Simulating tribological characteristics of Palm Methyl Ester (PME) lubricated contact

The study simulates the lubricant Stribeck curve for Palm Methyl Ester (PME) by coupling modified Reynolds solution with Greenwood and Tripp's rough surface contact model. The predicted lubricant Stribeck curves for PME is validated with measured data from a pin-on-disc tribometer. The Reynolds equation is modified to accommodate for the lubricant properties of PME (e.g. viscosity and density), which is mathematically described using Gibbs energy additivity approach. Solving the modified Reynolds equation would then provide the fluid film formation behaviour of PME, such as the contact pressure and film thickness. These fluid film parameters are then used as the input to determine the boundary and viscous friction of the investigated lubricated contact using Greenwood and Tripp's rough surface contact model. The proposed mathematical solution correlates well with experimental data and is shown to be capable of predicting lubricant Stribeck, capturing the frictional behavior for the whole range of lubrication regimes. The findings of the present study prepare for a mathematical foundation to further explore the use of biodiesel as an alternative biodegradable lubricant to mineral-based ones

Adhesive and molecular friction in tribological conjunctions

This thesis investigates the underlying causes of friction and ine ciency within an internal combustion engine, focusing on the ring-liner conjunction in the vicinity of the power-stroke top dead centre reversal. In such lubricated contacts, friction is the result of the interplay between numerous kinetics, with those at micro- and nano-scale interactions being signi cantly di erent than the ones at larger scales. A modi ed Elrod's cavitation algorithm is developed to determine the microscopic tribological characteristics of the piston ring-liner contact. Predicting lubricant tran- sient behaviour is critical when the inlet reversal leads to thin lms and inherent metal-to-metal interaction. The model clearly shows that cavitation at the trailing edge of the ring-liner contact generated pre-reversal, persists after reversal and pro- motes starvation and depletion of the oil lm. Hence, this will lead to boundary friction. A fractal based boundary friction model is developed for lightly loaded asperity con- tacts, separated by diminishing small lms, usually wetted by a layer of molecules adsorbed to the tips of the asperities. In nano-scale conjunctions, a lubricant layering e ect often takes place due to the smoothness of surfaces, which is governed by the surface and lubricant properties. A molecularly thin layer of lubricant molecules can adhere to the asperities, being the last barrier against direct surface contact. As a result, boundary friction (prevailing in such diminishing gaps) is actually determined by a combination of shearing of a thin adsorbed lm, adhesion of approaching as- perities and their plastic deformation. A model for physio-chemical hydrodynamic mechanism is successfully established, describing the formation of thin adsorbed lms between asperities. This model is e ectively integrated with separately devel- oped models that predict the adhesive and plastic contact of asperities.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Rheological Properties of Butterfly Pea- derived anthocyanins extracted using Ultrasonic Assisted Extraction method

 Anthocyanin from butterfly pea extract is used for the skin brightening, rejuvenating, and hydration of serum product as the phenolic compound have the antioxidants effect. Its stability generally influenced by pH, temperature, light, metal ions in media, and other factors. It is important to monitor the temperature fluctuations because rising temperatures will lead to the partial or complete degradation of natural anthocyanins, which will reduce the intensity of the colour. However, the rheology involving density and viscosity of anthocyanin derived from butterfly pea flower are yet to be verified. In this study, we investigate the rheological characteristics of synthetic skin infused with anthocyanin from butterfly pea. Two sources of anthocyanin were used in this study: liquid anthocyanin from Bionutricia Malaysia, and raw extracted anthocyanin from dried butterfly pea flower. The dried butterfly peas are extracted using the Ultrasonic Assisted Extraction (UAE) process in an ultrasonic water bath. Total anthocyanin content (TAC) and physicochemical analysis consist of measurement of density, viscosity, and shear stress of extract have been investigate throughout the process. The total anthocyanin content (TAC) of raw and liquid butterfly pea extract was determined to be 261.28 mg/L and 32.272 mg/L respectively from the obtained absorbance at wavelength 510 nm and 700 nm using UV-Visible Spectroscopy. It is discovered that the extracted anthocyanin indicates non-Newtonian behaviour and pseudoplastic rheology behaviour for both samples

Advancements of combustion technologies in the ammonia-fuelled engines

The worldwide decarbonisation movement has turned ammonia into one of the attractive alternative fuel for power generation. This paper reviews the progress of ammonia combustion technologies in spark ignition engine, compression ignition engine, and gas turbine. Relevant publications from prominent academic journals were acquired from credible scholarly databases and analysed. Ammonia dissociation and separate hydrogen supply were typically employed to deliver hydrogen to enhance ammonia reaction in the spark ignition engine. To achieve satisfactory engine performances with thermal efficiency of around 30%, a hydrogen mass fraction of roughly 10% is required for the ammonia/hydrogen engine. Engine parameters optimisation may be needed to increase hydrogen mass fraction further. Aqueous ammonia elevates heat release rate of full load compression ignition engine by almost 10%. However, prolonged ignition delay could potentially lead to higher engine noise levels. Multiple fuel injection optimisation is seemingly a more promising solution for improving ammonia compression ignition engine performances. In recent years, partial premixed combustion has gained considerable interest in hydrogen/ammonia gas turbine combustion research. This is mainly due to its ability to operate at equivalence ratio as low as 0.4, and in the slight fuel-rich regime. For operation at equivalence ratio 1.05, the nitric oxide concentration was decreased by a factor of approximately 5.9 when compared with that of stoichiometric condition. In all, ammonia offers a practical opportunity for sustainable power generation via internal combustion engines and gas turbine. Ground-breaking combustion technologies are crucial to boost the adoption of ammonia in these engines

