Showing papers on "Combustion published in 2017"

Activation of surface lattice oxygen in single-atom Pt/CeO2 for low-temperature CO oxidation

Abstract: To improve fuel efficiency, advanced combustion engines are being designed to minimize the amount of heat wasted in the exhaust. Hence, future generations of catalysts must perform at temperatures that are 100°C lower than current exhaust-treatment catalysts. Achieving low-temperature activity, while surviving the harsh conditions encountered at high engine loads, remains a formidable challenge. In this study, we demonstrate how atomically dispersed ionic platinum (Pt2+) on ceria (CeO2), which is already thermally stable, can be activated via steam treatment (at 750°C) to simultaneously achieve the goals of low-temperature carbon monoxide (CO) oxidation activity while providing outstanding hydrothermal stability. A new type of active site is created on CeO2 in the vicinity of Pt2+, which provides the improved reactivity. These active sites are stable up to 800°C in oxidizing environments.

Energy-Related Small Molecule Activation Reactions: Oxygen Reduction and Hydrogen and Oxygen Evolution Reactions Catalyzed by Porphyrin- and Corrole-Based Systems

Abstract: Globally increasing energy demands and environmental concerns related to the use of fossil fuels have stimulated extensive research to identify new energy systems and economies that are sustainable, clean, low cost, and environmentally benign. Hydrogen generation from solar-driven water splitting is a promising strategy to store solar energy in chemical bonds. The subsequent combustion of hydrogen in fuel cells produces electric energy, and the only exhaust is water. These two reactions compose an ideal process to provide clean and sustainable energy. In such a process, a hydrogen evolution reaction (HER), an oxygen evolution reaction (OER) during water splitting, and an oxygen reduction reaction (ORR) as a fuel cell cathodic reaction are key steps that affect the efficiency of the overall energy conversion. Catalysts play key roles in this process by improving the kinetics of these reactions. Porphyrin-based and corrole-based systems are versatile and can efficiently catalyze the ORR, OER, and HER. Becau...

Prediction and control of combustion instabilities in real engines

Abstract: This paper presents recent progress in the field of thermoacoustic combustion instabilities in propulsion engines such as rockets or gas turbines. Combustion instabilities have been studied for more than a century in simple laminar configurations as well as in laboratory-scale turbulent flames. These instabilities are also encountered in real engines but new mechanisms appear in these systems because of obvious differences with academic burners: larger Reynolds numbers, higher pressures and power densities, multiple inlet systems, complex fuels. Other differences are more subtle: real engines often feature specific unstable modes such as azimuthal instabilities in gas turbines or transverse modes in rocket chambers. Hydrodynamic instability modes can also differ as well as the combustion regimes, which can require very different simulation models. The integration of chambers in real engines implies that compressor and turbine impedances control instabilities directly so that the determination of the impedances of turbomachinery elements becomes a key issue. Gathering experimental data on combustion instabilities is difficult in real engines and Large Eddy Simulation (LES) has become a major tool in this field. Recent examples, however, show that LES is not sufficient and that theory, even in these complex systems, plays a major role to understand both experimental and LES results and to identify mitigation techniques.

Alternative fuels for internal combustion engines

Abstract: This review paper covers potential alternative fuels for automotive engine application for both spark ignition (SI) and compression ignition (CI) engines. It also includes applications of alternative fuels in advanced combustion research applications. The representative alternative fuels for SI engines include compressed natural gas (CNG), hydrogen (H 2 ) liquefied petroleum gas (LPG), and alcohol fuels (methanol and ethanol); while for CI engines, they include biodiesel, di-methyl ether (DME), and jet propellent-8 (JP-8). Naphtha is introduced as an alternative fuel for advanced combustion in premixed charge compression ignition. The production, storage, and the supply chain of each alternative fuel are briefly summarized, and are followed by discussions on the main research motivations for such alternative fuels. Literature surveys are presented that investigate the relative advantages and disadvantages of these alternative fuels for application to engine combustion. The contents of engine combustion basically consist of the combustion process from spray development, air–fuel mixing characteristics, to the final combustion product formation process, which is analyzed for each alternative fuel. An overview is provided for alternative fuels together with summaries of engine combustion characteristics for each fuel, in addition to its current distribution status and future prospects.

