Microwave-assisted ignition (MAI) is a promising technology to improve the ignition stability in internal combustion engines under lean conditions. To investigate the interplay between the microwave pulses and the electrical characteristics of ignition plasma, the high-time-resolved electrical characteristics of MAI are measured based on the discharge voltage and current profiles with microwave power varying from 0 to 1000 W. The effects of microwave pulse on the electrical characteristics in the breakdown and glow discharge phases are discussed respectively. The results show that the microwave-induced-voltage-decline (MIVD) occurs during the glow discharge phase, which originates from the increment of free electrons and the additional microwave field. However, this voltage decline is insignificant in the breakdown phase. Moreover, as the free electron number reaches a critical value, a shining plasma can be observed between the gap of electrodes and the voltage decline is stabilized to a “saturated voltage curve”. Ultimately, the effect of microwave plasma on the enhancement of ignition kernel area is explored. The result indicates that the enhancement effect increases with plasma duration rising. Those enhancements of earlier-generated plasmas are more significant than those of subsequent plasmas due to the distance limit of the plasma propulsive effect.

Preheating combustion/gasification technology enables efficient and environmentally friendly utilization of coal resources, but the research on the flow and reaction characteristics of high-temperature gas-solid mixed fuels produced by the technology still needs to be further explored. The flame can intuitively show the jet, mixing and reaction of fuel and oxidant at the outlet of the burner. Therefore, this study investigates the jet flame characteristics of high-temperature gas-solid mixed fuels on a self-designed test platform. High temperature and gas-solid mixing are the special features of the fuel in this study, which are different from other studies. Therefore, we first qualitatively compare the jet flame characteristics of high-temperature gas-solid mixed fuel with traditional fuel. The preliminary results indicate that high-temperature gas-solid mixed fuels exhibit higher reactivity and a faster reaction rate compared to pulverized coal. As a result, it shows different characteristics in flame shape, ignition delay and ignition mode. The jet flame shape of high-temperature gas-solid mixed fuels closely resembles that of the pulverized coal group combustion flame, displaying a continuous cloud-like structure similar to the shape of a gas-fueled flame. Furthermore, the flame image does not show any significant ignition delay phenomenon. Building upon these results, this study also quantitatively analyzes the geometric parameters, temperature distribution and oscillation frequency of the high-temperature gas-solid mixed fuel jet flame under different secondary air equivalence ratios and primary air equivalence ratios, so that we can have a deeper understanding of the influence of operating parameters on the combustion/gasification process.

Experimental and numerical investigations have been carried out on the effects of multi-swirl interaction patterns on self-excited unstable combustion characteristics based on a five-nozzle can combustor. The multi-swirl interaction patterns include equal swirl intensity interaction and strong-weak swirl interaction. The thermo-acoustic instability characteristics indicate that increasing the central nozzle swirl intensity transforms the interaction pattern from equal swirl intensity interaction to strong-weak swirl interaction, which can significantly weaken the thermo-acoustic coupling effect under low equivalence ratio conditions, and substantially reduce the dynamic pressure amplitude during unstable combustion. The instantaneous flame structures show that the multi-swirl flames exhibit chaotic oscillations under low equivalence ratio conditions. With equivalence ratios greater than 0.71, a clear flame interaction boundary appears, and the flames can exhibit periodic oscillations in a regular structure. However, different interaction patterns result in the completely different phase oscillations in the central and outer flames. The time-averaged flame structures also indicate that strong-weak swirl interaction leads to an increase in the flame angle and a decrease in the flame length for both the central and outer flames, and the variations in the flame angle and length have great impacts on the thermo-acoustic instability mode. The fuel-staging combustion characteristics demonstrate that the instability combustion conditions with a dominant frequency of 100 Hz are greatly broadened by the strong-weak swirl interaction pattern, and the overlapping operating conditions between this mode and other modes are greatly increased. This implies that it is more flexible to adjust the thermo-acoustic unstable mode, which is conducive to the passive suppression of thermo-acoustic instability.

Hybrid deflagration/auto-ignition flame structures coexist in the combustion of advanced engines. Decoupling exergy destruction caused by different irreversible processes under varied flame regimes is thus important for understanding engine thermodynamics. In this study, the flame propagation modes for the premixed DME/air mixtures are numerically investigated under engine-relevant conditions. Local entropy generation and exergy destruction characteristics are compared under different flame structures. Results reveal that as the typical premixed flame transition towards auto-ignition front, the exergy destruction from heat conduction and species mass diffusion gradually vanish and are dominated by chemical reaction. The distributions of temperature and species mole fraction in the flame domain are analyzed to clarify the exergy destruction behaviors caused by heat conduction and mass diffusion. Furthermore, by dividing the DME oxidation process into four stages, the main reaction channels that contribute to the increase in exergy destruction from chemical reaction have been identified. It is found that the production and consumption of CH₂O and HȮ₂ radical dominate the exergy destruction behavior during DME oxidation. On this basis, the kinetic mechanism of low-temperature chemistry causing greater exergy destruction is elucidated. Specifically, low-temperature chemistry leads to significant exergy destruction due to (a) the large irreversibility of itself and (b) (mainly) the enhancement of H₂O₂ loop reactions by low-temperature reaction intermediates. Thus the reduction of combustion irreversibility is promising to be achieved by reasonably regulating the fuel oxidation path.

The ignition tendency of diesel fuels is highly sensitive to ambient conditions and fuel properties. In this study, the ignition characteristics of different diesel surrogate fuels with the same derived cetane numbers (DCN) were measured and compared in varied thermodynamic and oxidizing environments. The combustion pressures, heat release rates, ignition delays, and combustion delays of the test fuels were compared. The experimental results showed that the diesel surrogate fuels with the same DCNs exhibit similar ignition propensity at standard DCN test conditions. Further, for the test conditions of high cetane fuels, high ambient temperatures, and sufficient oxygen concentrations, surrogate fuels with the same DCN have similar ignition behaviors, and using the DCN to evaluate fuel ignition tendency is appropriate. However, for the test conditions of low cetane fuels, low ambient temperatures, and reduced oxygen concentrations, different ignition behaviors are observed for the surrogate fuels with the same DCN, so at these conditions using DCN as the evaluation index for fuel ignition tendency may lead to higher uncertainty.