Friction analysis of Waste Palm Methyl Ester (WPME) under Stribeck lubrication regimes

This paper aims to investigate the tribological friction using the Stribeck curve lubrication regime using an alternative source of biodiesel. Replacement of current usage of fossil fuels is essential, therefore, it is important to develop a proper recycling, renewable and sustainable product that reduces global warming. Biodiesel also known as Fatty Acid Methyl Ester (FAME), is biodegradable, produced from a renewable source, non-toxic, and produces a minimum greenhouse gas emissions. To reduce raw material cost, waste cooking oil is one of the most suitable replacements of vegetable oil for biodiesel synthesis. Rheological behavior of Waste Palm Methyl Ester (WPME), such as kinematic viscosity, density, and acid value, was measured based on EN14214 and compared with Palm Methyl Ester (PME). The friction performance of WPME was evaluated using a pin on the disc tribometer machine. The influence of different operating conditions such as loads at 1kg, 2kg, 3kg and 4kg and sliding velocity range from 0.00625 m/s to 4 m/s were optimized in this study. The preliminary result shows significant changes on the Stribeck curve concerning the sliding speed and also loads. It is found that as for the same entrainment velocity and surface roughness, a higher load will initiate a higher temperature, thus lead to decreasing the viscosity and coefficient of friction. In summary, WPME is highly considered as a potential waste that can replace the current energy source

Morphology and growth of carbon nanotubes catalytically synthesised by premixed hydrocarbon-rich flames

Synthesis of carbon nanotubes (CNTs) was performed by using a laminar premixed flame burner at open atmospheric condition. The growth of CNTs on the substrate was supported catalytically by a transition metal under high temperature, hydrocarbon-rich environment. Analysis of the CNTs using high resolution electron microscope reveals the structure of synthesised nano-materials in disarray, clustered and tubular form. The graphitic structure of the CNTs are rather similar for all fuel-rich equivalence ratios tested, with an average diameter of ∼11–13 nm. Removal of the amorphous carbon and catalyst in the CNTs was performed via purification treatment using H2O2 and HCl solutions. Detail characterisation indicates the oxidation temperature of purified CNTs ranges between 497 and 529 °C. Deconvolution of the Raman spectra in the range of 900–1800 cm−1 shows the distinct characteristic bands of CNTs with IG/ID ratio of 0.66–0.72 for all the samples tested. In addition, the high level carbon concentration and sp2 Csingle bondC bond in the CNTs is shown by X-ray photoelectron spectroscopy analysis. The present study demonstrates that CNTs can be effectively synthesised from fuel-rich hydrocarbon flames at ϕ = 1.8–2.0 supported by nickel-based substrate

Synergistic nano-tribological interaction between zinc dialkyldithiophosphate (ZDDP) and methyl oleate for biodiesel-fueled engines

In biodiesel-fueled compression-ignition (CI) engines, dilution by unburned biodiesel has been found to have adverse effects on the boundary lubrication properties of additives in fully formulated engine lubricants. Such dilution of engine lubricants could be even more pronounced for CI engines running on higher blend concentrations of biodiesel. Given the nanoscopic nature of the interaction, this study seeks to determine the nano-tribological properties of an engine lubricant additive (e.g., zinc dialkyldithiophosphate (ZDDP)) when diluted with a fatty acid methyl ester (e.g., methyl oleate). Using lateral force microscopy (LFM) together with a fluid imaging technique, the lowest nanoscopic friction forces and coefficient of friction values (0.068-0.085) were measured for ZDDP when diluted with 70 vol% of methyl oleate. These values are also observed to be lower than those measured for neat ZDDP and neat methyl oleate, respectively, under similar conditions. Subsequently, interpreting the data with the Eyring thermal activation energy approach, it could then be elucidated that the lower frictional losses observed for the contact lubricated with this volumetric mixture are a result of the lower potential energy barrier and activation energy required to initiate sliding. These energy values are approximated to be 2.6% and 28.9% (respectively) lower than that of the contact lubricated with neat ZDDP. It was also found that the mixture, at this volumetric concentration, possesses the highest possible pressure activation energy (load-carrying capacity) along with the lowest possible shear activation energy (shearing), potentially indicating optimum tribological conditions for boundary lubrication. Thus, the findings of this study suggest that an optimum concentration threshold exists in which a synergistic nano-tribological interaction between additives and fatty acid methyl esters can be attained, potentially reducing boundary frictional losses of lubricated conjunctions. Such findings could prove to be essential in effectively formulating synergistic additive concentrations for engine lubricants used in biodiesel-fueled CI engines