A comprehensive review on combustion and stability aspects of metal nanoparticles and its additive effect on diesel and biodiesel fuelled C.I. engine.

Abstract: Nanofluids are described as a relatively new kind of colloidal solutions with a particle size smaller than one billionth of a meter (1–100 nm) suspended in the base fluid so as to enhance the thermophysical properties, which makes them an obvious choice for use in number of commercial applications including engineering, medical sciences, biotechnology, agriculture technology, transportation etc. With the advancement in nanotechnology during last few years, scientific community focuses on improvising combustion behavior, stability aspects, various engine performance parameters and emission characteristics of conventional diesel engine using nanoparticle laden diesel biodiesel fuel blends. Most recently few experimental works on above issues using nanosized metallic, non-metallic, organic and mixed particles in the base liquid fuel for diesel engine have appeared in the open literature. The obtained results are very encouraging due to multifold enhancement in thermo physical and chemical properties of modified fuel such as high surface to volume ratio, high reactive medium for combustion, enhanced heat and mass transport properties due to high thermal conductivity, improvement in flash point, fire point, pour point etc depending upon the type of nanoparticles used, their particle size and concentration with base fuel. Despite having all superiorities, somewhat unclear and contradictory results are found in the literature, further the experimental results of different researchers are not generalized so far as to reach at common consensus about this new approach of fuel modification. Keeping all these facts in mind, a serious attempt has been made to summarize the important published work on combustion and stability aspects of nanoparticle laden diesel, biodiesel fuels and their blends, and its effects on fuel and engine overall characteristics with the objective to provide a pathway to conduct further research in this area for utilizing maximum potential of nanoparticle fuel emulsion technology and to provide a promising future fuel for diesel engine.

Performances and emission characteristics of NH3–air and NH3CH4–air combustion gas-turbine power generations

Abstract: For the first time, NH 3 –air combustion power generation has been successfully realized using a 50 kW class micro gas turbine system at the National Institute of Advanced Industrial Science and Technology (AIST), Japan. Based on the global demand for carbon-free power generation as well as recent advances involving gas-turbine technologies, such as heat-regenerative cycles, rapid fuel mixing using strong swirling flows, and NO x reduction using selective catalytic reduction (SCR), allow us to realize NH 3 –air combustion gas-turbine system, which was abandoned in the 1960′s. In the present system, the combustor adopted gaseous NH 3 fuel and diffusion combustion to enhance flame stability. The NH 3 pre-cracking apparatus for combustion enhancement using generated H 2 was not employed. The NH 3 –air combustion gas-turbine power generation system can be operated over a wide range of power and rotational speeds, i.e., 18.4 kW to 44.4 kW and 70,000 rpm to 80,000 rpm, respectively. The combustion efficiency of the NH 3 –air gas turbine ranged from 89% to 96% at 80,000 rpm. The emission of NO and unburnt NH 3 depends on the combustor inlet temperature. Emission data indicates that there are NH 3 fuel-rich and fuel-lean regions in the primary combustion zone. It is presumed that unburnt NH 3 is released from the fuel-rich region, while NO is released from the fuel-lean region. When diluted air enters the secondary combustion zone, unburnt NH 3 is expected to react with NO through selective non-catalytic reduction (SNCR). NH 3 CH 4 –air combustion operation tests were also performed and the results show that the increase of the NH 3 fuel ratio significantly increases the NO emission, whereas it decreases the NO conversion ratio. To achieve low NO x combustion in NH 3 –air combustion gas turbines, it is suggested to burn large quantities of NH 3 fuel and produce both rich and lean fuel mixtures in the primary combustion zone.

