Methane-based Fuels Research Articles

Prospects of performance, emissions and cost of methane-based fuels in a spark-ignition engine compared to conventional Brazilian fuels

Brazil has a long history of using biofuels in the transport sector, especially due to the 40 years widespread use of ethanol and almost 20 years of biodiesel. Nevertheless, more efforts are needed to reduce even further the carbon emissions of the transport sector. In addition to ethanol, gaseous fuels such as biogas and biomethane are gaining ground due to their great potential to be obtained through biomass processing. To prospect the potential use of biomethane as a vehicle fuel in Brazil, compressed natural gas (CNG), another methane-based fuel with similar composition to biomethane, was tested and had its performance and emissions compared to hydrous ethanol and Brazilian gasoline at three different operating conditions in two different compression ratios: 3.0 bar, 6.0 bar and 9.0 bar IMEP at 1800 rpm, exploring compression ratios of 11.6:1 and 14.3:1. With CNG, engine operation at MBT was possible with both compression ratios. Ethanol presented border knock near MBT for the highest compression ratio and load, while the gasoline spark timing was knock-limited for both compression ratios at the highest load. Indicated efficiency of CNG was higher than that of gasoline and lower than that of hydrous ethanol. ISCO emissions were lower for CNG, while ISTHC and ISNOX were similar to gasoline. Due to the lower LHV of biomethane, a reduction in the ISNOX value could be expected with possible increase in methane slip. Regarding cost, biomethane is the fuel with the cheapest operating cost per kWh when considering the final price for industrial consumers in Brazil. It is still difficult to estimate large-scale production cost of biomethane, but its use in partial replacement of CNG would still be able to keep fuel market competitiveness, while reducing the carbon footprint.

Low-Emission Alternative Energy for Transport in the EU: State of Play of Research and Innovation

The 2030 Climate target plan of the European Commission (EC) establishes a greenhouse gases (GHG) emissions reduction target of at least 55% by 2030, compared to 1990. It highlights that all transport modes—road, rail, aviation and waterborne—will have to contribute to this aim. A smart combination of vehicle/vessel/aircraft efficiency improvements, as well as fuel mix changes, are among the measures that can reduce GHG emissions, reducing at the same time noise pollution and improving air quality. This research provides a comprehensive analysis of recent research and innovation in low-emission alternative energy for transport (excluding hydrogen) in selected European Union (EU)-funded projects. It considers the latest developments in the field, identifying relevant researched technologies by fuel type and their development phase. The results show that liquefied natural gas (LNG) refueling stations, followed by biofuels for road transport and alternative aviation fuels, are among the researched technologies with the highest investments. Methane-based fuels (e.g., compressed natural gas (CNG), LNG) have received the greatest attention concerning the number of projects and the level of funding. By contrast, liquefied petroleum gas (LPG) only has four ongoing projects. Alcohols, esters and ethers, and synthetic paraffinic and aromatic fuels (SPF) are in between. So far, road transport has the highest use of alternative fuels in the transport sector. Despite the financial support from the EU, advances have yet to materialize, suggesting that EU transport decarbonization policies should not consider a radical or sudden change, and therefore, transition periods are critical. It is also noteworthy that there is no silver bullet solution to decarbonization and thus the right use of the various alternative fuels available will be key.

Water and steam injection in micro gas turbine supplied by hydrogen enriched fuels: Numerical investigation and performance analysis

This paper investigates the energetic and environmental performance of micro gas turbine plant with two proposed concurrent improvements: the methane-based fuel enriched by hydrogen and the humidification of the plant cycle. The energetic and environmental benefits of both features are well-know, and the aim of this work is the analysis of their combined impact on the micro gas turbine operation. Despite enhancing fuel with H2 involves significant advantages like greenhouse emission reduction and a better combustion in case of low LHV fuels, most of commercial micro gas turbine combustors are not able to burn fuels with high hydrogen content unless structurally modified. On the contrary, has been demonstrated that humidified gas turbines (i.e., gas turbines with water injection, humid air turbine (HAT) and steam injection gas turbine (STIG) cycles) improve the combustion stability as well as electric power delivered and plant efficiency. Hence, in order to investigate the feasibility of the concurrent two features, the first step of this work was the thermodynamic analysis of a micro gas turbine supplied by methane-based fuels enriched with H2 up to 20%vol, considering both dry and humidified cycles. Since a combustion anomaly was detected, i.e., flashback, in the CFD study on the combustion chamber, a steam injection in the combustor has been added in the plant layout with the aim of overcoming the anomaly, and its effect on the combustion process has been analyzed also raising the hydrogen content up to 30%vol. The main outcome of this paper is the assessment of the feasibility of supplying the combustor of the proposed HGT-STIG micro gas turbine with a hydrogen enrichment up to 30%vol, achieving a safe and regular combustion mainly owing to a steam injection mass flow equal up to 125% of fuel flow.

