РАСЧЕТНО-ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ ОБЛАСТИ УСТОЙЧИВОГО ГОРЕНИЯ ПРИРОДНОГО ГАЗА С ВОЗДУХОМ

The relevance of the study is due to the need to organize stable low-emission low-temperature combustion of a lean mixture in a single-zone uncooled combustion chamber, which is an integral part of a micro-gas turbine power plant. The stable position of the flame front in combustion chambers of this type mainly depends on the ratio between the average flow rate of the combustible-air mixture and the rate of turbulent combustion. This ratio depends on many factors, the main of which are the pressure and temperature of the components supply, the excess air ratio, the pulsating speed of the gas flow and autoturbulization of the flame, the consumption of the combustible-air mixture. In this work, we investigate the effect of external heating of the components on the expansion of the lower combustion limit and on the stable position of the flame front. The aim of the study is to obtain areas of breakthrough, stable position and flame blowout when organizing low-temperature lean combustion with large values of the excess air ratio; determination of the ranges of relative flow rate, at which a stable position of the flame front is observed, using experimental data and the results of numerical modeling; development of recommendations for determining the geometric appearance of a single-zone uncooled chamber of a micro-gas turbine power plant in the presence of air and fuel gas recuperators. As a result, the dependences of the normal combustion rate on the excess air ratio were obtained taking into account the lower combustion limit, the relationship between the average flow rate and the turbulent combustion rate in various combus-tion modes, and ranges for the relative flow rate in the region of low-temperature stable combustion. Based on the developed gas-dynamic model, the geometric and gas-dynamic parameters and characteristics of turbulent combustion in the flow in the combustion chambers of micro-gas turbine power plants with a capacity of 100 and 300 kW with external heating of air and fuel gas using a turbocompressor with a compression ratio of 3.0 are determined and analyzed.

Combustion process of a Helmholtz-type valveless self-excited pulse combustor with continuous supply of gas and air were studied. The basic characteristics of pulse combustion and the effects of the operating parameters on the pulse combustion were investigated. The results show that the pressure, temperature and mass fraction of propane in the combustion chamber have the phase relations and the combustion process stimulates the acoustic oscillation. The pressure amplitude in the combustion chamber is increased with the excess air ratio and inlet mass flow rate. The calculated results were compared with the experimental data and the deviation was less than 9%. The calculated results are in qualitative agreement with the experimental data. The temperature in the combustion chamber was decreased with the increase of the excess air ratio, and was increased with the inlet mass flow rate.

When diesel fuel was evaporated on a high temperature wall in a combustion chamber, a deposit was formed on the wall. Deposit formation on the wall of the combustion chamber affected a decrease of thermal conductivity. However, it is difficult to investigate directly a behavior of a diesel deposit in a diesel engine. Therefore it is necessary to develop the measurement technique for understanding the behavior of the deposit in the combustion chamber. In this study, an engine head of a small DI diesel engine was drilled in order to insert a plug for sampling of the deposit in the combustion chamber, and the deposit on the surface of the plug was collected. By using the measurement system developed, effects of wall temperature of the cylinder head and excess air ratios on the deposit formation were investigated. Moreover, thermal resistance of a PM deposit layer was estimated using a simplified engine head wall model. As the results, deposit mass in the lower wall temperature was larger than that in the higher wall temperature under the condition of the same excess air ratio. It was also clear that the deposit mass in the lower excess air ratio was larger than that in the higher excess air ratio under the condition of the same wall temperature. According to estimation of thermal resistance of the PM deposit layer, it was clarified that thermal resistance of the deposit layer with around 10μm thickness was higher than that of aluminum diecast aroy with 5mm thickness.

To establish normal reference ranges of urinary flow rates in children. From a screening programme, 200 healthy children (96 girls and 104 boys, between 3 and 18 years old) with no renal, urological, psychological or neurological disorders were selected, and they provided 433 micturitions for analysis. The children were divided into those with body surface areas of < 0.92 m2, between 0.92 and 1.42 m2 and > 1.42 m2. The voided volume, maximum and average flow rates of urine were measured. Data were fitted by several mathematical functions and goodness-of-fit determined. The relationship between maximal or average flow rates and voided volume was best fitted by a logarithmic function. The maximal and average urine flow rate nomograms are given in centile form for each body surface area group in both girls and boys. Flow rates showed a close relationship with voided volumes in both sexes and for all body sizes. The average maximal and average flow rates were higher in girls than in boys. Normal nomograms of maximal and average urine flow rates of girls and boys at three different body surfaces are presented in centile form. These may be useful for diagnosing lower urinary tract disturbances in children over a wide range of body size and voided volumes.

