Search Results (34)

Based on the low-carbon transition needs of coal-fired boilers, this study conducted industrial trials of direct biomass co-firing on a 620 t/h high-temperature, high-pressure circulating fluidized bed (CFB) boiler, gradually increasing the co-firing ratio. It used compressed biomass pellets, achieving stable 20 wt% (weight percent) operation. By analyzing boiler parameters and post-shutdown samples, the comprehensive impact of biomass co-firing on the boiler system was assessed. The results indicate that biomass pellets were blended with coal at the last conveyor belt section before the furnace, successfully ensuring operational continuity during co-firing. Further, co-firing biomass up rates of to 20 wt% do not significantly impact the fuel combustion efficiency (gaseous and solid phases) or boiler thermal efficiency and also have positive effects in reducing the bottom ash and SO_x and NO_x emissions and lowering the risk of low-temperature corrosion. The biomass co-firing slightly increases the combustion share in the dense phase zone and raises the bed temperature. The strong ash adhesion characteristics of the biomass were observed, which were overcome by increasing the ash blowing frequency. Under 20 wt% co-firing, the annual CO₂ emissions reductions can reach 130,000 tons. This study provides technical references and practical experience for the engineering application of direct biomass co-firing in industrial-scale CFB boilers. Full article

This study aims to investigate the impact of combustion chamber geometry and biodiesel on the performance of diesel engines under various load conditions. Simulations were conducted using AVL FIRE software, followed by experimental validation to compare the performance of the prototype Omega combustion chamber with the optimized TCD combustion chamber (T for turbocharger, C for charger air cooling, and D for diesel particle filter). This study utilized four types of fuels: D100, B10, B20, and B50, and was conducted under different load conditions at a rated speed of 1800 revolutions per minute (rpm). The results demonstrate that the TCD combustion chamber outperforms the Omega chamber in terms of indicated thermal efficiency (ITE), in-cylinder pressure, and temperature, and also exhibits a lower indicated specific fuel consumption (ISFC). Additionally, the TCD chamber shows lower soot and carbon monoxide (CO) emissions compared to the Omega chamber, with further reductions as the load increases and the biodiesel blend ratio is raised. The high oxygen content in biodiesel helps to reduce soot and CO formation, while its lower sulfur content and heating value contribute to a decrease in combustion temperature and a reduction in nitrogen oxide (NOx) production. However, the NOx emissions from the TCD chamber are still higher than those from the Omega chamber, possibly due to the increased in-cylinder temperature resulting from its combustion chamber structure. The findings provide valuable insights into diesel engine system design and the application of oxygenated fuels, promoting the development of clean combustion technologies. Full article

To increase the jet momentum and improve the environmental adaptability, a combustion-driven SparkJet actuator with a Laval-configured outlet is proposed to improve the performance of the actuator. Numerical simulation results show that, compared to straight outlet combustion-driven actuators with outlet diameters of 2 mm and 2.8 mm, the maximum jet velocity of the Laval-configured actuator increases by approximately 100 m/s and 350 m/s, separately. while the peak times decrease by about 50% and 12%, respectively. The work frequency of the Laval-structured combustion-driven actuator is 1333 Hz, which is higher than the 1176 Hz of the straight-tube-structured combustion-driven actuator with an outlet diameter of 2 mm. The Laval configuration effectively improves the working performance of the actuator. As the equivalence ratio increases from 0.6 to 1, the actuator’s jet velocity increases by approximately 65 m/s and 311 m/s, respectively, and its maximum combustion temperature is raised from 2700 K to 3000 K. The saturation work frequency is nearly the same. The pressure and jet mass flow rate in the actuator drop as the atmospheric pressure declines, while the combustion-driven actuator still exhibits high working performance when the atmospheric pressure is low. The maximum outlet velocity, Mach number, pressure, and temperature increase by about 20%, 13%, 25%, and 6%, while the peak time increases by about 40% as the ignition position moves from the middle position to a 2.8 mm displacement toward the outlet. Full article

Methane–hydrogen–air mixtures present a viable alternative to conventional fuels, reducing CO₂ emissions while maintaining high energy density. This study numerically investigates their combustion characteristics in millimeter-scale reactors, focusing on flame stabilisation and combustion dynamics in confined spaces. A species transport model with volumetric reactions incorporated a detailed kinetic mechanism with 16 species and 41 reactions. The simulations employed a laminar flow model, second-order upwind discretisation, and SIMPLE algorithm for pressure–velocity coupling. The key parameters analysed include equivalence ratio, hydrogen volume fraction, inlet velocity, and gas pressure and their impact on fuel conversion efficiency and heat release was evaluated. The results indicate that hydrogen enrichment enhances flame stability and combustion efficiency, with optimal performance over 40% hydrogen content. Additionally, increased outlet pressure raises flame temperature by 15%, while larger reactor diameters reduce heat losses, improving combustion efficiency by 20%. Emissions of CO decrease significantly at higher hydrogen fractions, demonstrating the potential for cleaner combustion. These findings support the integration of methane–hydrogen mixtures into sustainable energy systems, providing insights for designing efficient, low-emission micro-combustors. Full article

