Higher Fuel Flow Rate Research Articles

Estimation of operating parameters of a reheat regenerative power cycle using simplex search and differential evolution based inverse methods

In this study, simplex search method (SSM) and a differential evolution (DE) based inverse algorithm are applied to estimate fuel flow rate (FFR), boiler pressure (BP) and steam turbine (ST) inlet temperature (STIT) of a ST based power cycle. First a theoretical model simulates the cycle performance in terms of net power, efficiency (energy and exergy) and total irreversibility at various FFRs, BPs and STITs. The forward model based results show that the net power increases linearly with FFR while also producing more irreversible losses at higher FFR. The cycle performance also improves at higher BP and STIT. The inverse analysis shows that the DE based method is more appropriate than the SSM where the searching range of parameters is specified and parameter estimation is done from the range of specified parameter values. In SSM, the estimation depends upon the chosen initial guess values and convergence criterion sometimes is not fulfilled with some guessed values of the parameters. Both the inverse methods, however give multiple combinations of parameters and thus provides sufficient scope at the hands of the designer to select the appropriate combinations of parameters required for meeting a particular power requirement.

Experimental Study on Performance Improvement of Laminar Flow-Based Fuel Cell

The polymer electrolyte fuel cell (PEFC) is one of the promising candidates for the next generation power sources, however, there have still remained some issues such as manufacturing cost, material durability, fuel crossover and difficulty in water management. Almost all of these issues are attributed to the membrane used. The laminar flow-based fuel cell (LFFC), which is actually membraneless, has recently been proposed to overcome these issues. In LFFC, liquid fuel and liquid oxidant are supplied, flowing parallel with a thin boundary of diffusion zone, across which protons travel and electricity is generated.This study aimed to improve the performance of LFFC and identify the factors that significantly influence the fuel cell performance. Here, the basic performance of a single cell LFFC, such as OCV and I-V characteristics, was investigated experimentally in conjunction with the internal flow visualization. Methanol solution was used as fuel and hydrogen peroxide solution or air was used as oxidant. Solutions were supported by sulfuric acid to enhance ionic conductivity. In I-V characteristics measurements, experimental parameters such as flow rate, oxidant concentration, operating temperature were varied to see how these parameters influenced the performance.The results showed that the fuel cell performance was improved at higher operating temperature and oxidant concentration, however, performance improvement was not achieved at higher fuel flow rate. The results also showed that reduction of the electrode length along the flow direction decreased the influence of the boundary layer depletion and thereby improved the fuel cell performance. It was also revealed that the fuel cell performance was improved by reducing the distance between the electrodes. In conclusion, oxidant was more important than fuel in LFFC.

Large Eddy Simulation of a Bluff-Body–Stabilized Flame With Close-Coupled Liquid Fuel Injection

Large eddy simulations (LES) are performed of a bluff-body–stabilized flame with discrete liquid fuel injectors located just upstream of the bluff-body trailing edge in a so-called “close-coupled” configuration. Nonreacting and reacting simulations of the Georgia Tech single flameholder test rig [Cross et al., 2010, “Dynamics of Non-premixed Bluff Body-Stabilized Flames in Heated Air Flow,” Proceedings of ASME Turbo Expo, Paper No. GT2010-23059] are conducted using an Eulerian–Lagrangian approach with a finite volume solver. Experimental data is first used to characterize the boundary conditions under nonreacting conditions before simulating reacting test cases at two different fuel mass flow rates. The two fuel mass flow rates not only result in different global equivalence ratios but different spatial distributions of fuel, especially in the near-field wake of the bluff body. The differing spatial distribution of fuel results in two distinct flame dynamics; at the high-fuel flow rate, large-scale sinusoidal Bérnard/von-Kármán (BVK) oscillations are observed, whereas a symmetric flame is seen under the low-fuel flow rate condition.