Combustion and emissions performance of a hybrid hydrogen–gasoline engine at idle and lean conditions

The third era in olive oil extraction sees a new generation of decanter that give the operator the possibility to chose time by time the type of working: two or three phase shifting from one solution to the other without stopping the machine and even intermediate solutions between two or three phase, making the most suitable adjustments, following olive variety, just as the machine works. A decanter centrifuge was employed during the experimental tests with variable differential speed between bowl and screw conveyor (􀀀n) and with regulation capability of oil-pulp ring levels. Thus permit to shift from three to two phase, reducing water added and discharging the following byproducts: dehydrated husk similar to that of three-phase and recovers a wet pulp that is the between the liquid phase and the solid phase. This paper aims to report the preliminary results of the energy and functional efficiency of the decanter when it works in the industrial scale plant and using a continuous method. The tests were carried out at two different flow rate values; for each flow rate the different variable differential speed between bowl and screw conveyor was varied at 15,50, 17,50 and 19,50. Quality olive, operating speed of the crusher machine and relative feed flow rate of the machine, the malaxing time and the degree of dilution of the paste, as well as the oil-pulp ring level were the same for all the trials. Irrespective of the flow rate and 􀀀n used, the machine tends to stabilize energy consumption in a very short time and values were quite similar to each other. The reductions in flow rate do not involve reductions of energy consumption indeed lead to the increase of absorption per unit mass of product worked. For all thesis studied, no significant changes of the oil recovery efficiency were found, indeed changing the flow rate and the 􀀀n a different distribution of the not extracted oil was found in the pulp and in the husk. To complete the knowledge, a set of tests changing also the oil-pulp ring levels, has been provided for the next olive oil season.

Experiments and CFD-analysis of vaneless diffusers demonstrate that in wide range of relative width there is a risk of flow separation at design flow rate as a flow angle after an impeller is too small. To avoid it the inlet part of a diffuser is made with decreasing width along radius. By the elementwise calculation the diffuser with relative width about 2%, narrowed initial part and conical surfaces with the divergence angle 30 between them is turned out to be the best variant of the considered.The diffuser within the stage with narrowed initial part and zero divergence angle has the highest efficiency when relative flow rates are less than design regime flow rate. The stage with diffuser with walls divergence angle 0045’ after narrowed part is less effective on 0.5% when relative flow rates are less than design regime. The maximum efficiency of this stage is 1.5% higher and efficiency is sufficiently higher at big flow rates.

The collection efficiency is the major indicator for the evaluation of the pollution rate and the environmental performance of the aluminium electrolysis process. This efficiency is proportional to the flow rate of the released gases at the chimney. Since December 2009, the normal flow rate has being decreasing and fluctuating in the Alucam smelting factory. At the Analysis step of the DMAIC methodology, the fundamental causes of the variations and the decrease in the gas normal fume flow rate were identified in a previous study. We intend here to stabilize the flow rate, to Improve the efficiency and to put into place a reliable mechanism of Control in order to maintain target variables within Six Sigma limits. Therefore, we propose an appropriate model of the pipeline network which permits us to identify the causes of the process low capability by excluding the interpretation controversy of the relation between the stopping of pots and the decrease in the fume collection and treatment installation. Then, we choose to achieve the modulation of the suction fan to adapt to changes in system load, and the replacement of the fan impeller to reach the continuous regulation of the flow rate. Benefits cannot be over emphasized because the company may improve on its collection and treatment efficiency, hence an effective reduction of dangerous gaseous fluoride emissions.

