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The cross-border power regulation constraint optimization model based on the improved differential evolution algorithm is studied to effectively regulate and constrain the cross-border power system, ensure the safe and stable operation of the cross-border power system and reduce emissions and fuel consumption. Build a cross-border power and energy Internet model with the tie line as the main medium to realize domestic and overseas information exchange. On this basis, take the minimum total emissions and the minimum total fuel consumption of the generator as the objective function, and take the unit output, system load, active power output and climbing constraints as the constraints, build a cross-border power regulation constraint optimization model, and apply the multi group improved differential evolution algorithm to solve the model, Obtain a cross-border power regulation and restriction scheme that minimizes the total emissions and the total fuel consumption of generators. The experimental results show that this method can realize the cross-border power regulation constraint optimization. After the power regulation constraint optimization, the total emissions and generator fuel consumption are small, and the power generation capacity can meet the load demand and achieve the balance of supply and demand.

The BCR/ABLp210 fusion gene is a classic biomarker of chronic myeloid leukemia, which can be divided into e13a2 and e14a2 isoforms according to different breakpoints. These two isoforms showed distinct differences in clinical manifestation, treatment effect, and prognosis risk. Herein, a strategy based on nanocluster beacon (NCB) fluorescence was developed to identify the e13a2 and e14a2 isoforms in one-pot. Because the fluorescence of AgNCs can be activated when they are placed in proximity to the corresponding enhancer sequences, thymine-rich (T-rich) or guanine-rich (G-rich). In this work, we explored an ideal DNA-AgNCs template as an excellent molecular reporter with a high signal-to-noise ratio. After recognition with the corresponding isoforms, the AgNCs can be pulled closer to the T-rich or G-rich sequences to form a three-way junction structure and generate fluorescence with corresponding wavelengths. Therefore, by distinguishing the corresponding wavelengths of AgNCs, we successfully identified two isoforms in one tube with the limitation of 16 pM for e13a2 and 9 pM for e14a2. Moreover, this strategy also realized isoform identification in leukemia cells and newly diagnosed CML patients within 40 min, which provides a powerful tool to distinguish fusion gene subtypes at the same time.

It is well known that the high spontaneous ignition risk of pressurized hydrogen poses a serious threat to hydrogen storage safety. Aiming to reveal the inhibition mechanism of the fuel-blending st...

Due to the increasing attention of low temperature combustion, more precise and convenient low temperature chemical reaction mechanism is needed in the combustion reaction flow modelling. However, ...

China has recently promised to reach carbon neutral before 2060. To achieve this ambitious goal, it is necessary to substantially increase the electricity production from clean sources, such as renewable power and nuclear power, to replace the previous share of coal power generation. Most of the nuclear reactors currently in operation in China are pressurized water reactors (PWR). The nuclear steam supply system (NSSS) in PWR is a complex nonlinear system. The steam bypass system ensures the steam generator’s cooling capacity in accident conditions and is essential for safe and efficient plant operation. Because of the broad transport delay and non-linearity in the steam bypass control system, it is difficult for the currently widely used proportional-integral-derivative (PID) control to obtain satisfactory control effects. Therefore, it is necessary and meaningful to design a suitable steam bypass control system for NSSS. The investigation of the steam bypass system is performed by MATLAB & Simulink for a large-scale PWR. The nonlinear model is developed by applying the mass and energy conservation equations of fluids and the critical flow correction. The state-space multivariable models are derived by linearizing the nonlinear model at different operation points. Open-loop simulation experiments have been carried out to study the steam bypass system’s dynamic, and the state-space model simulation results are validated by comparing with the results from the nonlinear model. The open-loop results show that the overall system has a considerable transport delay. Thus, a linear active disturbance rejection controller (LADRC) is designed for the steam bypass system. This research assumes that the model and the amount of delay are nearly unknown; however, the proposed controller still performs better than the existing Ziegler-Nichols (Z-N) tuned PID controller. The LADRC has a shorter settling time than the PID controller; the control system can satisfy the design purposes.

The BCR/ABL

As a novel alternative fuel and surrogate component, 2,6,10-trimethyl dodecane has received extensive attention. In order to provide the promise of designing and optimizing the internal combustion engines and propulsion systems by CFD, and provide more choice for branched surrogate component to develop more accurate surrogate model, a comprehensive detailed chemical kinetic model for 2,6,10-trimethyl dodecane has been developed based on 35 reaction classes to numerically describe its experimental observations. The proposed detailed mechanism for 2,6,10-trimethyl dodecane has been validated against with a wide range of experimental data which including ignition delay time, flow reactor and laminar flame speeds. The good agreement between the numerical and the experimental data is observed. Using the kinetic model reduction scheme, a high-temperature and a low-temperature chemical mechanisms were eventually obtained and validated against the detailed mechanism. The successful implementation of kinetic mecha...

As one of the most important clean fuels, methane plays a significant role in the energy supply system, and its combustion characteristics directly affect the efficiency and emission. In order to avoid the production of a large number of nitrogen oxides, the low temperature combustion associated with cool flame is getting more and more attention. But until now the cool flame characteristics of methane is still unclear, even its existence is controversial. In this work, the property of premixed methane/oxygen cool flame has been experimentally studied in a cylindrical reactor and numerically analyzed using different mechanisms. The effects of pressure, temperature and equivalence ratio on methane cool flame have been investigated experimentally. The experimental results show that the cool flame can be obtained in the range of 0.2–4.8 equivalent ratio. The lower limit of pressure of the cool flame region decreases with the increasing initial temperature. The sensitivity and reaction path have been analyzed through the numerical simulation, which reveals that the bifurcation in CH3 oxidation process has remarkable effects on cool flame formation.