The growth of the civil aviation industry has raised concerns about the impact of airport emissions on human health and the environment. The aim of this study was to quantify the emissions of sulfur dioxide (SO₂), nitrogen oxides (NO_X), and carbon monoxide (CO) from in-service aircraft via open-path Fourier-transform infrared (OP-FTIR) spectroscopy at Tianjin Binhai International Airport. The results suggest that the CO and NO_X emission indices (EIs) for five common aircraft/engine combinations exhibited substantial discrepancies from those reported in the International Civil Aviation Organization (ICAO) databank. Notably, during the idling, approach, and take-off phases, the CO EIs exceeded the ICAO’s standard values by (11.04 ± 10.34)%, (56.37 ± 18.54)%, and roughly 2–5 times, respectively. By contrast, the NO_X EIs were below the standard values by (39.15 ± 5.80)%, (13.57 ± 3.67)%, and (21.22 ± 4.03)% in the same phases, respectively. The CO and NO_X EIs increased by 31–41% and decreased by 23–24%, respectively, as the ambient temperature decreased from −3 °C to −13 °C. This was attributed to lower temperatures reducing fuel evaporation, leading to inefficient combustion and increased CO emissions and lowering the combustion temperature and pressure, resulting in reduced NO_X emissions. The CO EIs had a positive correlation with humidity (adjusted R²: 0.715–0.837), while the NO_X EIs were negatively correlated with humidity (adjusted R²: 0.758–0.859). This study’s findings indicate that humidity is a crucial factor impacting aircraft exhaust emissions. Overall, this research will contribute to the development of scientifically informed emission standards and enhanced environmental management practices in the aviation sector. Full article

High gravity (high-g) combustion can significantly increase flame propagation speed, thereby potentially shortening the axial length of aero-engines and increasing their thrust-to-weight ratio. In this study, we utilized the large eddy simulation model to investigate the combustion characteristics and flame morphology evolution of premixed propane–air flames in a channel with a backward-facing step. The study reveals that both the increase in centrifugal force and flow velocity can enhance pressure fluctuations during combustion and increase the turbulence intensity. The presence of centrifugal force promotes the occurrence of Rayleigh–Taylor instability (RTI) between hot and cold fluids. The combined effects of RTI and Kelvin–Helmholtz instability (KHI) enhance the disturbance between hot and cold fluids, shorten the fuel combustion time, and intensify the dissipation of large-scale vortices. The increase in fluid flow velocity can raise the flame front’s hydrodynamic stretch rate, thereby enhancing the turbulence level during combustion to a certain extent and increasing the fuel consumption rate. When a strong centrifugal force is applied, the global flame propagation speed can be more than doubled. Within a certain range, the increase in high-g field strength can enhance the intensity of RTI and accelerate the transition of RTI to the nonlinear stage. Full article

In this paper, the AUTODYN/Smoothed Particle Hydrodynamics (SPH) method was used to study the impact of reactive fragments on three-layer equidistant steel plates. The perforation characteristics of equidistant three-layer steel plates were investigated along with the parameters of combustion energy release from reactive fragments under varied impact velocities and shape conditions. The modification of the steel plates’ perforation diameter was investigated using the dimensional analysis approach. The shock wave pressure and chemical reaction characteristics were examined using the shock wave theory. The results show that within the examined impact velocity range, the perforation diameter initially increased and then decreased as the impact velocity of the reactive fragment rose. In addition, the perforation diameter was approximately 1.5–3 times the diameter of the reactive fragment. As the impact speed increased, the active reaction generated by the reactive fragments became more sufficient. The energy released contributed to the impact’s pressure rise; in addition, the temperature of the steel plate was raised in part by the reactive fragment impact, making the steel plate more prone to melting. The results of this investigation provide important support for a detailed understanding of the rules governing the failure of steel plates under the impact of reactive fragments as well as the combustion of reactive fragments under impact. Full article

