Oxygen-fuel Ratio Research Articles

The characteristics and mechanism NO formation during hydroxylated fuels/NH3 oxidation in oxy-fuel atmospheres

Oxy-fuel combustion, as an important technology to realize CCUS in the field of combustion, needs to control the generation of pollutants such as NOx while realizing CO2 capture, and the conversion of fuel-N to N2 is crucial. Previous experiments have provided insights into the influence of different atmospheres on NO during oxy-fuel combustion of alcohols. However, the specific reaction mechanism underlying how the atmosphere and hydroxyl fuels impact NO generation through the free radical pool remains unclear. In this study, the formation and reduction of NO during the oxidation of CH3OH/NH3 and C2H5OH/NH3 in O2/CO2, O2/H2O and O2/CO2/H2O atmospheres with oxy-fuel condition were investigated by simulation. In the NO generation stage, different H2O, CO2, O2 and fuel types have little effect on the peak of NO although they change the NH3→NO reaction path. In the process of NO reduction, stage 1 is the main reaction phase of NO→N2, and both CO2 and H2O are beneficial for the reduction of NO. But the reduction of NO by H2O was more pronounced. In the case of simultaneous addition of H2O and CO2, the reducing effect of H2O and CO2 alone on NO was attenuated. On the other hand, the reduction effect exerted by H2O and CO2 was stronger in high than in low oxygen-fuel ratio, stronger in C2H5OH than in CH3OH. The reduction of NO by H2O and CO2 is based on the general equation NO→N2+O2. H2O is used to promote the reaction in the positive direction by consuming O2 to convert it to H and OH, so that more of the element O is converted to OH than O2 to inhibit the production of NO. The CO2 contributes to the formation of less O2 during the reduction of N2 from NO by promoting reaction NO + N→O + N2, while the additional OH increases the "capacity" of O2 in the NO→N2+O2 reaction.

Study on combustion mechanism of methanol/nitromethane based on reactive molecular dynamics simulation

Oxygenated fuels and nitro fuels are effective strategies for addressing incomplete combustion by increasing the oxygen-fuel ratio. A computational approach based on reactive molecular dynamics simulations reveals oxidation mechanisms of temperature-induced effects on a mixed fuel of methanol and nitromethane. The method enables the demonstration of the initial reaction scheme of a binary fuel mixture, even for complicated interplay and coupling reactions. The results showed that the first reaction step of nitromethane was homolysis in poor-oxygen conditions, mainly via CH3NO2 → CH3 + NO2 (Net flux = 183, ratio = 92.89%). Methanol undergoes dehydrogenation reaction with the assistance of active radicals (OH, HO2, CH3, NO, and NO2), and the participation rates of these active groups are 60%, 17.14%, 8.57%, 7.62%, and 6.67%, respectively. The decomposition of nitromethane provided NO2 and CH3 radicals and significantly increased the amount of OH and NO via a reaction of NO2 + H → HNO2 → OH + NO. By fragment analysis, the main C1 intermediates are formed by pyrolysis of methanol/nitromethane such as formaldehyde, hydroxymethyl radical, and formyl radical. The CH3OH and CH2O are relatively stable, and the dehydrogenation is mainly highly active groups such as OH and NO. In contrast, the dehydrogenation of CH2OH and CHO free radicals is completed by self-cleavage or with the help of O2, NO2, etc. Our findings shed light on the oxidation behaviors of methanol/nitromethane mixed fuel in combustion.

