Chemical Kinetic Mechanism Research Articles

Numerical Investigation of the Effects of Engine Speed on Performance and Combustion Characteristics on a Converted Spark-Ignition Natural Gas Engine

In this study, the effects of different engine speed values on performance and combustion characteristics were investigated by converting a diesel engine to a spark-ignition engine using natural gas. In numerical analysis, G-equation combustion model, reduced methane chemical kinetic mechanism that represent natural gas consisting of 29 types and 171 equations, and RANS k-e turbulence model were used. Analyzes were performed at full load, 17.5:1 compression ratio, constant ignition timing, and 6 different engine speeds. In order to examine only the effect of speed, the initial value, boundary conditions and spark plug ignition time were considered constant. While engine power and fuel consumption increased with increasing engine speed, engine efficiency decreased. In addition, increasing engine speed also increased the ignition delay time and combustion duration, and the flame front reached the squish zone later.

Experimental and numerical study of the laminar burning velocity of syngas in oxyfuel conditions

ABSTRACT This study evaluates the laminar burning velocity of oxyfuel syngas mixtures. Experimental measurements were performed in standard conditions (298 K and 1 atm), varying the oxyfuel syngas composition (H2/CO/CO2/O2) and equivalence ratio for lean mixtures. The experimental setup uses the heat flux method, validated with CH4/air and H2/CO/air measurements. The results were compared with six chemical kinetic mechanisms developed for syngas, aiming at evaluating their predictive capabilities. The mixtures presented a tendency to the appearance of cellular instability in the flame front that was prevented to a certain extent. The CO2 effects on the flames were explored through numerical analysis, isolating the thermodynamic properties, transport properties, thermal radiation, and chemical effects. The CO2 or N2 effect as bath gas in the oxidizer is also evaluated in terms of the laminar burning velocity and mixture’s effective Lewis number. Limitations due to cellular instability were studied, analyzing the influence of fuel dilution and composition on the onset of cellular instability at the flames. The results showed a good prediction of the experimental data by the evaluated kinetic mechanisms. The expected reduction in the laminar burning velocity with CO2 dilution is primarily due to the effect of carbon dioxide’s thermodynamic properties, followed by its transport properties (when compared to N2 dilution), chemical effects, and heat losses by radiation. Cellular instability is attenuated with high dilution levels due to the reduction of hydrodynamic instability. At the same time, the increase of the H2 concentration in the mixture leads to more unstable flames due to both hydrodynamic and thermal-diffusive instability. A laminar burning velocity threshold above which the measurements were not possible due to the effects of cellular instabilities was identified and analyzed in detail.

LES/FGM investigation of ignition and flame structure in a gasoline partially premixed combustion engine

This paper presents a joint numerical and experimental study of the ignition process and flame structures in a gasoline partially premixed combustion (PPC) engine. The numerical simulation is based on a five-dimension Flamelet-Generated Manifold (5D-FGM) tabulation approach and large eddy simulation (LES). The spray and combustion process in an optical PPC engine fueled with a primary reference fuel (70% iso-octane, 30% n-heptane by volume) are investigated using the combustion model along with laser diagnostic experiments. Different combustion modes, as well as the dominant chemical species and elementary reactions involved in the PPC engines, are identified and visualized using Chemical Explosive Mode Analysis (CEMA). The results from the LES-FGM model agree well with the experiments regarding the onset of ignition, peak heat release rate and in-cylinder pressure. The LES-FGM model performs even better than a finite-rate chemistry model that integrates the full-set of chemical kinetic mechanism in the simulation, given that the FGM model is computationally more efficient. The results show that the ignition mode plays a dominant role in the entire combustion process. The diffusion flame mode is identified in a thin layer between the ultra fuel-lean unburned mixture and the hot burned gas region that contains combustion intermediates such as CO. The diffusion flame mode contributes to a maximum of 27% of the total heat release in the later stage of combustion, and it becomes vital for the oxidation of relatively fuel-lean mixtures.