Oxygenated sunflower biodiesel: spectroscopic and emissions quantification under reacting swirl spray conditions

The spray combustion characteristics of sunflower (Helianthus annuus) biodiesel/methyl esters (SFME) and 50% SFME/diesel blend and diesel were investigated via a liquid swirl flame burner. The swirl flame was established at atmospheric condition by using a combined twin-fluid atomiser-swirler configuration at varied atomising air-to-liquid ratios (ALR) of 2.0–2.5. Diesel flame showed a sooty flame brush downstream of the main reaction zone, as opposed to the biodiesel flame which showed a non-sooty, bluish flame core. Biodiesel flame exhibited a more intense flame spectra with higher OH* radicals as compared to diesel. Higher preheating main swirl air temperature led to higher NO emission, while CO correspondingly decreased. Sunflower-derived biodiesel generally exhibited slightly higher NO and CO levels than diesel when compared at the same power output, mostly due to higher flame temperature and fuel chemistry effect. By increasing ALR, a significant reduction of NO and CO for both fuel types were concurrently achieved, presenting a strategy to control emissions and atomise biodiesel with higher viscosity under swirl combustion mode

Liquid biofuels production and emissions performance in gas turbines: A review

The increasing demand for clean and sustainable energy sources provides the impetus for the development of alternative fuels. Recent development of fuel-flexible gas turbine technologies enables the use of alternative non-fossil fuels that could play key roles in contributing to the global efforts in meeting emissions targets. This review highlights the current state-of-the-art production and properties of alternative fuels such as straight vegetable oil (SVO), biodiesel, bioethanol, bio-oil, hydrogenated vegetable oil (HVO) and Fischer-Tropsch (FT) fuel. This is followed by the evaluation of combustion performances in gas turbines. All of the alternative liquid biofuels have shown their potentials in reducing regulated emissions such as NOx, CO and soot under favourable operating conditions. Both HVO and FT fuels show comparable performance as that of jet fuel and can be used in aviation gas turbines, although the present day high production cost restricts the large-scale adoption, limiting its utility. They also have considerably higher cetane number than the rest, making it easier for the fuel to ignite. As for stationary power generation gas turbines that need not carry payloads, the other four alternative biofuels of biodiesel, bioethanol, bio-oil and SVO are possible candidates despite the physics-chemical properties variations when compared to fossil fuels. Amongst them, the use of SVO and bio-oil in gas turbines would require the parallel development of fuel supply systems and atomisation technologies to improve the combustion of the fuels. In all, the alternative liquid fuels reviewed provides realistic opportunities for cleaner and more sustainable operation of aviation and power generation gas turbines. Profound understanding on the fundamental combustion characteristics of the fuels are essential to expedite their mass adoption in gas turbine applications

Environment impact and bioenergy analysis on the microwave pyrolysis of WAS from food industry: Comparison of CO2 and N2 atmosphere

The alarming output of waste activated sludge (WAS) from industries requires proper management routes to minimize its impact on the environment during disposal. Pyrolysis is a feasible way of processing and valorizing WAS into higher-value products of alternate use. Despite extensive research into the potential of WAS through pyrolysis, the technology's long-term viability and environmental impact have yet to be fully revealed. In addition, the environmental effects of utilizing different pyrolysis atmosphere (N2 or CO2) has not been studied before, although benefits of CO2 reactivity during pyrolysis have been discovered. This study evaluates the process's environmental impact, carbon footprint, and bioenergy yield when different pyrolysis atmospheres are used. The global warming potential (GWP) for a functional unit of 1 t of dried WAS is 203.81 kg CO2 eq. The heat required during pyrolysis contributes the most (63.7%) towards GWP due to high energy usage, followed by the drying process (23.6%). Transportation contributes the most towards toxicity impact (59.3%) through dust, NOx, NH3 and SO2 emissions. The initial moisture content of raw WAS (65%) greatly impacts overall energy consumption and environmental impact. Pyrolysis in an N2 atmosphere will result in a higher overall bioenergy yield (833 kWh/tonne) and a lower carbon footprint (−1.09 kg CO2/tonne). However, when CO2 was used, the specific energy value within the biochar is higher (22.26 MJ/kg) due to enhanced carbonization. The carbon content of gas derived increased due to higher CO yield. From an energy perspective, the current setup will achieve a net positive bioenergy yield of 561 kW (CO2) and 833 kW (N2), where end products like biochar, bio-oil and gas can be used for power production. Despite the energy-intensive process, microwave pyrolysis has excellent potential to achieve a negative carbon footprint. The biochar used for soil amendment served as a good carbon sink. The utilization of CO2 as carrier gases provides a pathway to utilize anthropogenic CO2, which helps reduce global warming. This work demonstrates microwave pyrolysis as a negative emission, bioenergy-producing approach for WAS disposal and valorization