Low calorific value fuelled distributed combustion with swirl for gas turbine applications

Distributed combustion offers significant performance improvement with near zero emissions for industrial gas turbine applications. Our efforts to further develop zero emission distributed combustion are explored here by utilizing swirl to the flow. The beneficial aspects of distributed swirl combustion using a cylindrical geometry combustor has shown low emissions of NO and CO, and significantly improved pattern factor using methane as the fuel at high thermal intensity. Biofuels, syngas and landfill gases offer superior use in gas turbine combustion. However, they are characterized by their low calorific value. Results are presented here from the distributed swirl combustor with simulated low calorific value fuels with defined mixture of methane diluted with nitrogen. The calorific value of the fuel obtained provided comparable adiabatic flame temperature and flame speed to those characteristic of low to medium calorific value syngas fuels. The results are compared with the methane fueled combustor. Experimental results from the distributed swirl combustor using methane fuel at an equivalence ratio of 0.6 and a heat release intensity of 27MW/m3-atm showed low levels of NO (∼9PPM) and low CO (∼21PPM) under non-premixed conditions. Novel Premixed Combustion design demonstrated 4PPM of NO and 11PPM of CO. In contrast methane diluted with nitrogen resulted in a dramatic decrease of NO emissions (30–50%), to provide NO emission of 7PPM (for non-premixed case) and 2.8PPM (premixed case), at the same conditions, with minimal impact on CO for all the conditions examined here. The combustor provided no instability or flame flashback at higher fuel flow rates (to maintain the same thermal load as with methane fuel). Results obtained with different calorific value fuels on the emissions of NO and CO, lean stability limit and OH* chemiluminescence are presented. The results showed favorable operation of the distributed swirl combustor for applications with both high and low calorific value fuels, such as, methane, synfuel and landfill gases to power the gas turbines without any combustor modifications.

Effects of a 70% biodiesel blend on the fuel injection system operation during steady-state and transient performance of a common rail diesel engine

The results of steady state and transient engine bench tests of a 2.0l common-rail passenger car diesel engine fuelled by B70 biodiesel blend are compared with the corresponding results of baseline tests with standard EN 590 diesel fuel. The macroscopic steady-state performance and emissions of the same engine has already been presented elsewhere. The current study demonstrates how the engine management system responds to different fuel properties, with focus to the fuel system dynamics and the engine’s transient response. A set of characteristic transient operation points was selected for the tests. Data acquisition of engine ECU variables was made by means of INCA software/ETAS Mac2 interface. Additional data acquisition regarding engine performance was based on external sensors. The results indicate significant differences in fuel system dynamics and transient engine operation with the B70 blend at high fuel flow rates. Certain modifications to engine ECU maps and control parameters are proposed, aimed at improvement of transient performance of modern engines run on high percentage biodiesel blends. However, a high pressure pump failure that was observed after prolonged operation with the B70 blend, hints to the use of more conservative biodiesel blending in fuel.

Parametric analysis of a hybrid power system using organic Rankine cycle to recover waste heat from proton exchange membrane fuel cell

Using fuel cell systems for distributed generation (DG) applications represents a meaningful candidate to conventional plants due to their high power density and the heat recovery potential during the electrochemical reaction. A hybrid power system consisting of a proton exchange membrane (PEM) fuel cell stack and an organic Rankine cycle (ORC) is proposed to utilize the waste heat generated from PEM fuel cell. The system performance is evaluated by the steady-state mathematical models and thermodynamic laws. Meanwhile, a parametric analysis is also carried out to investigate the effects of some key parameters on the system performance, including the fuel flow rate, PEM fuel cell operating pressure, turbine inlet pressure and turbine backpressure. Results show that the electrical efficiency of the hybrid system combined by PEM fuel cell stack and ORC can be improved by about 5% compared to that of the single PEM fuel cell stack without ORC, and it is also indicated that the high fuel flow rate can reduce the PEM fuel cell electrical efficiency and overall electrical efficiency. Moreover, with an increased fuel cell operating pressure, both PEM fuel cell electrical efficiency and overall electrical efficiency firstly increase, and then decrease. Turbine inlet pressure and backpressure also have effects on the performance of the hybrid power system.