Flame inhibition using nanotechnology

Flame inhibition is significant as it directly contributes to fire safety and prevention. Effective flame inhibition can reduce the spread and intensity of fires, protecting lives, property, and the environment. The research focused on the significant role of nanomaterials, specifically aluminum oxide (Al₂O₃), in improving fire retardation and enhancing fire inhibition performance. Nanoparticles can be used in flame inhibition, as they might merge two flame inhibition techniques: cooling and physical barriers. They offer unique properties due to their small size and high surface area, which can enhance their effectiveness in disrupting the combustion process. Nanoparticles can act as heat sinks, absorbing heat and reducing the temperature of the combustion zone (cooling method). They can also catalyze the formation of non-combustible gases or form a protective layer on the material's surface (physical method). Due to these properties, nanoparticles are increasingly studied and utilized for advanced flame retardant systems. Experimental work was carried out to accomplish the goal of the research. The fire inhibition test was performed within a pressure range between 3.2 and 5.3 cm of Hg, corresponding to a fuel-oxygen ratio of 9.3 % to 14.8 %, respectively. A novel nanoparticle material was involved in this analysis, including Al₂O₃. Based on the research analysis, the critical research results revealed that Al₂O₃ employment as a fire inhibitor provided a more enhanced impact of fire retardance and flame inhibition compared with conventional retardation materials, reflected in more sustainability and less adverse environmental effects.Furthermore, the experimental findings indicated that the flammability limits range between a lower flammability limit of approximately 9.3 % and an upper one of 14.8 % under specified amounts of pressure and temperature. In addition, increasing the inhibitor quantity could raise the lean flammability limit. Raising the nanomaterial mass would extend the flammability limits, altering the concentration of these nanoparticles to increase inhibitory effectiveness and change the lower and upper flammability limits.The study concluded that adjusting nanoparticle concentrations can significantly alter inhibitory effectiveness. The novelty lies in the use of a novel nanoparticle material, demonstrating improved sustainability and effectiveness in fire retardation of a highly flammable gaseous mixture.

A strategy to extend load operation map range in oxy-fuel compression ignition engines with oxygen separation membranes

The possibility of applying oxy-fuel combustion to a compression ignition engine (CIE) at different operating points regarding engine speed and load is studied in this work. To do so, a strategy is proposed to extend the load operation map range of a 2.2L turbocharged and direct-injection CIE under oxy-fuel combustion conditions using mixed ionic-electronic conducting membranes (MIEC) to acquire oxygen (O2) from the air. As nitrogen is not present in the intake flow, nitrogen oxide (NOx) emissions are eliminated, and carbon capture is allowed. The strategy consists of modifying exhaust gas temperature and oxygen-fuel ratio , generating temperature-lambda maps to decide the optimal combination in terms of engine performance. Thus, the system behavior is analyzed at three engine speeds (1250rpm, 2500rpm and 3500rpm) with different load levels and compression ratio (CR) of 20. The baseline engine model is calibrated with experimental data within part-load operation ranges, and an apparent combustion time model calibrated with computational fluid dynamics data is applied to simulate the combustion process under oxy-fuel combustion conditions. Finally, specific parameters are researched to verify whether the system produces enough energy to heat up the MIEC, generating the necessary oxygen. Indeed, a few of them have been found very useful as design parameters for finding out oxy-fuel engine operation limits and estimating MIEC design features.

The Confirmation of Thermal Boundary Parameters in an Oxygen Kerosene Fuel-Rich Rocket Engine

The thermal environment is an important factor in the design of liquid rockets. In this paper, theoretical analysis, numerical simulation and experimental testing are conducted to study the boundary thermal characteristics of a GOX/kerosene liquid rocket motor with a total flow rate of 120 g/s and an oxygen-fuel ratio of 1:1. We measured the axial temperature in different positions in the combustor using thermocouples and the heat flux using a flux meter. We found that the heat flux at 182 mm increases by 6.8% when a carbon deposit exists. For the theoretical results, after correcting the thermal conductivity by the volume fraction of carbon deposition, the theoretical heat flux (1.11 MW/m2, using the corrected thermal conductivity) and the numerical result (0.89 MW/m2, considering the injectors) are similar to the experimental value (0.937 MW/m2). This study validates the accuracy of theoretical and simulation calculation in this case, and provides verification data for future numerical calculation, as well as data for setting gas temperature at the wall in the simulation of the gas phase.

