Cheng Tung Chong

Spray Combustion Characteristics of Palm Biodiesel

The potential of palm methyl esters (PME) as an alternative fuel for gas turbines is investigated using a swirl burner. The main air flow is preheated to 623 K, and a swirling spray flame is established at atmospheric pressure. The spray combustion characteristics of PME are compared to diesel and Jet-A1 fuel under the same burner power output of 6 kW. Investigation of the fuel atomizing characteristics using phase Doppler anemometry (PDA) shows that most droplets are distributed within the flame reaction zone region. PME droplets exhibit higher Sautermean diameter (SMD) values than baseline fuels, and thus higher droplet penetration length and longer evaporation timescales. The PME swirl flame presents a different visible flame reaction zone while combusting with low luminosity and produces no soot. NOx emissions per unit mass of fuel and per unit energy are reduced by using PME relative to those of conventional fuels.

Spray Flame Study Using a Model Gas Turbine Swirl Burner

A model gas turbine burner was employed to investigate spray flames established under globally lean, continuous, swirling conditions. Two types of fuel were used to generate liquid spray flames: palm biodiesel and Jet-A1. The main swirling air flow was preheated to 350 °C prior to mixing with airblast-atomized fuel droplets at atmospheric pressure. The global flame structure of flame and flow field were investigated at the fixed power output of 6 kW. Flame chemiluminescence imaging technique was employed to investigate the flame reaction zones, while particle imaging velocimetry (PIV) was utilized to measure the flow field within the combustor. The flow fields of both flames are almost identical despite some differences in the flame reaction zones.

Flow field of a model gas turbine swirl burner

The flow field of a lab-scale model gas turbine swirl burner was characterised using particle imaging velocimetry (PIV) at atmospheric condition. The swirl burner consists of an axial swirler, a twin-fluid atomizer and a quartz tube as combustor wall. The main non-reacting swirling air flow without spray was compared to swirl flow with spray under unconfined and enclosed conditions. The introduction of liquid fuel spray changes the flow field of the main swirling air flow at the burner outlet where the radial velocity components are enhanced. Under reacting conditions, the enclosure generates a corner recirculation zone that intensifies the strength of the radial velocity. Comparison of the flow fields with a spray flame using diesel and palm biodiesel shows very similar flow fields. The flow field data can be used as validation target for swirl flame modelling.

Measurements of Non-reacting and Reacting Flow Fields of a Liquid Swirl Flame Burner

The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device. Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a 2-D particle imaging velocimetry(PIV) system. The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions, i.e., with and without the combustor wall. The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions. The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume. The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow. Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet, where the radial velocity components increase for both open and confined environment. Under reacting condition, the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity. The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants. The flow field data can be used as validation target for swirl combustion modelling.

Pyrolysis production of fruit peel biochar for potential use in treatment of palm oil mill effluent

Fruit peel, an abundant waste, represents a potential bio-resource to be converted into useful materials instead of being dumped in landfill sites. Palm oil mill effluent (POME) is a harmful waste that should also be treated before it can safely be released to the environment. In this study, pyrolysis of banana and orange peels was performed under different temperatures to produce biochar that was then examined as adsorbent in POME treatment. The pyrolysis generated 30.7-47.7 wt% yield of a dark biochar over a temperature ranging between 400 and 500 °C. The biochar contained no sulphur and possessed a hard texture, low volatile content (≤34 wt%), and high amounts of fixed carbon (≥72 wt%), showing durability in terms of high resistance to chemical reactions such as oxidation. The biochar showed a surface area of 105 m2/g and a porous structure containing mesopores, indicating its potential to provide many adsorption sites for use as an adsorbent. The use of the biochar as adsorbent to treat the POME showed a removal efficiency of up to 57% in reducing the concentration of biochemical oxygen demand (BOD), chemical oxygen demand COD, total suspended solid (TSS) and oil and grease (O&G) of POME to an acceptable level below the discharge standard. Our results indicate that pyrolysis shows promise as a technique to transform banana and orange peel into value-added biochar for use as adsorbent to treat POME. The recovery of biochar from fruit waste also shows advantage over traditional landfill approaches in disposing this waste.

Spray Characteristics of an Internal-Mix Airblast Atomizer

Detailed characterisation of spray atomization of an injector is important for combustor design and modelling. In this paper, the effects of air/fuel mass ratio on the spray characteristics of an internal-mix airblast atomizer were examined. Distribution of the spatial mean droplet axial velocity and size were measured simultaneously using a phase Doppler anemometry (PDA). In general, small droplets are distributed at the center of the spray with maximum velocity. The droplet size increases with increasing radial distance from the spray centreline, but the drop velocity decreases to a minimum at the spray edge. Increasing the atomizing air/fuel mass ratio reduces fuel droplet size due to increased shear.

