Oxygen-fuel Ratio Research Articles

A feasibility study of implementation of oxy-fuel combustion on a practical diesel engine at the economical oxygen-fuel ratios by computer simulation

To help achieve zero carbon emissions from inland waterway vessels, this implementation of oxy-fuel combustion on a practical diesel engine at the economical oxygen-fuel ratios were systematically studied and analysed in this paper. A 1-D simulation was used to explore the effect of various operating parameters for recovering the engine power when the engine is modified to the oxy-fuel combustion from conventional air combustion. The brake power of oxy-fuel combustion is only 26.7 kW that has a noticeable decline compared with 40 kW of conventional air combustion with fixed consumption of fuel and oxygen. By optimising some valuable parameters, like fuel injection timing, intake charge temperature, intake components, engine compression ratio and water injection strategy, a benefit of 6.8 kW has been acquired in the engine power. Afterwards, a remarkable benefit was obtained with the increase of lambdaO2 from 1.0 to 1.5, finally obtaining the same engine power with the conventional air combustion. Above all, taking advantage of various operating parameters, it is expected to further improve the value of the implement of oxy-fuel combustion on diesel engines at the economical oxygen-fuel ratios.

Review on the Oxidation of Metallic Thermal Sprayed Coatings: A Case Study with Reference to Rare-Earth Permanent Magnetic Coatings

Thermal spray fabrication of rare-earth permanent magnetic coatings (PMCs) presents potential manufacturing routes for micro-magnetic devices. Despite this potential, thermal spray of PMCs is still not widely explored due to oxidation concerns. It was established that oxidation leads to the loss of ferromagnetic phases in these materials and results in deterioration of magnetic performance. Although this review focuses on a specific class of material, i.e., magnetic materials, there is significant technical crossover to all classes of feedstocks that are employed in thermal spray processing. The oxidation mechanisms and the associated influencing factors are explored in this work to implement effective processing techniques during the deposition process. This paper reviews the various stages and mechanisms of oxidation in thermal spray processes. The factors that influence the extent of oxidation depend on the type of oxidation that is dominant and rely on the type of spray system, powder injection position, and the particle size of feedstock. Among the aspects that are reviewed include the oxygen-fuel ratio for high velocity oxygen-fuel (HVOF), current intensity, gas flow rate, particle size, spray distance, and substrate temperature. Protection strategies to minimize oxidation in thermal spray processes, such as gas shrouding and shielding, are presented.

Analysis and prediction of transient opacity spikes using dimensional modeling

Dimensional modeling, GT-Power in particular, has been used for two related purposes—to quantify and understand the inaccuracies of transient engine flow estimates that cause transient smoke spikes and to improve empirical models of opacity or particulate matter used for engine calibration. It has been proposed by dimensional modeling that exhaust gas recirculation flow rate was significantly underestimated and volumetric efficiency was overestimated by the electronic control module during the turbocharger lag period of an electronically controlled heavy duty diesel engine. Factoring in cylinder-to-cylinder variation, it has been shown that the electronic control module estimated fuel–Oxygen ratio was lower than actual by up to 35% during the turbocharger lag period but within 2% of actual elsewhere, thus hindering fuel–Oxygen ratio limit–based smoke control. The dimensional modeling of transient flow was enabled with a new method of simulating transient data in which the manifold pressures and exhaust gas recirculation system flow resistance, characterized as a function of exhaust gas recirculation valve position at each measured transient data point, were replicated by quasi-static or transient simulation to predict engine flows. Dimensional modeling was also used to transform the engine operating parameter model input space to a more fundamental lower dimensional space so that a nearest neighbor approach could be used to predict smoke emissions. This new approach, intended for engine calibration and control modeling, was termed the “nonparametric reduced dimensionality” approach. It was used to predict federal test procedure cumulative particulate matter within 7% of measured value, based solely on steady-state training data. Very little correlation between the model inputs in the transformed space was observed as compared to the engine operating parameter space. This more uniform, smaller, shrunken model input space might explain how the nonparametric reduced dimensionality approach model could successfully predict federal test procedure emissions when roughly 40% of all transient points were classified as outliers as per the steady-state training data.

