Combustion Systems Research Articles

An improved manifold-projection trajectory based method for chemical kinetic mechanism reduction

An improved manifold-projection trajectory based dimension reduction algorithm (MTDR) to automatically generate skeletal chemical kinetic mechanisms was proposed and validated in this study. This algorithm is implemented by constructing an approximate manifold-based trajectory of the combustion system using Euclidean distances between two adjacent points and cosine similarities between two adjacent vectors in the manifold space, and then evaluating the importance of species by calculating the error of manifold-based trajectories before and after the projection of the manifold. In this method, the nature of the combustion system is well reflected since the combustion process information can be captured by the location of the state point in the manifold space. The calculation during the reduction process is simplified by using the manifold-based trajectory instead of the complex differential equations. Compared to our previous work, this study improves the prediction accuracy of the reduced mechanisms through a more comprehensive error evaluation in the mechanism reduction process. The detailed mechanisms of fuels including iso-cetane, iso-octane and gasoline surrogate mixtures of toluene, iso-octane and n-heptane were reduced to portray the prowess of the algorithm. It’s demonstrated that the number of species of the fuels is reduced from 492, 254 and 1389 to 95, 87 and 427 within an acceptable error, respectively. Meanwhile, the case of iso-octane mechanism reduction was chosen to compare the performance of MTDR with traditional methods including path flux analysis (PFA) and directed relation graph with error propagation and sensitivity analysis (DRGEPSA), and it is shown that the MDTR can generate more compact mechanism under a broad range of error limits.

Technology assessment for the transition to a renewable electric grid

To reduce carbon emissions, generation of electricity from combustion systems is being replaced by renewable resources. However, the most abundant renewable sources – solar and wind – are not dispatchable, vary diurnally and are subject to intermittency, and produce electricity at times in excess of demand (excess production). To manage this variability and capture the excess renewable energy, energy storage technologies are being developed and deployed such as battery energy storage (BES), hydrogen production with electrolyzers (ELY) paired with hydrogen energy storage (HES) and fuel cells (FCs), and renewable natural gas (RNG) production. While BES may be better suited for short duration storage, hydrogen is suited for long duration storage and RNG can decarbonize the natural gas system. California Senate Bill 100 (SB100) sets a goal that all retail electricity sold in the State must be sourced from renewable and zero-carbon resources by 2045, raising the questions of which set of technologies and in what proportion are required to meet the 2045 target in the required timeframe as well as the role of the natural gas infrastructure, if any. To address these questions, this study combines electric grid dispatch modeling and optimization to identify the energy storage and dispatchable technologies in 5-year increments from 2030 to 2045 required to transition from a 60% renewable electric grid in 2035 to a 100% renewable electric grid in 2045. The results show that, by utilizing the established natural gas system to store and transmit hydrogen and RNG, the deployment of battery energy storage is dramatically reduced. The required capacity for BES in 2045, for example, is 40 times lower by leveraging the natural gas infrastructure with a concomitant reduction in cost and associated challenges to transform the electric grid.

Hydrochars derived from real organic wastes as carbonaceous precursors of activated carbons for the removal of NO from contaminated gas streams

The improvement of air quality in densely-populated urban regions constitutes an environmental challenge of increasing concern. In this respect, the abatement of NO emissions, primarily emanating from combustion processes associated with motor-vehicles, along with industrial/domestic combustion systems, represents one of the main problems. Here, three hydrochars from diverse organic residues were used as activated carbon precursors for their evaluation in the NO removal in two potential application scenarios. Hydrochars were physically activated at 800 °C with pure-CO2 or diluted-O2. These materials were tested in a lab-scale biofilter at different conditions (NO concentration, temperature, relative humidity, NO-containing gas and carbon particle size) and in a larger-scale biofilter to evaluate the long-term NO removal capacity. Hydrochar-derived carbons present a relatively well-developed micro- and mesoporous structure, with BET areas of up to 421 m2/g, and a variety of oxygen surface functionalities (carboxylic, lactone, carbonyl and quinone groups), especially concerning CO2-activated carbons. These exhibited an excellent behaviour at low NO concentration (5 ppmv) between 25 and 75 °C with removal capacities of ≈97 % and > 82 %, respectively; and still good-performance (≈66 %) in a more concentrated gas (120 ppmv). Whilst, carbons obtained by diluted-O2 activation from the same hydrochars, evidenced a higher removal capacity loss at high NO concentration. The O2 presence in the gas stream was confirmed as a crucial factor in the NO elimination, since both co-adsorb on the carbon surface favouring NO oxidation to NO2. Besides, the humidity in the airstream diminished the NO removal capacity from 0.88 to 0.51 mgNO/gcarbon, but still remained at 0.54 mgNO/gcarbon, when the carbon (in pellet) was operated at larger-scale biofilter in 9-fold longer test under humid air. Therefore, this study highlights the potential of renewable carbons to serve as cost-effective component in urban biofilters, to mitigate NO emissions from exhaust gases in biomass boilers and urban semi-close areas.

