Abstract: This paper presents a cold flow simulation study of a small gas turbine combustor performed using laboratory scale test rig. The main objective of this investigation is to obtain physical insight of the main vortex, responsible for the efficient mixing of fuel and air. Such models are necessary for predictions and optimization of real gas turbine combustors. Air swirler can control the combustor performance by assisting in the fuel-air mixing process and by producing recirculation region which can act as flame holders and influences residence time. Thus, proper selection of a swirler is needed to enhance combustor performance and to reduce NOx emissions. Three different axial air swirlers were used based on their vane angles i.e., 30°, 45°, and 60°. Three-dimensional, viscous, turbulent, isothermal flow characteristics of the combustor model operating at room temperature were simulated via Reynolds- Averaged Navier-Stokes (RANS) code. The model geometry has been created using solid model, and the meshing has been done using GAMBIT preprocessing package. Finally, the solution and analysis were carried out in a FLUENT solver. This serves to demonstrate the capability of the code for design and analysis of real combustor. The effects of swirlers and mass flow rate were examined. Details of the complex flow structure such as vortices and recirculation zones were obtained by the simulation model. The computational model predicts a major recirculation zone in the central region immediately downstream of the fuel nozzle and a second recirculation zone in the upstream corner of the combustion chamber. It is also shown that swirler angles changes have significant effects on the combustor flowfield as well as pressure losses.
Abstract: Due to environmental concerns, the recent regulation on automobile fuel economy has been strengthened. The market demand for efficient vehicles is growing and automakers to improve engine fuel efficiency in the industry have been paying a lot of effort. To improve the fuel efficiency, it is necessary to reduce losses or to improve combustion efficiency of the engine. VVA (Variable Valve Actuation) technology enhances the engine's intake air flow, reduce pumping losses and mechanical friction losses. And also, VVA technology is the engine's low speed and high speed operation to implement each of appropriate valve lift. It improves the performance of engine in the entire operating range. This paper presents a design procedure of DC motor and drive for VVA system and shows the validity of the design result by experimental result with prototype.
Abstract: High-velocity oxygen fuel (HVOF) thermal spraying
uses a combustion process to heat the gas flow and coating material.
A computational fluid dynamics (CFD) model has been developed to
predict gas dynamic behavior in a HVOF thermal spray gun in which
premixed oxygen and propane are burnt in a combustion chamber
linked to a parallel-sided nozzle. The CFD analysis is applied to
investigate axisymmetric, steady-state, turbulent, compressible,
chemically reacting, subsonic and supersonic flow inside and outside
the gun. The gas velocity, temperature, pressure and Mach number
distributions are presented for various locations inside and outside
the gun. The calculated results show that the most sensitive
parameters affecting the process are fuel-to-oxygen gas ratio and
total gas flow rate. Gas dynamic behavior along the centerline of the
gun depends on both total gas flow rate and fuel-to-oxygen gas ratio.
The numerical simulations show that the axial gas velocity and Mach
number distribution depend on both flow rate and ratio; the highest
velocity is achieved at the higher flow rate and most fuel-rich ratio.
In addition, the results reported in this paper illustrate that the
numerical simulation can be one of the most powerful and beneficial
tools for the HVOF system design, optimization and performance
analysis.
Abstract: Nowadays, the importance of energy saving is clearance to everyone. By attention to increasing price of fuels and also the problems of environment pollutions, there are the most efforts for using fuels littler and more optimum in everywhere. This essay studies optimizing of gas consumption in gas-burner space heaters. In oven of each gas-burner space heaters there is two snags to prevent the hot air (the result of combustion of natural gas) to go out of oven of the gas-burner space heaters directly without delivering its heat to the space of favorite environment like a room. These snags cause a excess circulating that helps hot air deliver its heat to the space of favorite environment. It means the exhaust air temperature will be decreased then when there are no snags. This is the aim of this essay to use maximum potential energy of the natural gas to make heat. In this study, by the help of a finite volume software (FLUENT) consumption of the gas-burner space heaters is simulated and optimized. At the end of this writing, by comparing the results of software and experimental results, it will be proved the authenticity of this method.
