The effect of hot surface temperature on diesel fuel deposit formation

The aim of this study is to investigate fuel deposits by using the hot surface deposition test (HSDT). In this test, diesel fuel droplets were repeatedly impinged to the hot surface and deposits were developed on it. The hot surface temperature affected the deposit formation. Different hot surface temperature showed different droplet-surface interaction, evaporation lifetime and wet/dry condition where various deposit development features resulted. The hot surface temperatures that located near MEP (maximum evaporation rate point) temperature have potential to reduce the deposit formation on the hot surface. The deposition within nucleate heat transfer boiling regime (lower than the MEP temperature) caused greater deposit accumulation on the hot surface compared to the deposition within transition heat transfer boiling regime (near the MEP temperature). Less total amount of deposit that was described as slow deposit development, resulted under non-overlapping impingement and dry deposit condition. Under the overlapping impingement and wet deposit condition, it caused the accumulation of greater total amount of deposit compared to the non-overlapping and dry deposit condition.     

Imaging and heat flux measurements of wall impinging sprays of hydrocarbons and alcohols in a direct-injection spark-ignition engine

The latest generation of fuel systems for direct-injection spark-ignition engines uses injection nozzles that accommodate a number of holes with various angles in order to offer flexibility in in-cylinder fuel targeting over a range of engine operating conditions. However, the high-injection pressures that are needed for efficient fuel atomisation can lead to deteriorating effects with regards to engine exhaust emissions (e.g. unburned hydrocarbons and particulates) from liquid fuel impingement onto the piston and liner walls. Eliminating such deteriorating effects requires fundamental understanding of in-cylinder spray development processes, taking also into account the diversity of future commercial fuels that can contain significant quantities of bio-components with very different chemical and physical properties to those of typical liquid hydrocarbons. This paper presents high-speed imaging results of spray impingement onto the liner of a direct-injection spark-ignition engine, as well as crank-angle resolved wall heat flux measurements at the observed locations of fuel impingement for detailed characterisation of levels and timing of impingement. The tests were performed in a running engine at 1500 RPM primarily at low load (0.5 bar intake pressure) using 20, 50 and 90 °C engine temperatures. Gasoline, iso-Octane, Butanol, Ethanol and a blend of 10% Ethanol with 90% Gasoline (E10) were used to encompass a range of current and future fuel components for spark-ignition engines. The collected data were analysed to extract mean and standard deviation statistics of spray images and heat flux signals. The results were also interpreted with reference to physical properties and evaporation rates predicted by a single droplet model for all fuels tested.     

Synthesis of nanofibrous carbon with herringbone structure on Ni-supported SiC particles using hot CVD apparatus

A nanofibrous carbon material having a herringbone structure was synthesized using Ni-supported silicon carbide (SiC) particles as the catalyst for the hot chemical vapor deposition (CVD) process using CH₄ as carbon source. The amount of the deposits during the CVD process strongly depended on the CVD treatment temperature. The enhancement of weight and the TG data indicated that the quantity synthesis of the deposits was achieved at 823 K. The specific surface area of the deposits was estimated at ca. 120 m² g^− 1. It was confirmed from the TEM images that the deposits synthesized in this study had a herringbone-like structure. From the data of Raman spectra and XRD patterns, the herringbone-like structure started to deposit after 30 minutes in the case of 823 K. The Ni-supported SiC can be used as the catalyst for the synthesis of nanofibrous carbon materials.     

CVD growth and field electron emission of aligned carbon nanotubes on oxidized Inconel plates without addition of catalyst

Direct growth of carbon nanotubes (CNTs) on Inconel 600 sheets was investigated using plasma enhanced hot filament chemical vapor deposition in a gas mixture of methane and hydrogen. The Inconel 600 sheets were oxidized at different temperatures (800 °C, 900 °C, 1000 °C, and 1100 °C) before CNT deposition. The structure and surface morphology of the pre-treated substrate sheets and the deposited CNTs were studied by scanning electron microscopy (SEM) and X-ray diffraction. The field electron emission (FEE) properties of the CNTs were also tested. The SEM results show that well aligned CNTs have been grown on the pre-treated Inconel sheets without addition of any catalysts and the higher treatment temperature resulted in CNTs with better uniformity, indicating that the oxidation pre-treatment of the substrate is effective to enhance the CNT growth. FEE testing shows that CNTs with better height uniformity exhibit better FEE characteristics.     

