Prediction of the flow inside a micro gas turbine combustor

The main purpose of this study is to predict the flow dynamics inside a micro gas turbine combustor model. The flow field inside the combustor is controlled by the liner shape and size, wall side holes shape, size and arrangement (primary, secondary and dilution holes), and primary air swirler configuration. Air swirler adds sufficient swirling to the inlet flow to generate central recirculation region (CRZ) which is necessary for flame stability and fuel air mixing enhancement. Therefore designing an appropriate air swirler is a challenge to produce stable, efficient and low emission combustion with low pressure losses. Four axial flat vane swirlers with 20 °, 30 °, 45 ° and 60 ° vane angle corresponding to swirl number of 0.27, 0.42, 0.74, and 1.285 respectively were used in this analysis to show vane angle effect on the internal flow field. The flow behavior was investigated numerically using CFD solver FLUENT 6.2. This study has provided physical insight into the flow pattern inside the combustion chamber. Results show that the swirling action is augmented with the increase in the vane angle, which leads to increase in the turbulence strength, recirculation zone size, and amount of recirculated mass. However, all these happen at the expense of the increase in pressure losses. In case of 20 ° swirler (swirl number < 0.4), the produced swirling flow is not enough to generate CRZ

Enhancement of palm oil blends atomization and spray using swirling flow

Blending of palm oil with petroleum derivatives and controlling the swirl flow strength and direction can overcome the poor physical properties of such fuel and enhance its spray atomization. In this work, evaluations of the blends with and without swirl flow were done by comparing their spray characteristics. Then they were compared with the spray characteristics of diesel fuel. The objectives of this research are to study the effects of blending ratios on the spray characteristics and to evaluate the effects of swirling flow on the spray characteristics. Two new designs of air swirlers were found to be capable of producing variable swirl flow strengths and directions. To characterize the spray of the Refined, Bleached, Deodorized Palm Oil (RBDPO)/diesel blends under different swirl strengths and directions, five blends of B5, B10, B15, B20 and B25 were physically blended on volume basis. The physical properties of the blends were experimentally and analytically determined. A Phase Doppler Particle Analyzer (PDPA) was used to measure the droplet size while direct photography was used to measure the spray angle. The Lagrangian Dispersed Phase Model (DPM) was used to simulate the spray of the various RPDPO/diesel blends in an unconfined domain. The three dimensional spray CFD model was first validated for the case of diesel spray with the experimental results. The validated model was then used to characterize the spray of RPDPO/diesel blends. The results showed that when the volume blending ratio increased to 0.25 (B25), the percentage increase in Sauter mean diameter (SMD) was 57.25% and percentage decrease in spray angle was 12.23% compared to the diesel fuel. The results also showed that when the swirl number increased from 0.654 to 1.57, a reduction of 46.39% in SMD was achieved with the improvement in the particle dispersion. In addition the results showed that when the direction of swirled air stream changed from co-rotating flows to the counter-rotating flows, the SMD was reduced by 13.99 % with better spatially dispersed spray due to the increase in the shear layers produced and the improved turbulent mixing. The findings suggest that the two blends B5 and B10 were comparable with diesel in terms of fuel physical properties and spray characteristics. It was also found that the optimum swirl number for B15 is 1.273, which resulted in 36.9 % reduction in SMD. This meant that this swirl number produced comparable spray characteristics to diesel spray for blend B15, and higher blends needed higher swirl numbers. Finally it was also found that the counter-rotating swirler is more appropriate for the RBDPO blends than the co-rotating swirle

Numerical investigation of the flow inside primary zone of tubular combustor model

