Combustion Kinetics Research Articles

Combustion and Performance Evaluation of Methanol (M15)-Fueled BS-VI Compliant Light-Duty Spark-Ignition Engine

Abstract This study investigated the effect of the methanol–gasoline blend (M15) on the combustion and performance characteristics of a commercial light-duty Bharat Stage-VI (BS-VI) 2020 spark-ignition (SI) engine. The M15 and baseline gasoline (G100) engine tests were performed at a wide range of engine loads and speeds. For the M15 operation, it was ensured that the lambda values matched with the baseline gasoline operation at each engine operating point by changing fuel quantity manually. The combustion characteristics of M15 were quite similar to gasoline at all operating points. Alcohol addition improves octane number and flame speed, which changes the combustion characteristics of the engine, but in this study, the combustion characteristics of M15 fuel were almost identical. It may be due to blending a small fraction of methanol and the engine's high compression ratio, which improved the combustion kinetics. The coefficient of variance of indicated mean effective pressure was slightly lower for M15 than gasoline, except at 1000 rpm, where the charge mixing might not be adequate at low engine speed for M15 due to lower methanol volatility. Engine's brake thermal efficiency improved with M15 fueling by ∼1%, compared to baseline gasoline, though brake-specific fuel consumption deteriorated by ∼6% due to the lower calorific value of M15. Higher combustion stability and possibly lower heat transfer losses, as observed from slightly higher exhaust gas temperature (EGT), might have improved the engine's performance for M15. This study demonstrated that M15 fueling exhibited identical combustion characteristics and higher thermal efficiency than baseline gasoline fueling at similar lambda values in a commercial light-duty BS-VI SI engine.

Effect of Metal Oxides on Combustion Characteristics of Excess Sludge

In this paper, it was studied that the effects of heating rate and four metal oxide on the combustion characteristics of excess sludge, such as CaO, Fe2O3, MgO and Al2O3, and the combustion kinetic parameters of sludge were obtained based on Coats-Redfern model. This result indicated that the ignition of sludge can be restricted with the increase of heating rate, but it was conducive to burnout, and the increasing about the flammability, stability and comprehensive combustion characteristic index of sludge. The addition of Fe2O3 and Al2O3 could improve the ignition performance of sludge to a certain extent, which was most obvious at the heating rate of 10 and 20 °C/min, respectively. Furthermore, the existence of Fe2O3, MgO and Al2O3 can improve the burnout performance of sludge, represented by MgO. Under the condition of low heating rate, the presence of Fe2O3 and MgO was beneficial to improve the comprehensive combustion characteristics of sludge. According to the distribution of combustion kinetics parameters, it was showed an increasing trend about the activation energy of sludge with the increase of heating rate at the range of 374.88-575.61 °C, which was also unfavorable to the combustion of fixed carbon. At the same heating rate, the activation energy decreased by adding Fe2O3 and Al2O3 at the range of 148.40-374.88 °C, which was beneficial to the release of volatiles and the combustion reaction, while the activation energy at the range of 374.88-575.61 °C decreased after adding CaO, which promoted the combustion of fixed carbon.

H2 impact on combustion kinetics, soot formation, and NOx emission of hydrocarbon fuel flames

Soot and carbon dioxide released from internal combustion engines became the key issues when using fossil fuels. The use of zero-carbon fuel, hydrogen, with hydrocarbon fuels can play an important role in reducing the exhaust effect on the environment and mitigating the reliance on nonrenewable energy resources. A numerical approach was executed to elucidate the H2 impact on combustion kinetics, soot formation, and NOx emission of hydrocarbon fuel under premixed and diffusion flame conditions. The results showed that hydrogen deteriorated the formations of particle number density, the volume fraction of soot, carbon monoxide, carbon dioxide and polycyclic aromatic hydrocarbons thru the reduction of small chain hydrocarbons at both premixed and diffusion flame conditions. The soot volume fraction and soot particle number density formation were prevailing in the air region of the combustion chamber at diffusion flame conditions. NO3 produced from fuel-related species such as CHO and air-related species such as NO. H2 reduced the peak molar fraction of small chain HC including CHO related species, resulting in a reduction in NO3 emissions. C3H3 species dominantly participated to reduce the CO2 and NO3 emissions, while C2H2 and C5H4CH2 were the main species to control the soot precursors formation in both HC fuel flames. Besides, NH3 emission was limited by C2H2 in DS flames.