In situ deposition of oxide layer using fuel additive and its effect on the oxidation of SM 45C blades for micro-gas turbines

In situ deposition of a silica-based oxide layer on carbon steel (SM45C) turbine blades was tried during the operation of a 13 kgf-class gas turbine engine using fuel additive, and its effect on the durability and the static oxidation at 700 °C of the blade was studied. The gas turbine was actuated by burning kerosene as fuel, for one turbine wheel with fuel additive (0.5 wt.% PDMS), and for another without additive. The oxide scales formed on the turbine blades were characterized using SEM, EDX and XRD. The results of the test revealed that the durability of SM45C turbine was prolonged more than 10 times when operated with additive than when operated without additive at the rotation speed of 30,000 rpm and a turbine exhaust temperature of 780 °C. Combustion with 0.5 wt.% PDMS gave a white residue containing up to 16.5 at.% Si in the wüstite-based scale. The influx of silicon oxide into the growing scale suppressed the formation of hematite on the surface of the blade during the operation. As the static oxidation test gives no difference in the oxidation rate between the two kinds of operated blades, the prolonged durability was attributed to the silicon oxide continuously supplied to the surface of the blade during the operation.     

Production of high-quality biodiesel fuels from various vegetable oils over Ti-incorporated SBA-15 mesoporous silica

Ti-incorporated SBA-15 mesoporous silica (shortly termed Ti-SBA-15) was a highly efficient and recyclable solid acid to synthesize high-quality biodiesel fuel (BDF) derived from various vegetable oils at moderate reaction condition, in comparison to siliceous SBA-15 and commercial TiO₂ catalysts with different anatase sizes, where the catalytically active sites mainly related to the tetrahedral-coordinated Ti(IV) species with weak Lewis acid nature. The TOF values of Ti-SBA-15 catalysts were around 18–166 h^− 1, an order of magnitude larger than those of commercial TiO₂ catalysts. A high-quality BDF containing more than 98.4 mass% of fatty acid methyl ester (FAME), which met with international fuel standard, was obtained over 3Ti-SBA-15 catalyst at 200 °C using a methanol/oil ratio of 108. Most importantly, the 3Ti-SBA-15 catalyst showed extremely high water and free fatty acid (FFA) tolerance levels, which were several ten times better than homogeneous and heterogeneous catalysts in conventional BDF production technology.     

Synthesis of diamond at sub 300 °C substrate temperature

Sulfur-assisted hot-filament chemical vapor deposition (HFCVD) was employed to grow nanocrystalline diamond at low substrate temperature, ∼ 300 °C, on molybdenum (Mo), and ∼ 250 °C, on polyimide film. The polyimide films remained flexible and strong after the deposition, clearly indicating that they did not experience temperatures near or above the glass transition temperature at ∼ 360 °C. The relative intensity of the diamond peak in the Raman spectra increases when the substrate temperature is decreased from ∼ 500 to ∼ 300 °C, a result that is inverted with respect to HFCVD without sulfur. This behavior was employed to obtain microcrystalline diamond on Mo at ∼ 270 °C. Profound changes induced to the gas phase chemistry and surface reactions when a trace amount of H₂S is added to the HFCVD process seem to enable these results.     

Chemical vapor deposition of pyrolytic boron nitride ceramics from single source precursor

Pyrolytic boron nitride ceramics were prepared on graphite substrates from borazine as the single source precursor by hot-wall chemical vapor deposition in deposition temperature range from 1300 °C to 1600 °C with a total pressure of 200 Pa. The chemical composition and the effect of deposition temperature on the morphology, phase, and structure of the pyrolytic boron nitride were investigated. A high purity product with stoichiometric B/N ratio is obtained. The deposition surface of the product exhibited a pebble-like structure, and the fracture surface showed an apparent laminar structure having a preferential (002) orientation parallel to the surface of the substrate at temperatures above 1400 °C. The product contained some turbostratic and amorphous boron nitride as evidenced from XRD and FTIR examinations. With the increase of deposition temperature, the crystallinity of the pyrolytic boron nitride increased with the turbostratic and amorphous boron nitride turned into hexagonal structure, and the crystallinity of the product became higher.     