Combustion enhancement and emission reduction in RCCI engine using green synthesized CuO nanoparticles with Cymbopogon martinii methyl ester and phytol blends

Cymbopogon martini, also known as Palmarosa, is a grass species in the Cymbopogon genus, native to India and widely cultivated in tropical regions for oil production. Phytol, a constituent of chlorophyll, has garnered attention in the biofuels industry due to its potential for conversion into biodiesel through transesterification. Its abundance and renewable nature underscore its relevance for sustainable development. This study investigates the energy potential of waste Cymbopogon martinii Methyl Ester (CMME) in engine combustion systems using reactivity-controlled compression ignition (RCCI) in a single-cylinder, four-stroke diesel engine for low-temperature combustion. The process involves blending low-reactivity fuel (LRF), such as phytol (Acyclic diterpene alcohol and a constituent of chlorophyll), with high-reactivity fuel (HRF), namely CMME, in carefully monitored proportions. CMME25 is used as the primary fuel, supplemented with varying amounts of phytol (10 %, 20 %, and 30 %). Heat release rate (HRR) analysis indicates that phytol improves combustion efficiency up to a 20 % blend in RCCI mode. However, exceeding a 30 % phytol blend reduces brake thermal efficiency (BTE). RCCI mode also shows decreased nitrogen oxide and smoke emissions but increased hydrocarbon (HC) and carbon monoxide (CO) emissions. Improved homogeneity and ignition delay result in higher peak pressure and HRR compared to traditional methods. Further investigation focuses on the effects of CuO nanoparticles on a CMME25 and PHY20 % blend in RCCI mode. CuO nanoparticles (50–100 ppm) enhance brake thermal efficiency, improve combustion parameters (ignition delay, HRR, and cylinder pressure), and reduce emissions. The study concludes that a blend of CMME25+PHY20 % with 100 ppm CuO in RCCI mode is a promising alternative to traditional diesel fuel, offering a sustainable and efficient energy solution.

Removal and complete combustion of 1,4-dioxane in water by a two-step reaction combining adsorption and catalytic combustion

Catalytic wet air oxidation is not so effective to decompose 1,4-dioxane in water, while there have been several studies on this reaction. As an alternative, we propose a two-step purification system for removal and complete combustion of 1,4-dioxane, where the first step is removing 1,4-dioxane from water by adsorption, and in the second step, the adsorbent is heated to release 1,4-dioxane, and the released 1,4-dioxane is completely combusted by gas-phase catalytic reaction. We had searched for adsorbents and combustion catalysts suitable for the system and found a high-silica MFI zeolite and Pt/SiO2, respectively. The high-silica MFI zeolite adsorbed up to 121 mg g−1 of 1,4-dioxane, and 1.1 mmol L−1 of 1,4-dioxane in water was almost completely removed by 10 g L−1 dose. The zeolite was reusable for adsorption-desorption cycles at least five times without any loss of the performance. Pt/SiO2 was highly active for the complete combustion of 1,4-dioxane even at 200 °C. By using the high-silica MFI zeolite and Pt/SiO2, we conducted the release of 1,4-dioxane from the zeolite by heating and the gas-phase catalytic combustion of 1,4-dioxane using two reactors connected in series, which were filled with the zeolite and Pt/SiO2, respectively, and demonstrated that all 1,4-dioxane was released by 300 °C and was completely combusted in the upstream and downstream reactors, respectively.