Integrating a high proportion of intermittent renewable energy provides a solution for the higher peak-shaving capacity of coal-fired power plants. Oxy-fuel combustion is one of the most promising carbon reduction technologies for coal-fired power plants. This study has proposed a novel oxy-fuel power plant that is coupled with both liquid O₂ storage and cold energy recovery systems in order to adapt to the peak-shaving requirements. The liquid O₂ storage system uses cheap valley electricity to produce liquid O₂ for a later use in the peak period to enhance the peak-shaving capacity. Meanwhile, the cold energy recovery system has been introduced to recover the physical latent energy during the phase change of liquid O₂ to increase the power generation in the peak period. Technical economies of three power plants, i.e. a 330 MW (e) oxy-fuel power plant as reference (Case 1), the same power plant coupled with only liquid O₂ storage system (Case 2), and the same power plant coupled with both liquid O₂ storage and cold energy recovery systems (Case 3), have been analyzed and compared. Thermodynamic performance analysis indicates that the peaking capacity of Case 3 can reach the range of 106.03 to 294.22 MW (e), and the maximum peak-shaving coefficient can be as high as 2.77. Exergy analysis demonstrates that the gross exergy efficiency of Cases 2 and 3 reaches 32.18% and 33.57%, respectively, in the peak period, which are significantly higher than that of 26.70% in Case 1. Economic analysis shows that through selling the liquid O₂ and liquid CO₂, combined with carbon trading, the levelized cost of electricity (LCOE) of the three cases have been greatly reduced, with the lowest one of 30.90 USD/MWh shown in Case 3. For a comprehensive consideration, Case 3 can be considered a future reference of oxy-fuel power plant with the best thermodynamic and economic performance.

The low net efficiency of oxy-fuel circulating fluidized bed (CFB) combustion is mainly due to the addition of air separation unit (ASU) and carbon dioxide compression and purification unit (CPU). High oxygen concentration is one of the effective methods to improve the net efficiency of oxy-fuel combustion technology in CFB. In this research, a series of calculation and simulation were carried out based on Aspen Plus platform to provide valuable information for further investigation on the CFB oxy-fuel combustion system with high oxygen concentration (40%, 50%). A CFB oxy-fuel combustion system model with high oxygen concentration was established including ASU, CPU and CFB oxy-fuel combustion and heat exchange unit. Based on the simulation data, energy and exergy efficiency were analyzed to obtain the following results. The cross-sectional area of furnace and tail flue of 50% CFB oxy-fuel combustion boiler are 43% and 56% of the original size respectively, reducing the construction and investment cost effectively. With the increase of oxygen concentration, the net efficiency of power generation increased significantly, reaching 24.85% and increasing by 6.09% under the condition of 50% oxy-fuel combustion. The total exergy loss increases with the increase of oxygen concentration. In addition, the exergy loss of radiation heat transfer is far higher than convection heat transfer.

Pressurised oxy-fuel combustion (POFC) is a clean and efficient combustion technology with great potential. Due to the recycling of flue gas, the concentration of steam in the flue gas is higher than that of conventional combustion, which enriches the free radical pool in the flue gas and thus affects the emission of gaseous pollutants. Therefore, further research into the effect of high steam concentrations on NO_x emission mechanisms in POFC is necessary. In this work, a fixed-bed reactor was used to conduct combustion experiments of volatiles and combined with chemical kinetic models to study the NO release characteristics for different pressures and steam concentrations in an O₂/CO₂ atmosphere at 800°C/900°C temperature. The results of the study indicated that the volatile nitrogen comes from the pyrolysis of part of pyrrole, pyridine, and all quaternary nitrogen in coal. The increase in temperature promoted the formation of NO during combustion. Higher pressure affects the main reaction pathway for NO formation, promoting NO consumption by HCCO and C₂O groups while enhancing the overall NO reduction. Steam promoted NO consumption by NCO. In addition, steam increased the amount of H/OH groups during the reaction, which affected both NO formation and consumption. However, from the overall effect, the steam still inhibits the emission of NO.

The large-scale integration of new energy generation has put forward higher requirements for the peak-shaving capability of thermal power. The circulating fluidized bed (CFB) depends on the advantages of a wide load adjustment range and low cost of pollutant control to become a good peak shaving power supply. However, the large delay and inertia caused by its unique combustion mode make it very difficult to change the load quickly. To further understand the factors that affect the load change of CFB, and explore the method of increasing CFB load change rate, the load change experiment on the combustion side was carried out in the 0.1 MW CFB experiment platform. The influence law of bed material amount and fuel particle size on load change of CFB combustion side was revealed for the first time. The results indicated that the increase of bed material amount was beneficial to improve the load change rate on the combustion side of CFB and reduce the carbon content of fly ash, but had no obvious effect on NO_x emission. When the bed height at rest increased from 200 mm to 400 mm, the load change rate of the CFB combustion side load from 50% to 75% increased from 0.78%/min to 1.14%/min, and the carbon content of fly ash at 75% load decreased from 26.6% to 24.9%. In addition, the reduction of fuel particle size positively improved the load change rate on the combustion side of the CFB and reduced NO_x emission but had a negative effect on reducing the carbon content of fly ash. When the fuel particle size decreased from 0–1 mm to 0–0.12 mm, the load change rate of CFB combustion side load from 50% to 75% increased from 0.78%/min to 1.09%/min, and the NO_x emission and carbon content of fly ash at 75% load decreased from 349.5 mg/m³ to 194.1 mg/m³ and increased from 26.6% to 31.8%, respectively.