CFD analysis of combustion and emission characteristics of biodiesel under conventional and late-injection based premixed combustion conditions

The paper deals with the questions of introducing the additive technology of selective laser melting (SLM) into the production of the main structural elements of a combustion chamber for ground-based gas pumping, power and transport gas turbines. A fundamentally new design of a low-emission two-circuit burner was developed, adapted for the manufacture of products with a complex geometry through the use of selective laser melting (SLM) of metal powders according to mathematical CAD-models with the help of an advanced production technology. Technical difficulties associated with the implementation of additive manufacturing technology were overcome. The process chain was tried out from design to manufacturing and quality control of finished structural elements under conditions of mass production. The deficiencies of the parts manufactured by the additive technology were revealed and ultimately eliminated. Successful development of burners for a low-emission combustion chamber using a new technology significantly reduces labor intensity and time of production while maintaining high quality.

Evolution, challenges and path forward for low temperature combustion engines

Статья посвящена вопросу снижения выбросов токсичных компонентов в камерах сгорания газотурбинных двигателей за счет использования слаботочных плазмохимических стабилизаторов. Проведен анализ нестационарных процессов в низкоэмиссионной камере сгорания газотурбинного двигателя с помощью современных инструментов вычислительной гидродинамики. Разработаны практические рекомендации по повышению экологичности горения газообразного топлива в низкоэмиссионной камере сгорания ГТД.

This study numerically analyses the effects of chamber modifications to investigate the improvement of in-cylinder combustion characteristics of the diesel engine using a computational fluid dynamics (CFD) approach. Five different modified chambers, namely, the double swirl combustion chamber (DSCC), bathtub combustion chamber (BTCC), double toroidal re-entrant combustion chamber (DTRCC), shallow depth combustion chamber (SCC), and stepped bowl combustion chamber (SBCC) were developed and compared with a reference flat combustion chamber (FCC). The effects of chamber modifications on temperature formation, velocity distribution, injection profiles, and in-cylinder turbulent motions (swirl and tumble ratio) were investigated. During the compression stroke, near top dead centre, the SCC showed a peak temperature of 970 K, followed by the FCC (968 K), SBCC (967 K), and DTRCC (748 K to 815 K). The DSCC and the SCC showed a high swirl ratio above 0.6, whereas the DTRCC and the BTCC showed a high tumble ratio of approximately 0.4. This study found that the SCC, BTCC, and DSCC have better combustion rates than the FCC in terms of temperature, heat release rate, and velocity distribution. However, the DTRCC showed poor temperature formation rates and rapid heat release rates (approx. 150 J/°CA), which can lead to rapid combustion and knocking tendencies. In conclusion, the DSCC and the SCC showed better combustion rates than the other chambers. In addition, turbulent motions inside the chambers avoided combustion in crevice regions. This study recommends avoiding chambers with wider bowls in order to prevent uneven combustion across the cylinder. Furthermore, split bowls such as the DSCC, along with adjusted injection rates, can provide better results in terms of combustion.

Objectives: The aim of this study was to document if stones at the lower ureter alter the micturition capability of the patients and to investigate whether endoscopic removal of these stones restores normal urinary flow rates or not in the 3 months of follow-up. Methods: Forty patients with lower ureteral stone (group 1) and 20 control subjects with proximal ureteral stone (group 2) were enrolled into the study. All patients underwent uroflowmetry testing before and 3 months after the treatment for endoscopic stone removal. The mean average and peak flow rates with a sufficient voided volume (≥150 ml) were evaluated before and after surgery and compared between the groups. Results: Mean values of the peak flow rates before and after surgery were 20.3 and 27.5 ml/s in group 1 and 22.5 and 23.6 ml/s in group 2, and the mean average flow rate values before and after surgery were 10.5 and 13.6 ml/s in group 1 and 11.4 and 12.1 ml/s in group 2. Statistically significant differences were determined between before and after ureteroscopy values were determined in terms of average (p < 0.05) and peak flow rates (p < 0.01) in group I; however, there no significant difference was seen in the control group. Conclusion: We document for the first time in the literature that patients with lower ureteric stones have a reduction in their urinary stream which resolves with endoscopic removal of the stones.

A comparative study on effects of homogeneous or stratified hydrogen on combustion and emissions of a gasoline/hydrogen SI engine