Characterizations the deposition behavior and mechanical properties of detonation sprayed Fe-based amorphous coatings

In this study, the spreading morphologies and deposition behaviors of molten droplet in a single detonation sprayed shot under different oxygen-fuel ratio conditions are characterized in detail to reveal the formation mechanism of Fe-based amorphous coatings. Additionally, the porosities, micro-hardness, amorphous phase content and wear behavior of the coatings were also carefully evaluated to correlate the relationship between preparation process parameters, particle deposition behavior, spreading morphology, and mechanical properties. The results indicate that the spraying oxygen-fuel ratio (OF) parameter can determine the microstructure change of the coating, which is considered to be a reflection of the molten state of the sprayed particles. The low OF reduces the combustion efficiency, making the coating particles deposited in a form similar to cold spraying, resulting in uneven coating structure. In the case of medium OF (2.00), amorphous particles can form completely melted droplets and spread well on the substrate, and produce a good metallurgical bond with the substrate. Thanks to the good spread of the amorphous droplets, the OF-2.00 coating displays a very uniform and dense structure and uniformly distributed microhardness, which also makes its wear resistance (0.63 × 10−6 mm3 N−1 m−1) increased by about 8 times compared with OF-1.43 coating.

Optimization design in single wagon-wheel fuel grain of hybrid rocket motor

The grain design of hybrid rocket motor is a design of proper fuel grain geometry and flow adjustment scheme based on the total impulse, thrust, chamber pressure, length and outer diameter of combustion chamber. And the laws of various parameters in the working process of motor are obtained through the internal ballistic calculation. Based on the overall indicators of the upper stage motor of launch vehicles, the grain design process of single wagon-wheel and the internal ballistic calculation of adjusting the oxidizer flow according to the thrust feedback under the preset thrust condition are established. According to the indicators of power system, the constant thrust is F=11kN, the total impulse is I≥1100kN·s, the outer diameter is Dt≤400mm and the chamber length is L≤1000mm. Furthermore, the comparison and optimization design on star-shaped and single wagon-wheel grain are carried out. The oxidizer is 98% hydrogen peroxide (HP), the fuel is hydroxyl-terminated polybutadiene (HTPB) based fuel (including 58% Al), and the optimal oxygen-fuel ratio (O/Fopt) is 1.3. According to the theory of constant regression rate of the burning surface, the changes of the burning line length and channel area of the single wagon-wheel grain with the regression of the combustion surface are calculated. The results show that when the expansion ratio is 100 and average combustion chamber pressure is 5 MPa, the burning area of single wagon-wheel grain increases by 16.9% compared with the star-shaped grain, the O/F is reduced during motor operation, and the average specific impulse of the engine is increased by nearly 2%. In this paper, a typical uniform-thickness single wagon-wheel fuel grain is adopted. According to the optimization design, when the spokes number is 6, the average specific impulse of the motor is the largest. With increasing the spokes angle coefficient, increasing the height of the spokes, and reducing the angle of the spokes, the burning area is increased and the channel area is reduced, thereby the regression rate and fuel flow are increased and the O/F is reduced during the working process. Then the average specific impulse and overall performance are improved. This research provides a reference for single wagon-wheel fuel grain of hybrid rocket motor, calculation of interior ballistic performance under preset thrust, and flow adjustment by thrust feedback.

Numerical study on the effects of intake charge on oxy-fuel combustion in a dual-injection spark ignition engine at economical oxygen-fuel ratios