Thermogravimetric Evaluation for the Pyrolysis Process of Pellets Produced from Quinoa and Amaranth Harvest Residues

In this study, the combustion properties of pellets produced from quinoa (C3 plant) and amaranth (C4 plant) harvest residues were evaluated by Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG) methods. Pelletizing was carried out at 25% moisture content and at a material temperature of 70 °C. 7.5% molasses was used as the adhesive. The pellets were heated from 25 °C to 1000 °C in a thermal analyzer at a tracking rate of 10 °C min-1 and in N2 gas environment. The mass loss and mass loss rate occurring in this temperature range were recorded simultaneously and expressed in thermograms. Combustion stages are observed as a peak in the DTG curve and these peaks represent the mass losses in the combustion stages. According to the analysis results, the highest mass loss rate in the evaporation zone of water in the quinoa plant was 2.12% at 96.65 °C, and in the amaranth plant at 2.34% at 101.7 °C. However, in the next step, the mass loss rate decreased in both pellets. At this stage of the analysis, the water in the pellets completely evaporated and the mass loss was 12.43% in quinoa and 13.38% in amaranth, according to the initial mass. With the increase of volatile matter output, the mass loss rate increased again, and the highest mass loss rates were realized as 6.42% and 4.96%, respectively, at 320 °C for quinoa and 315 °C for amaranth. The rate-determining stage in the combustion kinetics of coal and biomass is the semi-coke combustion stage. At this stage, the lowest mass loss (0.89%) occurred in both pellet samples. TGA and DTG results showed that there were no significant differences between the combustion stages of quinoa and amaranth pellets, and their combustion behaviors were generally close to each other.

Experimental research on flammability characteristics and ignition conditions of hybrid mixture emissions venting from a large format thermal failure lithium-ion battery

When the concentration of gas is below its lower flammable limit and the content of the particles is below its minimum explosible concentration, it can be explosible. Thermal abuse tests for 50 Ah lithium-ion batteries were conducted under an inert atmosphere. The battery failure venting emissions were collected and their composition was identified previously. It still needs further research for the flammability characteristics and ignition conditions for hybrid mixture emissions venting from a large format lithium-ion battery thermal failure. In this study, the likelihood, severity, and kinetics of the batteries' hybrid mixture emissions flammability have been researched. To analyze battery emission flammability characteristics, five indexes have been investigated; they are ignition temperature (Tig), ignition time (τig), maximum explosion pressure (Pmax), pressure rise maximum rate ((dP/dτ)max), and size-normalized maximum rate pressure rise (KSt). Based on quantitative analysis for the hybrid mixture flammability characteristics, it indicates that particle size and gas content can impact hybrid mixture emission flammability characteristics. As for the mixture with finer particles, the optimum combustion condition of the particle and gas concentration pairs were 0.3 and 0.7. The ignition temperature for the optimum combustion conditions was 495 °C. The pressure rising velocity was 23 Mpa/s during ignition. High solvent content and low particle concentration are the conditions for optimum combustion. This indicates that the gas admixture solvent plays a major role in the combustion kinetics of the mixture emission. This research offers a fundamental perspective and provides preventive and protective thermal safety designs that are more suitable for large format commercial battery thermal systems.