In this study, a numerical simulation of non-reacting flow inside a gas turbine combustor model was performed. The main target of this investigation is to get physical insight of the main vortex, responsible for the efficient mixing of fuel and air. Such models are necessary for developing and optimization of real combustors. Combustor swirler assists the fuel-air mixing process by producing recirculation region which can act as flame holders as well. Therefore, proper selection of a swirler is needed to stabilize the flame, to enhance combustor performance and to reduce NOx emissions. For that reason, several axial swirlers with different configurations were employed to show their effects on primary zone aerodynamics performance. The three-dimensional, steady, turbulent and isothermal flow inside the combustor model was simulated using a finite volume based CFD code FLUENT 6.2. The combustor model geometry was created by means of solid model CAD software then the meshing was generated using GAMBIT preprocessing software subsequently, and the solution and the results analysis were carried out in a FLUENT solver. The effects of different swirlers’ configurations and inlet mass flow rate on flow dynamics were examined. A two recirculation zones were predicted, the first one is a central recirculation and located in the region immediately downstream of the swirler and the second is corner recirculation and located in the upstream corner of the combustion chamber. The results show that swirlers’ configuration and inlet mass flow rate have a significant effect on the combustor flowfield and pressure losses. By the mean that as swirl number increases the central recirculation zone size, turbulence production and pressure loss increase

Combustor aerodynamics

This book describes the new innovation of gas turbine swirler. The novel swirler is a multiple entry swirler which allows the swirl number to vary on the same value of Reynolds number, by regulating the ratio between the axial and tangential flow momentum. Three–dimensional turbulence and isothermal flow characteristics of an abrupt combustor model with different type of swirler (axial, radial and multiple inlet) were simulated with Reynolds–Averaged Navier–Stokes (RANS) using ANSYS Fluent 12 software. Results of the different turbulence models used in swirling flow were reviewed and compared. The different swirler’ aerodynamic performance was investigated through Computational Fluid Dynamics (CFD) simulations. The aerodynamics performance includes shape and size of the Central Recirculation Zone (CRZ), turbulence intensity and pressure losses. It was found that the size of then CRZ and turbulence strength is directly proportional to the tangential axial air flow rate ratio. Therefore, proper selection of a swirler is needed to enhance combustor performance and to reduce exhaust emissions

Large eddy simulation and preliminary modeling of the flow downstream a variable geometry swirler for gas turbine combustors

This work presents a novel swirler with variable blade configuration for gas turbine combustors and industrial burners. The flow dynamics downstream the swirler was explored using Large Eddy Simulation (LES). The resolved turbulence kinetic energy in the region where the flow exhibits the main flow phenomena was well above 80% of the total turbulent kinetic energy of the flow. It was evidently shown that the new swirler produces a central recirculation zone and a Rankine vortex structure which are necessary for swirl flame stabilization. Two Reynolds-averaged NavierStokes (RANS) simulation cases utilizing the standard and realizable k-ε turbulence models were also conducted for two objectives. The first is to demonstrate the validity of RANS/eddy-viscosity models in predicting the main characteristics of swirling flows with comparison to the LES results. The second objective is to comparatively investigate the flow features downstream the new swirler in both co-rotating and counter-rotating blade configurations. The results show that the counter-rotating configuration produces higher turbulence kinetic energy and more compact recirculation zone compared to the co-rotating configuration

Performance characteristics of a supercharged variable compression ratio diesel engine fueled by biodiesel blends

Massive pressure was recently exerted on the automotive industry to explore sustainable and eco-friendly fuels. Biodiesel has attracted many researchers over the last decades as an important source of alternative fuel. The redeeming feature of biodiesel is that it reduces the emission of exhaust harmful gases, however, this feature comes at engine performance penalty. Therefore, this study was carried out to investigate the effect of varying the air flow and compression ratios on the performance of biodiesel-diesel fuel engines. The biodiesel was sourced from the transesterification of waste frying oil and was used in selected blends with ratios, by volume ranging from a volume of 0–50% biodiesel-diesel blend. A four strokes naturally-aspirated direct injection diesel engine was investigated in this study. The engine was equipped with a supercharger to increase the density of air supplied to the engine, and with another device to change the compression ratios. The engine brake power, brake specific fuel consumption and brake thermal efficiency were the performance parameters of the present work. The engine was kept running over a speed range from 1000 to 2000 rpm at 250 rpm intervals and three compression ratios (14, 16 and 18) under full load mode of operation, and different intake air pressures. The result indicated that forced induction operation using the supercharger increased the performance of the dual fuel mode by 25% at the highest compression ratio (18) compared to that of natural aspiration. On the other hand, it was revealed that the higher the compression ratio of the engine, the higher the performance obtained from the blend. In fact, supercharging the engine along with the higher compression ratio improved the penetration of the forced air into the fuel charge despite the biodiesel higher viscosity. The appropriate penetration of the biodiesel warranted the higher temperature and pressure in the engine cylinder, which in turn improved the combustion and performance of the dual fuel engine. Keywords: Diesel engine, Biodiesel, Supercharger, Compression ratio, Performanc