In order to decrease Carbon Dioxide (CO2) emissions, Oxy-Fuel Combustion (OFC) technology with Carbon Capture and Storage (CCS) is being developed in Internal Combustion Engine (ICE). In this article, a numerical study about the effects of intake charge on OFC was conducted in a dual-injection. Spark Ignition (SI) engine, with Gasoline Direct Injection (GDI), Port Fuel Injection (PFI) and P-G (50% PFI and 50% GDI) three injection strategies. The results show that under OFC with fixed Oxygen Mass Fraction (OMF) and intake temperature, the maximum Brake Mean Effective Pressure (BMEP) is each 5.671, 5.649 and 5.646 bar for GDI, P-G and PFI strategy, which leads to a considerable decrease compared to Conventional Air Combustion (CAC). [Formula: see text], [Formula: see text] and [Formula: see text] of PFI are the lowest among three injection strategies. With intake temperature increases from 298 to 378 K, the reduction of BMEP can be up to 12.68%, 12.92% and 12.75% for GDI, P-G and PFI, respectively. Meantime, there is an increase of about 3% in Brake Specific Fuel Consumption (BSFC) and Brake Specific Oxygen Consumption (BSOC). Increasing OMF can improve the performance of BMEP and BSFC, and the trend is more apparent under GDI strategy. Besides, an increasing tendency can be observed for cylinder pressure and in-cylinder temperature under all injection strategies with the increase of OMF.

Research on 2D Temperature Field Measurement Method of Mg/CO2 Combustion Flame Based on Color CCD

A new Mg/CO2 powder rocket propulsion system is proposed for Mars exploration. Accurate measurement of Mg/CO2 combustion flame temperature field has important reference value for understanding the combustion characteristics and operating conditions. In this paper, the two dimensional temperature field of the Mg/CO2 combustion flame is obtained by building a Mg/CO2 combustion device and colorimetric temperature measurement system based on the color charge coupled device (CCD). The influence of magnesium powder particle size, premixed Reynolds number, and CO2/Mg oxygen fuel ratio on the flame temperature of Mg/CO2 combustion are discussed. The results show that the maximum temperature of Mg/CO2 combustion flame under different working conditions is between 2500K and 2900K, and it increases with the increase of magnesium powder particle size, premixed Reynolds number, and oxygen-fuel ratio.

Microstructure and tribological properties of Fe-based amorphous coating prepared by detonation spray

The Fe-based amorphous coatings were successfully prepared on Q235 steel by detonation spray under different oxygen-fuel ratios (2.5, 2.0 and 1.7), and the resultant coatings were named as coating A, B and C. The wear behaviors of the coatings against Al2O3 ball were investigated by dry sliding wear tests. The results show that coating B with the porosity of 0.5 vol.% and microhardness of 766 ± 31 Hv, exhibits good wear-resistance properties with wear rates of 14.7 × 10−6 mm3N − 1m − 1, and the wear mechanism of the coatings changes from delamination wear to oxidative wear and abrasive wear, as the oxygen-fuel ratio changes from 2.5 to 1.7. Furthermore, it was found that the wear rate of coating B is more sensitive to the sliding speed. With the increase of the sliding speed (0.1 m s − 1~0.8 m s − 1), the wear mechanism of coating B changes from oxidative wear to delamination wear.

Flame temperature analysis in the oxycut process using acetylene gas: a numerical study

To cut metals, the oxycut process uses a preheating flame, usually composed of oxygen and a combustible gas, in addition to a flame-independent jet of oxygen. In the present work, the partially premixed combustion model of a finite volume-based software was applied to analyze the flame temperature in a cutting tip of acetylene. At the torch inlet boundary, the flow rates of oxygen and acetylene were adjusted to sweep a wide range of fuel-oxygen ratio. The results pointed a peak surrounding the stoichiometric ratio, at 3106 °C for the literature and 2650.93 °C for the numerical model, contrasting a deviation of 14.65%. The maximum temperature occurs at 52.38% of oxygen volume for the literature and 50.03% for the model, a difference of 2.35 percentage points only. It is concluded that the results of the numerical approach attained the ends of the research.