Abstract: In this work, the effects of scale on thermal behavior of the slab in a walking-beam type reheating furnace is studied by considering scale formation and growth in a furnace environment. Also, mathematical heat transfer model to predict the thermal radiation in a complex shaped reheating furnace with slab and skid buttons is developed with combined nongray WSGGM and blocked-off solution procedure. The model can attack the heat flux distribution within the furnace and the temperature distribution in the slab throughout the reheating furnace process by considering the heat exchange between the slab and its surroundings, including the radiant heat transfer among the slabs, the skids, the hot combustion gases and the furnace wall as well as the gas convective heat transfer in the furnace. With the introduction of the mathematical formulations validation of the present numerical model is conducted by calculating two example problems of blocked-off and nongray gas radiative heat transfer. After discussing the formation and growth of the scale on the slab surface, slab heating characteristics with scale is investigated in terms of temperature rise with time.
Abstract: Palm methyl ester (PME) is one of the alternative
biomass fuels to liquid fossil fuels. To investigate the combustion
characteristics of PME as an alternative fuel for gas turbines, combustion experiments using two types of burners under atmospheric
pressure were performed. One of the burners has a configuration
making strong non-premixed flame, whereas the other has a
configuration promoting prevaporization of fuel droplets. The results
show that the NOx emissions can be reduced by employing the latter burner without accumulation of soot when PME is used as a fuel. A
burner configuration promoting prevaporzation of fuel droplets is
recommended for PME.
Abstract: The experimental results on combustion of rice husk
in a conical fluidized bed combustor (referred to as the conical FBC)
using silica sand as the bed material are presented in this paper. The
effects of excess combustion air and combustor loading as well as the
sand bed height on the combustion pattern in FBC were investigated.
Temperatures and gas concentrations (CO and NO) along over the
combustor height as well as in the flue gas downstream from the ash
collecting cyclone were measured. The results showed that the axial
temperature profiles in FBC were explicitly affected by the
combustor loading whereas the excess air and bed height were found
to have minor influences on the temperature pattern. Meanwhile, the
combustor loading and the excess air significantly affected the axial
CO and NO concentration profiles; however, these profiles were
almost independent of the bed height. The combustion and thermal
efficiencies for this FBC were quantified for different operating
conditions.
Abstract: An effort has been taken to simulate the combustion
and performance characteristics of biodiesel fuel in direct injection
(D.I) low heat rejection (LHR) diesel engine. Comprehensive
analyses on combustion characteristics such as cylinder pressure,
peak cylinder pressure, heat release and performance characteristics
such as specific fuel consumption and brake thermal efficiency are
carried out. Compression ignition (C.I) engine cycle simulation was
developed and modified in to LHR engine for both diesel and
biodiesel fuel. On the basis of first law of thermodynamics the
properties at each degree crank angle was calculated. Preparation and
reaction rate model was used to calculate the instantaneous heat
release rate. A gas-wall heat transfer calculations are based on the
ANNAND-s combined heat transfer model with instantaneous wall
temperature to analyze the effect of coating on heat transfer. The
simulated results are validated by conducting the experiments on the
test engine under identical operating condition on a turbocharged D.I
diesel engine. In this analysis 20% of biodiesel (derived from
Jatropha oil) blended with diesel and used in both conventional and
LHR engine. The simulated combustion and performance
characteristics results are found satisfactory with the experimental
value.
Abstract: Internal combustion engines rejects 30-40% of the
energy supplied by fuel to the environment through exhaust gas. thus, there is a possibility for further significant improvement of efficiency with the utilization of exhaust gas energy and its conversion to mechanical energy or electrical energy. The Thermo-Electric
Generator (TEG) will be located in the exhaust system and will make use of an energy flow between the warmer exhaust gas and the external environment. Predict to th optimum position of temperature
distribution and the performance of TEG through numerical analysis.
The experimental results obtained show that the power output significantly increases with the temperature difference between cold
and hot sides of a thermoelectric generator.
Abstract: The objective of this study is to investigate the
combustion in a pilot-ignited supercharged dual-fuel engine, fueled
with different types of gaseous fuels under various equivalence ratios.
It is found that if certain operating conditions are maintained,
conventional dual-fuel engine combustion mode can be transformed to
the combustion mode with the two-stage heat release. This mode of
combustion was called the PREMIER (PREmixed Mixture Ignition in
the End-gas Region) combustion. During PREMIER combustion,
initially, the combustion progresses as the premixed flame
propagation and then, due to the mixture autoignition in the end-gas
region, ahead of the propagating flame front, the transition occurs with
the rapid increase in the heat release rate.