Comparative Study on Chemical Kinetics Mechanisms for Methane-Based Fuel Mixtures under Engine-Relevant Conditions

The use of natural gas in pure or in a blended form with hydrogen and syngas in spark ignition (SI) engines has received much attention in recent years. They have higher diffusion coefficient and laminar flame speed, a small quenching distance and wider flammability limit which compensate the demerits of the lean-burn natural gas combustion. Therefore, a careful examination of the chemical kinetics of combustion of gaseous fuel blends is of great importance. In this paper, performance of the various chemical kinetics mechanisms is compared against experimental data, accumulated for methane-based fuel blends under engine-relevant conditions to find the most appropriate mechanism in engine simulations. Pure methane, methane/syngas, and methane/propane blends are mainly studied at various temperatures, pressures, and equivalence ratios. The ignition delay time and laminar flame speed are used as quantitative metrics to compare the simulation results with the data from experiments. The mechanisms were shown to be mainly consistent with the experimental data of lean and stoichiometric mixtures at high pressures. It was also shown that the GRI-3.0 and 290Rxn mechanisms have high compatibility with the ignition delay times and laminar flame speed at high pressures and lean conditions, and they can be utilized for simulations of SI engine combustion due to their lower computational cost. The results of present research provide an important contribution to the methane-based fuel blends combustion simulation under SI engine-relevant conditions.

Experimental investigation on ammonia combustion behavior in a spark-ignition engine by means of laminar and turbulent expanding flames

Ammonia combustion appears as a meaningful way to retrieve stored amounts of excess variable renewable energy, and the spark-ignition (SI) engine has been proposed as a practical conversion system. The present work aims at elucidating the combustion characteristics of ammonia blends in engine-relevant turbulent conditions. To that end, laminar and turbulent flame experiments were conducted in a constant-volume vessel at engine-relevant conditions of 445 K and 0.54 MPa to assess the combustion behavior of ammonia/hydrogen/air, ammonia/methane/air and methane/hydrogen/air mixtures observed in an all-metal single-cylinder SI engine. Results show that the respective accelerating or decelerating effects of hydrogen or methane enrichment observed in the SI engine could not be sufficiently explained by the measured laminar burning velocities of the mixtures. Since the latter are very low, the studied combustion regimes are at the boundary between the thin and broken reaction zones regimes, and thus strongly influenced by flame-turbulence interactions. The quantification of the flame response to turbulence shows much higher effects for ammonia blends, than for methane-based fuels. The aforementioned opposite effects of ammonia enrichment with hydrogen or methane are observed on the turbulent burning velocity during the turbulent flame experiments and correlated to the thermochemical properties of the reactants and the flame sensitivity to stretch. The latter may explain an unexpected bending effect on the turbulent-to-laminar velocity ratio when increasing the hydrogen fraction in the ammonia/hydrogen blend. Nevertheless, a very good correlation of the turbulent velocity was found with the Karlovitz and Damköhler numbers, that suggests that ammonia combustion in SI engines may be described following the usual turbulent combustion models. This encourages further investigations on ammonia combustion for the optimization of practical systems, by means of dedicated experiments and numerical simulations.