As one of the most promising alternative fuel to diesel engines, dimethyl ether plays a significant role in improving combustion efficiency and decreasing emissions, and an in-depth understanding o...

Hydrogen addition is widely used to improve the combustion performance of single-component fuel. In this study, the effects of hydrogen addition on non-premixed ignition of iso-octane by hot air in a diffusion layer were examined and interpreted numerically. Detailed chemistry and transport were considered in simulation. The non-premixed ignition delay times at different hydrogen blending levels were obtained and analyzed. It was found that hydrogen addition greatly reduces the ignition delay. This is mainly due to the fact that the preferential mass diffusion of hydrogen over iso-octane significantly increases the local hydrogen blending level at the ignition kernel. Besides, for the non-premixed ignition process, two modes of reaction front propagation were identified through the analysis based on Damkohler number and consumption speeds. One is the reaction-driven mode characterized by local or sequential homogeneous autoignition; and the other is the diffusion-driven mode, which depends on the balance of mass diffusion, heat transfer and chemical reaction. These two modes lead to different ignition behaviors. For pure iso-octane with low mass diffusivity, ignition is mainly caused by local homogeneous reaction occurring at the most reactive position. With the increase of diffusion layer thickness, the local temperature at the most reactive position increases and therefore the non-premixed ignition delay time of pure iso-octane decreases. However, when hydrogen with high mass diffusivity is added into iso-octane, the non-premixed ignition is controlled by fuel diffusion. With the increase of diffusion layer thickness, the concentration gradient becomes smaller and thereby less hydrogen diffuses into the ignition kernel. Consequently, unlike pure iso-octane, the non-premixed ignition delay time of hydrogen/iso-octane blends increases with the diffusion layer thickness.

Usually premixed flame propagation and laminar burning velocity are studied for mixtures at normal or elevated temperatures and pressures, under which the ignition delay time of the premixture is much larger than the flame resistance time. However, in spark-ignition engines and spark-assisted compression ignition engines, the end-gas in the front of premixed flame is at the state that autoignition might happen before the mixture is consumed by the premixed flame. In this study, laminar premixed flames propagating into an autoigniting dimethyl ether/air mixture are simulated considering detailed chemistry and transport. The emphasis is on the laminar burning velocity of autoigniting mixtures under engine-relevant conditions. Two types of premixed flames are considered: one is the premixed planar flame propagating into an autoigniting DME/air without confinement; and the other is premixed spherical flame propagating inside a closed chamber, for which four stages are identified. Due to the confinement, the unburned mixture is compressed to high temperature and pressure close to or under engine-relevant conditions. The laminar burning velocity is determined from the constant-volume propagating spherical flame method as well as PREMIX. The laminar burning velocities of autoigniting DME/air mixture at different temperatures, pressures, and autoignition progresses are obtained. It is shown that the first-stage and second-stage autoignition can significantly accelerate the flame propagation and thereby greatly increase the laminar burning velocity. When the first-stage autoignition occurs in the unburned mixture, the isentropic compression assumption does not hold and thereby the traditional method cannot be used to calculate the laminar burning velocity. A modified method without using the isentropic compression assumption is proposed. It is shown to work well for autoigniting mixtures. Besides, a power law correlation is obtained based on all the laminar burning velocity data. It works well for mixtures before autoignition while improvement is still needed for mixtures after autoignition.

As promising alternatives to fossil fuels, hydrogen (H 2 ) and syngas are playing important roles in the development and control of high-efficiency, low-emission engines. Achieving accurate prediction of H 2 -fueled combustion requires a reliable chemical mechanism which, however, still exists considerable uncertainty. The laminar flame speed (LFS) has been widely employed to validate and optimize chemical mechanisms and to model turbulent premixed combustion. While in the literature there are extensive LFS data measured using the outwardly propagating spherical flame (OPF) method for hydrogen/air and syngas/air mixtures at normal temperature and pressure (NTP), the accuracy of the LFS data is not fully explored. This work aims to (i) review the uncertainty in the LFSs measured by different groups for hydrogen/air and syngas/air mixtures at NTP using the OPF method, and (ii) identify underlying sources of the uncertainty. It is found that there are considerable discrepancies in the LFS measurements, leading to these experimental data being unreliable for restraining the uncertainty of chemical models. The underlying sources of uncertainty are discussed in different flame propagation regimes and their contributions to the discrepancies are assessed individually using 1-D simulations. The results show that the contribution of ignition effects to the uncertainty depends strongly on the equivalence ratio and that the ignition effects could be one of the main sources of uncertainty for the LFSs of fuel-rich mixtures. Furthermore, it is found that the accuracy of measured LFSs is strongly affected by the choice of extrapolation model and flame radius range for extrapolation. The nonlinear extrapolation is less sensitive to the flame radius range than linear extrapolation, implying that using nonlinear extrapolation models can reduce the impact of the flame radius range selected on the uncertainty, especially for fuel-rich and/or fuel-lean mixtures. Nevertheless, strong nonlinear behavior between stretched flame speed and stretch rate still makes a major contribution to the very large discrepancies even when the nonlinear extrapolation models are used. To address the nonlinear stretch behavior, a new nonlinear extrapolation model NQH is proposed and it is shown to be more accurate than other models as pressure increases. Moreover, the recommendations on H 2 and syngas LFS measurements using the OPF method are provided.