Production of syngas from controlled microwave-assisted pyrolysis of crude glycerol

Conversion of crude glycerol into synthesis gas was studied by using controlled microwave-assisted pyrolysis method. Pyrolysis of crude glycerol in the presence of carbonaceous catalyst was performed in a fixed bed reactor under oxygen-deficient environment using a domestic microwave. The effects of inert carrier gas flow rate and pyrolysis temperature on the product yield were investigated. Characterisation of the gaseous product showed that hydrogen, methane and carbon dioxide are the main components in the gaseous product. High temperature and low inert carrier gas flow rate are effective in pyrolysing crude glycerol due to sufficient energy and residence time for complete cracking of vapour into small gaseous molecules. Peak hydrogen yield of 35.2% by volume was obtained at the carrier gas flow rate of 100 mL/min and 600 °C.

TEM and XRD Analysis of Carbon Nanotubes Synthesised from Flame

A premixed flame burner system was utilised to synthesise carbon nanotubes (CNTs). The morphologies of highly-graphitic carbon nanotubes were characterised by using transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). The XRD analysis shows the spectrum of a typical CNT, while TEM imaging shows the physical structure of the carbon nanotubes. CNTs were grown effectively on a Ni-contained substrate in an elevated temperature environment. The flame synthesised CNTs were of high crystalline, multi-wall structure, and contained relatively less impurities and amorphous carbon. The CNT intershell spacing values quantified using TEM and XRD are 0.317 nm and 0.344 nm respectively. CNTs produced from flame synthesis are based on the tip-growth model and vapor-liquid-solid (VLS) mechanism.

Synthesis of Carbon Nanotubes from Rich Premixed Propane/Air Flame

The present study focuses on the derivation of carbonaceous material from rich premixed propane/air mixture using a laminar flame burner. The presence of Nickel catalyst (Ni) and the effect of equivalence ratio on the synthesis of carbon nanotubes (CNTs) were investigated. Samples were collected from the flame synthesized wire mesh and analyzed using a Field emission scanning electron microscope (FESEM). FESEM imaging shows that the CNTs obtained were of the multi-walled type. The presence of nickel catalyst results in the production of CNTs and the rich equivalent ratio of φ = 2.2 produces the highest yield of CNT in terms of weight and coverage area on the wire mesh.

Effects of the Biodiesel Fuel Physical Properties on the Swirl Stabilised Spray Combustion Characteristics

An increasin g interest in biofuel applications in modern engines requires a better understanding of biodiesel combustion behaviour. Many numerical studies have been carried out on unsteady combustion of biodiesel in situations similar to diesel engines, but very few studies have been done on the steady combustion of biodiesel in situations similar to a gas turbine combustor environment. The study of biodiesel spray combustion in gas turbine applications is of special interest due to the possible use of biodiesel in the power generation and aviation industries. In modelling spray combustion, an accurate representation of the physical properties of the fuel is a first important step, since spray formation is largely influenced by fuel properties such as viscosity, density, surface tension and vapour pressure. In the present work, a calculated biodiesel properties database based on the measured composition of Fatty Acid Methyl Esters (FAME) has been implemented in a multi-dimensional Computational Fluid Dynamics (CFD) spray simulation code. Simulations of non-reacting and reacting atmospheric-pressure sprays of both diesel and biodiesel have been carried out using a spray burner configuration for which experimental data is available. A pre-defined droplet size probability density function (pdf) has been implemented together with droplet dynamics based on phase Doppler anemometry (PDA) measurements in the near-nozzle region. The gas phase boundary condition for the reacting spray cases is similar to that of the experiment which employs a plain air-blast atomiser and a straight-vane axial swirler for flame stabilisation. A reaction mechanism for heptane has been used to represent the chemistry for both diesel and biodiesel. Simulated flame heights, spray characteristics and gas phase velocities have been found to compare well with the experimental results. In the reacting spray cases, biodiesel shows a smaller mean droplet size compared to that of diesel at a constant fuel mass flow rate. A lack of sensitivity towards different fuel properties has been observed based on the non-reacting spray simulations, which indicates a need for improved models of secondary breakup. By comparing the results of the non-reacting and reacting spray simulations, an improvement in the complexity of the physical modelling is achieved which is necessary in the understanding of the complex physical processes involved in spray combustion simulation. Copyright