Simulation of SOFC performance using a modified exchange current density for pre-reformed methane-based fuels

Numerical simulations can be used to visualize and better understand various distributions such as gas concentration and temperature in solid oxide fuel cells (SOFCs) under realistic operating conditions. However, pre-existing models generally utilize an anode exchange current density equation which is valid for humidified hydrogen fuels – an unrealistic case for SOFCs, which are generally fueled by hydrocarbons. Here, we focus on developing a new, modified exchange current density equation, leading to an improved numerical analysis model for SOFC anode kinetics. As such, we experimentally determine the exchange current density of SOFC anodes fueled by fully pre-reformed methane. The results are used to derive a new phenomenological anode exchange current density equation. This modified equation is then combined with computational fluid dynamics (CFD) to simulate the performance parameters of a three-dimensional electrolyte-supported SOFC. The new modified exchange current density equation for methane-based fuels reproduces the I–V characteristics and temperature distribution significantly better than the previous models using humidified hydrogen fuel. Better simulations of SOFC performance under realistic operating conditions are crucial for the prediction and prevention of e.g. fuel starvation and thermal stresses.

Direct-methane solid oxide fuel cells with an in situ formed Ni–Fe alloy composite catalyst layer over Ni–YSZ anodes

Coking on Ni surfaces limits the direct application of methane-based fuels in SOFCs with Ni-cermet anodes. Loading an anodic catalytic layer with a high catalytic activity for CH4 conversion can effectively protect the Ni-based anode from coking and increase the cell durability. In this work, a Ni–Fe alloy composite catalyst was prepared by reducing perovskite La0.7Sr0.3Fe0.8Ni0.2O3-δ (LSFN) and then evaluating its catalytic activity in the partial oxidation of CH4. The catalyst was applied on a conventional Ni–8 mol.% Y-stabilized ZrO2 (YSZ) anode for methane SOFCs using two methane-containing fuels (97% CH4–3% H2O and 30% CH4–70% air). The catalyst-modified cells showed much higher performances and durability than the conventional cell using a Ni–YSZ anode, indicating the potential application for direct-methane SOFCs.

Enhanced coking resistance of a Ni cermet anode by a chromates protective layer

Abstract Ni-based anodes of SOFCs are susceptible to coking, which greatly limits practical application of direct methane-based fuels. An indirect internal reformer is an effective way to convert methane-based fuels into syngas before they reach anode. In this work, catalytic activity of a redox-stable perovskite La0.7Sr0.3Cr0.8Fe0.2O3-δ (LSCrFO) for methane conversion was evaluated. The catalyst was fabricated as an anodic protective layer to improve coking resistance of a Ni cermet anode. Using wet CH4 as a fuel, the LSCrFO-modified cell showed excellent power output and good coking resistance with peak power density of 1.59 W cm−2 at 800 °C. The cell demonstrated good durability lasting for at least 100 h. While the bare cell without the protective layer showed poor durability with the cell voltage fast dropped from 0.75 V to 0.4 V within 30 min. Under wet coal bed methane (CBM) operation, obvious performance degradation within 35 h (1.7 mV h−1) was observed due to the influence of heavy carbon compounds in CBM. The pre- and post-mortem microstructures and carbon analysis of the anode surface and catalyst surface were further conducted.

A Comprehensive Model for the Auto-Ignition Prediction in Spark Ignition Engines Fueled With Mixtures of Gasoline and Methane-Based Fuel

The introduction of natural gas (NG) in the road transport market is proceeding through bifuel vehicles, which, endowed of a double-injection system, can run either with gasoline or with NG. A third possibility is the simultaneous combustion of NG and gasoline, called double-fuel (DF) combustion: the addition of methane to gasoline allows to run the engine with stoichiometric air even at full load, without knocking phenomena, increasing engine efficiency of about 26% and cutting pollutant emissions by 90%. The introduction of DF combustion into series production vehicles requires, however, proper engine calibration (i.e., determination of DF injection and spark timing maps), a process which is drastically shortened by the use of computer simulations (with a 0D two zone approach for in-cylinder processes). An original knock onset prediction model is here proposed to be employed in zero-dimensional simulations for knock-safe performances optimization of engines fueled by gasoline-NG mixtures or gasoline-methane mixtures. The model takes into account the negative temperature coefficient (NTC) behavior of fuels and has been calibrated using a considerable amount of knocking in-cylinder pressure cycles acquired on a Cooperative Fuel Research (CFR) engine widely varying compression ratio (CR), inlet temperature, spark advance (SA), and fuel mixture composition, thus giving the model a general validity for the simulation of naturally aspirated or supercharged engines. As a result, the auto-ignition onset is predicted with maximum and mean error of 4.5 and 1.4 crank angle degrees (CAD), respectively, which is a negligible quantity from an engine control standpoint.

