FUEL AND COMBUSTION
Year:2016 | Volume:9 | Issue:1|Papers Count:7

In the present work, the relations between three output quantities measured in an experimental combustor and two input quantities of overall equivalence ratio (j) and secondary fuel injection rate (Qsec) were studied. The three measured output quantities of the combustor are the amount of NOx emission, noise level, and the level of pressure oscillations generated by the combustion field. The experimental combustor has certain applications in power plant gas turbines. In order to study the relations between the measured output and input quantities of the combustor, two different data mining approaches were utilized. Specifically, in this research, Multilayer Perceptron (MLP) Neural Network and Response Surface Method (RSM) techniques were employed to provide an estimation of the nonlinear relationship between the inputs and outputs of the combustor. The related experiments were already performed using four different types of secondary fuel injectors (with different designs) for an overall equivalence ratio between j=0.7~0.9, along with different amounts of secondary fuel injection rate in the range of Qsec=0.6~4.2 l/min. The results show that, in general, both the MLP neural network and RSM approaches have good predicting capability for estimation of noise level, level of pressure oscillations, and NOx emission. However, the degree of agreement between the predicted and measured values would even be enhanced for the case of NOx emission. Also, comparing the two data mining methods, the results indicate that the MLP neural network has better prediction ability for estimation of various combustor parameters than the RSM, for the cases of different injectors.

In this paper, the effects of varying intake air temperature and pressure on RCCI engine are investigated. Combustion in an RCCI engine is controlled by varying the fuel reactivity in the combustion chamber, but it also affects some initial states and consequently performance parameters such as NOx formation and Ringing Intensity. In this paper, iso-octane as a low reactivity fuel and n-heptane as a high reactivity fuel have been used, and both speed and load have been swept to investigate the engine performance parameters. Different points in the engine performance interval from 1300rpm to 3100rpm have been considered, while varying the iso-octane to n-heptane ratio in a total fuel mass of 60mg and 100mg. The intake air temperature has been varied from -20o to 60o and its pressure from 30 to 60kPa. Lower NOx and Ringing Intensity and higher thermal efficiency are the best criteria for a good combustion in an RCCI engine. Therefore, based upon these criteria, the best conditions for a normal combustion are determined by varying the intake air temperature and pressure.

The purpose of the current study is to investigate the effects of gas flow in anode channel and within anode electrode on concentration impedance of a solid oxide fuel cell. The gas phase mass transport is modelled using transient conservation equations (momentum and species equations). Results show that gas flow and mass transport in the gas channel results in a depressed semicircle in the Nyquist plot with low relaxation frequency (less than 10Hz). In addition, gas transport in the thick porous anode leads to a Warburg diffusion impedance with relatively higher relaxation frequency (around 100Hz). The influences of parameters such as inlet gas velocity, electrode thickness and inlet gas compositions are also investigated and the results are discussed. From the simulation results, it is found that the EIS simulation produces a tool for both analysing experimental results of EIS and performance optimization of fuel cells. In addition, the developed simulation tool may allow for a reduction in the amount of costly trial and error experiments.

The present numerical study investigates the effects of a step in a micro scale combustor on blow out limit and outer wall temperature. Also, the effects of the equivalence ratio of hydrogen-air mixture and combustion material on the emitter efficiency are scrutinized. The effects of the step in combustor is studied from two viewpoints: first the existence of the step, and second the step height and combustor diameter. The results showed that blow out limit is increased when using a step at the entrance of the combustion chamber. Besides, the mean wall temperature increases, while the flame temperature in the micro burner shows a more uniform behavior. It was observed, by comparing combustor 2 and 3, that the combustor with the lowest step height had higher (mean) wall temperature. On the other hand, the combustor with larger diameter achieves higher mean wall temperature. In this study, the effects of the equivalence ratio and conduction heat transfer coefficient on radiation efficiency of the micro burner are also investigated. It was observed that the maximum emitter efficiency of the micro burner is achieved for lean mixture. It was also observed that the conduction heat transfer coefficient has an optimum value.

In this paper, the operating parameters of a swirl injector were studied as a function of Reynolds number (Re) and Weber number (We). Spray cone angle, liquid sheet breakup length and injector discharge coefficient are the parameters which their dimensionless variations were studied to characterize the injector behavior in terms of Re and We. At the end, these experimental results were compared with those of some famous models, such as LISA. All the experiments were prformed using a simplex swirl injector. Moreover, water was used as the operating fluid sprayed in atmospheric conditions. The Shadowgraphy imaging method was used to visualize the injection spray. Experimental results show that by increasing Re, the injection regime varies from Dripping Mode to Atomization Mode at Re=3´104, and by further increasing Re, the fully developed mode (that creates a clear conical sheet) is achieved at Re=3.7´104. Also, results show that the breakup length varies with We-0.5Re0.6 linearly. Although increasing Re initially increases the spray cone angle, but beyond a specific Re, this trend is stopped.

Nowadays, the world is facing the air pollution and global warming crisis, in which the role of internal combustion engines is significant. On the other hand, in spite of diversities in its composition, compressed natural gas is considered as one of the best choices among alternative fuels. This investigation aims to explore the effects of hydrogen enrichment on formation of pollutants and greenhouse gases in engines working with natural gas at high compression ratios distributed in the city of Tehran. To accomplish this, a previously validated detailed chemical mechanism is embedded with a comprehensive one-dimensional engine model and the results are verified with experimental observations on fuel and air mass flow rates and in-cylinder pressure profile for a single-cylinder gas-fuelled spark ignition test engine, at constant engine speed of 2000rpm and compression ratio of 16. The verified model is then employed for performance and emission predictions under different amounts of hydrogen enrichment. The results indicate that with increase in the volume of hydrogen, the amount of emitted CO, CO2 and CH4 reduces, whereas despite the rise in the maximum in-cylinder pressure, the indicated mean effective pressure decreases.

In the current paper a new approach is provided for prediction of Lean blow out, based on combining cold flow numerical simulations with test results in a particular combustion chamber based on loading parameter. Two approaches are presented to calculate these parameters using Ansys Fluent software. In the first method, only the species transport motif and in second method, the evaporation and atomization of kerosene fuel have been implicated to achieve more accurate results. Finally, the results of these two methods and also a code based on semi-empirical model were compared with experimental results. The errors of the semi-empirical code, first and second numerical methods were obtained as 46.73, 11.48 and 1.86, respectively.