Understanding adhesion induced by calcium compounds at 900 °C using model particles

In waste and biomass combustion plants, ash adheres to the inside of the combustors and surfaces of air heaters, etc., accumulating over time and causing operational problems due to the deposited ash layer. Here, we evaluated the adhesion properties of calcium-rich ash using synthetic ash. Specifically, we investigated the role of Ca-Al in ashes. The adhesion of Ca-Al synthetic ash and mixed ash of Ca-Al and SiO2, which is included in ash and utilized as a bed material in fluidized-bed combustion systems, was investigated. Adhesion was found to increase when three conditions were met: Ca/Al molar ratio >1, SiO2 coexistence, and 900 °C. The increase in tensile strength of the powder bed corresponded to shrinkages in volume, specific surface area, and total pore volume, suggesting solid phase sintering as the cause of increased adhesion. Adding alumina nanoparticles to the highly adherent sample successfully suppressed the adhesion increase.

The Heat Flux Method for hybrid iron–methane–air flames

Recently, a cyclic energy storage concept was proposed involving the use of metal powder as CO2-free energy carrier, known as the metal fuel cycle. In this cycle, the burning of iron powder is considered as the discharge agent of the energy carrier. However, for this cycle to be an efficient one, a better understanding of the laminar burning velocity of iron powder is required. This study presents a newly developed burner based on the Heat Flux Method (HFM), which can measure the burning velocities of flat hybrid iron–methane–air flames. Since laminar iron flames are difficult to stabilize and have – even for micron-sized particles – burning velocities in close proximity to their terminal velocity, methane is used as a stabilizing agent. In this paper, the design of the new burner system is presented with results for burning velocities of iron–methane–air flames. The results show a steady decrease in burning velocity when iron is added to a stoichiometric methane–air flame down to 16 cm/s. It is hypothesized that in the case of relatively low iron concentrations, the iron acts as a heat sink within these flames, consequently reducing the flame temperature and laminar burning velocity. For these low concentrations, methane is the governing fuel. At concentrations above 250 g/m3, the reduction of the burning velocity comes to a halt, and the iron becomes the governing fuel in the flame. A comprehensive error analysis reveals that the primary sources of uncertainty stem from fluctuations in the iron content and parabolic fitting of the thermocouple measurements in the HFM.Novelty and Significance statementThe novelty of this study is a newly developed burner based on the well-known Heat Flux Method (HFM). In accordance with the HFM, a new burner was designed to facilitate stable flat adiabatic hybrid iron–methane–air flames for the first time and measure its key parameter, the adiabatic burning velocity. Further, a metered iron powder dispersion system was developed for accurate iron mass flow measurements. The results show a steady decrease in burning velocity when iron is added to a stoichiometric methane–air flame in relatively low concentrations and show a very weak dependence of the burning velocity on the iron content at iron concentrations above 250 g/m3. These findings enable the validation of 1D simulations for iron-laden flames. A detailed assessment of the measurement uncertainties reveals that the largest source of uncertainty can be derived back to the stability of iron mass flow, leading to small flame propagation fluctuations on relatively short intervals.

Analysis of the Effects of Structural Parameters on the Thermal Performance and System Stability of Ventilation Air Methane-Fueled Reverse-Flow Oxidation Reactors

Ventilation air methane (VAM) from coal mining is a low-grade energy source that can be used in combustion systems to tackle the energy crisis. This work presents a numerical analysis of the thermal and stabilization performance of a VAM-fueled thermal reversal reactor with three fixed beds. The effects of the combustion chamber/regenerator height ratio (β), heat storage materials, and porosity on the oxidation characteristics are evaluated in detail. It is shown that the regenerator temperature tends to vary monotonically with β due to the coupling effect of the gas residence time and heat transfer intensity. The optimal β is determined to be 4/6, above which the system may destabilize. Furthermore, it is found that regardless of the methane volume fraction, the regenerator with mullite inserted has the highest temperature among the heat storage materials investigated. In contrast, the temperature gradually decreases and the system becomes unstable as SiC is adopted, signifying the importance of choosing proper thermal diffusivity. Further analysis reveals that the porosity of the heat storage materials has little effect on the system stability. Decreasing the porosity can effectively reduce the oscillation amplitude of the regenerator temperature, but it also results in greater pressure losses.