Stoichiometric analysis of air oxygen consumption in modern vehicles using natural and synthetic fuels

The study presents analysis results obtained for stoichiometric reactions of fuel oxidization in air for various motor fuels (such as gasoline, diesel fuel, gaseous fuel) and for biomass-converted and coal-based artificial fuels (such as ethanol, methanol, etc.) and also for hydrogen. Based on the analysis results, comparison is carried out for the specific air consumptions and carbon dioxide emissions of the combustion products.At a temperature of, which is an ultimate combustion process temperature to be dictated by the achievable properties of structural materials made available for the state-of-the-art engine engineering, the air excess factors are found, the actual air and fuel consumptions are determined, and carbon dioxide emissions are evaluated for the variety of fuels.The calculated data are presented for the greenhouse effect caused by the use of the various natural and synthetic fuels in transport applications.In the cases of using hydrocarbon and hydrogen fuels, an abnormally high consumption of the atmospheric air is theoretically evaluated. To reduce the environmental impact, methane-based fuels, bio-ethanol and bio-methanol-based fuels are to be recommended for wider transport vehicle applications.The analysis method presented in the study offers a universal tool to be instrumental in performing analysis of any fuel compositions both already existing and to be developed for future applications.

Enhanced coking resistance of Ni cermet anodes for solid oxide fuel cells based on methane on‐cell reforming by a redox‐stable double‐perovskite Sr 2 MoFeO 6‐δ

Carbon deposition on a Ni-based anode is troublesome for the direct power generation from methane-based fuels using solid oxide fuel cell. In this paper, a redox-stable double-perovskite SrMoFeO (SMFO) is applied as an independent on-cell reforming catalyst over a Ni-YSZ anode to improve coking resistance. The morphology, catalytic activity and electrochemical performance for wet methane/coal-bed gas (CBG) are investigated. A Ni-YSZ anode supported cell with SMFO generates a high power output of 1.77 W·cm and exhibits favorable stability operated on wet CH at 800°C. Post-mortem micro-structural analyses of cells indicate the cell operated on CBG shows coking probably due to the heavy carbon compounds in CBG.

Degradation of Metal-Supported Cells with Ni-YSZ or Ni-Ni3Sn-YSZ Anodes Operated with Methane-Based Fuels

The most common solid oxide fuel cell (SOFC) anode material, nickel - yttria stabilized zirconia (YSZ), displays excellent catalytic properties for fuel oxidation and good electronic conductivity. However, nickel-based anodes can cause carbon deposition when hydrocarbon fuels are used [1]. Nickel catalyzes the formation of carbon filaments in the presence of hydrocarbons under reducing conditions, resulting in coverage of the active sites of the anode, and potentially also to dissolution, precipitation, and metal dusting [2]. It is possible to avoid carbon deposition if sufficient steam is present such that the rate of carbon removal is comparable to or faster than the rate of carbon deposition. However, there is a corresponding decrease in electrical efficiency associated with dilution of the fuel. Metals with electronic structures similar to that of carbon may form an alloy with nickel at the surface, thus reducing carbide formation, and as a consequence, coking [3]. Tin, for example, has been reported to reduce carbon deposition on a Ni-YSZ cermet when present in low amounts such as 1 wt.% of tin with respect to nickel [4,5]. However, volatilization of a metallic tin phase at SOFC operating temperatures may present a problem for long term operation. To increase the stability of tin-containing anodes, we fabricated Ni-Ni3Sn-YSZ anodes using a hybrid solution-precursor / suspension plasma spray (SPPS-SPS) process and compared them to nickel-YSZ anodes made using the same process parameters. Thermogravimetric analyses in a 4% CH4 (balance nitrogen) atmosphere showed that the presence of tin in the anode reduced the rate of carbon deposition. Furthermore, higher amounts of tin resulted in less coking. Ni-Ni3Sn-YSZ and Ni-YSZ anodes were incorporated into metal-supported SOFCs that consisted of a porous metal support (Sandvik Sanergy), samaria-doped ceria (SDC) barrier layer, anode as previously described, YSZ electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3-δ-SDC cathode. Cells were tested at 750°C with air as the oxidant and fuel consisting of 65% CH4, 32% H2, and 3% H2O. The cells were held at a current density of 0.15 A·cm-2 for 500 hours. The cell without tin in the anode began to degrade after approximately 200 hours and catastrophically failed at approximately 425 hours. After testing, we observed that the anode had disintegrated, and as a result, the electrolyte and cathode were completely detached from the metal support. On the other hand, the cell with an anode containing tin did not catastrophically fail, and the cell remained intact after 500 hours of operation. Over 500 hours, the cell potential degraded from 0.841 V to 0.743 V, and scanning electron micrographs showed that the anode had delaminated from the electrolyte in some areas. Nonetheless, the cell with the Ni-Ni3Sn-YSZ anode degraded significantly less than the cell containing a Ni-YSZ anode, suggesting that the addition of Ni3Sn to an anode could be a useful strategy for improving durability of SOFC anodes using hydrocarbon fuels.