Co-combustion of municipal solid waste and hydrochars under non-isothermal conditions: Thermal behaviors, gaseous emissions and kinetic analyses by TGA–FTIR

Co-combustion of municipal solid waste (MSW) with hydrochars was proposed as an effective way for both simultaneous treatments of MSW with biomass and energy recovery. In this work, thermogravimetric analyzer coupled with Fourier transform infrared spectrometer was employed to study the (co-)combustion, gaseous emissions and combustion kinetics characteristics of MSW, hydrochars and their blends. The addition of hydrochars to MSW leads to lower burnout temperatures and the shorter combustion time. Hydrochar prepared at 200 °C (SD200) has a better co-combustion performance than hydrochars prepared at 230 (SD230) and 260 °C (SD260) in term of ignition, burnout and comprehensive combustion characteristic index, hydrochar prepared at 260 °C has a better co-combustion evenness. The addition of hydrochar to MSW changed the gaseous products emission patterns of MSW and reduced the release of CO, HCN, NO and HCl. Kissinger-Akahira-Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods were used to estimate the activation energy of MSW, SD200 and their blends, the minimum average activation energy was observed when the SD200 blending ratio was 70%, which was 75.65 kJ mol−1 by KAS and 82.12 kJ mol−1 by FWO, respectively.

Effect of particle size on the kinetics of pure oxygen combustion of coke

Non-isothermal thermogravimetry technique was used to analyze three groups of coke samples (S-ZD, M-ZD, and L-ZD) of varying particle sizes. The effect of particle size on kinetic parameters was studied in a pure oxygen atmosphere. The ignition (Ti), peak (Tp), and burnout (Tf) temperatures and the flammability (C) and combustion characteristic (Sn) indexes were determined by varying the heating rate (β). The activation energy (Eα) was evaluated following the Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods. Ti, Tp, Tf, C, and Sn correlated positively with the increase in β in a pure oxygen atmosphere. The order of ignition was L-ZD > M-ZD > S-ZD, and the Eα values for the S-ZD, M-ZD, and L-ZD samples were 98.49, 98.35, and 95.17 kJ·mol−1 (FWO) and 90.32, 90.92, and 89.25 kJ·mol−1 (KAS), respectively. Particle size exerted little effect on the kinetics of coke combustion.

Conversion of sewage sludge from industrial wastewater treatment to solid fuel through hydrothermal carbonization process

Sludge is the unwanted solid waste produced during the treatment of industrial wastewater. The hydrothermal carbonization process (HTC) can be used to convert sewage sludge into a coal-like solid fuel. The effects of solid-to-liquid ratio and feed water pH on the physicochemical properties of hydrochars were investigated. According to the results, hydrothermal treatment enhanced the fuel characteristics of hydrochar with a high HHV and fixed carbon. Adding 0.8 M acetic acid resulted in the highest rate of energy recovery at 96.98 %. The observed H/C and O/C atomic ratios of HTC-0.4AA have been lowered to levels comparable to lignite coal. ICP-OES confirmed the presence of the metal in the hydrochar product. Examining the thermogravity analysis of raw materials and hydrochars with a TGA analyzer was then used to determine the combustion kinetics. In addition, combustion characteristics indicate that HTC improves the S combustibility index.

An experimental and modeling study on auto-ignition of ammonia in an RCM with N2O and H2 addition

Deep insights into the combustion kinetics of ammonia (NH3) can facilitate its application as a promising carbon-free fuel. Due to the low reactivity of NH3, experimental data of NH3 combustion can only be obtained within a limited range. In this work, nitrous oxide (N2O) and hydrogen (H2) were used as additives to investigate NH3 auto-ignition in a rapid compression machine (RCM). Ignition delay times for NH3, NH3/N2O blends, and NH3/H2 blends were measured at 30 bar, temperatures from 950 to 1437 K. The addition of N2O and H2 ranged from 0 to 50% and 0 to 25% of NH3 mole fraction, respectively. Time-resolved species profiles were recorded during the auto-ignition process using a fast sampling system combined with a gas chromatograph (GC). An NH3 combustion model was developed, in which the rate constants of key reactions were constrained by current experimental data. The addition of N2O affected the ignition of NH3 primarily through the decomposition of N2O (N2O (+M) = N2 + O (+M), R1) and direct reaction between N2O and NH2 (N2H2 + NO = NH2 + N2O, R2). The rate constant of R2 was constrained effectively by experimental data of NH3/N2O mixtures. Two-stage ignition behaviors were observed for NH3/H2 mixtures, and the corresponding first-stage ignition delay times were reported for the first time. Experimental species profiles suggested the first-stage ignition resulted from the consumption of H2. The oxidation of H2 provided extra HO2 radicals, which promoted the production of OH radicals and initiated first-stage ignition. Reactions between HO2 radicals and NH3/NH2 dominated the first-ignition delay times of NH3/H2 mixtures. Moreover, the first-stage ignition led to the fast production of NO2, which acted as a key intermediate and affected the following total ignition. Consequently, the reaction NH2 + NO2 = H2NO + NO (R3) was constrained by total ignition delay times.