Hydrodynamic focusing in microfluidic membraneless fuel cells: Breaking the trade-off between fuel utilization and current density

Microfluidic membraneless fuel cell (MFC) is a promising fuel cell type due to its simple structure without the need of proton conducting membrane. However, the common disadvantage is the low fuel utilization. Previous works have shown that adopting a conventional method to increase the fuel utilization would cause a low power density. This study shows that the use of hydrodynamic focusing technology can overcome the trade-off problem between the fuel utilization and the current density. A numerical model has been developed to simulate the MFC operation with the fuel stream being hydrodynamically focused by a buffer stream. The results indicate that both fuel utilization and current density can be increased by properly adjusting the buffer flow rate to enhance the flow focusing. The optimal performance is achieved when the buffer-to-fuel flow rate ratio is around 25. Moreover, high fuel flow rate and shallow channel shape have proven beneficial to the cell performance with the use of hydrodynamic focusing technology. It is predicted that a MFC with a current density above 100 mA cm −2 is capable of achieving fuel utilization up to 50%, which is considerably higher than the previously reported value of 5–8%.

Impact of co-flow air on buoyant diffusion flames flicker

This paper describes experimental investigation of co-flow air velocity effects on the flickering behaviour of laminar non-lifted methane diffusion flames. Chemiluminescence, high-speed photography, schlieren and Particle Imaging Velocimetry (PIV), have been used to study the changes in the flame/vortex interactions as well as the flame flickering frequency and magnitude by the co-flow air. Four cases of methane flow rates at different co-flow air velocities are investigated. It has been observed that the flame dynamics and stability of co-flow diffusion flames are strongly affected by the co-flow air velocity. When the co-flow velocity has reached a certain value the buoyancy driven flame oscillation was completely suppressed. The schlieren and PIV imaging have revealed that the co-flow of air is able to push the initiation point of the outer toroidal vortices beyond the visible flame to create a very steady laminar flow region in the reaction zone. Then the buoyancy driven instability is only effective in the plume of hot gases above the visible flame. It is observed that a higher co-flow rate is needed in order to suppress the flame flickering at a higher fuel flow rate. Therefore the ratio of the air velocity to the fuel velocity, γ, is a stability controlling parameter. The velocity ratio, γ, was found to be 0.72 for the range of tested flow rates. The dominant flickering frequency was observed to increase linearly with the co-flow rate ( a) as; f = 0.33 a + 11. The frequency amplitudes, however, were observed to continuously decrease as the co-flow air was increasing.

Influence of the Primary Jets and Fuel Injection on the Aerodynamics of a Prototype Annular Gas Turbine Combustor Sector

Transverse dilution jets are widely used in combustion systems. The current research provides a detailed study of the primary jets of a realistic annular combustion chamber sector. The combustor sector comprises an aerodynamic diffuser, inlet cowl, combustion dome, primary dilution jets, secondary dilution jets, and cooling strips to provide convective cooling to the liner. The chamber contracts toward the end to fit the turbine nozzle ring. 2D PIV is employed at an atmospheric pressure drop of 4% (isothermal) to delineate the flow field characteristics. The laser is introduced to the sector through the exit flange. The interaction between the primary jets and the swirling flow as well as the sensitivity of the primary jets to perturbations is discussed. The perturbation study includes: effect of partially blocking the jets, one at a time, the effect of blocking the convective cooling holes, placed underneath the primary jets and shooting perpendicular to it. In addition, the effect of reducing the size of the primary jets as well as off-centering the primary jets is explained. Moreover, PIV is employed to study the flow field with and without fuel injection at four different fuel flow rates. The results show that the flow field is very sensitive to perturbations. The cooling air interacts with the primary jet and influences the flow field although the momentum ratio has a 100:1 order of magnitude. The results also show that the big primary jets dictate the flow field in the primary zone as well as the secondary zone. However, relatively smaller jets mainly influence the primary combustion zone because most of the jet is recirculated back to the CRZ. Also, the jet penetration is reduced with 25% and 11.5% corresponding to a 77% and 62% reduction of the jet’s area, respectively. The study indicates the presence of a critical jet diameter beyond which the dilution jets have minimum impact on the secondary region. The jet off-centering shows significant effect on the flow field though it is in the order of 0.4 mm. The fuel injection is also shown to influence the flow field as well as the primary jets angle. High fuel flow rate is shown to have very strong impact on the flow field and thus results in a strong distortion of both the primary and secondary zones. The results provide useful methods to be used in the flow field structure control. Most of the effects shown are attributed to the difference in jet opposition. Hence, the results are applicable to reacting flow.