Experimental Study of Low Temperature Diesel Combustion Sensitivity to Engine Operating Parameters

This work elucidated which engine operating parameters have the greatest influence on Low temperature diesel combustion (LTC) and emissions. Key parameters were selected and evaluated at low and intermediate speed and load conditions using fractional factorial and Taguchi orthogonal experimental designs. The variations investigated were: about ± 5% in EGR rate, fuel injection quantity and engine speed respectively; and ± 10 °C in intake charge temperature. The half-fractional factorial results showed that the interactions among these parameters were negligible for a specific load/speed point. The Taguchi orthogonal method could be used as an efficient DoE tool for studying the multi-parameter ‘small-scale transients’ that a diesel engine would be likely to encounter when operating in LTC modes. LTC showed the most significant sensitivity to EGR rate variations, where an increase from 60% to 63% in EGR rate doubled THC and CO emissions and reduced combustion stability. LTC was also sensitive to the fuel injection quantity with an increase in injected mass lowering the overall oxygen-fuel ratio and thereby increasing THC and CO emissions. These two parameters influenced the oxygen concentration in the intake charge; which was identified to be a decisive parameter for the LTC combustion and emissions. Intake charge temperature affected the total charge quantity trapped in the cylinder and showed noticeable influence on CO emissions for the low speed intermediate load condition. Variations in engine speed showed a negligible influence on the LTC combustion processes and emissions.

Cermet coatings with Fe-based matrix as alternative to WC–CoCr: Mechanical and tribological behaviours

Recently, cermet coatings with Fe-based metal matrix have emerged as a less hazardous and more environmentally friendly alternative to WC–Co-based ones, which have known inhalation toxicity problems. This study therefore aimed to validate WC-based cermet coatings with Fe-based matrix, obtained using a commercially available feedstock powder, as an alternative to WC–CoCr.HVOF-sprayed WC–15wt.%FeCrAl layers were therefore obtained using different oxygen and fuel (kerosene) flow rates and powder feed rates; their mechanical and tribological properties were compared to HVOF-sprayed WC–10wt.% Co–4wt.%Cr.The WC–FeCrAl coatings always exhibited equi-biaxial compressive residual stress state and possessed dense microstructures, with homogeneous metal matrix, but they contained more oxide inclusions than WC–CoCr. Their characteristics were significantly affected by the normalised oxygen-fuel ratio (λ).Small but meaningful differences existed between the ball-on-disc sliding wear rates of the various WC–FeCrAl coatings, the best sample being that with the most favourable combination of compressive residual stress, low oxidation and high hardness/modulus (H/E) ratio. Its sliding wear resistance was comparable to that of WC–CoCr. The cyclic ball impact resistance of WC–FeCrAl layers was also comparable to that of WC–CoCr, but the dry particle abrasion resistance was inferior, because of the brittleness induced by the oxide inclusions.

INFLUENCE OF PROCESS PARAMETERS ON THE PERFORMANCE UNIFORMITY OF DETONATION GUN SPRAYED WC-Co COATINGS

Based on the orthogonal experiment, the effects of oxygen-fuel ratio and spraying dis- tance on physical and mechanical properties of D-gun sprayed WC-Co coatings were investigated. An ideal coating with the uniform dense microstructures, high hardness and elastic modulus, and excellent wear resistance was obtained by technology optimization. The phase identifications and microstructure observation of the optimized WC-Co coating were conducted by XRD and SEM, respectively. The coating showed near-isotropic behaviors, which has been verified by the comparisons of mechanical and wear properties between cross section and surface. The mechanisms how the spraying parameters affected near-isotropic characters of the D-gun sprayed WC-Co coating were analyzed and discussed.

Quantitatively Evaluating the Effect of Oxygen/Fuel Ratio on Fe2+ Content in HVOF-Sprayed Ni-Zn Ferrite Coatings

This article quantitatively describes the dependence of Fe2+ content in Ni-Zn ferrite coatings on the oxygen-fuel (O/F) ratio in high velocity oxy-fuel (HVOF) spraying. Fe2+ is detrimental to the magnetic properties of ferrites and should be tightly controlled. Methods were developed for calibrating energy dispersive x-ray analysis and for calculating Fe2+ content. The results show that the atomic percentage of the Fe2+ decreased from 25 to 15 at.% by increasing the O/F ratio from 80 to 110% of the stoichiometric ratio. The effect of O/F ratio has also been observed on in flight particle temperature, microstructure, and deposition efficiency. Simulations on the chemical reactions during HVOF spraying demonstrated that Fe2+ was produced only by the reduction of Fe3+ and that oxygen and zinc losses by the decomposition of ZnO in fact increased the percentage of oxygen in the coatings.