Fluorescence-free quantitative measurements of nitric oxide and major species in an ammonia/air flame with Raman spectroscopy

Raman spectroscopy is a powerful technique that allows for simultaneous measurements of multiple species; however, it suffers from low signal intensity and, in diagnostics of ammonia (NH3) combustion, strong flame fluorescence. The current work re-introduces a multipass setup to perform enhanced quantitative Raman spectroscopy measurements of major species and nitric oxide (NO) in a premixed laminar lean (φ = 0.9) NH3 flame. A way to deal with the strong flame reaction-zone fluorescence is proposed and validated. The measurements were performed using both the second (532 nm, NO detection) and third (355 nm, major species and temperature) harmonics of an Nd:YAG laser. The acquired data sets were compared to the simulation data obtained with two chemical kinetic mechanisms. The reported average post-flame concentration of NO reaches a plateau at 3900 ± 120 ppm, and the detection limit is 700 ppm. The 355 nm excitation wavelength proved to provide close to no flame fluorescence, which allowed for measurements across the entire flame from reactants to products. Thus, major species profiles were acquired, and the concentration and temperature results are in good agreement with the simulation data. Lastly, possible error sources are estimated and ways to minimize them are proposed.

Experimental and kinetic modeling study on auto-ignition properties of ammonia/ethanol blends at intermediate temperatures and high pressures

The auto-ignition properties of ammonia (NH3)/ethanol (C2H5OH) blends close to engine operating conditions were investigated for the first time. Specifically, the ignition delay times (IDT) of ammonia/ethanol blends were measured in a rapid compression machine (RCM) at elevated pressures of 20 and 40 bar, five C2H5OH mole fractions from 0% to 100%, three equivalence ratios (ϕ) of 0.5, 1.0 and 2.0, and intermediate temperatures between 820 and 1120 K. The measurements reveal that ethanol can drastically promote the reactivity of ammonia, e.g., the auto-ignition temperature with merely 1% C2H5OH in fuel decreases accordingly around 110 K at 40 bar as compared to that of neat ammonia. Moreover, the promotion efficiency of ethanol is higher than hydrogen and methane with a factor of 5 and 10 under the same condition. Different dependences of IDT on the equivalence ratio were observed with different ethanol fractions in the blends, i.e., the IDTs of the 5%, 10% and 100% C2H5OH in fuel decrease with an increase of ϕ, but an opposite trend was observed in the mixture with 1% C2H5OH. A new chemical kinetic mechanism for NH3/C2H5OH mixtures was developed and it is highlighted that the addition of cross-reactions between the two fuels is necessary to obtain reasonable simulations. Basically, the newly developed mechanism can reproduce the measurements of IDT very well, whereas it overestimates the reactivity of the stoichiometric and fuel-rich mixture with 1% C2H5OH in fuel. The sensitivity, reaction pathway, as well as rate of production analysis indicated that the ethanol addition to ammonia fuel blends provides key interaction pathways and enriches the O/H radical pool which further promotes the auto-ignition process.

Shock-tube study of the ignition and product formation of fuel-rich CH4/ozone/air and natural gas/ozone/air mixtures at high pressure

The influence of ozone on the ignition delay times and product formation of methane and natural gas was determined in a high-pressure shock tube at fuel-rich conditions (ϕ = 2 and 10), ozone concentrations of 550 ppm, temperatures between 850 and 1700 K and pressures of about 30 bar. The addition of ozone causes a strong reduction of the ignition delay times for temperatures below 1100 K. Product concentrations were determined with fast sampling and GC/MS analysis for the experiments at ϕ = 10. Experiments and simulations show that CO, H2, H2O, C2H2, C2H4, C2H6, CO2, C3H6, and benzene are the main products. A comparison to similar studies with additives such as n-heptane, dimethyl ether, diethyl ether, dimethoxymethane and experiments without additives shows that C2H2, C2H4, and benzene concentrations are decreased, whereas CO concentrations are increased when ozone is used as additive. The experimental results were compared to simulations with chemical kinetics mechanisms from literature. The measured ignition delay times agree well with the simulations. A comparison of measured and simulated product distributions shows that the temperature dependence of the product formation is predicted well but that there are deviations of the absolute concentrations up to a factor of two for acetylene and benzene contrary to studies with other additives.