Iron based oxygen-carrier-aided oxy-fuel combustion of coal char: Reactivity and oxygen transfer mechanism

Adding an active oxygen carrier to the inert bed material may favor the oxygen distribution in fluidized bed (FB) combustors. This so-called method “Oxygen-carrier-aided combustion, OCAC” has been applied recently to air combustion in FB boilers, but could also be potentially interesting in oxy-fuel combustion. Here we analyze OCAC in oxy-fuel combustion by experimental determination of the reactivity of char from three coals (lignite, bituminous and anthracite coal) using three oxygen carriers (OC, analytical reagent Fe2O3, hematite, and steel slag). The tests were conducted in a micro thermo-gravimetric analyzer (micro-TGA) and the combustion kinetics was determined for the nine combinations of char and OC. Additional tests were conducted in a macro-TGA i.e., much sample in a big ceramic crucible, to evaluate the phase composition and crystal quality using X-ray diffraction (XRD) to the combustion residues collected at various degrees of carbon conversion (0.2, 0.5, and 0.8). The results show that the burnout temperature decreases with OCs as the combustion rate increases, while the ignition temperature hardly changes. The enhancement of the rate of char combustion by OCs is in the following order: steel slag < hematite < AR-Fe2O3. The lower the fuel rank, the stronger the effect of the oxygen carrier. The combustion kinetics of chars using OC has a higher activation energy and pre-exponential factor than pure char. The enlarged lattice constant of Fe2O3 measured by XRD during the char combustion indicates that the redox reactions of Fe2O3 accelerate the oxidization of char by enhancing the rate of oxygen transport to the carbon surface.

Experimental study on the in-situ combustion retorting of domanik oil shale

Oil shale is a critical strategic resource with enormous reserves. In-situ combustion technology offers great potential for the development of oil shale reserves. In this study, the combustion behavior and kinetics of Domanik oil shale were investigated using High Pressure Differential Scanning Calorimetry. Additionally, the thermal behavior of the oil shale during combustion was studied by using a self-designed Porous Medium Thermo-Effect Cell. Furthermore, the stability of the combustion front and the upgrading effect of the combustion process were investigated with Visual Combustion Tube, and the produced oil was analyzed to evaluate its quality. The results showed that the combustion process of oil shale is characterized by two reaction stages. The oil shale was found to form enough coke residue during the oxidation reactions to allow for stable propagation of a combustion front. The produced oil was of better quality compared to the naturally produced bitumen in oil shale, which indicates that the combustion process had a good upgrading effect. The findings of this study provide a better understanding of the in-situ upgrading process of kerogen and provide significant knowledge about the combustion mechanism of oil shale for its potential development using the in-situ combustion technology.