Thermoelectric generation (TEG) has shown great potential in waste heat recovery and power supply in special environments, and has drawn increasing attention in recent years. As the basis of TEG system design and operation management, the deep understanding of its dynamic characteristics is directly related to the reliability and economy of the system. Due to the complexity of the TEG system structure, it is difficult to obtain its detailed dynamic characteristics by simplified computational fluid dynamics (CFD) simulation method. Therefore, it is necessary to build a three-dimensional dynamic numerical simulation tool that can fully describe the whole working process of TEG to provide a powerful analysis tool for TEG design and control system optimization. In this study, based on the open-source CFD software OpenFOAM, a three-dimensional thermoelectric generator dynamics solver (TEGFoam) which can describe the whole process of flow, heat transfer, fuel combustion and electricity conversion in detail was built. Through the abundant experimental data, the accuracy and usability of the proposed model and TEG solver were fully verified. The test results reveal that the numerical model can reproduce the characteristics of TEG system, and the TEGFoam can be used for structure design and operation optimization of TEG.

Thermoelectric generator (TEG) is a promising technology for waste heat recovery. Typical TEG module has a multi-material-layers sandwiched structure, in which the inherent inner-connection-and-contact (ICC) effects and side-surface heat loss may significantly degrade TEG performance. Therefore, quantitative assessment and analysis of the ICC effects and side-surface heat loss simultaneously are crucial for the optimization design of a TEG module. However, existing researches usually emphasize on the two factors separately and qualitatively. In this work, the whole ICC effects of interconnectors, solders and contact surfaces are equivalent to extra assumed ICC layers at both ends of thermoelement for the first time, and based on that a three-dimensional numerical model is established in COMSOL Multiphysics software with simultaneously considering the side-surface heat transfer coefficient ha of thermoelement. The ICC effects of a TEG module are identified by using BOBYQA optimization algorithm in COMSOL to match experimental data. It shows that, as ha increases, the recognized ICC thermal and electric resistances present linear opposite change; when ha > 12 Wm−2K−1, non-physical negative ICC electric resistance emerges. Then, based on the identified ICC effects and reasonable ha (≈5 Wm−2K−1), the results between present model and analytical theory are compared and discussed under the condition of fixed fill factor. Furthermore, multi-parameters optimization of the TEG is carried out for maximum output power, efficiency, power/cost ratio and their equally weighted multi-objective, respectively. The results show that (1) the optimal parameters such as thermoelement length Lopt and fill factor Fopt vary significantly depending on different optimization objectives; (2) the ICC effects can approximately double the Lopt and Fopt corresponding to maximum efficiency or power/cost ratio, while the ICC effects show negligible influence on the Fopt corresponding to maximum output power or equally weighted multi-objective.

A surrogate formulation methodology is proposed by directly using functional groups CH3, CH2, CH,C and phenyl to build the surrogate models for the FACE (fuels for advanced combustion engines) A an...

Effect of dimethyl ether (DME) addition on PAH and soot formation mechanisms as well as particle-size distribution function (PSDF) behavior of C2H4 premixed burner-stabilized stagnation (BSS) flame was studied. A wide range of DME addition from pure C2H4 to pure DME was considered. The sectional aerosol dynamics model with detailed gas- and particle-phase kinetic mechanism was employed for the simulations. The results indicate that soot growth rate by nucleation, and especially the H-abstraction C2H2 addition (HACA) mechanism and polycyclic aromatic hydrocarbons (PAH) condensation increased significantly inside the stagnation boundary layer, due to strong flame-wall interaction. The PSDF curve in the post-flame region was unimodal, while that in the stagnation boundary layer was bimodal. The first peak of the PSDF curve in the stagnation boundary was resulted from the enhanced nucleation rate, and the second peak was due to the intensified soot surface growth by HACA reaction and PAH condensation. The rich premixed C2H4 BSS flame did not exhibit the synergistic effect of DME addition on PAH and soot formations. Soot formation rate decreased monotonously with DME addition for the C2H4 premixed BSS flame. Topology of soot PSDF behavior of the C2H4 premixed BSS flame changed significantly when DME addition exceeded above 20%.

A comprehensive three-component surrogate for emulating the physical and combustion characteristics of three types of jet fuel, namely, S-8, Jet-A, and RP-3, has been developed by the methodology o...

To solve the problem of active power fluctuation and oscillation in the process of turbine’s throttle steam valve activity test, the mechanism and solutions were studied based on the real accident data from a thermal power unit. Theoretical analysis on the test control logic, valve actuator and valve flow characteristic was performed, and the results show that the main reason for the power fluctuation is the large deviation between actual valve flow characteristic and the designed one in the process of turbine’s throttle steam valve activity test. Moreover, the unreasonable control logic setting amplified the power fluctuation. After that, the reverse adjustment of primary frequency reset and power closed-loop control intensifies the fluctuation to power oscillation. The static and dynamic experiments both confirm that field test calibration of the valve flow characteristic is an effective way to reduce the active power fluctuation. Meanwhile, optimizing the control logic based on actuator’s characteristic and operation parameters can also relieve or even eliminate the power fluctuation and oscillation.