Abstract: One of the important applications of gas turbines is
their utilization for heat recovery steam generator in combine-cycle technology. Exhaust flow and energy are two key parameters for
determining heat recovery steam generator performance which are mainly determined by the main gas turbine components performance
data. For this reason a method was developed for determining the
exhaust energy in the new edition of ASME PTC22. The result of this investigation shows that the method of standard has considerable
error. Therefore in this paper a new method is presented for modifying of the performance calculation. The modified method is
based on exhaust gas constituent analysis and combustion calculations. The case study presented here by two kind of General
Electric gas turbine design data for validation of methodologies. The
result shows that the modified method is more precise than the ASME PTC22 method. The exhaust flow calculation deviation from
design data is 1.5-2 % by ASME PTC22 method so that the deviation regarding with modified method is 0.3-0.5%. Based on precision of
analyzer instruments, the method can be suitable alternative for gas
turbine standard performance test. In advance two methods are
proposed based on known and unknown fuel in modified method procedure. The result of this paper shows that the difference between
the two methods is below than %0.02. In according to reasonable esult of the second procedure (unknown fuel composition), the
method can be applied to performance evaluation of gas turbine, so that the measuring cost and data gathering should be reduced.
Abstract: This paper details a new concept of using compressed air as a potential zero pollution power source for motorbikes. In place of an internal combustion engine, the motorbike is equipped with an air turbine transforms the energy of the compressed air into shaft work. The mathematical modeling and performance evaluation of a small capacity compressed air driven vaned type novel air turbine is presented in this paper. The effect of isobaric admission and adiabatic expansion of high pressure air for different rotor diameters, casing diameters and ratio of rotor to casing diameters of the turbine have been considered and analyzed. It is concluded that the work output is found optimum for some typical values of rotor / casing diameter ratios. In this study, the maximum power works out to 3.825 kW (5.20 HP) for casing diameter of 200 mm and rotor to casing diameter ratio of 0.65 to 0.60 which is sufficient to run motorbike.
Abstract: Numerical study of two dimensional supersonic
hydrogen-air mixing layer is performed to investigate the effect of
turbulence and chemical additive on ignition distance. Chemical
reaction is treated using detail kinetics. Advection upstream splitting
method is used to calculate the fluxes and one equation turbulence
model is chosen here to simulate the considered problem. Hydrogen
peroxide is used as an additive and the results show that inflow
turbulence and chemical additive may drastically decrease the
ignition delay in supersonic combustion.
Abstract: The article presents test results on the changes
occurring in sewage sludge during the process of its storage. Tests
were conducted on mechanically dehydrated sewage sludge derived
from large municipal sewage treatment plants equipped with
biological sewage treatment systems. In testing presented in the paper
the focus was on the basic fuel properties of sewage sludge: moisture
content, heat of combustion, carbon share. In the first part of the
article the overview of the issues concerning the sewage sludge
management is presented and the genesis of tests is explained.
Further in the paper, selected results of conducted tests are discussed.
Changes in tested parameters were determined in the period of a 10-
month sewage storage.
Abstract: The fundamental aim of extended expansion concept is
to achieve higher work done which in turn leads to higher thermal
efficiency. This concept is compatible with the application of
turbocharger and LHR engine. The Low Heat Rejection engine was
developed by coating the piston crown, cylinder head inside with
valves and cylinder liner with partially stabilized zirconia coating of
0.5 mm thickness. Extended expansion in diesel engines is termed as
Miller cycle in which the expansion ratio is increased by reducing the
compression ratio by modifying the inlet cam for late inlet valve
closing. The specific fuel consumption reduces to an appreciable level
and the thermal efficiency of the extended expansion turbocharged
LHR engine is improved.
In this work, a thermodynamic model was formulated and
developed to simulate the LHR based extended expansion
turbocharged direct injection diesel engine. It includes a gas flow
model, a heat transfer model, and a two zone combustion model. Gas
exchange model is modified by incorporating the Miller cycle, by
delaying inlet valve closing timing which had resulted in considerable
improvement in thermal efficiency of turbocharged LHR engines. The
heat transfer model, calculates the convective and radiative heat
transfer between the gas and wall by taking into account of the
combustion chamber surface temperature swings. Using the two-zone
combustion model, the combustion parameters and the chemical
equilibrium compositions were determined. The chemical equilibrium
compositions were used to calculate the Nitric oxide formation rate by
assuming a modified Zeldovich mechanism. The accuracy of this
model is scrutinized against actual test results from the engine. The
factors which affect thermal efficiency and exhaust emissions were
deduced and their influences were discussed. In the final analysis it is
seen that there is an excellent agreement in all of these evaluations.