Influence of Oxygen Concentration on Combustion Kinetics and Gas Products of a Polyurethane–Coal Mixture

Polyurethane materials are often used in mines to fill the geological structural areas for pretreatment and plugging. These areas are primarily high-incidence areas of coal spontaneous combustion (CSC). Polyurethane will promote the spontaneous combustion of the remaining coal because of its superior thermal insulation performance. Previous studies have focused on the effect of polyurethane on the spontaneous combustion of coal in air atmosphere, without considering the variation of oxygen concentration in the mining area. The paper investigates the effect of polyurethane on the spontaneous combustion of coal in the mining area under different oxygen concentration conditions according to the variation law of oxygen concentration in the mining area. Herein, thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) coupled methods were used to study the kinetics and gas release laws of a polyurethane–coal mixture. The critical temperature of coal increases with the decrease of oxygen concentration. When the oxygen concentration exceeds 10%, the shift of the thermogravimetric curve to the right is smaller, indicating that the oxygen concentration has less influence on the combustion of a polyurethane–coal mixture. When the oxygen concentration is less than 10%, the shift of the thermogravimetric curve toward a higher temperature is more prominent, indicating that the oxygen concentration has a greater influence on the thermogravimetric curve. Simultaneously, the maximum value of DTG increases with the increasing oxygen concentration. The main gas products of coal pyrolysis are CO2, CH4, and H2O, while those of polyurethane pyrolysis are mainly CO2, CO, CH4, and H2O during the pyrolysis process. The amount of CO2 during the pyrolysis of various proportions of coal and polyurethane is the main difference in the gas products. Coal can promote the pyrolysis of polyurethane to some extent. The characteristic temperature rises and falls as the proportion of polyurethane in the polyurethane–coal mixture changes. In the actual monitoring, small amounts of H2O, CO2, and CO gases appear in the starting phase, then a large increase in the amount of gases can be considered that polyurethane is involved in the relevant combustion reactions, which can avoid misjudgment of the spontaneous combustion of coal in the mining area.

Finding a way through the “misty” evaluation of the flammability and explosivity of kerosene aerosols

• JetA1 mist flammability and explosivity are assessed in a confined explosion vessel. • Influence of initial conditions on explosion sensitivity and severity is studied. • JetA1 mists with a small droplet size have a higher rate of pressure rise. • The MIE of JetA1 mist may be lower than that of vapors at low temperatures. • The vapor/liquid ratio of a mist is a key parameter of its explosion severity. In the context of assessing hydrocarbon mist ignition sensitivity and explosion severity, an original test method is proposed, focusing on kerosene JetA1 mists but is applicable to other hydrocarbons. Experiments were carried out in a modified apparatus based on the 20L explosion sphere. Fine control of the gas/liquid ratio and flow rates, the mist concentration, and the ignition energy and duration, was ensured by a specifically customized control system guaranteeing the flexibility and compliance of the test apparatus. The droplet size distribution (DSD) and the level of turbulence of the JetA1 mist cloud were first determined by an in-situ laser diffraction sensor and by Particle Image Velocimetry, respectively. The lower explosive limit (LEL), the minimum ignition energy (MIE), the limiting oxygen concentration (LOC), the maximum explosion overpressure (P max ), and the maximum rate of pressure rise (dP/dt max ) were then determined for different mist concentrations, ambient temperatures, initial turbulence levels, energies, and DSD. Tests showed that the LEL mist of JetA1 mists of an average diameter of 8 µm is around 94 g/m 3 , a value which increases to 220 g/m 3 with increasing DSD. This value also tends to decrease considerably with increasing temperatures. Moreover, at a JetA1 concentration of 125 g/m 3 , P max and dP/dt max as high as 6 bar and 192 bar/s respectively were reached, the latter increasing to about 480 bar/s at T = 60 °C. These mists were shown to be ignitable using energies as low as 200 mJ, which is lower than that of vapors at low temperatures, and a limiting concentration of oxygen of 15.8 % v/v . The potential presence of hydrocarbon mist should therefore be an element that requires reconsidering the classification of hazardous areas. Finally, to stress the influence of the vapor-liquid ratio present in the cloud before ignition on the combustion kinetics, an evaporation model based on the d 2 -law was developed estimating the evaporation time and the vapor quantity at different initial temperatures or droplet diameters. Findings were shown to be well coherent allowing the proposition of a new technique for determining hydrocarbon mist safety criteria. Finally, results have shown that JetA1 mists can ignite at temperatures below the liquid’s flashpoint under varying turbulence levels and droplet size distributions.