From theoretical reaction dynamics to chemical modeling of combustion

Abstract: The chemical modeling of combustion treats the chemical conversion of hundreds of species through thousands of reactions. Recent advances in theoretical methodologies and computational capabilities have transformed theoretical chemical kinetics from a largely empirical to a highly predictive science. As a result, theoretical chemistry is playing an increasingly significant role in the combustion modeling enterprise. The accurate prediction of the temperature and pressure dependence of gas phase reactions requires state-of-the-art implementations of a variety of theoretical methods: ab initio electronic structure theory, transition state theory, classical trajectory simulations, and the master equation. In this work, we illustrate the current state-of-the-art in predicting the kinetics of gas-phase reactions through sample calculations for some prototypical reactions central to combustion chemistry. These studies are used to highlight the success of theory, as well as its remaining challenges, through comparisons with experiments ranging from elementary reaction kinetics studies through to global observations such as flame speed measurements. The illustrations progress from the treatment of relatively simple abstraction and addition reactions, which proceed over a single transition state, through to the complexity of multiwell multichannel reactions that commonly occur in studies of the growth of polycyclic aromatic hydrocarbons. In addition to providing high quality rate prescriptions for combustion modelers, theory will be seen to indicate various shortcomings in the foundations of chemical modeling. Future progress in the fidelity of the chemical modeling of combustion will benefit from more widespread applications of theoretical chemical kinetics and from increasingly intimate couplings of theory, experiment, and modeling.

Extension of the ReaxFF Combustion Force Field toward Syngas Combustion and Initial Oxidation Kinetics

Abstract: A detailed insight of key reactive events related to oxidation and pyrolysis of hydrocarbon fuels further enhances our understanding of combustion chemistry. Though comprehensive kinetic models are available for smaller hydrocarbons (typically C3 or lower), developing and validating reaction mechanisms for larger hydrocarbons is a daunting task, due to the complexity of their reaction networks. The ReaxFF method provides an attractive computational method to obtain reaction kinetics for complex fuel and fuel mixtures, providing an accuracy approaching ab-initio-based methods but with a significantly lower computational expense. The development of the first ReaxFF combustion force field by Chenoweth et al. (CHO-2008 parameter set) in 2008 has opened new avenues for researchers to investigate combustion chemistry from the atomistic level. In this article, we seek to address two issues with the CHO-2008 ReaxFF description. While the CHO-2008 description has achieved significant popularity for studying large ...

A review on prognostics and health monitoring of proton exchange membrane fuel cell

Abstract: Fuel cell technology can be traced back to 1839 when British scientist Sir William Grove discovered that it was possible to generate electricity by the reaction between hydrogen and oxygen gases. However, fuel cell still cannot compete with internal combustion engines although they have many advantages including zero carbon emissions. Fossil fuels are cheaper and present very high volumetric energy densities compared with the hydrogen gas. Furthermore, hydrogen storage as a liquid is still a huge challenge. Another important disadvantage is the lifespan of the fuel cell because of their durability, reliability and maintainability. Prognostics is an emerging technology in sustainability of engineering systems through failure prevention, reliability assessment and remaining useful lifetime estimation. Prognostics and health monitoring can play a critical role in enhancing the durability, reliability and maintainability of the fuel cell system. This paper presents a review on the current state-of-the-art in prognostics and health monitoring of Proton Exchange Membrane Fuel Cell (PEMFC), aiming at identifying research and development opportunities in these fields. This paper also highlights the importance of incorporating prognostics and failure modes, mechanisms and effects analysis (FMMEA) in PEMFC to give them sustainable competitive advantage when compared with other non-clean energy solutions.

Ultrasensitive WO3 gas sensors for NO2 detection in air and low oxygen environment

Abstract: We report here on the results of a study into the response of a tungsten oxide based low power MEMS gas sensor to ppb of nitrogen dioxide at low levels of ambient oxygen. It was found that the resistive gas sensors not only had a high sensitivity to NO2 (3.4%/ppb vs. 0.2%/ppb obtained for commercial MOX) but can still operate reliably at lower oxygen levels (down to 0.5%) - albeit with slightly longer response and recovery times. The optimal operating temperature was determined to be ca. 350 °C and so easily within the range of a MEMS based SOI CMOS substrate. The response was sensitive to significant changes in ambient humidity, but was found to have low cross-sensitivity to CO, hydrogen, methane, and acetone even at much higher ppm levels. We believe that these tungsten oxide gas sensors could be exploited in harsh applications, i.e. with a low oxygen (lean) environment often associated in the exhaust gases from combustion systems.