The operating principles of Circulating Fluidized Bed (CFB) boilers involve a significant amount of heat accumulation, which forms the thermal inertia of the boiler and hinders the improvement of its variable load response rate. This study aims to characterize the thermal inertia of CFB boilers by evaluating the change in the boiler’s heat accumulation corresponding to the change in unit power generation. The thermal inertia of a 330 MW CFB boiler was determined through the collection of operating data under four different operating conditions of 30%, 50%, 75%, and 100% load. The study proposes to substitute the existing refractory material with a metal grille to reduce the thermal inertia of the boiler. The effect of the metal grille on heat transfer was confirmed through verification on a 440 t/h CFB boiler, and its performance change and thermal inertia reduction were further predicted. The results indicate that over 50% of the total thermal inertia of CFB boilers originates from the refractory material. The use of metal grille in place of refractory material improved heat transfer in the furnace, resulting in a decrease of the furnace chamber temperature by 13°C in the 330 MW CFB boiler. This reduction of thermal inertia by 30%–35% will facilitate faster load lifting and lowering of the boiler, fulfilling the requirement for flexible peaking.

Thermochemical energy storage based on CaO/CaCO₃ cycles has obtained significant attention as an alternative energy storage solution for concentrated solar power plants. In view of the applicability of fluidized bed reactors for CaO/CaCO₃ heat storage, it is imperative to study the factors related to the heat release performance of CaO. This work presents an exothermic experiment on calcined limestone under fluidization, exploring the impact of initial temperature, CO₂ concentration, particle size, superficial gas velocity, and number of cycles on the exothermic performance of CaO. The result indicates that CaO with high initial temperature leads to higher exothermic temperature, with better exothermic stability under cycles. An optimal initial temperature range of 600°C–650°C exists with an actual CaO conversion rate deviating merely 2% from theoretical conversion. Higher CO₂ concentration augments the exothermic temperature and rate of CaO, while also improves the effective conversion of CaO. Nevertheless, high CO₂ concentrations exacerbate the sintering and deactivation of CaO. High superficial gas velocity and small particle size shorten the exothermic time by increasing heat dissipation, but has minimal effect on the exothermic properties. Finally, the exothermic properties of CaO under fluidized and static conditions are studied. The result shows that exothermic temperature and exothermic rate of CaO under fluidization are enhanced, displaying higher heat storage performance than that under static state. This study provides valuable insights for optimizing the exothermic performance of CaO in fluidized bed reactors, contributing to advanced thermochemical energy storage for concentrated solar power plants.

Controversies still exist over the necessity of equipping with an emergency water supply system in the supercritical circulating fluidized bed/CFB unit. To resolve the dispute, research on the safety of the heating surfaces in the supercritical CFB boiler during the electricity failure accident under the assumption of not putting the emergency water supply system into use must be conducted. However, due to the low incidence rate of this accident, no relevant data have been reported yet. To provide useful data for the related research, a breakdown accident of the main feed water pump that happened in a 350 MW supercritical CFB boiler was introduced in this work. The analysis of the physical processes in both the furnace and water side of the boiler during this accident was performed. Then the discussion on the similarities and discrepancies between the two accidents was carried out. It was found out that with appropriate handling, the data collected in two periods of the breakdown accident of the main feed water pump can provide a reference for the verification of the prediction model of the electricity failure accident. Finally, a preliminary prediction model was established as the first step of the verification work.

In this paper, a numerical model was built by ANSYS FLUENT to investigate the heat transfer performances of supercritical water in a circumferential non-uniformly heated vertical tube. The Shear Stress Transport (SST) k-ω model was adopted for describing turbulence. The operating parameters are chosen according to a 660 MW ultra-supercritical CFB boiler. The heat transfer performances under different operating parameters, such as boiler load, flow direction and heat flux distribution are analyzed. The temperature and heat flux on inner wall varies along the circumference and show symmetric distributions. The overall heat transfer performances at each cross section are better than the local heat transfer performance of midpoint of heating side. Flow direction has a great influence on heat transfer performance; it changes the radial distribution of axial velocity and then affects the turbulence distribution. Therefore, upward flow condition shows a better heat transfer performance. Smaller heat flux improves both the overall and local heat transfer performances. Reducing the heat flux area is not conducive to the overall heat transfer, but does not affect the local heat transfer at the midpoint of heating side. Finally, a new correlation is fitted based on the simulated results of supercritical water heat transfer with circumferential non-uniform heat flux distributions.

In this paper, an online tracking simulation system for the 660 MW ultra-supercritical circulating fluidized bed (USCFB) boiler is established, and a tracking simulation test is conducted for the cold start-up process of the boiler. The system comprises two parts: the USCFB boiler model and a tracking mechanism based on sliding mode control algorithm. The USCFB boiler model includes a water-steam system, an air-flue gas system, a material supply system, and an ash circulation system. The online tracking simulation system receives the same control signal as the plant and runs synchronously in digital space. The tracking mechanism updates model parameters to eliminate deviations between simulation values and measured values. The SMC-based multi-input, multi-output algorithm is based on a state-space model, providing two distinct advantages. Firstly, it enables more efficient elimination of deviations; secondly, it exhibits robustness against uncertainties associated with simulation model behavior and measurement noise. Finally, this paper conducts tracking simulation research on the cold start-up process of the boiler.

Based on the fully three-dimensional (3-D) and two-dimensional (2-D) comprehensive CFD (Computational Fluid Dynamics) combustion models for a circulating fluidized bed boiler, a simplified 3-D computational domain considering the corrections of furnace side wall openings is proposed. It aims to compensate for the deficiencies of the large amount of computation in the fully 3-D model and improve the air and gas flow treatments at the openings in the simplified 2-D model. Three different computational domains, named as the fully 3-D model, simplified 3-D model and 2-D model, were implemented to perform a comparative CFD analysis in an ultra-supercritical circulating fluidized bed boiler including the hydrodynamics, penetration depth of secondary air, temperature and species distribution. The simulation results computed by the simplified 3-D model yield better agreement with the fully 3-D simulation results than those of the 2-D model. The simplified 3-D model is recommended as an alternative computational domain for the conventional 2-D model in the numerical simulation of large-scale circulating fluidized bed boiler.