A multiple inlet swirler for gas turbine combustors

The central recirculation zone (CRZ) in a swirl stabilized gas turbine combustor has a dominant effect on the fuel air mixing process and flame stability. Most of state of the art swirlers share one disadvantage; the fixed swirl number for the same swirler configuration. Thus, in a mathematical sense, Reynolds number becomes the sole parameter for controlling the flow characteristics inside the combustor. As a result, at low load operation, the generated swirl is more likely to become feeble affecting the flame stabilization and mixing process. This paper introduces a new swirler concept which overcomes the mentioned weakness of the modern configurations. The new swirler introduces air tangentially and axially to the combustor through tangential vanes and an axial vanes respectively. Therefore, it provides different swirl numbers for the same configuration by regulating the ratio between the axial and tangential flow momenta. The swirler aerodynamic performance was investigated using four CFD simulations in order to demonstrate the impact of tangential to axial flow rate ratio on the CRZ. It was found that the length of the CRZ is directly proportional to the tangential to axial air flow rate ratio

Experimental investigation of spray characteristics of refined bleached and deodorized palm oil and diesel blends using phase doppler particle alyzer

The unstable oil prices in the world market lead many countries to seek an alternative fuel to substitute petroleum oil. Palm oil derived fuel is one of such alternatives, which can be used as fuel in several methods, such as preheating, blending with other petroleum fuels, trans-esterification and etc. The objective of this paper is to characterize the spray of the refined, bleached, and deodorized palm oil (RBDPO) and diesel blends. Five blends B5, B10, B15, B20 and B25 were physically blended using lab scale dynamic double propeller mixer and the main physical properties (density, viscosity and surface tension) that have the main effect on the spray pattern were measured. A phase doppler particle analyzer (PDPA) was used to characterize the spray including particles Sauter mean diameter (SMD). Direct photography was used to determine the spray angle for the different blends. Results show that as the percentage of RBDPO increases in the blend, the SMD increases and the spray angle decreases. The percentage increase in the SMD from B0 to B25 was approximately 15% while the decrease in the spray angle is 9.44°. It can be concluded that the blends B5 and B10 could be used in the power engines without fuel system modification. However evaluation of the combustion performance should be done for all blends

Turbulence modelling: basic, capabilities and areas of needed research

Turbulence modeling is one of the three key elements in Computational Fluid Dynamics (CFD). The other two elements, which are the grid generation and the algorithm development, have been dramatically evolved using very precise mathematical theories. However, this is not the case when it comes to turbulence modeling, in fact, some CFD researchers regard turbulence modeling as the black magic of CFD. The lack of these precise theories in turbulence modeling stems from the ambiguity of the turbulence phenomena itself, indeed, in turbulence modeling, it is tried to mathematically approximate a phenomenon which is not yet physically understood. Scientists started to consider turbulence in fluids more than a century ago. Nowadays, a comprehensive theory for turbulence has been not found yet. However, in this long period of time scientists have produced a huge library of mathematical models that can be used to approximate the physics occurring in a turbulent flow. Most of these models are based on physical reasoning and dimensional analysis, that is, none of these models provide an exact mathematical description of turbulence