Nowadays, quantity of coal-fired power plant and its single unit capacity are greatly improved in China, and power grid’s frequency and peak-load regulation range become wider. Based on the basic regulation theory and unit’s characteristics, this paper indicates the limitations of unit’s original control strategies and such limitations have produced great damages to coal-fired boilers through assessment of 2 years statistical data of boiler tube explosion in regional power grid. Under field tests, the quantified boiler heat storage capacity of six typical thermal power units in the power grid is provided. Comparisons of these six coal-fired boilers are made for getting the relationships between BHSC and boilers’ tube explosion ratio under the in-depth frequency and peak-load regulation. The results show that unit’s boiler heat storage capacity varies greatly amongst boilers with different types and is inversely proportional to boiler’s installed capacity and steam parameter class, and boiler heat storage capacity is inversely proportional to boiler’s tube explosion ratio, which is in conformity with the theory analysis. After that, in-depth frequency and peak-load regulation tests of thermal power units are carried out, respectively. The results show pulverized coal-fired boiler with small boiler heat storage capacity is not suitable for in-depth frequency and peak-load regulation for the safety of power grid and unit itself, while the circulating fluidized bed boiler and pulverized coal-fired boiler with larger boiler heat storage capacity have better adaptability for these functions. Some effective control strategies of frequency and peak-load regulation are presented in load’s rate and range by boiler heat storage capacity of units.

Flexible thermoelectric generator (TEG) became an attractive technology that has been widely used especially for curved surfaces applications. This study aims an optimal design of a flexible TEG for human body application. The flexible TEG is part of a sensor and supplies required electrical power for data transmission by the sensor. The TEG module includes ink based thermoelements made of nano-carbon bismuth telluride materials. One flexible fin conducts the body heat to the TEG module and there are two fins that exchange the heat from the cold side of the TEG to the ambient. The proposed design is supposed to produce 10 μV to feed the used sensor in the thermoelectric system. In this design, the effect of heat transfer coefficient due to natural convection on the power generation is studied.

Accurate and efficient performance prediction of thermoelectric generators (TEG) is important for integrated and multi-parameter optimization especially in large-scale energy harvesting applications. In this paper, a comprehensive analytical model coupled with non-identical temperature-dependent material properties and effective heat transfer coefficient (EHTC) of both-sides heat exchangers is built to investigate the internal and external characteristics of the TEG. Parametric optimization of the TEG is carried out to maximize the output power and efficiency over a wide range of EHTCs, fill factor, and geometry of thermoelectric (TE) elements. The developed model can be efficiently solved by function solver (i.e. fsolve) in Matlab software, and its accuracy is validated with previous multi-physics numerical TEG model. The results show that statistical parameters of the TE element present non-linear behavior with variation of electrical load resistance. The optimal load ratio is larger than unit, and it reduces monotonically with increment of the cold-side EHTC, but changes inversely with the hot-side EHTC. For a fixed sum value of both-sides EHTCs, there are two different optimal ratios of the hot-side EHTC to the cold-side EHTC for maximum efficiency and power. In addition, the optimal length and cross-sectional area ratio of the TE elements are investigated with detailed analysis.

Cool flame due to low-temperature chemistry (LTC) has received great attention recently. However, previous studies mainly focused on cool flames in homogenous systems without transport or non-premixed cool flames in droplet combustion or counterflow configuration. There are only a few studies on premixed cool flames, and the transient initiation and propagation of premixed cool flames are still not well understood. In this study, the initiation, propagation and disappearance of one-dimensional premixed cool flames in dimethyl ether (DME)/air mixture is investigated through transient simulation considering detailed chemistry and transport. The premixed cool flame governed by LTC can be initiated by a hot spot. When the hot spot temperature is not high enough to directly trigger the high-temperature chemistry (HTC), only the LTC reactions take place initially and thereby a cool flame is first initiated. During the cool flame propagation, HTC autoignition occurs at the hot spot and it induces a hot flame propagating behind the cool flame. Therefore, double-flame structure for the coexistance of premixed cool and hot flames is observed. Since the hot flame propagates much faster than the cool flame, it eventually catches up and merges with the leading cool flame. A well-defined cool flame speed is found in this study. We inverstigate different factors affecting the cool flame speed and the appearance of hot flame. It is found that at higher equivalence ratio, higher initial temperature or higher oxygen concentration, the premixed cool flame propagates faster and the hot flame appears earlier. Three chemical mechanisms for DME oxidation are considered. Though these three mechanisms have nearly the same prediction of hot flame propagation speed, there are very large discrepancy in the prediction of cool flame propagation speed. Therefore, experimental data of premixed cool flame speed are useful for developing LTC.