Coal slime can be disposed in quantity and fully utilized in a well-designed circulating fluidized bed (CFB) boiler, but the nitrogen oxides (NO_x) and sulphur dioxide (SO₂) emissions generated in the combustion of coal slime have contributed to serious atmospheric pollution. High Temperature & Post-combustion Technology, a novel and high-efficient way to reduce the NO_x emission in the process of combustion, is applied to a 75 t/h CFB boiler burning exclusively coal slime, which will succeed to meet the ultra-low NO_x emission standard. To further explore an appropriate method to reduce the SO₂ emission under the condition of new technology, the experiments were conducted on a 75 t/h CFB boiler with post-combustion chamber to study the influence of limestone addition on the combustion and emission characteristics of coal slime. The experimental results showed that High Temperature & Post-combustion Technology combined with the sorbent injection in the furnace is a very promising technology to control the NO_x and SO₂ emissions simultaneously. Limestone addition can cause the slight decrease in combustion temperature. Limestone addition will lead to the increase in NO_x emission in the combustion of coal slime. In 75 t/h coal slime CFB boiler, the desulfurization efficiency of limestone injection in furnace is close to 98%, achieving the ultra-low SO₂ emission. To meet the standard of ultra-low NO_x and SO₂ emission, the two technologies for simultaneous removal of NO_x and SO₂ emissions are economical and feasible currently: Removal of SO₂ under ultra-low NO_x emission and Removal of NO_x under ultra-low SO₂ emission.

Post-combustion technology of circulating fluidized bed can largely reduce the emission of nitrogen oxides (NO_x) in the process of combustion and succeed in meeting the ultra-low NO_x standard for some fuels like Shenmu coal. Exploring the potential of synergistic control of the emissions of NO_x and sulphur dioxide (SO₂) under post-combustion technology has become a direction that needs further study. The experiments were conducted on a 0.1 MW (thermal) circulating fluidized bed (CFB) test platform, composed of a CFB main combustor and post-combustion chamber (PCC). The paper focuses on the effects of air distribution ratio and temperature in CFB and limestone addition on NO_x and SO₂ emissions. The experimental results showed that compared with traditional CFB combustion, post-combustion technology can reduce NO_x emission largely, but lead to a slight increase in SO₂ emission. The higher SO2 emissions at post-combustion can lead to less NO_x emission. With the decrease in λ_CFB, NOx emission first decreased and then increased; by contrast, SO₂ emission with λ_CFB first increased and then decreased. Under post-combustion, when λCFB was 0.9, NO_x emission was the minimum, while the SO₂ emission was the largest. Combustion temperature and limestone addition has less adverse effects on NO_x emission under post-combustion, compared with traditional CFB combustion. Limestone injection into the furnace is applicable under post-combustion, and the sulfur removal efficiency under post-combustion is very high, almost equivalent to that under traditional combustion.

The co-combustion of biomass and coal can positively impact the environment and reduce the cost of power generation. However, biomass fuels have many limitations. Circulating fluidized bed (CFB) preheating combustion is suitable for co-combusting coal and biomass because of better fuel adaptability. In the cement industry, fuel combustion and raw meal decomposition in precalciners affect cement quality and cause pollutant emissions. The preheating combustion method used in precalciners can improve combustion performance and reduce NO_x emissions. This study investigated the preheating characteristics of a coal-biomass mixed fuel in a cement precalciner. The effects of load, biomass type, and biomass proportion on the preheated fuel and the conditions of the CFB were investigated. The results indicated that a lower load reduces the combustible components in gaseous and solid preheated fuels. However, due to the gas volume remains constant under different loads, a lower load also increases temperature and intensifies the reaction. The carbon chain and microscopic structural activities of preheated fuels are considerably enhanced, facilitating their combustion in precalciners and reducing nitrogen oxides in rotary kilns. Furthermore, adding biomass can improve the reactivity of a fuel subjected to preheating. Thus, biomass fuels (e.g., rice husks) exhibit high combustion efficiency, and thus high energy utilization. The present study achieved better pore structure and molecular activity using preheated fuel from a CFB preheater. In addition, the improvement of pore structure and molecular activity increases with the proportion of the biomass.

The entrained flow gasification has been identified as the most promising gasification technology. Serious environmental pollution and waste of land resources are caused by the increasing amount of storage and production of coal gasification slag. The aim of this work is to explore the feasibility of high-temperature combustion and melting technology for treating coal gasification fine slag and determine the important parameters of system operation. The flow properties and molten slag structure characteristics of three fine slags from different entrained flow gasifiers were studied. Depending on the melting mechanism of melt-dissolution, the melting time of fine slags is short. Three fine slags all produce glassy slags, which is conducive to slag discharge. The degree of polymerization of silicate melt is proportionate to the amount of SiO₂ in the slag. A part of Al³⁺ exist in the form of [AlO₄]^5– because of the effect of CaO and Na₂O, as the network former. Finally, the degree of polymerization of the three type molten slag was calculated by considering the role of Si and Al in molten slag and the property of each one.

To guide the application of gasification agent staging in circulating fluidized bed (CFB) gasifiers, a cold model test was implemented to study the effects of air staging on the operation of the CFB system. The results show that the re-entrainment of the solid in the downward solid flow by the secondary air jet reduces the back-mixing of solid into the dense phase zone and increases the total entrainment rate. The uniformity of axial solid holdup profile in the riser is improved by air staging. With increasing secondary air ratio, the solid concentration in the dense and dilute phase zones increases because the solid in the standpipe is transferred into the riser. After air staging, the pressure drop of the cyclone significantly increases, which results from the disturbance of the inside flow field and the increase in inlet solid concentration. Within the experimental range, the failure of the system appears as gas leakage in the standpipe. This failure can be understood as the mismatch of the mass balance and pressure balance of the system after air staging. Therefore, the results also provide guidance for the matching design of key components for the implementation of gasification agent staging.