5143 Resource-based data availability for erbB2-driven breast cancer in Asian women: experts' opinion

In this study, simplex search method (SSM) and a differential evolution (DE) based inverse algorithm are applied to estimate fuel flow rate (FFR), boiler pressure (BP) and steam turbine (ST) inlet temperature (STIT) of a ST based power cycle. First a theoretical model simulates the cycle performance in terms of net power, efficiency (energy and exergy) and total irreversibility at various FFRs, BPs and STITs. The forward model based results show that the net power increases linearly with FFR while also producing more irreversible losses at higher FFR. The cycle performance also improves at higher BP and STIT. The inverse analysis shows that the DE based method is more appropriate than the SSM where the searching range of parameters is specified and parameter estimation is done from the range of specified parameter values. In SSM, the estimation depends upon the chosen initial guess values and convergence criterion sometimes is not fulfilled with some guessed values of the parameters. Both the inverse methods, however give multiple combinations of parameters and thus provides sufficient scope at the hands of the designer to select the appropriate combinations of parameters required for meeting a particular power requirement.

Experimental Investigation of the Acoustic Field in a Bluff-Body Combustor

Experimental results on the longitudinal acoustic field generated by a methane-air turbulent flame stabilized downstream of a bluff body (V-gutter) confined in a rectangular duct are presented. The V-gutter runs straight across the width of the rectangular cross-section of the duct. The fuel is injected at some distance upstream of the bluff body, as in practical combustors. Varying the distance between the fuel injection and the bluff body alters the degree of fuel-air mixing and hence influences the flame structure, and consequently the nature of the generated acoustic field. Other geometrical variations considered are the length of the combustor duct, the axial location of the bluff body, and the width of the bluff body. The flow rates of air and fuel are varied widely to traverse conditions of generation of low-amplitude broadband noise to those of excitation of high-amplitude discrete tones. The observed dominant frequencies are expressed in terms of non-dimensional numbers such as the Helmholtz number and the Strouhal number, representing the natural acoustic modes and the free-field vortex shedding process, respectively. It is seen that, as the flow conditions are varied, the amplitude of the dominant frequency steeply rises, accompanying an abrupt jump in the dominant frequency from a constant Helmholtz number regime to a constant Strouhal number regime. High-speed images of CH* chemiluminescence of the flame zone exhibit periodic shedding of vortical structures at the same dominant frequencies as in the observed acoustic spectra. These results show that the natural acoustic modes shift to follow the vortex shedding trend with the Reynolds number of the air-flow, under conditions of excitation of loud discrete tones. Higher fuel flow rates are observed to be capable of exciting higher acoustic modes to exhibit the above behaviour. A larger location of the bluff body away from the fuel injection location, and a lesser width of the bluff body, tend to excite acoustic oscillations of lower amplitude.