Effect of Aluminum on Heat Flux from a Simulated Rocket Propellant Flame

Aluminum particles have been shown to enhance the performance in propellant systems by reacting and releasing significant chemical energy that contributes to the overall heat release. However, the heat transfer characteristics from a propellant to a target are not well understood. In this study, impinging flow geometries of a simulated propellant flame seeded with aluminum particles were investigated. Although the contribution of aluminum was the main focus of this study, inert powders of alumina-titania and yttria stabilized zirconia were also used to compare and quantify the heat flux contributions of reacting, melting, and nonmelting powders, respectively. An oxygen-acetylene torch seeded with aluminum, alumina-titania, or yttria stabilized zirconia was used to analyze the different heat transfer characteristics from each material. Copper coupons captured and quenched reacting particulates from the flame. A scanning electron microscope with energy dispersive spectroscopy and a differential scanning calorimeter were used to examine the degree of completion of aluminum oxidation. Results show that yttria stabilized zirconia experience a 1.9% increase in heat flux compared with gas-only flames. Flames seeded with alumina-titania showed an 80.2% increase in heat flux, whereas aluminum particles provide a 232.7% gain over gas-only flames. Results from the differential scanning calorimeter show that aluminum consumption percentages for flames with a 2.5 oxygen-fuel ratio are an average of 8.6% higher than those for a 1.5% oxygen-fuel ratio. The percent of aluminum consumed in the reaction generally increases with standoff distance.

Droplet combustion experiments in varying forced convection using microgravity environment

A new microscopic model of the interaction between droplet flames and fine vortex tubes which compose a coherent structure of turbulence was developed. Three non-dimensional numbers were introduced to extend the length scale and time scale so as to be suitable for microgravity experiments using droplets of combustion of about 1 mm in diameter. An experimental apparatus for combustion of a single droplet and that of an array of two droplets in varying airflow was developed, and experiments were performed in microgravity and normal gravity at pressures up to 2.0 MPa for n-nonane and ethanol as fuels. Variations of the instantaneous burning rate constant, K i, in response to the varying flow velocity was successfully observed. At high pressure, the effects of droplet Reynolds number Re on K i was clearly seen, while the effects of natural convection, which increases K i with Re, was seen in normal gravity even in the forced airflows. As for the experiments on combustion of an array of two droplets, K i reduction of the downstream droplet became weak when the flow direction was varied. However, the K i reduction of the downstream droplet for flow direction variations was clearly seen for n-nonane droplets but almost not for ethanol droplets. The interaction mechanism between upstream and downstream droplets is considered to result from the elimination of oxidizer supply to the downstream droplet, indicating strong interaction effects of n-nonane droplets for a stoichiometric oxygen-fuel ratio of n-nonane (i.e., 14.0) greater than that of ethanol (i.e., 3.0).

04/00928 Deactivation and regeneration of Pt/γ-alumina and Pt/ceria-alumina catalysts for methane combustion in the presence of H 2S : Fullerton, D. J. et al. Catalysis Today, 2003, 81, (4), 659–671

Catalytic combustion of gasified biomass over Pt/Al2O3 was investigated to clarify its dependence on the fuel gas composition and the air-fuel ratio. An experimental study was performed using synthetic mixtures of the main components in gasified biomass: carbon monoxide, hydrogen, methane, carbon dioxide, water, benzene (model aromatic compound), ammonia, and inert (argon or nitrogen). Results showed that carbon monoxide and hydrogen ignited simultaneously over the catalyst used, with methane having a higher ignition temperature than that of carbon monoxide and hydrogen. The ignition temperature for carbon monoxide and hydrogen decreased as the oxygen-fuel ratio and inert concentration increased. The presence of water vapor in the feed had an inhibiting effect on the ignition of carbon monoxide, whereas the opposite was observed for methane. Methane ignition was favored by the presence of carbon monoxide and hydrogen, not only because their combustion heated the catalyst but also because it attenuated the oxygen inhibition of methane combustion under certain conditions. These effects were explained by co-adsorption phenomena involving fuel components and oxygen. Ammonia was found not to influence the combustion of the other components and was completely converted to nitrogen monoxide over the used catalyst.