The poor-reactivity anthracite urgently needs more ways for large-scale and high-quality utilization. Due to the advantage of good fuel adaptability, the circulating fluidized bed (CFB) gasification technology has the potential of high-quality utilization of anthracite. In this paper, one kind of anthracite from Shanxi province, China, was employed to be gasified in a pilot-scale CFB gasifier. It is found that at the operating temperature of 1049°C and oxygen concentration of 60.75%, the gas with a concentration of combustibles of 66% and a low heating value of 7.93 MJ/m³ (at about 25°C and 101.325 kPa) was produced in the CFB gasification process. However, the overall gasification efficiency was not desired because a large amount of gasification fly ash (GFA) escaped and its yield was up to 22%. In this case, the cold gas efficiency was below 48% and the carbon conversion ratio was only 62%. Further analysis reveals that the GFA was featured with a developed pore structure and the specific surface area (SBET) reached 277 m²/g. This indicates such GFA has a potential to use as activated carbon (AC) or AC precursor. Basis on this, steam activation experiments of the GFA produced were conducted to investigate the activation characteristics of GFA and thereby to determine its activation potential. Experimental results indicate that increasing temperature sharply accelerated the activation process, while did not impair the maximum activation effect. After activation, the SBET of GFA maximumly increased by 63%, reaching 452 m²/g. With the progress of activation, the pore structure of GFA presents a three-stage evolution process: development, dynamic balance, and collapse. Such a process can be divided and quantified according to the carbon loss. In order to achieve an optimal activation of GFA, the carbon loss shall be controlled at ~15%. This work provides a new scheme for high-quality utilization of anthracite.

As the major primary energy source in China, coal has been proved to be capable to improve its physical and chemical characteristics by the pretreatment of the self-preheating burner. In this study, the effects of altering operating conditions including preheating temperature (T_p) and primary air equivalence ratio (λ_p) on preheating characteristics of three typical pulverized coal were investigated on a bench-scale test rig. The high-temperature coal gas compositions along the axis of the riser and at the outlet of the self-preheating burner were measured, and the coal char and coal tar produced in the preheating process were collected and analyzed separately. The results indicated that with the significant release of volatile and the occurrence of chemical reactions, cracks and micropores emerged on the surface of the particles, making the pore structure on the surface more developed, and T_p had the most significant effect on the structure of coal particles. Additionally, there were evident differences in the corresponding operating conditions when the preheating characteristics of the three typical coal reached optimally. And preheating had the strongest influence on the degree of anthracite modification. With respect to coal tar, the increase of T_p and λ_p further promoted its secondary cracking and oxidation, resulting in a decrease in production yield. In this study, for bituminous coal and lignite, a large amount of coal tar were produced during preheating and the highest production yields could reach 5.74% and 6.15%, respectively. While for anthracite, the production yield was intensely low due to its own coal properties, all below 1.02%.

Dry reforming of methane (DRM) process has attracted much attention in recent years for the direct conversion of CH₄ and CO₂ into high-value-added syngas. The key for DRM was to develop catalysts with high activity and stability. In this study, LaNiO₃ was prepared by the sol-gel, co-precipitation, and hydro-thermal methods to explore the influence of preparation methods on the catalyst structure and DRM reaction performance. The regeneration properties of the used LaNiO₃ catalysts were also investigated under steam, CO₂, and air atmospheres, respectively. The results showed that LaNiO₃ prepared by sol-gel method showed the best DRM performance at 750°C. The DRM performance of the samples prepared by hydro-thermal method was inhibited at 750°C due to the residual of Na+ ions during the preparation process. The regeneration tests showed that none of the three atmospheres could restore LaNiO₃ perovskite phase in the samples, but they could eliminate the carbon deposits in the samples during the DRM reaction, so the samples could maintain stable DRM performance at different cycling stages.

Hydrogen is an attractive energy carrier due to the high conversion efficiency and low pollutant emission. Chemical looping hydrogen production (CLHP) is an available way for producing high purity hydrogen with relatively low penalty energy and CO₂ is captured simultaneously. Three reactors are usually contained for CLHP system including air reactor (AR), fuel reactor (FR) and steam reactor (SR). In current work, we focus on the performance of CLHP system, which is the basement for operation and design. Numerical simulations are carried out for analyzing the flow behavior and the numerical structure is built according to the experimental unit constructed at Southeast University, China. Results show that the operation of L-valve influences most the solid circulating rate of system and particles pass L-valve easily with large aeration rate. Mass distribution results indicate that fuel reactor has the capacity for particles storage. Increase of gas inlet rate of steam reactor leads to more particles leave steam reactor and accumulate into fuel reactor. L-valve can prevent the gas leakage between reactors and it will be adopted for reactive unit. Combining the operation of fuel reactor and L-valve, the system can reach steady state and get the regulating ability.

The impacts of the cavity leakage flow on the shrouded stator aerodynamic performance were investigated by modelling the annular cascade mainstream with the seal cavity flow path based on the validated numerical method. Meanwhile, the interactions between the cavity leakage and the mainstream were also determined in the current study. The development of hub corner separation under the action of leakage was discussed and the total pressure loss coefficient as well as the entropy-based loss coefficient was employed to evaluate the performance changes at different seal clearances and cavity rotational speeds. The results show that the cavity leakage flow induces a new vortex near the blade leading edge and plays an important role in the development of passage vortex and the size of concentrated shedding vortex. By increasing the seal clearance with more cavity leakage flow rate, an increase in the pitchwise extent of the separation region under 15% span is significant and the total pressure loss in the separation core increases. In addition, with the increase of cavity rotating speed, the starting point of corner separation moves backward, reducing the size and depth of the hub corner separation. The mainstream loss reduction in combination with the entropy increase in the seal cavity causes the entropy-based loss coefficient to perform a trend of decreasing first and then increasing with the cavity speed.