Investigation of a combustion driven oscillation in a refinery flare: Part B: Visualisation of a periodic flow instability in a bifurcating duct following a contraction

A flow visualisation study was performed to investigate a periodic flow instability in a bifurcating duct within the tip of the flares at the Shell refinery in Clyde, NSW, to verify the trigger of a combustion-driven oscillation proposed in Part A of this study, and to identify its features. The model study assessed only the flow instability, uncoupled from the acoustic resonance and the combustion that are also present in the actual flare. Three strong, coupled flow oscillations were found to be present in three regions of the fuel line in the flare tip model. A periodic flow separation was found to occur within the contraction at the inlet to the tip, a coupled, periodic flow oscillation was found in the two transverse “cross-over ducts” from the central pipe to the outer annulus and an oscillating flow recirculation was present in the “end-cap” region of the central pipe. The dimensionless frequency of these oscillations in the model was found to match that measured in the full-scale plant for high fuel flow rates. This, and the strength of these flow oscillations, gives confidence that they are integral to the full-scale combustion-driven oscillation and most likely the primary trigger. The evidence indicates that the periodic flow instability is initiated by the separation and roll-up of the annular boundary layer at the start of the contraction in the fuel section of the flare tip. The separation generates an annular vortex which interacts with the blind-ended pipe downstream, leading to a pressure wave which propagates back upstream, initiating the next separation event and repeating the cycle. The study also investigated flow control devices with a view to finding a practical approach to mitigate the oscillations. The shape of these devices was constrained to allow installation without removing the tip of the flare. This aspect of the study highlighted the strength and nature of the coupled oscillation, since it proved to be very difficult to mitigate the oscillation in this way. An effective configuration is presented, comprising of three individual components, all three of which were found to be necessary to eliminate the oscillation completely.

Bifurcations and structure of surface interacting methane–air diffusion flames

Methane–air diffusion flames near surfaces are modeled using numerical bifurcation theory. Ignition, extinction, and stability boundaries are studied as functions of fuel flow rate and oxidizer strain rate, using three reaction mechanisms of varying complexity (a one-step reaction, a C 1 reaction mechanism, and the Gas Research Institute [GRI 1.2] mechanism). It is found that as the fuel flow rate increases, the ignition temperature increases, whereas the extinction temperature decreases. For sufficiently high fuel flow rates and low oxidizer strain rates, the flame separates from the surface, and extinction cannot be caused by thermal quenching. In the absence of surface heat loss, two distinct extinction branches are found, namely, a blowoff or stretch limit branch at high fuel flow rates and a thermal quenching limit branch at low fuel flow rates. The complexity of the reaction mechanism affects primarily the blowoff branch at high fuel flow rates but not the thermal quenching branch due to the O 2 leaking through the reaction zone at low strain rates. Surface radiation alters the bifurcation behavior, beyond an absolute stability curve. The theoretically predicted flame structure and stability limits compare well with experimental results. Implications for modeling of extinction of complex condensed fuels are also discussed.

Effect of Fuel Flow Rate to the flow Structure and Vortex Shedding behind a Bluff Body.

A fiber Laser Doppler Velocimeter(LDV)was used to measure a flow field behind a bluff body at high fuel flow rate condition which was considered to be close to the real operating circumstances in reacting flow. These results were compared to that of low fuel flow rate condition in smooth combustion in order to understand the reason of the onset of rough combustion characterised by flame stretch, noise generation and oscillating combustion. It was found that as the fuel flow rate increased, the reverse flow regions started to show very complex shapes because of the fuel jet penetration. At the end, the recirculation zones combined surrounding the jet. This recirculation zone combination hindered the growth of the recirculation zone itself. Therefore, the air entrainment flow rate into the flame holding regions was not proportional to the increase of bulk air velocity and fuel flow rate. Oscillating frequency was observed in velocity power spectrum at high fule flow rate. The very sharp peak at high frequency was due to the vortex shedding. The main reason of rough combustion at high fuel flow rate were found to be the lack of air entrainment caused by the combination of the recirculation zones together with the vortex shedding behind the bluff body.