Combustion and emission characteristics for various swirler geometries and fuel heating values in a premixed low swirl combustor system

This study investigated combustion and emission characteristics with various swirler parameters (i.e., swirl angle and perforated screen blockage) and fuel heating values (4,000 kcal/Nm3∼9,560 kcal/Nm3, 16.3 MJ/kg∼55.5 MJ/kg in SI unit) using the premixed low swirl combustor system. Flashback limits were evaluated as a flame stability and flame structures were analyzed by acquiring chemiluminescence (OH* and CH*) and OH-Planar Laser Induced Fluorescence (PLIF) signals. NOx and CO emissions were evaluated by calculating emission indices (EINOx and EICO). As a result, the swirl angle did not affect flame stability, whereas screen blockage increased flashback limits. The highest screen blockage (β = 0.8) showed the flashback limit of 5.6 kW, around 1.5 times higher than the lowest screen blockage (β = 0.6). Also, the blockage affected the radical distributed position due to the ratio between swirling and non-swirling flow. The lower heating value fuel showed reduced flashback limits, decreased radical intensities, and lower emissions (EINOx and EICO). The lowest heating value gas (HV 4000) had an EINOx of less than 0.5 g/kg and an EICO of less than 5 g/kg, respectively. In conclusion, these findings would be helpful databases for optimizing heating values to solve environmental pollution issues.

Detection of Precursors of Thermoacoustic Instability in a Swirled Combustor Using Chaotic Analysis and Deep Learning Models

This paper investigates the role of chaotic analysis and deep learning models in combustion instability predictions. To detect the precursors of impending thermoacoustic instability (TAI) in a swirled combustor with various fuel injection strategies, a data-driven framework is proposed in this study. Based on chaotic analysis, a recurrence matrix derived from combustion system is used in deep learning models, which are able to detect precursors of TAI. More specifically, the ResNet-18 network model is trained to predict the proximity of unstable operation conditions when the combustion system is still stable. The proposed framework achieved state-of-the-art 91.06% accuracy in prediction performance. The framework has potential for practical applications to avoid an unstable operation domain in active combustion control systems and, thus, can offer on-line information on the margin of the combustion instability.

Prediction of flame transfer function and combustion instability on a partially premixed swirling combustor by the system identification and CFD methods

Combustion instability can lead to high amplitude oscillations of pressure in the combustion chamber, which would seriously affect the normal operation of the combustion system. In order to reduce the cost and time of combustion chamber design and testing, combustion instability of the partially premixed swirl combustor was predicted, by solving the Helmholtz equation coupled the flame transfer unction (FTF). In the experimental study, by changing the equivalence ratio, the pressure in the combustion chamber appeared to oscillate in different forms including combustion noise, intermittent oscillation and limit cycle oscillation, while the frequency of the self-excited oscillations was obtained to be 165 Hz at the equivalence ratio of 0.7. In Computational Fluid Dynamics (CFD) Simulations, by applying Discrete Random Binary Signal (DRBS) excitation at the inlet, the FTF has been calculated by system identification method, where the excitation results of perturbation signals with different magnitudes were studied. And the result was basically consistent with the FTF calculated by the single-frequency excitation method, which means that the system identification method is suitable for calculating the FTF of the partially premixed swirl combustor. The pulse excitation method has been proposed to determine the selection of the filtering order, and the accuracy of the method has been validated through comparing the FTF results obtained by using different filter orders for discrimination. Moreover, coupling the FTF into the Helmholtz equation, the oscillation frequency of the system was predicted as 159.7 Hz, compared with the experimentally measured oscillation frequency of 165 Hz, which verified that the model could be effectively used for the prediction of oscillation frequency in the partially premixed combustion systems.