Flexible thermoelectric generator became an attractive technology for its wide use especially for curved surfaces applications. This study proposes design of a flexible thermoelectric generator, which is part of a sensor and supplies required electrical power for human body application. The thermoelectric generator module has ink-based thermoelements which are made of nano-carbon bismuth telluride materials. Flexible fins conduct the body heat to the thermoelectric uni-couples, extended fins exchange the heat from the cold side of the thermoelectric generator to the ambient. A fully developed one-dimensional steady-state numerical model including temperature-dependent thermoelectric properties of different materials is built to reveal basic characteristics and optimal design criteria of the thermoelectric generator. Results show that ambient temperature presents significant influence on thermoelectric generator performance, but thermal resistance from blood to skin surface and contact thermal resistance at skin surface has negligible influence. A very low air velocity, e.g. 0.01 m/s is enough to ensure a considerable temperature difference through the thermoelectric element. Increasing thermoelectric elements thickness and thermoelectric module row number in a proper range can significantly enhance thermoelectric generator performance. The maximum output power can reach 0.2 μW/cm2, which indicates the proposed design is promising for supplying human body sensors. In addition, the basic optimal design criteria of the flexible thermoelectric generator and its relative merits are discussed and presented.

Compressed air energy storage is a promising large-scale energy storage technology. Integrating ejectors in the energy-release stage of compressed air energy storage systems is widely recognized as an effective way to improving system efficiency; however, there is a lack of detailed modelling and analysis regarding the optimal working parameters of ejectors. In this study, the thermodynamic models of a 10 MW thermal-storage compressed air energy storage system with or without an ejector (system I and system II, respectively) are established under constant-pressure operation. A one-dimensional semi-empirical model is used to determine the maximum entrainment ratio of the ejector under specific conditions of motive air pressure, a low-pressure air source, and constant-pressure operation. The results show that (1) in system I, the maximum entrainment ratio is positively correlated with motive air pressure, while the total energy-release time, the total amount of entrained low-pressure air, and the total energy-release work present parabolic-like variations as motive air pressure increases; (2) different low-pressure air sources change these performance parameters significantly; (3) compared between systems I and II, the rise amplitude of round-trip efficiency and the profit are positively correlated with motive air pressure for most constant-pressure operations; (4) the optimal rise amplitude of round-trip efficiency and profit of the ejector can reach around 10% and 275$, respectively. In addition, two methods to determine the optimal low-pressure air source for the ejector are proposed for real and design-stage compressed air energy storage systems, while three principles to determine the optimal motive air pressure of the ejector are proposed through a comprehensive analysis of performance parameters.

The kinetics and soot and NO x emission characteristics of the CH 4 /dimethyl ether (DME) jet diffusion flames (JDFs) are studied by experiments and simulations with a detailed chemical mechanism. The results showed that decomposition of DME in the pyrolysis zone generated massive CH 3 , which changed the local flame structure and soot-correlated chemistry to some extent. Due to reductions of the incipient species concentrations including benzene (A1), pyrene (A4), C 3 H 3 , and C 2 H 2 , soot loading of the CH 4 JDF decreased by reducing margins with DME addition. A1 and thus soot formation rates due to DME addition were most sensitive to the recombination reaction of C 3 H 3 (C 3 H 3 + C 3 H 3 = A1). With respect to the CH 4 /DME JDFs, NO x was emitted mainly through the thermal and prompt pathways. The thermally-generated EI NOx increased exponentially with DME addition because of the increasing enhancement of OH concentration in the radical pool. By contrast, the promptly-generated EI NOx decreased in reducing margins with DME addition because of the reducing decrease in CH concentration. The synergistic effect of DME addition on the total NO x emission, i.e. the overall EI NOx decreased firstly and then increased with DME addition, was examined in this paper. Additionally, it is reported that the 40%CH 4 /60%DME case was comprehensively optimal in terms of soot and NO x emission reductions.

Water vapor dilution has great impact on fundamental combustion processes such as ignition, flame propagation and extinction. In the literature, there are many studies on how water vapor addition affects flame propagation and extinction limit. However, the influence of water vapor addition on ignition receives little attention. In this study, numerical simulations considering detailed chemical mechanisms are conducted for the ignition of methane, n -butane and n -decane/air/water vapor mixtures. The emphasis is spent on examining the effects of water vapor dilution on the ignition of these fuels at normal and reduced pressures. The minimum ignition energies (MIE) at different dilution ratios and initial pressures are obtained. It is found that at normal and reduced pressures, the MIE is proportional to the inverse of pressure and it increases exponentially with water vapor dilution ratio. A general correlation among the MIE, pressure and dilution ratio is proposed for each fuel. Furthermore, for stoichiometric methane/air/water vapor mixtures, the chemical and radiation effects of water vapor dilution are isolated and quantified. It is found that the three-body recombination reaction greatly increases the MIE and reduces the dilution limit.

In this paper, the moderate or intense low-oxygen dilution (MILD) technology was employed to reduce NOx emission index of the DME flame, whose NOx emission was expected high due to its higher adiabatic flame temperature. Experiments and modeling were conducted to study NOx emission mechanism of the DME-MILD jet diffusion flame. Various co-flow temperatures ( T c o ∗ ) and oxygen concentrations ( X O 2 ∗ ) were involved to investigate dependence of NOx emission mechanism on hot dilution level. NOx formation pathway in all subzones was clarified, employing the reaction path and sensitivity analyses. The results showed that for the DME-MILD jet flame, NOx was generated mainly through the NNH and N2O pathways, which was rather different from the traditional DME jet diffusion flame. EINOx increased gradually with the increment in X O 2 ∗ or T c o ∗ . A strong NO NO2 conversion process and ultra-clean performance were verified for the DME-MILD jet flame.