Oxidation study of n-propylamine with SVUV-photoionization molecular-beam mass spectrometry

This work reports the experimental results of n-propylamine (NPA) oxidation in a jet-stirred reactor at 1 atm within 625–875 K, equivalence ratios from 0.5 to 2.0. Oxidation products and intermediates were identified and quantified with synchrotron vacuum ultraviolet photoionization mass spectrometry. Apart from various hydrocarbons, oxygenated and nitrogenous species reported in previous studies of amines, several intermediates were newly detected, including formamide (H2NCHO), nitromethane (CH3NO2), nitrous acid (HNO2), 2-propen-1-ol (C3H5OH) and 2-propenal (C2H3CHO). A detailed kinetic model consisting of 277 species and 2314 reactions was developed with reasonable predictions against the measured data. The rate-of-production and sensitivity analyses results show that NPA oxidation at low temperatures is dominated by the reaction with HO2. Particular attention was paid to the main oxidation product HCN, because its formation is affected by both fuel structure and reaction temperature. The equivalence ratio changes have an opposite effect on HCN concentration in NPA oxidation compared with the pyrrole oxidation and ethylamine flame. In the current study, the peak mole fraction of HCN decreases with increasing equivalence ratio, because the formation of CN triple bond in HCN requires successive H-abstractions, dominantly controlled by the concentrations of OH/HO2 radicals and O2. In addition, a comparison between the experimental results of NPA oxidation and pyrolysis was performed to illustrate the effect of O2 concentration on reaction routes. Current results provide a preliminary insight into the combustion kinetics of more complicated aliphatic amines.

Self-propagating high-temperature synthesis of heterophase materials in the Zr–Mo–Si–B system. Kinetics and mechanisms of combustion and structure formation

The paper focuses on the study of the combustion kinetics and mechanisms of elemental mixtures in the Zr–Mo–Si–B system, as well as the analysis of phase and structural transformation stages in the combustion wave. A thermodynamic analysis of potential chemical reactions occurring in the combustion wave was carried out. The reaction of ZrB2 formation is preferred in the range of 298–2500 K. Above 2200 K, the formation of MoB becomes more thermodynamically advantageous as compared to MoSi2. Phase stability estimates of combustion products showed that ZrB2, MoSi2 and MoB phases are in equilibrium. Experimental dependences Тc(Т0) and Uc(Т0) are linear, which implies an unchanged combustion mechanism at T0 = 298÷800 K. Preheating leads to an increase in Uc. Similarly, an increase in the proportion of Zr and B in the mixture has a similar effect, i.e. an increase in heat emission and Tc. With a minimum content of Zr and B, the interaction between Mo and Si with the formation of MoSi2 by the reaction diffusion mechanism is decisive. As the proportion of Zr and B increases, the rise of T0 to 750 K does not affect the Tc. Eeff values (50–196 kJ/mol) confirm the significant influence of liquid-phase processes on the combustion kinetics. The mechanism of structure formation was studied. A Si–Zr–Mo melt is formed in the combustion front. The primary grains of ZrB2 and MoB crystallize from this melt as it is saturated with boron. At the same time, the melt spreads over the surface of Zr and Mo particles. This leads to the formation of ZrSix, MoSix films. Core-shell structures are formed behind the combustion front, which disappear as they move towards the post-combustion zone. The phase composition of products is formed in the combustion front in less than 0.25 s.