Study of Effects on Performances and Emissions of a Large Marine Diesel Engine Partially Fuelled with Biodiesel B20 and Methanol

The impact of fossil fuel utilisation in different combustion systems on climate change due to greenhouse gas accumulation in the atmosphere is rather evident. A part of these gases comes from the large engines used for propulsion in marine applications. In the continuous global effort made by engine manufacturers to mitigate this negative impact, one way is represented by the utilisation of alternative fuels such as biodiesel and methanol, based on dedicated research to fulfil the more stringent regulations concerning pollutant emissions issued by piston heat engines. In this study, a numerical investigation was conducted on a four-stroke large marine diesel engine (ALCO 16V 251C) at several engine speeds and full load conditions. Different blends of diesel–methanol and biodiesel B20–methanol with methanol mass fractions of 10% and 20% were considered for theoretical analysis in two techniques of methanol supply: direct injection mode of a blend of base fuel diesel/biodiesel B20 with methanol and injection of methanol after the intercooler, and direct injection of the base fuel. The results show that, if 10% in power loss can be acceptable, then for diesel–methanol 10%, in the direct injection technology, the NOx emission can be reduced up to 19%, but with a compromise of an 8% increase in SOOT emission, while for biodiesel B20–methanol 10%, with the same direct injection method, the NOx emissions increase by up to 58% with the benefit of reducing SOOT by up to 23% relative to the original diesel fuel operation. For a 20% methanol fraction in blend fuel, the drop in power is more than 10% regardless of the method of methanol supply and the base fuel, diesel, or B20 used.

Radiative Heat Flux Measurement in a Semi-Industrial Oxyfuel Combustion Chamber with Biomass and Coal

Oxyfuel is a combustion technology where the oxidant consists mainly of oxygen and carbon dioxide instead of oxygen and nitrogen. Since carbon dioxide has strongly absorbing bands in the thermal spectrum, the radiation properties of the flame change in an oxyfuel atmosphere compared to conventional combustion. When retrofitting an existing air-fired combustion system to an oxyfuel process, the oxygen content in the oxidant must be adjusted so that similar values for heat transfer by radiation are achieved. This measure allows the system to be operated with otherwise unchanged parameters. In this work, the thermal radiation of natural gas, pulverised walnut shells and lignite under an air and oxyfuel atmosphere is investigated in a semi-industrial combustion chamber with water-cooled membrane walls, at different oxygen concentrations and combustion parameters. While the radiative heat fluxes for natural gas with an oxygen content of 28 vol% in the oxidant are significantly higher than those for firing with air, the values for lignite are still below the air-firing, even with an oxygen content of 30 vol%. For walnut shells, the oxyfuel results are close to the air case for all oxygen concentrations between 27 and 33 vol%. The walnut shells show higher radiative emissions than the lignite at the same thermal output. For non-swirled flames, the radiative heat flux is lower than for swirled flames.

Iron powder particles as a clean and sustainable carrier: Investigating their impact on thermal output

The utilization of iron powder as a sustainable energy carrier, conducive to a carbon-free future, has garnered substantial attention due to its commendable attributes such as high energy density, widespread availability, and absence of emissions. To harness its potential optimally, a comprehensive understanding of the combustion behavior of iron powder and the development of corresponding combustion technologies are imperative. This study endeavors to investigate the influence of iron powder particle size, as well as the flow rate of air and iron powder, on the temperature at the exit of the ignition chamber. Experimental trials were conducted utilizing a metal cyclonic combustor (MC2) equipped with a system for feeding iron powder. The findings reveal that an increase in the diameter of iron particles corresponds to an elongation of the path from the ignition chamber to the outlet. Consequently, this elongation induces prolonged ignition delay time and burning duration. Notably, larger particles exhibit enhanced combustion efficiency in comparison to their smaller counterparts. The outcomes demonstrate that particles approximately 50 µm in size achieve an efficiency of 94%, as opposed to 72% for particles below 20 µm. Temperature measurements and spectrometric analysis expose a discernible relationship between particle size and temperature during combustion, elucidating that larger particles yield higher temperatures. Comprehending the intricate correlation between particle size and combustion behavior is crucial for optimizing combustion systems when utilizing iron powder as an energy carrier. By controlling particle size and combustion conditions, the efficiency and efficacy of iron powder combustion processes can be enhanced, thereby contributing to cleaner and more sustainable energy solutions. The implications of this study extend to the enhancement of burner system design and functionality, along with an overall improvement in combustion efficiency. These findings hold significance within the realm of combustion science, presenting opportunities for the development of more sustainable and environmentally friendly energy solutions. Implementing the insights derived from this research empowers researchers to harness the potential of iron powder as an energy carrier, thereby advancing progress toward a greener future through environmentally conscious combustion processes.

