet that drives the periodical shedding observed at large scale. Results suggest that the sheet cavity becomes stabile when the section is scaled down to a certain point because re-entrant jet cannot fully develop.
COBISS.SI-ID: 12534555
Until 2016 power plants within the EU will have to meet new limits on emissions as dictated by EU regulations. One of the major challenges is to reduce emissions of nitrogen oxides (NOx) due to health and ozone-formation concerns. Combustion optimisation is one of the primary measures for reducing NOx emissions from boilers burning coal, oil, or natural gas. The optimisation can be achieved by excess air control, boiler fine tuning and balancing the fuel and air flow to the various burners in order to reach minimum NOx formation. In this paper, a multi-step-ahead prediction of NOx emissions that can provide a basis for on-line control is presented. About 9 days’ worth of real data were acquired from an operator of a coal-based power plant for this study. It begins with a presentation of measured variables, pre-processing of the data and a definition of performance measures. Feature selection analysis follows, identifying the variables important for multi-step NOx prediction. In this respect, the impact of primary variables that are directly related to the combustion process is compared against that of other variables important in boiler operation and some transformed variables. Based on optimal features, a model comparison study including linear (ARX and ARMAX) and nonlinear (NN and SVR) modelling approaches is presented. Results of the model comparison study reveal that for the analysed boiler, nonlinear models do not improve the robust prediction performance of a linear ARX model. In the last part of the paper, an adaptive modelling approach further investigates the potential improvements in NOx prediction. A comparison of static and adaptive versions of the linear ARX model reveals that the adaptive approach does not improve prediction performance significantly. Hence the static ARX model in combination with an optimally selected set of input variables and extracted features is recommended for the multi-step NOx prediction of the coal-based boiler.
COBISS.SI-ID: 12317723