H-abstractions by O2, NO2, NH2, and HO2 from H2NO: Theoretical study and implications for ammonia low-temperature kinetics

Unraveling the low-temperature chemistry of ammonia is still an open challenge in combustion kinetics, yet of primary importance because of the novel combustion concepts operating in these conditions, as well as of the rising interest on ammonia as an energy carrier. In this work, a fundamental investigation of the H-abstraction reactions from H2NO by O2, NO2, NH2, and HO2 was performed. These reactions, which belong to the radical-radical abstraction class, associate a high sensitivity to the key low temperature ammonia combustion parameters, to a high uncertainty in rate constant values. Theoretically, the investigation of reactions belonging to this class is complicated by their intrinsic multireference nature. To address this issue, a structured theoretical methodology that relies heavily on the use of CASPT2 calculations was devised. The predicted rate constants highlighted significant deviations from the rates commonly adopted in the state-of-the-art mechanisms, most often based on analogies and estimations. In order to understand their impact on ammonia low-temperature kinetics, the obtained rates were integrated into a kinetic model, which was used to investigate ammonia oxidation and ignition at low-temperature and oxygen-rich conditions. It was found that O2 and NH2 play the major role, as abstractors, in regulating ammonia oxidation and ignition. In particular, ignition delay time predictions proved extremely sensitive to the adopted rates: modifying each of them within their theoretical uncertainty caused deviations by even an order of magnitude, and totally changed the predictive features of the mechanism. The kinetic analysis highlighted then the need of a targeted optimization of the critical rates, downstream of the present work and within their uncertainty boundaries, to further refine the mechanism capability over a wide range of operating conditions.

Experimental and kinetic modeling study of α-methylnaphthalene laminar flame speeds

α-Methylnaphthalene (AMN) is the primary reference bicyclic aromatic compound of diesel, and it is commonly used as a component of diesel, kerosene and jet-fuel surrogates formulated to describe real fuel combustion kinetics. However, few experimental data on neat AMN combustion are available in the literature. This work provides the first measurements of laminar flame speed profiles of AMN/air mixtures at 1 bar varying the initial temperature from 425 to 484 K, and equivalence ratio (φ) between 0.8 and 1.35 paving the way for the kinetic study of AMN combustion chemistry at high temperatures (>1800 K). The experimental data obtained in a spherical reactor are compared with kinetic model simulations. Specifically, the AMN kinetics is implemented from its analogous monocyclic aromatic compound, i.e., toluene, through the analogy and rate rule approach. This method allows to develop kinetic mechanisms of large species from the kinetics of smaller ones characterized by analogous chemical features, namely the aromaticity and the methyl functionality in the case of toluene and AMN. In doing so, it is possible to overcome the need of high-level electronic structure calculations for the evaluation of rate constants, as their computational cost increases exponentially with the number of heavy atoms of the selected species. To assess the validity of this approach, ab initio calculations are performed to derive the rate constants of the H-atom abstraction reactions by H, OH and CH3 radicals from both toluene and AMN. The kinetic model obtained satisfactorily agrees with the measured laminar flame speed profiles. Sensitivity and flux analyses are performed to investigate similarities and differences between the main reaction channels of toluene and AMN combustion, with the former leading to ∼6 cm/s faster flame speed at almost identical conditions (P=1 bar, T∼425 K), as evidenced by both kinetic model simulations and experimental findings.

Theoretical kinetics of HO2 + C5H5: A missing piece in cyclopentadienyl radical oxidation reactions

The resonantly-stabilized cyclopentadienyl radical (C5H5) is a key species in the combustion and molecular growth kinetics of mono and poly-aromatic hydrocarbons (M/PAHs). At intermediate-to-low temperatures, the C5H5 reaction with the hydroperoxyl radical (HO2) strongly impacts the competition between oxidation to smaller products and growth to PAHs, precursors of soot. However, literature estimates for the HO2 + C5H5 reaction rate are inaccurate and inconsistent with recent theoretical calculations, thus generating discrepancies in global combustion kinetic models. In this work, we perform state-of-the-art theoretical calculations for the HO2 + C5H5 reaction including variable reaction coordinate transition state theory for barrierless channels, accurate thermochemistry, and multi-well master equation (ME) simulations. Contrary to previous studies, we predict that OH + 1,3-C5H5O is the main reaction channel. The new rate constants are introduced in two literature kinetic models exploiting our recently developed ME based lumping methodology and used to perform kinetic simulations of experimental data of MAHs oxidation. It is found that the resonantly-stabilized 1,3-C5H5O radical is the main C5H5O isomer, accumulating in relevant concentration in the system, and that the adopted lumping procedure is fully consistent with results obtained with detailed kinetics. The reactivity of C5H5O with OH and O2 radicals is included in the kinetic mechanisms based on analogy rules. As a result, C5H5O mostly reacts with O2 producing smaller C3/C4 species and large amounts of C5H4O, suggesting that further investigations of the reactivity of both C5H5O and C5H4O with oxygenated radicals is necessary. Overall, this work presents new reliable rate constants for the HO2 + C5H5 reaction and provides indications for future investigations of relevant reactions in the sub-mechanisms of cyclopentadiene and MAH oxidation.