Numerical simulation of a spark ignition ammonia marine engine for future ship power applications

Given the current state of global carbon emissions, China has proposed the objectives of achieving carbon peaking by 2030 and carbon neutrality by 2060. To meet the requirement of zero-carbon and achieve the application of pure ammonia fuel in low-speed two-stroke marine engines, this paper proposes the Groove Diversion-Assist Ignition (GDAI) combustion system, which can effectively control the temperature, fuel distribution, and flow rate in the spark plug region near the top dead center and finally achieve the spark ignition of pure ammonia without any change in compression ratio and scavenging temperature. At the same time, the boundary conditions for the ignition of ammonia fuel have also been studied. The results show that enhancing the initial temperature can alleviate the requirement for spark ignition energy, and a minimum energy level of 75 mJ remains necessary for effective spark ignition of ammonia. Furthermore, the utilization of spark ignition of ammonia fuel can achieve a maximum thermal efficiency of 51.32%, representing a 2.8% increase in overall thermal efficiency compared to the diesel mode. Additionally, the application of ammonia fuel can relief the NOx emissions compare to diesel fuel, which provides a new and effective utilization way for the application of ammonia fuel on the marine engine.

Multi-Criteria Optimization of a Laboratory Top-Lit Updraft Gasifier in Order to Reduce Greenhouse Gases and Particulate Matter Emissions

Air pollution from combustion processes is harming human health and the environment. To mitigate this, one needs to adopt cleaner energy production methods, in particular, to optimize combustion systems in order to minimize pollutants and increase efficiency. Flue gas analysis and particulate matter (PM) monitoring, starting from the prototype phase, is crucial to minimize and regulate pollutant emissions. This article analyses the emissions of pollutants and particulate matter from a combustion test gasifier working on the Top-Lit Updraft (TLUD) principle in order to optimize functionality and reduce exhaust emissions. Three experiments were performed in which the primary (gasification) air flow rate (GA) was kept constant at 25 L/min, and the secondary (combustion) air flow rate (CA) was adjusted to obtain a CA/GA ratio of 2 (50 L/min), 3 (75 L/min), and 4 (100 L/min) respectively. Based on a multi-criterial analysis, the optimal CA/GA ratio for TLUD combustion is 3, offering a well-rounded performance in output temperatures, PM and greenhouse gases (GHG) emissions, and efficiency, while the CA/GA ratio of 4 has good PM and GHG emissions performance but lower efficiency, and the CA/GA ratio of 2 is the least favorable due to its poor performance in output temperatures, PM and GHG emissions.

Comparative study of combustion processes generated by the use of different fuels: energy and exergy analysis

Through energy and exergy analysis, the present work revisits the combustion processes generated using different fuels (CH4, C3H8, H2, LPG, Natural gas and Biogas) under the same operating conditions. First, numerical computations, in which the turbulent dynamic k-ϵ model coupled with a probability density function (PDF) approach together with different sub-models that ensure the reliability of the results, are used. Then, the First and Second Laws of thermodynamics are applied to all fuel combustion cases considered previously to predict the energy loss, exergy destruction and their corresponding efficiencies. Next, variations in the air factor, the air inlet temperature and the fuel inlet temperatures are considered to analyse the response of combustion system performance as well as energy and exergy losses for the different fuels under investigation. The results show an amelioration of combustion parameters for the mixture of fuel and air using values of λ greater than 1. Also, the preheating of the inlet air temperature has a positive effect on energetic parameters. However, preheating the inlet fuel does not take a considerable role in the efficiency amelioration and loss reduction of the combustion system. It further turns out that biogas features higher energy efficiency compared to other fuels, at approximately 89.64%, while hydrogen fuel exhibits higher exergy efficiency at around 78.70% followed by biogas with 74.96%.