Review on the management of RCCI engines

Abstract: RCCI (reactivity controlled compression ignition) engines are found to be capable of achieving higher thermal efficiency and ultra-low NOx and PM emissions. The reactivity controlled combustion is accomplished by creating reactivity stratification in the cylinder with the use of two fuels characterized by distinctly different cetane numbers. The low reactivity (i.e., low cetane number) fuel is firstly premixed with air and then charged into the cylinder through the intake manifold; later, the high reactivity (i.e., high cetane number) fuel is injected into the charged mixture through a direct injector. Subsequently, the reactivity stratification is formed. By strategically adjusting the ratio of two fuels and injection timings, the produced reactivity gradient is able to control the combustion phasing and mitigate the pressure rise rate, as well as the heat release rate. Alternatively, structural factors such as CR (compression ratio) and piston bowl geometries can also affect the combustion characteristics of RCCI. Besides the engine management, the fuels that could be utilized in RCCI engines are also crucial to determine the evaporation, mixing, and combustion processes. To gain a comprehensive knowledge on the state-of-the-art of RCCI combustion, detailed review on the management of RCCI engines has been presented in this paper. This review covers the up-to-date research progress of RCCI including the use of alternative fuels and cetane number improvers, and the effects of fuel ratio, different injection strategies, EGR rate, CR and bowl geometry on engine performance and emissions formation. Moreover, the controllability issues are addressed in this article.

Biomass combustion technology development – It is all about chemical details

Abstract: Biomass fuels differ in many ways from the conventional fossil fuels used in combustion processes, such as coal. They often have high moisture contents, lower heating values, and a variety of minor constituents, such as chlorine, sulfur, phosphorus, nitrogen, and a variety of ash-forming metals. These special properties of biomass fuels cause several challenges, but in many cases also provide advantages, to their use in combustion processes. Design of the combustion devices and choice of their operating parameters are very dependent on the detailed properties of the biomass fuel or fuels to be used. Often these challenges are connected to the fate and chemistry of the many minor constituents or impurities of the fuels. This paper reviews some of such chemical details related to biomass combustion that are important to take into consideration in the use of biomass combustion processes. The focus of the paper is in large, industrial scale combustion technologies for biomass and biomass derived waste fuels, either in district heating or also power production. Areas discussed are biomass particle conversion and biomass char oxidation reactivity, nitrogen and sulfur reactions in furnaces, superheater fouling and corrosion due to biomass ashes, low-temperature corrosion, and bed sintering in fluidized bed furnaces. The advances in understanding chemical details of biomass combustion have strongly contributed to the development of more reliable and efficient boiler technologies. Unresolved challenges are still connected to simultaneous combustion of several different biomasses and interaction of fuel ashes in such applications.

Effects of physicochemical properties of biodiesel fuel blends with alcohol on diesel engine performance and exhaust emissions: A review

Abstract: In recent years, alternative fuel studies have been conducted thoroughly by researchers through their experimental work Depletion of fossil fuel raised the attention of researchers to investigate renewable energy sources such as biodiesel and alcohol There is a lack of literature review study on the viability of alcohol acting as additive in biodiesel-diesel fuel blends Thus, this review paper studies on the effects of various alcohol additives in biodiesel-diesel fuel blends on combustion behaviour, performance and emission characteristics of diesel engines The physicochemical properties of alcohol and biodiesel are rigorously discussed, in which they are the main factors in determining the quality of the blended fuel The aim of this paper is to identify the potential of alcohol fuel as an additive in the blended biodiesel and diesel fuel in correspond to the type of alcohol, blending ratio and engine operation conditions Wide range of results from previous research studies with different types of compression-ignition engine, different engine operation conditions and varieties of alcohol-biodiesel-diesel fuel blending ratios were collected in this literature review study Combustion behaviour such as coefficient of variations (COV), in-cylinder pressure, ignition delay, heat release rate and combustion duration are presented Low cetane number and high latent heat of vaporization of alcohol cause a longer ignition delay, produce higher rate of heat release and lower in-cylinder pressure when compared with that of diesel fuel Low density and viscosity of alcohol improve the spray characteristics and enhance air-fuel mixing process In terms of engine performance analysis, the presence of oxygen in alcohol fuel promotes a more complete combustion; hence, resulting in an increase of thermal efficiency In turn, emissions of carbon monoxide (CO), hydrocarbon (HC) and particulate matter (PM) are decreasing