Usage of Rapeseed Oil and Ethanol in a Diesel Engine

Introduction. Alternative fuels in IC-engines make it possible to reduce the harmful effects of exhaust gases on the environment without the use of expensive cleaning systems, diversify the fuel market, and reduce the consumption of non-renewable energy recourses, while research aimed at studying the use of alternative fuels makes it possible to find optimal options for replacing non-renewable raw materials. The purpose of the work is to study the effect of using ethanol in a standard tractor diesel engine with volumetric mixing and combustion from flare resulting from the autoignition of a rapeseed oil pilot portion and to optimize separate cyclic fuel deliveries to obtain maximum energy and environmental effect. Materials and Methods. The article deals with the description of the results of the use of rapeseed oil and ethanol in a serial tractor diesel engine of dimension 2F 10.5/12.0 with separate fuel injection directly into the combustion chamber. In the course of experimental studies, the working process was indicated by a piezo quartz pressure sensor installed in the cylinder head, fuel and air consumption were measured, and samples of exhaust gases to study the gas composition and determine the content of toxic components and smokiness were taken. Results. The exact ethanol and rapeseed oil delivery was determined; the values of the average effective pressure, the average temperature of gases in the cylinder, and active and full heat generation were obtained. It is shown that with an increase in the cyclic ethanol delivery, the proportion of heat from kinetic combustion increases, while the diesel process is characterized by an increase in the proportion of diffusion combustion when the load increases. The analysis of the processes inside the cylinder when the engine runs on ethanol and rapeseed oil in comparison with the traditional diesel process is carried out. Discussion and Conclusion. The use of rapeseed oil and ethanol can completely replace the traditional fuel of petroleum origin for an operating diesel engine by installing additional fuel equipment and modifying the head of cylinder block through mounting an additional nozzle. In this case, the environmental performance of the diesel engine improves significantly.

Intrinsic combustion kinetics of rapid-pyrolysis Zhundong coal char

Driven by the demand for accurate intrinsic kinetics for the prediction of the combustion rate of purely fired Zhundong coal (ZDC) in a slag tapping boiler, the surface activation function (SAF) and intrinsic kinetic parameters of two types of rapid-pyrolysis ZDC chars were revealed via the isothermal and nonisothermal thermogravimetric analysis methods. The isothermal kinetic results show that the activation energy (E), reaction order and SAF of these two chars were the same, at 146 kJ/mol, 0.78 and X0.44 (1 – X)−0.48, respectively. Therefore, the difference in the intrinsic reaction rate between these two chars was caused only by the different pre-exponential factors, which are mainly influenced by the specific surface area and catalytic elements in char ash. Nonisothermal kinetic parameters were obtained via the isothermal model-fitting method (ISOM), thereby using the isothermal SAF to fit the nonisothermal data at different heating rates (βs). The results indicate that the E values of the two chars were 148.95 ± 3.12 kJ/mol and 146.16 ± 1.66 kJ/mol, indicating that β has little influence on E. These measured values are consistent with the isothermal E values, so the ISOM is suitable for the determination of the nonisothermal kinetics of rapid-pyrolysis char combustion.