Combustion Synthesis of Nano CeO<sub>2</sub> and its Application as a Catalytic Agent in Peptidomimetics

An eco-friendly cerium oxide nanoparticle was prepared through a solution combustion system with a novel fuel plant seed source Albizzia richardiana. The synthetic technique involves the Albizzia richardiana plant seeds as a fuel and cerium nitrate as an oxidizer (basis of cerium) was added in stoichiometric quantity in a well washed silica crucible and stirred for several minutes until persistent uniform solution was made. Then the mixture was kept in a heat up heating chamber at 500 °C. After dehydration and decomposition of homogeneous solution, the obtained CeO2 nanoparticles were thoroughly characterized using FT-IR, XRD and SEM morphological analysis. The synthesized nano CeO2 was a better catalytic agent for the production of Nα-Fmoc/Cbz-keto-1,2,3-triazole equivalents through the three-constituent reaction between amino acyl chloride equivalents of Fmoc/Cbz-protected amino acids, phenyl acetylene and sodium azide. Keto-1,2,3-triazoles were set upon by refluxing amino acyl chlorides with NaN3 and phenyl acetylene in presence of CeO2 nano particles in methanol. After a simple workup, the desired products obtained were fully categorized by FTIR, HRMS, proton and 13C NMR techniques.

Combustion Behavior of Cellulose Ester Fibrous Bundles from Used Cigarette Filters: Kinetic Analysis Study.

This study is focused on the detailed examination of the combustion properties and kinetic analysis of a cellulose acetate fibrous bundle (CAFB), separated from used cigarette filters. It was shown that the faster rate of CAFB heating allows a large amount of heat to be supplied to a combustion system in the initial stages, where the increase in heating rate has a positive response to ignition behavior. The best combustion stability of CAFB is achieved at the lowest heating rate. Through the use of different kinetic methods, it was shown that combustion takes place through two series of consecutive reaction steps and one independent single-step reaction. By optimizing the kinetic parameters within the proposed reaction models, it was found that the steps related to the generation of levoglucosenone (LGO) (by catalytic dehydration of levoglucosan (LG)) and acrolein (by breakdown of glycerol during CAFB burning-which was carried out through glycerol adsorption on a TiO2 surface in a the developed dehydration mechanism) represent rate-controlling steps, which are strongly controlled by applied heating rate. Isothermal predictions have shown that CAFB manifests very good long-term stability at 60 °C (which corresponds to storage in a sea shipping container), while at 200 °C, it shows a sudden loss in thermal stability, which is related to the physical properties of the sample.

Numerical investigation of equivalence ratio effects on Flex-Fuel mixing controlled combustion enabled by prechamber ignition

There is interest in adapting renewable and low-carbon intensity fuels to heavy-duty engines to help displace criteria and greenhouse gas emissions associated with diesel combustion. Low-carbon fuels have inherently low cetane numbers and thus pose a significant challenge when considering direct substitution in diesel combustion systems. Use of an actively fueled prechamber as an ignition source to initiate mixing-controlled combustion (PC-MCC) of low-cetane fuels is becoming an attractive combustion mode to alleviate the identified reactivity deficit. This work focuses on the utilization of an active prechamber to facilitate diesel-like combustion of bioethanol-gasoline fuel blends in a heavy-duty engine. Recent results in this emerging technology suggest that ignition quality is uniquely coupled to prechamber equivalence ratio. In this numerical study, the fundamental implications of prechamber equivalence ratio on the ignition performance of direct injected fuels ranging from E10 to E100 are investigated using CONVERGE. Parametric studies of the prechamber operating strategy were assessed at diesel-like conditions to characterize the performance trends relative to a diesel baseline at the same boundary conditions. Simulation results indicate that PC-MCC is flex-fuel capable and achieves diesel-like ignition qualities and combustion processes for all fuels considered under stoichiometric and rich prechamber conditions. To characterize the equivalence ratio trends observed, a novel inflow boundary modeling technique was utilized to prescribe turbulent jets in place of the prechamber where selective speciation of the jet composition was conducted to isolate the ignition contributions of radical and reacting species in lean, stoichiometric, and rich jets. The inflow boundary modeling suggests that excess fuel and combustion intermediates present in jets produced from stratified and fuel-rich prechamber operation promotes higher jet temperatures and as such are superior ignition sources. Relative to a lean prechamber jet, the peak temperature of a reacting jet from a rich prechamber was up to 600 K hotter at fixed distances from the orifice exit. Radicals also demonstrated an influence on the ignition process, but the combustion mode was identified to be thermally dominant.