Degradation of Metal-Supported Cells with Ni-YSZ or Ni-Ni3Sn-YSZ Anodes Operated with Methane-Based Fuels

Ni-Ni3Sn-YSZ and Ni-YSZ anodes were incorporated into metal-supported SOFCs that consisted of a porous metal support (Sandvik Sanergy), samaria-doped ceria (SDC) barrier layer, anode as previously described, YSZ electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3-δ-SDC cathode. Cells were tested at 750°C with air as the oxidant and fuel consisting of 65% CH4, 32% H2, and 3% H2O. The cells were held at a current density of 0.15 A·cm-2 for 500 hours. The cell without tin in the anode began to degrade after approximately 200 hours and catastrophically failed at approximately 425 hours. After testing, we observed that the anode had disintegrated, and as a result, the electrolyte and cathode were completely detached from the metal support. On the other hand, the cell with an anode containing tin did not catastrophically fail, and the cell remained intact after 500 hours of operation. Over 500 hours, the cell potential degraded from 0.841 V to 0.743 V, and scanning electron micrographs showed that the anode had delaminated from the electrolyte in some areas. Nonetheless, the cell with the Ni-Ni3Sn-YSZ anode degraded significantly less than the cell containing a Ni-YSZ anode, suggesting that the addition of Ni3Sn to an anode could be a useful strategy for improving durability of SOFC anodes using hydrocarbon fuels.

Controlled deposition and utilization of carbon on Ni-YSZ anodes of SOFCs operating on dry methane

Solid oxide fuel cells (SOFCs) are promising power-generation systems to utilize methane or methane-based fuels with a high energy efficiency and low environmental impact. A successive multi-stage process is performed to explore the operation of cells using dry methane or the deposited carbon from methane decomposition as fuel. Stable operation can be maintained by optimizing the fuel supply and current density parameters. An electrochemical impedance analysis suggests that the partial oxidization of Ni can occur at anodes when the carbon fuel is consumed. The stability of cells operated on pure methane is investigated in three operating modes. The cell can run in a comparatively stable state with continuous power output in an intermittent methane supply mode, where the deposition and utilization of carbon is controlled by balancing the fuel supply and consumption. The increase in the polarization resistance of the cell might originate from the small amount of NiO and residual carbon at the anode, which can be removed via an oxidation-and-reduction maintenance process. Based on the above strategy, this work provides an alternative operating mode to improve the stability of direct methane SOFCs and demonstrates the feasibility of its application.

Impacts of Hydrogen and Carbon Dioxide Addition on Knock Resistance of Methane-based Fuels

Impacts of Hydrogen and Carbon Dioxide Addition on Knock Resistance of Methane-based Fuels

Effects of Fuel Composition on Knock Resistance of Methane-Based Fuel Blends

Effects of Fuel Composition on Knock Resistance of Methane-Based Fuel Blends

Development of a novel flamelet-based model to include preferential diffusion effects in autoignition of CH4/H2 flames