Detonation initiation is a prerequisite to normal operations of an oblique detonation engine (ODE), and initiation-assistant measures are imperative in cases of initiation failure that occur in a length-limited combustor under wide-range flight conditions. This study numerically investigates the initiation characteristics of oblique detonation waves (ODWs) in H₂-fueled ODE combustors at wide-range flight Mach numbers Ma_f or flight altitudes H_f. Failures of ODW initiation are observed at both low Ma_f and high H_f if no measure is taken to assist initiation. Through analyses of the flow fields and theoretical predictions of the ignition induction length L_ind, the data reveal that the detonation failure at low Ma_f is raised by the significant decrease in the post-shock temperature due to insufficient shock compression, leading to a significant increase in L_ind. The detonation failure at high H_f is caused by the rapid decrease in the combustor inflow pressure as H_f increases, which also results in an increase in L_ind. With further identifications of the key flow structures crucial to detonation initiation, an initiation-assistant concept employing a transverse H₂ jet is proposed. The simulation results show that through an interaction between the incident oblique shock wave and the jet shock wave, the transverse jet helps to initiate an ODW in the combustor at a low Ma_f, and the initiation location is relatively fixed and determined by the jet location. At high H_f, a Mach reflection pattern is formed in the combustor under the effects of the transverse jet, and detonative combustion is achieved by the generated Mach stem and its reflected shock waves. The proposed concept of using transverse jets to assist detonation initiation provides a practical reference for future development of ODEs that are expected to operate under wide-range flight conditions. Full article

Gas turbines are used in the energy sectors as propulsion and power generation technologies. Despite technological advances in power generation and the emergence of numerous energy resources, gas turbine technology remains important due to its flexibility in load demand following, dynamical behavior, and the ability to work on different fuels with minor design changes. However, there would be no ambitious progress for gas turbines without reliable modeling and simulation. This paper describes a novel approach for modeling, identifying, and controlling a running gas turbine power plant. A simplified nonlinear model structure composed of s-domain transfer functions and nonlinear blocks represented by rate limiters, saturations, and look-up tables has been proposed. The model parameters have been optimized to fit real-world data. The verified model was then used to design a multiple PI/PD control to regulate the gas turbine via the inlet guide vane and fuel vales. The aim is to raise and stabilize the compressor’s differential pressure or pressure ratio, as well as raise the set-point of the temperature exhausted from the combustion turbine; as a result, energy efficiency has been improved by an average of 237.16 MWh saving in energy (or 8.96% reduction in fuel consumption) for a load range of 120 MW to 240 MW. Full article

A thermal energy storage–updraft gasification device is a type of reactor that should be considered for use in solid waste gasification research that can save energy. However, the operating parameters and internal flow field during its operation remain unclear. In this study, a numerical model of the thermal energy storage–solid waste gasification device based on the computational fluid dynamics dense discrete phase model (CFD-DDPM) which had almost never been used before was established, and an innovative method that causes particles to be piled to simulate the gasification process was proposed according to the updraft fixed bed gasification characteristics; meanwhile, solid waste gasification experiments were conducted on the device. This study focused on the influence of moisture content and excess air coefficient on the gasification process of solid waste particles, and the velocity, pressure, temperature, and species distribution of the internal flow field of the device were analyzed. Simulation results showed that the higher the moisture content of particles, the greater the amplitude of changes in the internal physical field of the device. The fluid pressure drop is around 25 Pa–75 Pa for different working conditions. The combustible species of the gas of moist particles raise slightly with the increase in excess air coefficient, while the dry particles have the opposite effect. Compared with other gasification devices of the same type, the hydrogen production of this device is about 2–3 times higher. Our findings could facilitate the analysis, predict the operation status, and provide a theoretical basis for the improvement of this device. Full article

As water is facing increasing pressures from population and economic growth and climate change, it becomes imperative to promote the protection, restoration and management of this resource and its watersheds. Since water quality depends on multiple factors both natural and anthropic, it is not easy to establish their influences. After the October 2017 fires that affected almost 30% of the Mondego hydrographic basin in Central Portugal, 10 catchments were selected for periodic physical-chemical monitoring. These monitoring campaigns started one month after the fires and lasted for two hydrological years, measuring the electric conductivity (EC), pH, dissolved oxygen (DO), turbidity (Turb), alkalinity (Alk), major and minor ions, and trace elements. The obtained data were then statistically analysed alongside the geomorphological characteristics of each catchment coupled with features of land-use and occupation. From the results, it was possible to establish that fire-affected artificial areas, through the atmospheric deposition and surface runoff of combustion products, had the most impact on surface water quality, increasing As, K⁻, Ca²⁺, Mg²⁺, NO₃⁻, SO₄²⁻ and Sr, and consequently increasing electrical conductivity. Agricultural land-use seems to play a major influence in raising the water’s EC, Cl, K⁻ and Na²⁺. Regarding natural factors such as catchment geology, it was found that the extent of igneous exposures influences As, and the carbonate sedimentary units are a source of Ca²⁺ and HCO₃²⁻ concentrations and impose an increase in alkalinity. Rainfall seems, in the short term, to increase the water concentration in Al and NO₃⁻, while also raising turbidity due to sediments dragged by surface runoff. While, in the long-term, rainfall reduces the concentrations of elements in surface water and approximates the water’s pH to rainfall features. Full article