A review on nanostructured WC–Co coatings

Unique mechanical properties of nanostructured materials motivate a worldwide interest to synthesize nanostructured coatings. Nanostructured WC–Co coatings have been extensively investigated because of the importance of WC–Co coatings in industrial applications, usually with respect to wear resistance requirements. The present paper has reviewed the studies in this field, including synthesis of nanostructured WC–Co powder, concern on decomposition of nanostructured WC particles, influence of spraying parameters on microstructure and mechanical properties of nanostructured coatings. Significant achievements in this field are: (1) It is possible to produce nanostructured WC–Co powders without non-WC/Co phases in quantities although a high percentage of non-WC/Co phases is frequently reported in conventional WC–Co powder; (2) By controlling agglomerate size of feedstock powder, fuel chemistry and fuel–oxygen ratio, the decomposition of WC particles can be reasonably eliminated so as to synthesize near nanostructured WC–Co coating with a low amount of non-WC/Co phases; and (3) Increased hardness, toughness and wear-resistance can be obtained in near nanostructured WC–Co coatings that are properly synthesized.

Near-nanostructured WC-18 pct Co coatings with low amounts of non-WC carbide phase: Part I. Synthesis and characterization

Near-nanostructured WC-18 pct Co coatings, with low amounts of non-WC carbide phases, have been synthesized using high velocity oxygen fuel (HVOF) thermal spraying under spraying conditions of varying fuel chemistry, fuel-oxygen ratio, and powder particle size. The results show that the temperature the particles experience during spraying depends on the preceding parameters. Compared to available published results on WC-Co system coatings, nanostructured WC-18 pct Co coatings, synthesized in these experiments, contain very low amounts of non-WC carbide phase (less than 10 pct vol). This is comparable to that of the conventional WC-12 pct Co coating, prepared in the present study for comparison purposes. Regardless of whether the binder phase in the agglomerated feedstock powder particles melt or not, the WC particles do not appear to experience significant growth as a result of the spraying. The size of WC particles remains in the 200 to 500 nm range, consistent with that present in the feedstock powder. The as-received near-nanostructured WC-18 pct Co feedstock powder exhibits morphological characteristics that lead to low amounts of non-WC carbide phases in the coatings. The microstructure and phase constitution of the coatings depend on particle size of the feedstock powder and flame characteristics of the fuels during spraying. A higher particle temperature causes more decomposition of the WC phase but reduces porosity in the coatings, this occurs with higher flame temperature and smaller particle sizes. Propylene fuel produces less decomposition of the WC phase despite the higher flame temperature and, thus, provides the best combination of dense coating with low amount of non-WC phase.

Catalytic combustion of gasified biomass over Pt/Al 2O 3

Catalytic combustion of gasified biomass over Pt/Al 2O 3 was investigated to clarify its dependence on the fuel gas composition and the air-fuel ratio. An experimental study was performed using synthetic mixtures of the main components in gasified biomass: carbon monoxide, hydrogen, methane, carbon dioxide, water, benzene (model aromatic compound), ammonia, and inert (argon or nitrogen). Results showed that carbon monoxide and hydrogen ignited simultaneously over the catalyst used, with methane having a higher ignition temperature than that of carbon monoxide and hydrogen. The ignition temperature for carbon monoxide and hydrogen decreased as the oxygen-fuel ratio and inert concentration increased. The presence of water vapor in the feed had an inhibiting effect on the ignition of carbon monoxide, whereas the opposite was observed for methane. Methane ignition was favored by the presence of carbon monoxide and hydrogen, not only because their combustion heated the catalyst but also because it attenuated the oxygen inhibition of methane combustion under certain conditions. These effects were explained by co-adsorption phenomena involving fuel components and oxygen. Ammonia was found not to influence the combustion of the other components and was completely converted to nitrogen monoxide over the used catalyst.

The effect of back diffusion of intermediate hydrogen on methane-air and propane-air flames diluted with nitrogen in a stagnation flow

Experimental studies on the behavior, structure, and extinction of laminar, premixed methane-air and propane-air flames diluted with nitrogen in a stagnation flow are made using counterflow, twin flames established in the forward stagnation region of a porous cylinder. The extinction limits of the twin flames, the flame separation distance at extinction, and the concentrations of some stable species on the stagnation surface for flames very near the extinction limit are measured over the whole composition range of fuel-air-nitrogen flames. The experiments are made under the condition of a constant stagnation velocity gradient. The concentration distributions of stable species across the twin flames are also measured for flames near extinction. An anomalous relationship between the flame separation distance Δ c at extinction and the equivalence ratio ϕ of the mixture is found for rich methane flames, but not for propane flames. Comparisons between the concentrations of some stable species measured on the stagnation surface and those expected from equilibrium considerations reveal that the underlying cause of the occurrence of this anomalous relationship between Δ c and φ is attributed to preferential diffusion of the intermediate hydrogen across the divergent flow lines toward the unburned gas mixture (i.e., back diffusion). On the other hand, it is found that, for rich propane flames, preferential diffusion of oxygen, back diffusion of the intermediate hydrogen, and the Lewis number effect of the deficient reactant (i.e., oxygen) remarkably shift the local gas composition in the flame zone toward a lower fueloxygen ratio.