This study reports on the development of a flamelet-based reduction method for autoignition of hydrogen enriched methane-based fuels. The main focus is on the inclusion of preferential diffusion effects in the Flamelet Generated Manifolds (FGM) technique for autoigniting flames. Such a development of the FGM methodology is inevitable since investigations with detailed chemistry indicate that preferential diffusion strongly affects autoignition of these mixtures. First, a novel flamelet configuration based on Igniting Mixing Layer (IML) flamelets is proposed to accommodate preferential diffusion in a flamelet database. At the next stage, transport equations for controlling variables are derived with additional terms to account for preferential diffusion effects. The extended FGM model has been evaluated by comparing its predictions with those of detailed chemistry in both laminar and turbulent situations. In laminar situations, it is revealed that the model is able to predict accurately autoignition time scales of one-dimensional hydrogen enriched flames. The turbulent situations are studied by performing Direct Numerical Simulations (DNS) of a two-dimensional unsteady mixing layer. In this configuration, the proposed model yields a precise prediction of autoignition time scales as well. The model has also been assessed using the widely used Igniting Counter-Flow (ICF) flamelets instead of IML flamelets which leads to less accurate predictions especially at high hydrogen contents. The predictive power of the proposed model combined with simplicity of its implementation introduces an attractive reduced model for the computation of turbulent flames.

Assessment of Chemical Markers for Heat-Release Rate Correlations in Laminar Premixed Flames

There is considerable interest in formulating practical correlations for the quantification of heat-release rate in flames via appropriate chemical markers, mainly due to difficulties in obtaining a direct estimation of the former. Experimental and numerical studies performed in methane-air flames have identified corrections between suitable kinetic information and heat-release rate. The present work investigates the validity of corrections developed for methane to the combustion of other fuel classes (e.g., alcohols, unsaturated hydrocarbons, and aromatics), and proposes a methodological approach for the development of generic correlations. Numerical assessment of such correlations and their underlying methodology is performed on the basis of experimental data from 24 laminar premixed flames, utilizing a single, in-house, recently published C1–C6 detailed chemical kinetic model. It is shown that the proposed correlations are valid for methane-based fuels but they are largely inadequate for unsaturated fuels under rich conditions and for oxygenated fuels under most conditions. It is shown that heat-release rate is correlated with the dominant carbon path and that the oxidation chemistry of the parent alkyl radical is of pronounced importance. Alternatives to the proposed heat-release rate correlations are also proposed and assessed.

Autoignition Delay Time Measurements of Methane, Ethane, and Propane Pure Fuels and Methane-Based Fuel Blends

Autoignition delay experiments in air have been performed in an atmospheric flow reactor using typical natural gas components, namely, methane, ethane, and propane. Autoignition delay measurements were also made for binary fuel mixtures of methane/ethane and methane/propane, and ternary mixtures of methane/ethane/propane. The effect of CO2 addition to the methane-based fuel blends on autoignition delay times was also investigated. Equivalence ratios for the experiments ranged between 0.5 and 1.25, and temperatures ranged from 930 K to 1140 K. Consistent with past studies, increasing equivalence ratio and increasing inlet temperatures over these ranges decreased autoignition delay times. Furthermore, addition of 5–10% ethane or propane decreased autoignition delay time of the binary methane-based fuel by 30–50%. Further addition of either ethane or propane showed less significant reduction of autoignition delays. Addition of 5–10% CO2 slightly decreased the autoignition delay times of methane fuel mixtures. Arrhenius correlations were used to derive activation energies for the ignition of the pure fuels and their mixtures. Results show a reduction in activation energies at the higher temperatures studied, which suggests a change in ignition chemistry at very high temperatures. Measurements show relatively good agreement with predictions from a detailed kinetics mechanism, specifically developed to model ignition chemistry of C1-C3 alkanes.

Experimental and Detailed Kinetic Modeling of the Oxidation of Methane and Methane/Syngas Mixtures and Effect of Carbon Dioxide Addition

The oxidation of methane-based fuels was studied experimentally in a fused silica jet-stirred reactor (JSR) operating at 1–10 atm, over the temperature range 900–1450 K, from fuel-lean to fuel-rich conditions. Similar experiments were performed in the presence of hydrogen, carbon dioxide, hydrogen and carbon dioxide, and syngas (COH2). A recently proposed kinetic reaction mechanism (Le Cong et al., 2007) for modeling the oxidation of hydrogen, CO, methane, methanol, formaldehyde, and natural gas over a wide range of conditions including JSR, flame, shock tube, and plug flow reactor was used. The chemical kinetic modeling of the present experiments was successfully performed; the computations were also in good agreement with literature laminar burning velocities, flame structures, plug-flow reactors concentration profiles, and ignition delays. Reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuel mixtures studied here. The kinetic reaction scheme proposed helps understanding the effect of the additives, namely syngas and carbon dioxide, on the oxidation of methane.