A skeletal chemical kinetic mechanism for ammonia/n-heptane combustion

Progressively stricter pollutant emission targets in international agreements have shifted the focus of combustion research to low carbon fuels. Ammonia is recognized as one of the promising energy vectors for next-generation power production. Due to the low flame speed and high auto-ignition temperature, ammonia is often burned with a high reactivity pilot fuel (e.g. diesel). However, chemical kinetic mechanisms describing the combustion of ammonia and large hydrocarbon fuels (such as n-heptane, a surrogate of diesel) are less developed. In this work, a skeletal chemical kinetic mechanism for n-heptane/ammonia blend fuels is proposed using a joint decoupling methodology and optimization algorithm. A sensitivity analysis of the ignition delay times of the ammonia/n-heptane mixture is performed to identify the dominant reactions. A genetic algorithm is used to optimize the mechanism further. The final skeletal mechanism is made up of 69 species and 389 reactions. The skeletal ammonia/n-heptane mechanism is validated against the experimental data for combustion of pure ammonia, ammonia/hydrogen and ammonia/n-heptane mixtures, including the global combustion characteristic parameters such as ignition delay times measured in shock tubes or rapid compression machines, laminar burning velocities measured in heat flux burners or spherical flame vessels, and species data measured in jet-stirred reactors. Comparing the results from the skeletal mechanism with those from other mechanisms from the literature is conducted to evaluate the mechanism further. The present skeletal mechanism can well predict the combustion processes for a wide range of conditions, and the mechanism is computationally efficient, showing good potential to model ammonia/n-heptane combustion with good accuracy and efficiency.

Study of mechanism of ammonia decomposition and oxidation: From NOx reduction to ammonia auto-ignition problem

A chemical kinetic mechanism for ammonia decomposition and combustion from the CRECK modeling group is analyzed in this study with respect to the fast and slow chemical processes and the results are used to generate skeletal mechanisms for different applications. As examples two regimes of system parameters are chosen: values typical for engine exhaust gas systems (low temperature ammonia decomposition and NOX reduction) and a high temperature ignition problem studied by flow reactors and shock tube experiments. The mechanism is first tested and compared to existing experimental results. A time scale analysis is implemented to study the mechanism. A combination of local and global analysis based on the Global Quasi-Linearisation (GQL) concept is suggested and employed to estimate the number of relatively fast and slow processes governing the system dynamics. A GQL decomposition into invariant sub-spaces is used to determine the complimentary sub-sets of relatively fast and slow reactions. These are used to devise specific skeletal mechanisms for the chosen applications, which are verified in the considered parametric ranges. The suggested approach can be used to identify rate limiting processes, study how the coupling of relatively fast and slow (slaved) reactions proceed. The latter is extremely important for mechanism development and model reduction. The results show a very good agreement not only with respect to the ignition delay times, but also with the results from flow reactor experiments.

Laminar burning velocities of pyrrole/air flames: Experimental and comprehensive modeling study

Adiabatic laminar burning velocities for pyrrole/air flames were experimentally determined using the heat flux method, over equivalence ratios ranging from 0.6 to 1.3, at atmospheric pressure and initial temperature of 338 K. The detailed kinetic model of the authors was extended by the reactions of pyrrole and its intermediates based on previous theoretical studies and analogies to reactions of similar species. A comparison of new experimental and computational results using the present and the CRECK detailed chemical kinetic mechanisms was conducted and discussed. A modification of the rate constant of reaction C4H5N+OHH2O+PYRLYL was suggested that dramatically improved the present model performance. The present and the CRECK models were then compared with other experimental targets available in the literature. Some discrepancies between experiments and model predictions and among models themselves were observed. Notwithstanding, the present model showed overall good performances in reproducing laminar burning velocities, speciation data in reactors, and ignition delay times in shock tubes. Sensitivity analyses were performed to delineate the importance of different reaction classes in pyrrole chemistry and to underline possible sources of the observed disagreements.

Experimental and Modeling Evaluation of Dimethoxymethane as an Additive for High-Pressure Acetylene Oxidation.