Detonation in a cryogenic hydrogen-oxygen mixture

A closed model has been constructed for stationary detonation in a heterogeneous gas-droplet mixture; studies have been made on the structures of the subsonic and supersonic zones, and it has been found that there is substantially incomplete combustion of the c phase at the Jouguet point with certain initial oxygen-fuel ratios. It has been found that for 30<do<300 μm, the speed of the droplets relative to the front at the Chapman-Jouguet point is greater than the gas speed when there is incomplete combustion, while the detonation speed is only slightly dependent on the initial droplet diameter; there may be two stationary states or only one in accordance with the fuel-oxidant ratio. The higher detonation speed corresponds to complete burnup (in [4, 5], the number of states was only odd).

Near-limit downward propagation of hydrogen and methane flames in oxygen [sbnd]nitrogen mixtures

Measurements are reported on nitrogen concentrations required to prevent downward propagation of hydrogen oxygen and methane oxygen flames in open tubes of 2.5 and 5.1 cm diameter. Limits plotted as functions of the fuel oxygen ratio show that quenching is most difficult the fuel-lean side for hydrogen flames and near stoichiometric for methane flames. Cellular patterns were observed near flammability limits, and near-limit flame speeds were measured. Results are interpreted mainly in terms of conductive losses from cellular flames since alternative mechanisms appear to produce qualitatively inconsistent predictions.

Gas-phase oxidation of aldehydes in the low-temperature region: I—Propanal and propanal-2,2-d 2

The oxidation of propanal has been studied below the ignition region. The nature and relative concentration of products depend on both the temperature and the fuel-oxygen ratio due to the alternative reactions for the propionyl radical: C 2H 5 C ̇ +O 2⇌C 2H 5CO 3· (2) C 2H 5 C ̇ O(+M)→C 2H 5· + CO(+M) . (4) The products are described in terms of the subsequent reactions of peroxypropionyl and ethyl radicals, which, in competition, lead to the formation of peroxypropionic acid and ethyl hydroperoxide. By using propanal-2,2-d 2, the mechanism of several reactions are elucidated; in particular, the formation of acetaldehyde.

The atomic absorption spectroscopy of lead

Lead can be determined by atomic absorption spectroscopy at 3 wavelengths. The relative sensitivities are 1:1.5:300. No interferences were found from the cations studied. Anionic interferences were numerous and extensive, but were removed by adding EDTA. The use of a “T” -piece increased the sensitivity of atomic absorption when flame atomizers were used. However, extreme care was necessary in controlling flame conditions both with respect to oxygen-fuel ratio and the type of solvent used. The absorption by combustion products in the flame was high, and in many cases, much greater than that of the lead itself. The most sensitive conditions for the determination of lead appeared to be as follows: wavelength, 2170 A; solvent, aqueous or organic; flame, oxy-hydrogen, with the hydrogen atomizing the sample (reversed from normal). Aflame adapter enabled detection limits of 0.013 p.p.m. to be reached.

Thermochemical equilibrium in hydrocarbon-oxygen reactions involving polyatomic forms of carbon

Equilibrium composition and flame temperatures have been calculated for the reaction of acetylene and ethylene with oxygen over a range of mixture ratios. Emphasis has been placed on the determination of conditions necessary for the formation of solid carbon in the products. The influence of the presence of long-chain carbon molecules on the mixture ratio and temperature required for carbon deposition has been investigated. Premixed flames of acetylene and ethylene with oxygen have been studied experimentally to determine the correlation between theoretical calculations and actual combustion reactions. Calculations indicate that, for acetylene, carbon begins to appear in the condensed form at an equivalence ratio (actual fuel oxygen ratio divided by the stoichiometry ratio) of approximately 2·7 when the only forms of carbon vapour considered are monatomic and diatomic. The equilibrium flame temperature is 3 275°K. If longer chain forms of carbon vapour are considered (consistent with a triple point pressure of about 100 atm 4 000°K) then carbon formation begins at an equivalence ratio of 3·37 and the flame temperature would be 3095°K. This difference is not so pronounced with the other hydrocarbons considered. Experimentally, conclusive evidence of carbon formation was apparent at an equivalence ratio of 2·9. Based upon the property data used, the experimental evidence would indicate the presence of carbon molecules containing up to five atoms of carbon. Of these forms the odd number species probably redominate.