Methane has a narrow range of flammable limits, low flame speed and poor ignition characteristics, which limit its utilization in internal combustion engines. However, this issue can be remedied through the use of CH₄/DME blends, because DME has better ignition and combustion characteristics. In this study, the effects of pressure and blending ratio on the combustion characteristics of CH₄/DME blended fuels were investigated by using a high-pressure diffusion counterflow system, a constant volume combustion bomb, and CHEMKIN software. The reaction pressures are 0.1 MPa, 0.2 MPa, 0.3 MPa, and the blending ratios are 100% DME, 75% DME+25% CH₄, 50% DME+50% CH₄ and 25% DME+75% CH₄ (mol%). The results show that the laminar flame speed, flame temperature, and extinction limit of CH₄/DME blended fuel decrease as the CH₄ blending ratio or pressure increases. CH₄ addition and increasing pressure both lead to the competition for OH and H radicals between CH₄ and DME. However, the increase of CH4 mole fraction can also increase the path flux of CH₄+H= CH₃+H₂, while the increase of pressure can decrease this path flux. Moreover, increasing pressure can promote all reaction processes and reaction rates.

Natural gas/diesel dual-fuel combustion strategy has a great potential to reduce emissions for marine engines while the high fuel consumption is the major problem. Pre-chamber system is commonly employed as the ignition system on large-bore dual-fuel marine engines especially under lean-burn condition, due to its advanced ignition stability and engine efficiency. However, the ignition and combustion mechanism in such dual-fuel pre-chamber engine is still unclear and the effects of in-cylinder swirl flow and mixture stratification on combustion require further investigation specifically. This paper numerically studied the detailed ignition mechanism and combustion process in a marine engine equipped with a pre-chamber ignition system, and revealed the flame development process in main chamber. Moreover, the effects of mixture stratification and swirl ratio on the combustion rate and further engine thermal efficiency are investigated under decoupled condition. The results mainly show that the jet flame develops along the pre-chamber orifice centerline at the initial stage and premixed combustion play an important role, while after that, heat release zone only exist at flame surface, and premixed flame propagation controls the combustion process. In addition, with higher swirl ratio the combustion rate increases significantly due to the wider ignition area. Mixture stratification degree plays a role in accelerating the combustion, either too high or too low stratification degree reduce the combustion rate, while a moderate stratification increases the combustion rate. And appropriate stratification degree by verifying the gas injection parameters can reduce fuel consumption in 0.3%.

The interaction mechanism of internally-staged-swirling stratified flame is complex, and the pilot flame has a manifest influence on flame stability. To study this, a series of experimental investigations for the pilot flame has been carried out in a model swirl combustor by only supplying the pilot fuel. The CH* chemiluminescence images of the pilot flame are acquired by a high-speed camera with a CH* bandpass filter, whose dynamic characteristics are identified by image statistical analysis and proper orthogonal decomposition (POD) analysis. And the fast algorithm based on matrix theory proposed in this paper increases the operation efficiency and operability of POD. With the pilot equivalence ratio Φ increase, the pilot flame gradually shows an unstable state, whose POD energy distribution is significantly different. In the unstable state, the flame dynamics include three modes—spiral motion mode, flame shedding mode, and axial oscillation mode, whose formation reasons have also been further analyzed in combination with the experimental characteristics. And the fast Fourier transform (FFT) analysis of the time coefficients for the first four POD modes indicates all the dominant frequency is 280 Hz, which means the model combustor is in resonance. In addition, a sensitivity analysis based on the different image resolutions further reveals the robustness of the POD method and its optimization direction. These results emphasize the important influence of the pilot fuel flow rate on the stability of the pilot flame.

Spray experiments of RP-3 jet fuel at non-evaporating and evaporating environments were studied on a constant volume spray chamber, and diffusive back-imaging technique was used to capture the transient spray development processes. Spray tip penetration, projected spray area and cone angle of RP-3 jet fuel were derived from the spray development images, and compared to those of diesel fuel. It is observed that non-evaporating sprays of RP-3 jet fuel and diesel fuel do not exhibit significant differences, as their spray penetration distances, projected spray areas and spray cone angles are consistent at most test conditions. The evaporating sprays of RP-3 jet fuel produce shorter liquid-phase penetration distances and lower projected spray areas than those of diesel fuel, and these differences are particularly pronounced at low ambient temperatures. However, fuel effects on the evaporating spray cone angle are insignificant. Further, increased ambient density or ambient temperature shortens the liquid-phase spray penetration distance and reduces the liquid-phase spray area, and these effects are more pronounced for diesel fuel than RP-3 jet fuel.

Some ash related problems, such as slagging at furnace bottom and fouling at the air pre-heater surface, are frequently encountered during circulating fluidized bed gasification (CFBG) of Zhundong coal. Low ash fusion temperatures (AFTs) and intense sodium release should be responsible for those problems. In industry, coal blending is deemed to be a feasible method to both improve AFTs and control sodium release. In this work, Wuhai coal was selected as blending coal. The ratio is varied from 0% to 40% by mass with 10% interval. The mixed samples were gasified by steam at 950°C in a lab-scale furnace. Some key indices, such as sodium release behaviors, ash slagging characteristics and char gasification performances, were investigated by ICP-OES, AFTs, XRD and TG analyzers, respectively. The results indicated that coal blending could significantly decrease sodium release behaviors. For ash slagging characteristics, it is surprised to find that three out of four AFTs (deformation temperature, softening temperature, hemispherical temperature) show an U-shaped correlation with blending ratio, indicating that a low ratio possibly causes more severe ash slagging problem. It is ascribed to the formation of substantial percentage of fusible Na-containing silicates and aluminosilicates. In addition, coal blending greatly increases ST-DT, implying that the ability of resistance to bed temperature fluctuation is markedly enhanced. Due to the high level of alkali and alkaline species, the synergistic effect is clearly observed during co-gasification. Taking all key indices into consideration, 30% blending ratio of Wuhai coal is recommended.