High-temperature thermoelectric generation (TEG) system that driven by combustion is an efficient way for simultaneously providing heat and electric power, but its application prospect is restricted by very low ratio of electric power to heat supply. In this work, an annular high-temperature TEG system is extended by adding medium-temperature TEG modules, and correspondingly a novel two-stage annular multi-hole burner with baffle construction is specially designed to replace original single-stage annular multi-hole burner. The optimal geometric dimensions of the new burner are obtained by conducting a simplified 2D model in ANSYS. Experiment results show that, due to the new burner design, the inner-wall temperature of the high-temperature TEG module is averagely increased by 73 K, bringing an electric power rise of 14.8%; in comparison with the single-stage high-temperature TEG system, the total electric power generation of the high- and medium-temperature coupled TEG system is greatly improved by 73.8%. To further improve the electric performance of the high-temperature TEG module, a well-developed multi-physics field coupled model which containing 2D combustion reactions in the new burner and 1D multi-physical thermoelectric (TE) effects is established to reveal the optimal length and number of TE element, and to assess the optimization of cold-side heat sink.

Efficient and multiple analysis of receptor protein dimers is highly necessary, due to their important role in the occurrence and development of cancer. Herein, we report a turn-on strategy to visualize human epidermal growth factor receptor (HER) dimers on cell surfaces. By taking advantages of specific aptamer recognition and proximity-induced fluorescence activation of DNA-templated sliver nanoclusters (DNA/AgNCs) by guanine (G)-rich sequence, we attached the two kind of DNA/AgNCs sequence with different fluorescence properties to the corresponding HER aptamer to form aptamer-functionalized AgNCs probes, and attached G-rich sequence to the corresponding HER aptamer as enhancer. In the presence of protein dimers, after aptamer specific recognition and binding, it will draw the dark AgNCs probes close to the G-rich probes and then excite corresponding fluorescence. As a result, this approach has successfully realized imaging of HER2:HER2 homodimer and HER2:HER3 heterodimer at the same time, which was provided a new idea for the simultaneous detection of multiple HER2 dimers in situ. This AgNCs-based light up strategy provides a potential tool for further investigation of protein dimerization on cell surface, which is more conducive to the mechanism research, accurate classification and treatment of cancer.

Cas12a shows great promise in DNA sensing applications due to its target-triggered collateral trans-cleavage activity. But the cleavage effect towards probes modified on nanomaterials is less understood. In this work, an analogy analysis is performed to explore the cleavage properties of Cas12a system on the surface of nanomaterials by using gold nanoparticles (AuNPs) and graphene oxide (GO). The fluorescence of FAM-tagged probes is quenched by nanomaterials due to fluorescence resonance energy transfer (FRET). The trans-cleavage activity of Cas12a was activated to promiscuously digest the single-stranded part of probes, thereby modulating FRET effect between FAM labels and nanomaterials. The results showed that GO had better quenching ability and Cas12a-induced fluorescence recovery than AuNPs, and the double-stranded DNA probe with staggered end can lead preferable trans-cleavage efficiency, proving low steric hindrance of nanomaterials and appropriate orientation of probes play critical roles in Cas12a-modulated FRET with nanomaterials. Then, by integrating Cas12a system and GO-based post-quenching strategy, a DNA biosensor was developed with extremely high fluorescence response and low initial background. It is expected that this work will be of particularly useful for investigation of the interaction between CRISPR/Cas proteins and nanomaterials, as well as developing CRISPR-based point-of-care (POC) diagnostic platforms.

A novel mechanism reduction method that integrates path flux analysis with multi generations and sensitivity analysis (MPFASA) is proposed to reduce the complex detailed chemistry and to generate skeletal mechanisms. At first, the path flux analysis with multi generations (MPFA) method is used to efficiently reduce detailed mechanisms; then the sensitivity analysis (SA) method is applied to further eliminate the redundant species and their related reactions on the basis of the skeletal chemistry obtained by the MPFA method. Detailed mechanisms of methane and n-heptane are reduced by the MPFASA method, which are validated in the context of autoignition and perfectly stirred reactor for methane/air and n-heptane/air mixtures, over a wide range of operating conditions. The comparison shows that the skeletal mechanisms generated by the MPFASA method can well reproduce the results of detailed mechanisms and contain a much smaller number of species and reactions than those obtained by using the MFPA met...

The laminar flame speed is one of the most important combustion properties of a combustible mixture. It is an important target for chemical mechanism validation and development, especially at fuel-lean and high pressure conditions. In this study, the laminar flame speeds of two types of lean high-hydrogen syngas/oxygen/helium mixtures were measured at normal and evaluated pressures up to 10 atm using a dual-chambered high pressure combustion facility. Similar to experiments, numerical simulations of outwardly spherical flame propagation were conducted. Three chemical mechanisms for syngas available in the literature were considered in simulation and their performance in terms of predicting the stretched flame speeds, laminar flame speeds and burned Markstein lengths was examined through comparison between experimental and simulation results. It was found that at both normal and elevated pressures, the present experimental results agree well with those predicted by simulations using these three chemical mechanisms. Therefore, these chemical mechanisms for syngas can well predict the laminar flame properties of lean high-hydrogen syngas. Besides, the laminar flame speeds measured in the present work were compared with those measured from the heat flux method and large difference was observed.