The high-pressure oxidation of acetylene–dimethoxymethane (C2H2–DMM) mixtures in a tubular flow reactor has been analyzed from both experimental and modeling perspectives. In addition to pressure (20, 40, and 60 bar), the influence of the oxygen availability (by modifying the air excess ratio, λ) and the presence of DMM (two different concentrations have been tested, 70 and 280 ppm, for a given concentration of C2H2 of 700 ppm) have also been analyzed. The chemical kinetic mechanism, progressively built by our research group in the last years, has been updated with recent theoretical calculations for DMM and validated against the present results and literature data. Results indicate that, under fuel-lean conditions, adding DMM enhances C2H2 reactivity by increased radical production through DMM chain branching pathways, more evident for the higher concentration of DMM. H-abstraction reactions with OH radicals as the main abstracting species to form dimethoxymethyl (CH3OCHOCH3) and methoxymethoxymethyl (CH3OCH2OCH2) radicals are the main DMM consumption routes, with the first one being slightly favored. There is a competition between β-scission and O2-addition reactions in the consumption of both radicals that depends on the oxygen availability. As the O2 concentration in the reactant mixture is increased, the O2-addition reactions become more relevant. The effect of the addition of several oxygenates, such as ethanol, dimethyl ether (DME), or DMM, on C2H2 high-pressure oxidation has been compared. Results indicate that ethanol has almost no effect, whereas the addition of an ether, DME or DMM, shifts the conversion of C2H2 to lower temperatures.

Effect of recess shape on combustion performance and knocking characteristics for a downsized gasoline rotary engine

The combustion of a downsized boosted spark ignition rotary engine (RE) is significantly affected by the rotor recess shape owing to the influence this structure has on the flame propagation and the turbulence flow. However, comprehensive assessments on both knocking and combustion performance of an RE for different recess shapes are generally lacking. Therefore, a three-dimensional dynamic simulating model coupling with the suitable turbulent model and the reduced chemical kinetic mechanism was established and validated. The numerical model was implemented for evaluating the influences of varying recess shapes on combustion performance and knocking characteristics of a downsized RE. Results showed that the end-gas auto-ignition of the RE mainly occurred in the trailing side of the elongated chamber due to the unidirectional flow field and a long distance away from spark plugs. It should be noted that the present results indicated that the knocking intensity was directly proportional to heat release rate. Moreover, the size and quantity of the vortex caused by the recess shape during the combustion process were the fundamental reason for determining the knocking and performance of the RE. Importantly, suppressing the formation of the vortexes in the elongated chamber during the combustion process could significantly reduce the knocking intensity of the RE, and then improved engine performance. In addition, under the present operating conditions, the elongated chamber structure with the leading deep recess was found to reduce the knocking intensity by 75% compared to that with the maximum knocking intensity, which increased indicated mean effective pressure and indicated thermal efficiency of the downsized RE. Therefore, considering knocking characteristics and combustion performance, the elongated chamber structure with the leading deep recess was the best choice for the RE used in boosted conditions. • Effect of recess shape on knocking combustion of a SI RE was analyzed numerically. • The autoignition of the RE occurred in the trailing side of the elongated chamber. • The KI was directly proportional to the heat release rate. • Suppressing vortex formation in the combustion phase significantly reduced the KI. • The LDR dramatically suppressed knocking and then enhanced engine performance.

Nanosecond pulsed plasma assisted combustion of ammonia-air mixtures: Effects on ignition delays and [formula omitted] emission

Computational investigation of plasma assisted combustion of ammonia-air mixtures in constant volume and constant pressure reactors are conducted, to determine the impact of operating conditions on ignition delays and NOx emissions. Due to the lack of a chemical kinetic mechanism for plasma discharge of ammonia (NH3)/air mixtures, a mechanism has been assembled in this work using well-validated plasma reactions of NH3 with O2 and N2, alongside plasma kinetics of air from the literature. The impact of the reduced electric field (E/N), equivalence ratio, pressure, pulse frequency and the energy density on the ignition delays and NO/NO2 emission is discussed. At lower E/N, vibrational-to-translational (VT) relaxation of the vibrational states of NH3 and N2 is observed to play a dominant role in the gas heating process on account of the higher vibrational energy contribution. The ignition event is observed to be faster for fuel-lean mixture (ϕ = 0.5) compared to stoichiometric and fuel-rich (ϕ = 1.2) conditions owing to the lower consumption of OH radicals through the reactivity-inhibiting reaction NH3+OH→NH2+H2O between plasma pulses for leaner mixtures. Nevertheless, the fuel-lean mixture is observed to exhibit higher production of NOx than stoichiometric and fuel-rich mixtures, resulting from plasma chemistry involving oxygen radical and electronic excited states of N2. At the higher pressure of 3 atm, the pressure dependent recombination reaction H+O2+M→HO2+M is found to delay the ignition by limiting the reactive radicals compared to the corresponding 1 atm case. Higher rates of collisional quenching at higher pressures during the inter-pulse gaps resulted in lesser amount of electronically excited states of N2 and O2, which resulted in lower production of air-bound NOx during the pulses. Pulse frequency and energy density per pulse are seen to exhibit an inversely proportional effect on the ignition delay times. Most importantly, a faster ignition and lower production of NOx is observed in the case of plasma discharges compared to thermal energy deposition, owing to the enhanced production of OH radicals and the reforming of NH3 to produce N2 with plasma, respectively. Interesting roles of fuel-radicals such as NH2 and NH in both producing and reducing NO at different instants have also been discussed.