Characterization and optimization of an autothermal diesel and jet fuel reformer for 5 kWe mobile fuel cell applications

The present paper describes the characterization of an autothermal reformer designed to generate hydrogen by autothermal reforming (ATR) from commercial diesel fuel (～10 ppm S) and jet fuel (～200 ppm S) for a 5 kW_e polymer electrolyte fuel cell (PEFC). Commercial noble metal-based catalysts supported on 900 cpsi cordierite monoliths substrates were used for ATR with reproducible results. Parameters investigated in this study were the variation of the fuel inlet temperature, fuel flow and the H₂O/C and O₂/C ratios. Temperature profiles were studied both in the axial and radial directions of the reformer. Product gas composition was analyzed using gas chromatography.It was concluded from the experiments that an elevated fuel inlet temperature (≥60 °C) and a higher degree of fuel dispersion, generated via a single-fluid pressurized-swirl nozzle at high fuel flow, significantly improved the performance of the reformer. Complete fuel conversion, a reforming efficiency of 81% and an H₂ selectivity of 96% were established for ATR of diesel at P = 5 kW_e, H₂O/C = 2.5, O₂/C = 0.49 and a fuel inlet temperature of 60 °C. No hot-spot formation and negligible coke formation were observed in the reactor at these operating conditions. The reforming of jet fuel resulted in a reforming efficiency of only 42%. A plausible cause is the coke deposition, originating from the aromatics present in the fuel, and the adsorption of S-compounds on the active sites of the reforming catalyst.Our results indicate possibilities for the developed catalytic reformer to be used in mobile fuel cell applications for energy-efficient hydrogen production from diesel fuel.     

Low temperature deposition of titanium oxide containing thin films in trench features from titanium diisopropoxide bis(dipivaloylmethanate) in supercritical CO2

We studied supercritical carbon dioxide fluid deposition of titanium oxide (TiO₂) in trench features on Si substrates using a flow-type deposition apparatus from titanium diisopropoxide bis(dipivaloylmethanate), aiming at fabricating conformal films at a relatively low temperature. We investigated the deposition rate and step coverage under a fluid temperature from 40 to 60 °C, a pressure from 8.0 to 10.0 MPa, and a substrate temperature from 80 to 120 °C. They were dependent on the fluid density, indicating that the solubility difference between the bulk fluid and the neighborhood of the substrate surface plays a decisive role for the deposition. An excellent conformal filling of the trench features was achieved from the fluid of 60 °C under 8 MPa on the substrate kept at 80–100 °C. The XPS spectra of the deposited film suggested partial formation of TiO₂, and the XRD spectra showed the existence of some crystalline TiO₂ (anatase).     

Low temperature atomic layer deposition of SiO2 thin films using di-isopropylaminosilane and ozone

Silicon dioxide (SiO₂) films are deposited by atomic layer deposition (ALD) at low temperatures from 100 to 200 °C using di-isopropylaminosilane (SiH₃N(C₃H₇)₂, DIPAS) as the Si precursor and ozone as the reactant. The SiO₂ films exhibit saturated growth behavior confirming the ALD process, showing a growth rate of 1.2 Å/cycle at 150 °C, which increases to 2.3 Å/cycle at 250 °C. The activation energy of 0.24 eV, extracted from temperature range of 100–200 °C, corresponds to the reported energy barrier for reaction between DIPAS and surface –OH. The temperature dependence of the growth rate can be explained in terms of the coverage and chemical reactivity of the thermally activated precursor on the surface. The ALD-SiO₂ films deposited at 200 °C show properties such as refractive index, density, and roughness comparable to those of conventionally deposited SiO₂, as well as low leakage current and high breakdown field. The fraction of Si–O bond increases at the expense of Si–OH at higher deposition temperature.     