Coal slime has low ash content, and adding coal slime during coal gangue combustion may have influence on combustion character; and at this process, NO will emit, and lead to environmental pollution. O₂/CO₂ atmosphere is conducive to NO emission reduction. Thus combustion characteristics and NO emissions during co-combustion of coal gangue and coal slime in O₂/CO₂ atmospheres were studied. The results showed the addition of coal slime increased the combustion activity of the mixed fuels in both air and O₂/CO₂ atmospheres. During co-combustion, there are synergistic effects between them at the fixed carbon combustion stage, and higher blending ratio of coal slime leads to stronger synergistic effect. Furthermore, this study also showed that with the increasing of coal slime blending ratio, the emission concentration of NO increases gradually; with the increase of temperature and O₂ concentration, the NO emission concentration also gradually increases, and higher O₂ concentration leads to shorter time required for the complete release of NO. Besides that, the results also demonstrate that the proportion of pyrrole and nitrogen oxide in the ashes increases with the increase of combustion temperature, and pyridine and quaternary nitrogen gradually disappear, while the total nitrogen content in ash decreases with the increase of temperature. The results will contribute to a better understanding of the co-combustion process of coal gangue and coal slime in O₂/CO₂ atmosphere, and provide basic data for the practical industrial application of coal gangue and slime.

The structure of the trapped-vortex cavity and radial flameholder can maintain stable combustion under severe conditions, such as sub-atmospheric pressure and high inlet velocity. This article reports a complete study of combustion characteristics for this design. The flow field of the physical model was obtained by numerical simulation. The pilot combustion characteristics, including the combustion process, combustion efficiency, and wall temperature distribution, were studied by experiments. The pilot combustion can be divided into three modes under different fuel flow rates and inlet conditions. In “cavity maintained (CM)” mode, pilot flame exists at both sides of the cavity zone, rotating with the main vortex. In “cavity-flameholder maintained (CFM)” mode, the combustion process occurs both inside the cavity and behind the flameholder. While in “flameholder maintained (FM)” mode, the cavity will quench, and the combustion is maintained by the radial flameholder only. Due to the difference in the flow field, the flame pattern and propagation direction vary under different combustion modes. The combustion efficiency, influenced by combustion modes, shows an increase-decrease-increase curve. The wall temperature distribution is also affected; the cavity wall temperature decreases under large fuel flux while the temperature of the burner-back plate continues to rise to a maximum value.

Bunsen burner is a typical geometry for investigating the turbulence-flame interaction. In most experimental studies, only turbulence intensity u′ and integral scale l₀ are used to characterize the turbulent flow field, regardless of the perforation geometry of perforated plates. However, since the geometry influences the developing process and vortex broken, the plate geometry has to be considered when discussing the flame-turbulence interaction. In order to investigate conditions at the same l₀ and u′ using different geometries, large eddy simulation of CH₄/air flames with dynamic TF combustion model was performed. The model validation shows good agreement between Large Eddy Simulation (LES) and experimental results. In the non-reacting flows, the Vortex Stretching of circular-perforated plate condition is always larger than that of slot-perforated plate condition, which comes from the stresses in the flow fields to stretch the vorticity vector. In reacting flows, at the root of the flame, the Vortex Stretching plays a major role, and the total vorticity here of circular-perforated plate condition is still larger (53.8% and 300% larger than that of the slot-perforated plate at x/D=0 and x/D=2.5, respectively). More small-scale vortex in circular-perforated plate condition can affect and wrinkle the flame front to increase the Probability Density Function (PDF) at large curvatures. The 3D curvature distributions of both cases bias to negative values. The negative trend of curvatures at the instant flame front results from the Dilatation term. Also, the value of the Vortex Stretching and the Dilatation at the flame front of circular-perforated plate condition is obviously larger.

Diesel from direct coal liquefaction (DDCL) is a new type of engine alternative energy. But its hydrocarbon composition and physicochemical properties are quite different from those of Petro diesel. In this study, a premixed constant volume combustion chamber (CVCC) system with soot particle sampling devices was built. The soot particles in the spray flame were sampled and photographed by thermophoresis probe and transmission electron microscope (TEM). An automatic processing code based on Matlab software was developed to process the TEM images and extract the micro morphology parameters of the soot particles. This study has systematically studied the effects of sampling location, injection pressure, ambient density and oxygen concentration on the micro morphology of soot particles. The ambient density refers to the initial gas density in the CVCC. The results showed that various morphologies and sizes of soot particles coexisted in the upstream of the spray flame. During the evolution of soot particles from upstream to downstream in the flame, the size of soot aggregates gradually decreased, while the maturity of soot aggregates increased. With the increase of injection pressure, ambient density and oxygen concentration, the average sizes of soot aggregates and primary soot particles decreased, but the fractal dimensions of soot aggregates increased gradually. Under the same combustion condition and in-flame sampling location, the average projection area, gyration radius and primary soot diameter of soot aggregates produced by DDCL were significantly lower than those of Petro diesel. The structure of soot particles from DDCL was more compact than that of Petro diesel.

Design, development, and testing of LPRE (Liquid Propellant Rocket Engine) are difficult and expensive tasks. Prior to full-scale design, it is indispensable to optimize important parameters at sub-scale. Propellants flow rates are low for a sub-scale or laboratory scale combustion chambers. It is hard to satisfy chamber cooling and chill feed lines quickly with low flow rates of propellants. This paper proposes a detailed procedure for testing of a laboratory scale semi-cryogenic combustion chamber. Many tests were conducted with a small scale adjustable length combustion chamber. The injection head of the chamber was interchangeable. Liquid-liquid pressure swirl injector and like impinging injectors were used with two different injection heads. Liquid oxygen and kerosene were used as oxidizer and fuel, respectively. Oxidizer to fuel mixing ratio was 0.29–0.45 and the total propellant mass flow rate was 0.06–0.1 kg/s. Problems were faced during testing, including, explosion in the combustion chamber, fuel injector blockage, unstable combustion, incomplete chilling and blockage of cooling water channel, etc. A detailed procedure is designed on the basis of the lessons learned which was experimentally proved.