An experimental and detailed kinetic modeling study of the pyrolysis and oxidation of DMF over a wide range of conditions

A new chemical kinetic mechanism of DMF (N, N-dimethylformamide) is proposed. To assess the reliability of the mechanism, high pressure shock tube, single pulse shock tube and constant volume reactor were used to experimentally evaluate ignition delay times, high temperature pyrolysis, and laminar flame speeds of DMF, respectively. Ignition delay times of DMF/ “air” were measured for equivalence ratios of 0.5, 1.0, and 2.0, pressures of 2.0 and 10.0 bar, and temperature ranging from 900 to 1430 K. Additionally, ignition delay times of DMF/acetone/air were measured for equivalence ratios of 0.5 and 1.0, pressures of 2.0 and 10.0 bar, and temperature ranging from 900 to 1430 K. High temperature pyrolysis products of DMF/acetone mixtures, diluted in argon, were studied at 5.0 bar, temperatures between 1000 and 1600 K. Flame speed measurements of DMF/air were obtained for pressures of 100 and 200 kPa, temperatures of 398, 423, and 448 K, and equivalence ratios from 0.7 to 1.4. Simultaneously, a chemical kinetics mechanism was developed to simulate the experimental results using ChemKin Pro, with sensitivity and flux analysis being carried out to elucidate limitations and possible refinements.

Experimental and numerical investigation of the auto-ignition characteristics of cylinder oil droplets under low-speed two-stroke natural gas engines in-cylinder conditions

Auto-ignition of cylinder oil droplets in the cylinder of low-speed two-stroke gas engines may cause the pre-ignition. To verify and understand the mechanism of the auto-ignition of cylinder oil droplets, experimental research and numerical analysis were carried out to investigate the auto-ignition behaviors of cylinder oil droplets under in-cylinder conditions of low-speed two-stroke natural gas engines. The experimental equipment includes an optical rapid compression machine to simulate the engines’ in-cylinder conditions and a dual-camera system to capture the cylinder oil droplets' ignition processes. The numerical simulation model contains a transient multi-component evaporation model and a multi-step chemical reaction kinetic mechanism. The evaporation of cylinder oil droplets and the ignition of oil vapor in the cylinder of the rapid compression machine were simulated. The optical experiment verified that breaking a single large-size droplet into the droplet group consisting of the small basic droplets could greatly shorten ignition delay and form multiple ignition hot points intensifying the pre-ignition. The overall ignition delay decreases with the increase of the temperature for large oil droplets, while the ignition delay is not monotonous with the temperature change for small oil droplets. The ignition radius and the vapor/air ratio of ignition moment were obtained by combining experiment and simulation. The ignition radius is reduced as the temperature and pressure increase. And the vapor/air ratio of ignition moment could be reduced by decreasing ambient temperature and increasing ambient pressure. The effect of methane on the overall ignition delay of oil droplets depends on the initial droplet diameter. The auto-ignition of small-size single oil droplets could induce natural gas pre-ignition was valid. And these findings are beneficial to understanding the mechanisms of pre-ignition induced by cylinder oil droplets auto-ignition, and the design of low-speed two-stroke gas engines.

Chemical kinetic interactions and sensitivity analyses for 2-ethylhexyl nitrate-doped PRF91 using a reduced mechanism