Abstract: A mathematical model based on a mass and energy
balance for the combustion in a cement rotary kiln was developed.
The model was used to investigate the impact of replacing about
45 % of the primary coal energy by different alternative fuels.
Refuse derived fuel, waste wood, solid hazardous waste and liquid
hazardous waste were used in the modeling. The results showed that
in order to keep the kiln temperature unchanged, and thereby
maintain the required clinker quality, the production capacity had to
be reduced by 1-15 %, depending on the fuel type. The reason for the
reduction is increased exhaust gas flow rates caused by the fuel
characteristics. The model, which has been successfully validated in a
full-scale experiment, was also used to show that the negative impact
on the production capacity can be avoided if a relatively small part of
the combustion air is replaced by pure oxygen.
Abstract: To calculate the temperature distribution of the slab in
a hot rolled reheating furnace a mathematical model has been
developed by considering the thermal radiation in the furnace and
transient conduction in the slab. The furnace is modeled as radiating
medium with spatially varying temperature. Radiative heat flux within
the furnace including the effect of furnace walls, combustion gases,
skid beams and buttons is calculated using the FVM and is applied as
the boundary condition of the transient conduction equation of the
slab. After determining the slab emissivity by comparison between
simulation and experimental work, variation of heating characteristics
in the slab is investigated in the case of changing furnace temperature
with various time and the slab residence time is optimized with this
evaluation.
Abstract: Generation of electricity from coal has increased over
the years in the United States and around the world. Burning of coal
results in annual production of upwards of 100 millions tons (United
States only) of coal combustion products (CCPs). Only about a third
of these products are being used to create new products while the
remainder goes to landfills. Application of CCPs mixed with
composted organic materials onto soil can improve the soil-s
physico-chemical conditions and provide essential plant nutritients.
Our objective was to create plant growth media utilizing CCPs and
compost in way which maximizes the use of these products and, at
the same time, maintain good plant growth. Media were formulated
by adding composted organic matter (COM) to CCPs at ratios
ranging from 2:8 to 8:2 (v/v). The quality of these media was
evaluated by measuring their physical and chemical properties and
their effect on plant growth. We tested the media by 1) measuring
their physical and chemical properties and 2) the growth of three
plant species in the experimental media: wheat (Triticum sativum),
tomato (Lycopersicum esculentum) and marigold (Tagetes patula).
We achieved significantly (p < 0.001) higher growth (7-130%) in the
experimental media containing CCPs compared to a commercial mix.
The experimental media supplied adequate plant nutrition as no
fertilization was provided during the experiment. Based on the
results, we recommend the use of CCPs and composts for the
creation of plant growth media.
Abstract: Cogeneration may be defined as a system which
contains electricity production and regain of the thermo value of
exhaust gases simultaneously. The examination is based on the data-s
of an active cogeneration plant. This study, it is aimed to determine
which component of the system should be revised first to raise the
efficiency and decrease the loss of exergy. For this purpose, second
law analysis of thermodynamics is applied to each component due to
consider the effects of environmental conditions and take the quality
of energy into consideration as well as the quantity of it. The exergy
balance equations are produced and exergy loss is calculated for each
component. 44,44 % loss of exergy in heat exchanger, 29,59 % in
combustion chamber, 18,68 % in steam boiler, 5,25 % in gas turbine
and 2,03 % in compressor is calculated.
Abstract: To understand working features of a micro combustor,
a computer code has been developed to study combustion of
hydrogen–air mixture in a series of chambers with same shape aspect
ratio but various dimensions from millimeter to micrometer level.
The prepared algorithm and the computer code are capable of
modeling mixture effects in different fluid flows including chemical
reactions, viscous and mass diffusion effects. The effect of various
heat transfer conditions at chamber wall, e.g. adiabatic wall, with
heat loss and heat conduction within the wall, on the combustion is
analyzed. These thermal conditions have strong effects on the
combustion especially when the chamber dimension goes smaller and
the ratio of surface area to volume becomes larger.
Both factors, such as larger heat loss through the chamber wall
and smaller chamber dimension size, may lead to the thermal
quenching of micro-scale combustion. Through such systematic
numerical analysis, a proper operation space for the micro-combustor
is suggested, which may be used as the guideline for microcombustor
design. In addition, the results reported in this paper
illustrate that the numerical simulation can be one of the most
powerful and beneficial tools for the micro-combustor design,
optimization and performance analysis.