Gas-tight yttria-doped barium zirconate thin film electrolyte via chemical solution deposition technique

A 500 nm thick yttria-doped barium zirconate (BZY) proton conducting electrolyte film, fabricated via a low-cost and high-throughput chemical solution deposition (CSD) technique, was sintered at a remarkably low temperature of 1000 °C, which is much lower than the typical solid state sintering temperature of minimum 1300 °C. Therefore, the detrimental issues, commonly encountered in solid state sintering, such as barium evaporation and phase separation, were not observed. Gas-tightness of the BZY film was confirmed by 8 h of stable open circuit voltage (OCV) at 1.08 V from a button fuel cell with NiO-BZY anode substrate and LSCF cathode. The application of the film is aimed at the electrolytes of intermediate to low temperature solid oxide fuel cells (SOFCs).     

Bicomponent droplets evaporation: Temperature measurements and modelling

Development of improved energy conversion systems, having higher efficiencies and lower emissions, is central to reducing the production of green-house gases and to meeting air quality standards for other emissions. In non-premixed combustion systems, vaporization of the droplets and mixing of the vapour with the surrounding oxidizer control the overall rate of energy release. Droplet vaporization is affected by the nature of the liquid petroleum that contains species having extremely different volatilities. A fine understanding of multi-component droplet vaporization is therefore an important issue to optimize the combustion systems. This paper presents the application of a recently developed technique to measure the temperature of bi-component droplets. Based on the three-color laser-induced fluorescence (LIF) technique, droplet temperatures can be measured regardless of the composition. The method requires adding a small amount of a fluorescent organic dye to the fuel which is composed of ethyl-alcohol and acetone. The accuracy of the measurement is about ±1.3 °C. In this study, the emphasis is placed on the evaporation of the binary mixture in a hot air plume, the temperature of which (around 650 °C) largely exceeds the boiling point of the liquid components. An extensive study of the influence of the initial composition and droplet diameter is carried out. Finally, the experimental results are compared to an evaporation model based on the discrete components approach.     

Graphitized filament plasma enhanced CVD deposition of nanocrystalline diamond

A novel approach to the deposition of polycrystalline diamond is presented. The technique is based on the hot filament chemical vapour deposition technique (HFCVD). While it is similar to a high plasma power “bias enhanced growth” HFCVD, it relies on a graphite filament rather than on a metal one. It was found that with an appropriate choice of the growth parameters, 4–9% CH₄ in H₂, filament temperature > 2200 °C, 25 mBar gas pressure, plasma power > 500 W, a long filament lifetime can be achieved, when a simultaneous deposition of graphitic carbon on the hot graphite filament and of nanocrystalline diamond on a substrate facing the filament assembly is realized. In this paper the growth of nanocrystalline diamond films and their characterization (SEM, XRD, AFM) are presented. While the technique is promising for low cost, large area deposition of nanocrystalline diamond films, also the growth of microcrystalline diamond has been observed.     

High temperature mechanical properties of laminated ZrB2–SiC based ceramics

Two laminated ZrB₂-SiC based ceramics were prepared by tape casting and subsequent hot pressing, with BN (LZB) and graphite (LZG ) as interface layers. The LZB specimen presents flexural strength of 381 MPa at room temperature and 111 MPa at 1500 °C; while the LZG specimen shows flexural strength of 414 MPa at room temperature and 377 MPa at 1500 °C. In addition, the flexural strength of LZG specimen is always higher than that of the LZB specimen in the temperature range from room temperature to 1500 °C. Such higher strength is attributed to the healing of surface microcracks and pores by the SiO₂ glass phase, producing less glass phase in graphite interface layers at high temperature.     

Investigations on the properties of ceria–zirconia-supported Ni and Rh catalysts and their performance in acetic acid steam reforming

The production of hydrogen via steam reforming of acetic acid was examined over Ni and Rh supported on a CeO₂–ZrO₂-mixed oxide. The catalysts were tested at 550–650–750 °C using steam/carbon = 3. Steam reforming, water gas shift, and decarboxylation are the main reactions taking place over the support alone. In parallel, dehydrogenation leads to the formation of carbon deposits on the surface of the mixed oxide. The addition of the metals enables the reforming reactions to proceed with high rates producing hydrogen yields close to thermodynamic equilibrium even at 650 °C. The oxygen exchange reactions are enhanced leading to much lower coke deposition. The nature of the metal affects not only the quantity but also the quality and the location of the carbon deposits, as evidenced from temperature-programing oxidation tests. The synergy of the support and metal is the key factor for the low coke deposition, which is even lower for the Rh catalyst.     