A numerical and experimental investigation about the chemical kinetic interactions between 2-ethylhexylnitrate (EHN) and PRF91 was performed in this study. Rapid compression machine experiments were conducted to investigate the effect of EHN on the autoignition reactivity of the fuel, and a reduced chemical kinetic mechanism was developed including an EHN sub-model. Experiments showed that the ignition delay decreases as the fuel is doped with EHN, but the effect of the doping level of EHN on the ignition is highly non-linear. Moreover, experiments showed that the EHN effectiveness is lowest during the transition between the low-temperature regime and the negative temperature coefficient (NTC) regime, and it rapidly increases as the temperature increases. Both detailed and (developed) reduced mechanisms were validated against the experimental results, allowing a more in-depth EHN-fuel chemistry study. Additionally, ignition delay sensitivity and EHN effectiveness sensitivity analyses were performed with the reduced mechanism to identify the reactions that control the interaction between EHN and the fuel. As the result, EHN thermal decomposition is only relevant for very low temperatures. The chemistry of EHN-doped fuel is more sensitive to intermediate temperature reactions than that of straight fuel, especially at lower temperatures, due to the effect of EHN on the NTC behavior of the fuel. Finally, the chemistry of EHN-doped fuel is very sensitive to NO2-to-NO reactions, especially at high temperatures, because these reactions transform the NO2 generated by EHN into NO, which is a very effective fuel reactivity enhancer.

Understanding the effects of doping a regular E10 gasoline with EHN in an HCCI engine: Experimental and numerical study

In this study, the effects of doping a regular E10 gasoline with 2-ethlyhexyl nitrate (EHN) are investigated under homogeneous charge compression ignition conditions. Experiments are performed in a 1-liter single-cylinder engine fueled with both straight and EHN-doped E10 gasoline. Numerical studies are performed with an internal combustion engine single-zone reactor utilizing detailed chemical kinetic mechanism with EHN and NOx chemistry and a surrogate fuel. The kinetic model reproduces the experimental data well for the straight fuel at high initial temperature (TBDC) conditions, whereas the low temperature heat release (LTHR) is under-predicted. Adding EHN reduces the required TBDC, while EHN thermal decomposition rate has to be significantly reduced to accurately reproduce the experimental result, by preventing over-estimation of EHN effect and LTHR. EHN decomposition generates NO2 and 3-heptyl radicals. Using the well-matched mechanism, the numerical results indicate that among the product of EHN decomposition, NO2 decreases the autoignition reactivity whereas the production of 3-heptyl radical is the main source for enhancing the low-to-intermediate chemistry by which OH production is accelerated. The production of 3-heptyl radical is highly sensitive to the EHN decomposition reactions. Despite the reactivity enhancement, increase in NOx emission is observed when the fuel-doping increases.

Universal Kinetic Mechanism Describing CO2 Photoreductive Yield and Selectivity for Semiconducting Nanoparticle Photocatalysts.

Photocatalytic conversion of CO2 to generate high-value and renewable chemical fuels and feedstock presents a sustainable and renewable alternative to fossil fuels and petrochemicals. Currently, there is a dearth of kinetic understanding to inform better catalyst design, especially at uniform reaction conditions across diverse catalytic species. In this work, we investigate 12 active, stable, and unique but common nanoparticle photocatalysts for CO2 reduction at room temperature and low partial pressure in aqueous phase: TiO2, SnO2, and SiC deposited with silver, gold, and platinum. Our analysis reveals a single consistent chemical kinetic mechanism, which accurately describes the yield and selectivity of all single-carbon containing (C1) products obtained in spite of the diverse catalysts employed. Formaldehyde is predicted as the first product in the reaction network and we report, to the best of our knowledge, the highest selectivity to date toward formaldehyde during CO2 photoreduction when compared against all other C1 products (∼80%) albeit at low CO2 conversion (<0.5 μmol gcat-1 h-1, <16.8 nmol m-2 h-1). Further, we observe a volcano-like relationship between the electron-transfer rate of a given photocatalyst for CO2 reduction and the net rate at which reduced products are produced in the reaction mixture taking into account unfavorable product oxidation. We establish an empirical upper limit for the maximum rate of production of CO2 reduction products for any nanoparticle photocatalyst in the absence of a hole-scavenging agent. These results form the basis for the design and optimization of the next generation of highly efficiency and active photocatalysts for CO2 reduction.

Usage of Converter Gas as a Substitute Fuel for a Tunnel Furnace in Steelworks.