The migration characteristics of heavy metals in co-combustion of sewage sludge and high alkali coal in circulating fluidized bed were studied by experiments and simulations. Temperature plays a crucial role in thermodynamic equilibrium distribution and migration characteristics of heavy metals. At the temperature range of 700°C–1200°C, Hg is completely gaseous and the proportion of Pb, Ni, and Cd in the gas phase is also high. As is mainly elemental in the system, and the proportion of Cr in the solid phase is large. Zn compounds are diverse and mostly solid materials. The volatility of Cu is not strong, and it will become gaseous when the temperature exceeds 1700°C. The proportion of heavy metals in the gas phase decreases as the excess air ratio increases. In an oxygen-rich atmosphere, most of Zn and Ni are converted to oxides; Pb and Cd are converted to crystalline silicate; Cu is converted to partial aluminate; Cr compound is decomposed to form Cr₂O₃; they are good for the solidification and controlling of heavy metals. The elemental Hg is converted to HgCl₂ and the elemental As is converted to AsCl₃. Temperature also has a great influence on the volatilization rate of heavy metals. The higher the temperature, the shorter the time they reach the maximum volatility.

In slag tapping furnaces, char particles undergo a series of complex structural evolution before and after being captured by the liquid slag layer. The evolution results affect the carbon conversion rate and are affected by temperature fluctuations, especially in the ash melting temperature zone. Experimental study on structure evolution of bituminous char prepared at around ash melting temperature was carried out on a fixed bed. The morphology, specific surface area and mineral chemical composition were measured at different temperatures. Experimental results show that the number density and the size of ash droplets exuded on the char surface increased significantly with the increasing temperature. The ash specific surface area from gasification was slightly greater than that from combustion. The residual content of chloride in the char become 1% and the contents of Fe, K, Mg and Na decrease significantly during the pyrolysis process across the ash melting temperature zone. The diffraction intensity of oldhamite increase which indicates the reaction of carbon substrate with minerals during the evolution; the diffraction intensity of quartz dramatically decreases for the reason of anorthite generation. The ignition and burnout temperatures of char were found to increase and the combustion stability decreased with the increasing pyrolysis temperature.

For the improvement of reheat steam quality and performance of double reheat coal-fired utility boiler under wide load operation, a variety of temperature regulation ways were utilized to adjust the energy distribution between different heating surfaces. In this paper, thermodynamic calculation based on the fundamental heat transfer theory was conducted for the analysis of temperature regulation strategy effects to steam temperature. In consideration of the specific overlapping heating surface arrangement, the compartment model was adopted to solve this problem. Response surface methodology (RSM) was used to analysis the effect of each temperature regulating variables on the steam temperature and boiler efficiency; then the polynomial model was fitted to predict the primary and secondary steam temperature simultaneously. Results showed that the flue gas recirculation rate has a relatively significant influence on the steam temperature, the maximum temperature deviation between fitting value and calculation value is 3.85°C in 75%THA; the quadratic model can well predict the steam temperature under different operation conditions in wide load change. The variation of flue gas baffle has a significant influence on the boiler efficiency, compared to the flue gas recirculation and angle of burner oscillation. The influence of various factors on the reheat steam temperature is flue gas baffle > flue gas recirculation > angle of burner oscillation.

This paper reports an investigation of carbon deposition on the venturi component of a gas turbine combustor fueled with ethanol/kerosene fuel blends. China RP-3 kerosene and its ethanol blends (10%, 30%, and 50% ethanol by weight) were used in a gas turbine model combustor. Each combustion test of carbon deposition was conducted at 0.3 MPa for an hour. Measuring carbon deposition became difficult because of the special structure of venturi which is a component of swirl cup air atomization nozzle. An image processing method called planar reconstruction, was developed to evaluate the amount of carbon deposition semi-quantitatively. To study the morphology and structure of the deposition for different test fuels, a Scanning Electron Microscope (SEM) was employed to visualize the detailed structures of carbon deposition. Results show that with the increasing addition of ethanol, the amount of carbon deposition decreases, and the morphology of carbon changes significantly. For pure kerosene case, small spherules and flake graphite were closely interwoven on venturi surface. For other fuel blends, small spherules were not observed, and flake graphite neatly stacked and lined on the venturi surface. These results indicate that the mechanism of carbon deposition can vary significantly, due to the change of fuel’s molecular structures; the current study shows that the morphology and structure of carbon deposition of kerosene were altered remarkably by the ethanol addition. 

Dual-volume Helmholtz dampers with two resonant frequencies are proposed to simultaneously attenuate longitudinal and azimuthal thermo-acoustic instabilities in annular combustors. Thermo-acoustic instabilities in a swirled annular combustor equipped with dual-volume dampers are numerically investigated by the Helmholtz method, combined with a measured flame transfer function and the established damper impedance model. Furthermore, the influences of the damper number and circumferential configurations on oscillation attenuations and mode structures are explored. The established dual-volume damper model is well validated by the impedance tube tests. Numerical results indicate velocity fluctuation levels of the longitudinal and azimuthal modes decline after installing Helmholtz dampers, whereas those of the azimuthal modes further decrease by around 16% after using four retuned dual-volume dampers. The eigenfrequencies of the first longitudinal and azimuthal modes decrease and increase after installing dampers, respectively. After installing dual-volume dampers, the difference between the pressure fluctuation in the plenum and combustion chamber is reduced, and pressure waveforms of the azimuthal modes along the circumferential direction shifts. The pressure distribution of azimuthal modes becomes more uniform after using more dual-volume dampers. The specific absorption frequency band for azimuthal modes introduced by the dual-volume damper may lead to decreased oscillations and mode evolutions. The maximal absorbing ability can be approached by installing dampers with the same angle between adjacent dampers. When dampers are unevenly distributed, the symmetry between two azimuthal modes is broken and standing modes will emerge.