An improved path flux analysis with a multi generations (IMPFA) method is proposed to eliminate unimportant species and reactions, and to generate skeletal mechanisms. The production and consumption path fluxes of each species at multiple reaction paths are calculated and analysed to identify the importance of the species and of the elementary reactions. On the basis of the indexes of each reaction path of the first, second, and third generations, the improved path flux analysis with two generations (IMPFA2) and improved path flux analysis with three generations (IMPFA3) are used to generate skeletal mechanisms that contain different numbers of species. The skeletal mechanisms are validated in the case of homogeneous autoignition and perfectly stirred reactor of methane and n-decane/air mixtures. Simulation results of the skeletal mechanisms generated by IMPFA2 and IMPFA3 are compared with those obtained by path flux analysis (PFA) with two and three generations, respectively. The comparisons of ignition ...

The maximum pressure rise rate during gas explosions in enclosures and the deflagration index are important explosion characteristics of premixture. They can be used to quantify the potential severity of an explosion. However, there are large discrepancies in the deflagration index measured by different researchers for the same methane/air or hydrogen/air mixture. In this study, outwardly propagating spherical flames in a closed vessel are simulated by considering detailed chemistry as well as temperature-dependent thermal and transport properties. From simulation, the maximum pressure rise rate and deflagration index of methane, hydrogen and their mixtures are obtained. The influence of equivalence ratio, initial temperature and initial pressure on the maximum pressure rise rate and deflagration index is examined. It is found that the deflagration index has not been accurately measured in previous experiments, and that experiments conducted in cylindrical vessels have under-predicted greatly the deflagration index. For hydrogen/methane mixtures with hydrogen blending level above 70%, the deflagration index is observed to increase exponentially with hydrogen blending level. Moreover, the deflagration index is found to be greatly affected by initial pressure; while the initial temperature has little influence on deflagration index. Finally, based on theoretical analysis we propose a correlation to calculate the maximum pressure rise rate and deflagration index of methane at a broad range of initial pressure. The performance of this correlation is examined and it is demonstrated to provide accurate prediction.

A methodology of surrogate fuel formulation by directly using molecular structure and functional groups for both oxygenated and hydrocarbon fuels is proposed and investigated. The novelty of this method is to construct surrogate fuel mixtures by directly matching the molecular structure and the key functional groups instead of using the combustion property targets explicitly. This method is tested by using two different classes of fuels, biodiesel and jet fuel. For biodiesel, by using four functional groups such as CH3 , CH2 , CH2 CH CH , and COO CH3, a surrogate mixture of methyl-9-decenoate, 1,4-hexadiene and n-dodecane is formulated to demonstrate the efficacy of this method by comparing the resulting gas phase combustion targets between the formulated surrogate and biodiesel. For jet fuels, five functional groups such as CH3, CH2, CH, C, and phenyl were used to construct the Princeton 1st and 2nd generation surrogate jet fuel mixtures. The simulated results are compared with the experimental data and the results predicted by other surrogate fuel formulation methods. The comparisons show that the present method can formulate surrogated mixtures of both oxygenated and hydrocarbon real fuels and reproduce the combustion characteristics. Therefore, this method can be used not only for biodiesel and jet fuels, but also for other alternative fuels.

In this paper, the flame length (Lf), width (Wf), and volume (Vf) behaviors of the jet diffusion flame were experimentally and theoretically studied. Various fuel nozzle diameters (df), fuel jet velocities (uf), and air co-flow velocities (uco) were involved in the experiments to investigate their impacts on flame characteristics systematically. Additionally, the analytical solutions for the flow field, fuel concentration, Lf, Wf, and Vf of the jet diffusion flame were derived by theoretical analysis. The results show that flame shape and dimensions of the jet diffusion flame depended on fuel jet Reynolds number (Ref) inherently. At the laminar regime, the dimensionless flame length normalized by df (Lf*) was proportional to Ref. At the laminar–turbulent transitional regime and fully-turbulent regime, Lf* kept nearly constant. The dimensionless flame width (Wf*) remained basically unchanged at the laminar or fully-turbulent regime; but it increased fairly quickly with the increment in Ref at the laminar–turbulent transitional regime. The dimensionless flame volume (Vf*) increased linearly with Ref at the laminar regime, and parabolically with Ref at the laminar–turbulent transitional regime. At the fully-turbulent regime, Vf* kept constant. Besides, with the increase in uco, Lf* maintained nearly unchanged, and Wf* decreased exponentially. Based on the above behaviors, new forms of correlations for Lf*, Wf*, and Vf* of the jet diffusion flame were proposed presently. Comparisons of these correlations with the existing ones in the literature were also conducted in this paper. Moreover, Lf*, Wf*, and Vf* correlations for the dimethyl ether/air jet diffusion flames were developed herein.