Microstructure and corrosion resistance of Fe-based amorphous coating prepared by detonation spray

The Fe-based amorphous coatings were successfully prepared on the surface of Q235 carbon steel by detonation spraying process under different oxygen-fuel ratio (2.5, 2.0 and 1.7), and the resultant coatings were named as coating A, B and C. The macro-structure and corrosion behaviors of the coating were investigated in detail by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. It was found that the corrosion resistance is correlated with the microstructure, phase component, and porosity of Fe-based amorphous coating. The morphology of the microdomains showed that coating B was highest dense and had no obvious defects, and the thickness, porosity was about 220 ± 10 μm, and 0.5% respectively. The electrochemical tests showed that Fe-based amorphous coating has effective protection for Q235 carbon steel in 3.5 wt% NaCl solution, and coating B has the highest corrosion potential (−283 mV vs −501 mV for coating A, −336 mV for coating C), and lowest corrosion current density (5.14 μA cm−2 vs 17.54 μA cm−2 for coating A, 9.71 μA cm−2 for coating C), and the highest the |Z| value (103.7 vs 103.1 for coating A, 103.4 for coating C), which indicates that coating B has superior corrosion resistance. Besides, as the oxygen-fuel ratio changes from 2.5 to 1.7, the corrosion mechanism of the coating changes from inner corrosion to galvanic corrosion.

Optical Measurements of In-Flame Soot in Compression-Ignited Methyl Ester Flames

This study investigates in-flame sooting characteristics of biodiesel surrogates in compression-ignited spray flames. The aim of the study is to produce reliable experimental data on in-flame soot for validation of kinetic mechanisms and soot models. A rapeseed oil biodiesel [rapeseed oil methyl ester (RME)] was compared to neat methyl oleate (MO) and methyl decanoate (MD). In addition, neat n-heptane was chosen as a baseline fuel and the effect of blending n-heptane and MD on soot production was investigated. The study was performed in a single-cylinder research engine with optical access to a single spray for varying ambient gas temperatures (825–990 K). The in-flame soot was measured by a high-speed diffuse back-illuminated extinction imaging system, and the flame lift-off length (FLOL) and the corresponding estimated equivalence ratio at FLOL was measured from high-speed OH* chemiluminescence imaging. Results show that RME has the highest tendency to soot, closely followed by MO, independent of the FLOL equivalence ratio. Having almost identical fuel properties, this is likely due to the higher degree of unsaturation in RME compared to MO. When comparing MD to n-heptane, a much lower in-flame soot production rate is observed despite the fact that MD has a higher number of carbon–carbon bonds, concluding that the high fuel oxygen ratio in MD is effectively reducing in-flame soot production. Generally, for FLOL equivalence ratio leaner than ∼2, no in-flame soot was produced for all ambient gas temperatures. The in-flame soot production rate also showed a clear ambient gas temperature dependence for constant FLOL equivalence ratios, where the soot production rate increased with increased gas temperatures.

The Effects of Non-uniform Distribution of Oxidizer Flow on High-Frequency Combustion Instability

The numerical calculation of three-dimensional unsteady combustion for the combustion chamber of LOX/kerosene high pressure staged combustion rocket engine was carried out. By changing the offset ratio of oxygen mass flow rate in the edge area of the injector face, computational studies were conducted to investigate the effects of non-uniform distribution of oxidizer flow on combustion instability for a liquid-propellant rocket engine. The calculation results show that the offset ratio of oxygen mass flow rate changes the distribution of heat release in the combustion chamber. Within a certain range of offset ratio, the non-uniform distribution degree of oxidizer flow enhances the coupling between the pressure and heat release. As a result, it leads to an increase in the pressure oscillation amplitude in the combustion chamber. However, if the offset ratio is too large, the oxygen-fuel ratio will be too small in some regions, which will reduce coupling between the pressure and heat release and increase the damping of combustion instability.

Hydrogen production via methanol oxidation on platinum oxide thin film catalyst: Influence of methanol-to-oxygen ratio

Platinum oxide (PtOx) thin films deposited by means of radio frequency (rf) magnetron sputtering on oxidized Si substrate were investigated under realistic conditions as efficient catalysts promoting oxidation of methanol to produce hydrogen. The main focus was given to the role of reactant mixture (methanol + oxygen) composition at different surface temperatures. Freshly deposited PtOx changes its chemical state and morphology during the initial reaction leading to strongly corrugated metallic Pt layer with small amounts of stable Pt2+ cations providing a crucial ingredient for its specific catalytic properties. With growing temperature or methanol-to-oxygen molar ratio the reaction selectivity of such catalyst generally shifts from pathways producing water to those generating hydrogen. The efficiency for a given reaction route can be thus maximized via independent tuning of the fuel-oxygen ratio and surface temperature. The most intensive hydrogen evolution with the lowest relative amount of CO by-product (but relatively high abundance of methanolic residuals) was achieved with mildly oxygen lean feed above 500 K. The highest selectivity for partial oxidation of methanol pathway (>80%) can be, on the other hand, obtained with stoichiometric or oxygen rich mixture.