Converter gas (BOFG) is a by-product of the steel manufacturing process in steelworks. Its usage as a substitute fuel instead of natural gas for fueling a metallurgical furnace seems to be reasonable due to potential benefits as follows: CO2 emission reduction into the ambient air and savings in purchasing costs of natural gas. Results of theoretical analysis focused on implementing converter gas as a fuel for feeding a tunnel furnace for either steel plate rolling, steel sheet hardening in its real working condition or both, are discussed. The analysis was focused on the combustion chemistry of the converter gas and its potential ecological and economic benefits obtained from converter gas usage to heat up steel in a tunnel furnace. Simulations of combustion were conducted using a skeletal chemical kinetic mechanism by Konnov. The directed relation graph with error propagation aided sensitivity analysis (DRGEPSA) method was used to obtain this skeletal kinetic mechanism. Finally, the model was validated on a real tunnel furnace fueled by natural gas. Regarding exhaust emissions, it was found that nitric oxide (NO) dropped down from 275 to 80 ppm when natural gas was replaced by converter gas. However, carbon dioxide emissions increased more than three times in this case, but there is no possibility of eliminating carbon dioxide from steel manufacturing processes at all. Economic analysis showed savings of 44% in fuel purchase costs when natural gas was replaced by converter gas. Summing up, the potential benefits resulting from substituting natural gas with converter gas led to the conclusion that converter gas is strongly recommended as fuel for a tunnel furnace in the steel manufacturing process. Practical application requires testing gas burners in terms of their efficiency, which should provide the same amount of energy supplied to the furnace when fed with converter gas.

The Laminar Burning Velocities of Stoichiometric Methane–Air Mixture from Closed Vessels Measurements

The present work aims to evaluate the performance of the constant-volume method by several sets of experiments carried out in three different closed vessels (a sphere and two cylinders) analyzing the obtained results in order to obtain accurate laminar burning velocities. Accurate laminar burning velocities can be used in the development of computational fluid dynamics models in order to design new internal combustion engines with a higher efficiency and lower fuel consumption leading to a lower degree of environmental pollution. The pressure-time histories obtained at various initial pressures from 0.4 to 1.4 bar and ambient initial temperature were analyzed and processed using two different correlations (one implying the cubic low coefficient and the other implying the burnt mass fraction). The laminar burning velocities obtained at various initial pressures are necessary for the realization of a complete kinetic study regarding the combustion reaction and testing the actual reaction mechanisms. Data obtained from measurements were completed and compared with data obtained from runs using two different detailed chemical kinetic mechanisms (GRI 3.0 and Warnatz) and with laminar burning velocities from literature. Our experimental burning velocities ranging from 35.3 cm/s (data from spherical vessel S obtained using the burnt mass fraction) to 37.5 cm/s (data from cylindrical vessel C1 obtained using the cubic law) are inside the interval of confidence as reported by other researchers. From the dependence of the laminar burning velocity on the initial pressure, the baric coefficients were obtained. These coefficients were further used to obtain the overall reaction orders. The baric coefficients (ranging between −0.349 and −0.212) and the overall reaction orders (ranging between 1.42 and 1.50) obtained in this study fall within the reference range of data specific to methane–air mixtures examined at ambient initial temperature.

Shock tube study of natural gas oxidation at propulsion relevant conditions

Global climate change and rising crude oil prices have motivated search of clean, sustainable and economic fuel. Methane, having the highest hydrogen to carbon ratio is ideally the best option towards carbon neutral emissions and reduce greenhouse gas emissions. However, there the economic benefits are minimal when using pure methane because of purification costs. Natural gas primarily consists of methane but with appreciable amounts of C2C4 alkanes which significantly impact oxidation performance, especially when compared to pure methane at high pressures and temperatures, studies of natural gas have been scarce and there is new interest in studying natural gas for its application to propulsion devices. This single pulse shock tube study investigates the effect of natural gas composition on species yields as a function of temperature at various stoichiometric conditions (φ ≈ 0.5, 1.0, 2.0) and high pressure (240 atm) over a nominal reaction time of 2.5 ms. The experimentally measured speciation results for one real natural gas sample from Boise, ID (USA) and a reference natural gas sample are compared to species yield predictions using well established chemical kinetic mechanisms, to check the feasibility of using these mechanisms in the design of propulsion devices. The chemical kinetic simulations are carried out using the constant pressure approach as well as the changing pressure approach which considers the exact measured pressure change in the shock tube. The experiments provide a large speciation data set for optimizing chemical kinetic mechanisms for natural gas applications and to understand the effect of composition on natural gas chemical kinetics. The predictions vary significantly between models tested and effect of composition variation was evident. Aramco Mech 3.0 could predict the experiments almost perfectly, especially at fuel rich conditions.