In this work, the spontaneous ignition of high-pressure accidentally released hydrogen in a one-dimensional tube was numerically studied using the high-order WENO reconstruction method, multi-component diffusion model and detailed kinetics mechanism. The result shows that the spontaneous ignition of high-pressure hydrogen jet is essentially a non-premixed ignition process between compressed hot air and expanded low-temperature fuel. It is found that increasing the molecular weight of the fuel can greatly reduce the air temperature and thereby improve the storage safety. Further analysis of the reacting mixing layer reveals that the autoignition occurs in a fuel-lean condition where the fuel mass fraction is less than 0.02. During the reaction front propagation, two types of flames are observed in the H2/air diffusion layer, which are a diffusion flame near the stoichiometric position and a premixed flame in the fuel-rich space. The reaction pathway analysis demonstrates that the two types of flames are controlled by the low temperature radical destruction reaction (R1: H + O2(+M) HO2(+M)) and the high temperature radical formation reaction (R9: H + O2 O + OH), respectively. Moreover, the sensitivity evaluation of different reactions on the ignition delay indicates that the two reactions also play a dominate role on the overall combustion rate. In the end, the flame front displacement speed calculation shows that the contribution of diffusion to the reaction front evolution is always slightly greater than that of chemistry except the ignition timing.

The early CO2 formation is a characteristic for the methyl esters group of biodiesel. A new reaction pathway was added to skeletal methyl esters mechanism for improving the prediction of early CO2 formation. The methyl decanoate, methyl 9-decenoate, methyl 5-decenoate and methyl stearate sub-mechanisms with added reaction pathway were optimized by adjusting reaction rate constants for more accurate prediction. Based on decoupling methodology, a new skeletal mechanism for methyl butanoate was constructed by integrating detailed H2/CO/C1 sub-mechanism, reduced C2-C3 sub-mechanism and methyl butanoate sub-mechanism. These improved mechanisms were validated well in a shock tube for ignition delay times and in a jet-stirred reactor for major species concentrations over wide operating conditions, respectively. When compared to available mechanism in the literature, the present mechanism has good improvement for the prediction of early CO2 formation. Moreover, the effect of newly added reactions on ignition delay times was analyzed by sensitivity analysis method. Added reaction of Fuel Radical = ME2J + Short Chain Hydrocarbon mainly causes the influence on ignition delay time at high temperature, and decrease the reactivity of oxidation of fuel radical. The reaction of OCHO + M H + CO2 + M dominates the early CO2 formation, and makes less contribution to production of CO2 with higher temperature. The improved mechanisms, which consist of methyl esters from a relatively short to long carbon chain, have a good performance for the prediction of early CO2 formation.

An efficient surrogate fuel formulation methodology, which directly uses the chemical structure information from nuclear magnetic resonance (NMR) spectroscopy analysis, has been proposed. Five functional groups, paraffinic CH2, paraffinic CH3, aromatic C-CH, olefinic CH-CH2, and cycloparaffin CH2, have been selected to show the basic molecular structure of the fuels for the advanced combustion engines (FACE) fuels. A palette that contains six candidate components, n-heptane, iso-octane, toluene, 2,5-dimethylhexane, methylcyclohexane, and 1-hexene, is chosen for different FACE fuels, based on the consideration that surrogate mixtures should provide the representative functional groups and comparable molecular sizes. The kinetic mechanisms of these six candidate components are chosen to assemble a detailed mechanism of each surrogate fuel for FACE gasoline. Whereafter, the accuracy of FACE A and F surrogate models was demonstrated by comparing the model predictions against experimental data in homogeneous ignition, jet stirred reactor oxidation, and premixed flame.

An automated hierarchical framework, Global Pathway Analysis (GPA), is presented to understand complex chemical kinetics. The behaviour of the reacting system at macro level is bridged to the elementary reaction level by Global Pathways, which are the chemical pathways from an initial reactant species to a final product species. For each Global Pathway, its dominancy and effect on the system, such as those on the production or consumption of radicals, are quantified to understand its contribution to the system. Four examples are presented as demonstration: First, the classical second explosion limit of hydrogen is found to be resulted from the change of dominancy of a pressure-dependent Global Pathway, which consumes radical via H + O2 + M = HO2 + M reaction. Next, it is found that the negative temperature coefficient (NTC) regime of n-heptane is resulted from the competition between a low-temperature Global Pathway and a high-temperature Global Pathway. Third, a non-monotonic relation between autoignition delays and toluene ratio in toluene/n-decane mixture is analysed. This automated framework has been placed in public domain. Reduced kinetic models can be generated based on Global Pathways too. Finally, this methodology is demonstrated using DNS simulation results of the extinction and re-ignition of a turbulent non-premixed flame. The differences between simulation results are investigated using two different kinetics models via the analysis of global pathways.

Behaviors of premixed CH4/air flame in mesoscale channels with and without cavities were experimentally investigated. No stable symmetric flame was observed in the channel without cavities and flame is prone to inclining and pulsating. In contrast, flame can be effectively anchored in the presence of cavities. When the inlet velocity is increased sufficiently high, curved fluctuating flame front appears. Blow-off limits of the channel with cavities are several times larger than the corresponding burning velocity of incoming CH4/air mixture, while the flashback limits are almost the same as the straight channel counterparts. These indicate that the cavities have a strong ability to extend the operational range of inlet velocity. Numerical simulation demonstrates that combined effects, i.e., the formation of recirculation zone and low velocity zone in the cavities, preferential diffusion effect, as well as the preheating effect of upstream inner walls, are major mechanisms responsible for flame stabilization. Furthermore, numerical result reveals that large strain rate and heat loss rate exist at the transition point between the ramped cavity wall and the downstream inner wall, which results in flame splitting at high inlet velocity due to local extinction, and eventually leads to flame blow-off. In summary, the combustion behaviors in the mesoscale channel with cavities strongly depend on the interactions between the reaction zone, conjugate heat exchange and flow field. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.