An experimental analysis on the influence of fuel borne additives on the single cylinder diesel engine powered by Cymbopogon flexuosus biofuel

Abstract: Researchers all around the world are making strenuous efforts to find alternative fuel to ameliorate the problem of depletion of fossil fuel. we have identified a novel plant based biofuel, namely Cymbopogon flexuous biofuel. It has excellent fuel properties and is widely available in India and it seems to have the potential to make India self-sufficient in energy production. Cerium oxide nanoparticles were synthesized using sol–gel combustion methods. Their structural, morphological and elemental properties were studied with the help of XRD, SEM, TEM and EDS respectively. On volume basis, 20% raw Cymbopogon flexuous biofuel was blended with diesel fuel, and various proportions of Cerium oxide nanoparticles, namely C20-D80 + 10 ppm, C20-D80 + 20 ppm andC20-D80 + 30 ppm were prepared. The properties like density, kinematic viscosity, calorific value of the test fuel were measured as per ASTM standards and compared with those of diesel fuel. An experimental study of its performance, emission, and combustion behavior was conducted at varied load conditions at a constant speed of 1500 rpm. NO x and smoke emission was simultaneously reduced by 3% and 6.6% respectively as compared with biofuel blend. Due to higher thermal stability and oxygen buffer of Cerium oxide nanoparticle the brake thermal efficiency was higher by 4.76% and cylinder pressure and heat release rate was also higher.

Effect of reaction pathway and operating parameters on the deoxygenation of vegetable oils to produce diesel range hydrocarbon fuels: A review

Abstract: Growing demand for fossil fuels and related environmental issues have directed global attention towards development of alternative fuels from renewable sources. In this regard, biodiesel synthesized from vegetable oils and animal fats has shown potential as alternative to diesel fuel owing to its comparable fuel properties and combustion characteristics. However, higher oxygen content in biodiesel has raised some technical issues for its long term utilization in engines. Subsequently, the second generation liquid hydrocarbon fuels are being developed via catalytic deoxygenation of fatty acids present in vegetable oils. Presently, the research focus is on the pathways for catalytic deoxygenation like hydrodeoxygenation, decarboxylation, and decarbonylation. In hydrodeoxygenation, use of hydrogen gas and sulfided metal catalysts ensure higher conversion of vegetable oil into hydrocarbon fuel compared to the other two pathways. On the contrary, decarboxylation and decarbonylation are mostly hydrogen-free processes ensuring economical production of hydrocarbon fuel from vegetable oils. Hence, the techno-economical issues related to deoxygenation process need to be addressed for its commercial viability. Further, key operating parameters like nature of catalysts and supports, catalyst amount, reaction temperature, reaction atmosphere, hydrogen partial pressure, feed type, feed rate, type of solvent, H2/fatty acid molar ratio etc. are reported to have substantial influence on the hydrocarbon yield and selectivity. This review paper expounds a comparative assessment on the various deoxygenation pathways with their reaction mechanisms to opt for the suitable pathway for conversion of vegetable oils into hydrocarbon fuels based on yield and selectivity of the desired product, ease of use, economy etc. It also explicates the influence of various operating parameters to obtain optimum hydrocarbon conversion and selectivity during catalytic deoxygenation of vegetable oils and related feedstock.