A study of the electrical characteristics of an oxy-fuel flame

Electrical phenomena useful for oxy-fuel process sensing are demonstrated at signal level voltages applied to an oxy-fuel cutting torch. The current-voltage characteristic of the flame between the torch and work is recorded while varying torch-to-plate standoff, fuel-oxygen ratio, total flow rate, and plate temperature. At ±10V, typical currents are on the order −100μA to 25μA, and the I-V characteristic exhibits three regimes. At low currents, the relationship between voltage and current is linear. At positive currents, transition to saturation is heavily curved around 10–20μA. Negative currents do not totally saturate in this voltage range, but there is an abrupt transition to a new slope, which we describe as “partial” saturation. The properties of these regimes demonstrate strong repeatable links to standoff and fuel-oxygen ratio. Flow rate and plate temperature also demonstrate correlation to these electrical properties despite substantial scatter.

The effect of oxygenated fuel properties on diesel spray combustion and soot formation

Diesel engines have advantages due to their potential for high fuel conversion efficiency. However, it is necessary to reduce pollutant emissions, particularly NOx and soot to meet emission mandates. Many studies have shown that oxygenated fuel additives can effectively reduce soot emissions. In this research, to investigate the effect of oxygenated fuel properties on combustion and soot emission, CFD simulations were carried out using newly developed chemical mechanisms for various oxygenated fuels such as tri-propylene glycol methyl ether, methyl decanoate, and dimethyl ether. The results show that the formation of soot precursors decreases with increased oxygen content and decreased number of C–C bonds in the fuel. The fuel molecular structure strongly affects soot formation in addition to fuel-air mixing. Comparisons of fuel blends (oxygenated fuels with n-hexadecane) including methyl decanoate, which have the same fuel oxygen ratio, show that the effects of the ignition delay and lift-off length control soot formation for fuels with similar fuel oxygen ratio and number of C–C bonds.

Effects of Oxygen-fuel Ratio on Structure and Property of Detonation Gun Sprayed WC Coating

Effects of Oxygen-fuel Ratio on Structure and Property of Detonation Gun Sprayed WC Coating

Experimental Investigation and Comparison of Pulverized Coal Combustion in CO2/O2− and N2/O2−Atmospheres

This paper presents results from measurements of flue gas components and spontaneous emission originated from excited OH-molecules of pulverized coal combustion in air- and CO2/O2−atmospheres. Measurements were conducted for various local oxygen-fuel ratios and O2 contents of the CO2/O2−atmosphere. For this purpose a swirl burner (60kWth) specially designed for oxy-fuel combustion was used. In the present study, measurements in the flame of the swirl burner were performed in a vertical downward fired test furnace. A CCD-camera system was used to capture spontaneous emission of excited OH-molecules. Furthermore, the global flue gas emissions were measured in the stack to gain data for a general description of the combustion process. The measurements were performed for combustion with air and with a premixed oxy-fuel atmosphere. Two different oxy-fuel atmospheres were tested (21 vol.-% O2/ 79 vol.-% CO2 and 25 vol.-% O2/ 75 vol.-% CO2). In addition the oxygen-fuel ratio in the proximity of the burner was varied between 1.0 and 0.6 while the global oxygen-fuel ratio was fixed at 1.3. Global concentrations of CO and NO in the flue gas as well as profiles of the spontaneous emission of OH-molecules are presented and discussed within this paper. Based on these measurements flame structures and flame characteristics are identified.

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.