Optical reflectivity studies of GaN and AlN chemical beam epitaxy on GaAs(100)

The deposition of gallium nitride and aluminium nitride thin films on GaAs(100) substrates by chemical beam epitaxy is reported. In-situ dynamic optical reflectivity has been used to compare growth rates of the nitride layers as a function of substrate temperature with their arsenide analogues. The relative growth efficiency of gallium nitride/gallium arsenide from triethyl gallium was found to be in the range 75–85%. The growth temperature for gallium nitride extends to higher temperatures, compared with gallium arsenide, probably due to lower evaporation rates of Ga bound to the nitride surface. At the same beam equivalent pressure, the growth rate of aluminium nitride from ethyldimethyl aluminium alane is approximately one-third of that for gallium nitride from triethyl gallium. Atomic force microscopy reveals that the gallium nitride surface formed at 500 °C is facetted, whereas an aluminium nitride surface deposited at 400 °C exhibits a rounded columnar type growth habit. Reflection anisotropy spectra indicate that atomic nitrogen readily reacts with the GaAs(100)-c(4×4) As stabilized surface at temperatures as low as 400 °C but without the gross facetting that has been observed at higher temperatures.     

Densification,microstructure and mechanical properties of hot pressed tantalum carbide

Monolithic tantalum carbide (TaC) ceramics were prepared by hot pressing in order to investigate the effect of hot pressing temperature on the densification behavior, microstructure and mechanical properties of TaC. Monolithic TaC sample hot pressed at 2000 °C for 45 min under 40 MPa, with relative density value above 97%, Vickers hardness of 15.7 GPa and fracture toughness of 4.1 MPa m^1/2 was obtained. Fracture surfaces investigations of the samples, which were carried out using the SEM analysis, showed a significant grain growth by increasing the hot pressing temperature from 1700 to 2000 °C. Also, based on the X-ray diffraction pattern, a decrease in the lattice parameter of hot pressed TaC sample was observed.     

Thermal chemical vapor deposition grown graphene heat spreader for thermal management of hot spots

Graphene of different layer numbers was fabricated using thermal chemical vapor deposition (TCVD), and it was demonstrated as a heat spreader in electronic packaging. Platinum thermal evaluation chips were used to evaluate the thermal performance of the graphene heat spreaders. The temperature of a hot spot driven at a heat flux of up to 430 W cm⁻² was decreased from 121 °C to 108 °C (ΔT ≈ 13 °C) with the insertion of the monolayer graphene heat spreader, compared with the multilayer (n = 6–10) ones’ temperature drop of ∼8 °C. Various parameters affecting the thermal performance of graphene heat spreaders were discussed, e.g. layer numbers of graphene, phonon scattering, thermal boundary resistance. We demonstrate the potentials of using a complementary metal oxide semiconductor compatible TCVD process to utilize graphene as a heat spreader for heat dissipation purposes.     

In situ microscopy observation of liquid flow,zirconia growth,and CO bubble formation during high temperature oxidation of zirconium diboride–silicon carbide

The oxidation of ZrB₂–SiC composites at 1450–1650 °C was directly observed with in situ optical microscopy. Video frames showed the flow of silicate liquids, the formation of zirconia deposits, and the growth and collapse of gaseous bubbles on the oxide surface. Contrast in the incandescence of in situ images is analyzed as spatial variations in hue and intensity and related to differences in emissivity of the oxide scale surface features by comparing these hot images with room temperature images. Above 1450 °C, gaseous bubbles were observed to grow and collapse causing perturbations in the liquid oxide on the surface. The bubbles are associated with the evolution of CO from SiC oxidation and the onset is related to the critical temperature where the partial pressure of CO under the oxide scale exceeds atmospheric pressure.