The annual increase in demand for electrical power is accompanied by a significant combustion of hydrocarbon fuels and, accordingly, significant CO₂ emissions into the atmosphere, which, in turn, result in increasing the surface temperature of our planet. In addition, hydrocarbon fuel reserves are also depleted every year, which raises the question of the efficient use of fossil fuels. One of the promising solutions to this problem is introducing a technology that allows using the excess gas pressure at gas distribution points in order to generate additional electrical energy. As a rule, a radial turboexpander is used to convert the kinetic energy of natural gas at low power. In this paper, we study a method to reduce losses in a volute inlet of a radial expander. Based on our research, we could find that the use of two symmetrical fins in the volute inlet pipe makes it possible to decrease the turbulent kinetic energy by 1.29% and to reduce the energy losses in the inlet pipe by 2.18%. Full article

ORC power units represent a promising technology for the recovery of waste heat in Internal Combustion Engines (ICEs), allowing to reduce emissions while keeping ICE performance close to expectations. However, the intrinsic transient nature of exhaust gases represents a challenge since it leads ORCs to often work in off-design conditions. It then becomes relevant to study their transient response to optimize performance and prevent main components from operating at inadequate conditions. To assess this aspect, an experimental dynamic analysis was carried out on an ORC-based power unit bottomed to a 3 L Diesel ICE. The adoption of a scroll expander and the control of the pump revolution speed allow a wide operability of the ORC. Indeed, the refrigerant mass flow rate can be adapted according to the exhaust gas thermal power availability in order to increase thermal power recovery from exhaust gases. The experimental data confirmed that when the expander speed is not regulated, it is possible to control the cycle maximum pressure by acting on the refrigerant flow rate. The experimental data have also been used to validate a model developed to extend the analysis beyond the experimental operating limits. It was seen that a 30% mass flow rate increase allowed to raise the plant power from 750 W to 830 W. Full article

The leakage and diffusion of hazardous gases from steam methane reforming (SMR) equipment are investigated by Flame Acceleration Simulator (FLACS) software to optimize the layout of combustible gas detectors. A typical accident scenario, with the gases leaked from converter tubes with leak apertures of 5 mm, 25 mm, and 100 mm and medium pressure of 0.1 MPa, 1 MPa, and 10 MPa, is established. At the same time, the influence of the environment wind speeds from 0.2 m·s⁻¹ to 6 m·s⁻¹ on the diffusion process is also investigated. The research results show that the leakage source concentration and diffusion distance positively correlate with the leakage aperture. Suggestion on the distance between combustible gas detectors and possible leak point is within 5 m, 10 m, and 15 m in the scenario of the leak aperture of 5 mm (small-hole leak aperture), 25 mm (middle-hole leak aperture), and 100 mm (big-hole leak aperture). The most dangerous scenario is at the static ambient wind speed, and the diffusion process strengthens with the raising of wind speed. The turning point scenario occurs at a wind speed of 1 m·s⁻¹, where the flammable area is minimal. The medium pressure relates to the jet speed of the combustible gases. The wind speed should be comprehensively determined when considering the layout of the combustible gas detectors affected by this factor. The orthogonal experimental design shows that the most significant influence factor on the diffusion process of the combustible gas is the leak aperture, followed by the medium pressure and, finally, by the ambient wind speed. Recommendations are listed for the optimization of the layout of gas detectors in related enterprises. Full article

Renewable fuels are alternative resources that find use in the power generation, agricultural, and transportation sectors. The sustainable utility of these renewable fuels mostly addresses the socio-economic issues of a country and reduces its dependency on fossil fuels. In addition, being environmentally friendly allows them to handle global warming more effectively. Two B20 fuel blends were produced using methyl esters of cashew nutshell and jamun seed oils to test the performance of the common rail direct injection engine. To improve the engine performance, injection parameters such as nozzle geometry, injection time, and injector opening pressure are used. Improved brake thermal efficiency and lower emissions of smoke, hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) were achieved with the help of advancing the injection timing, raising the injector opening pressure, and increasing the number of injector nozzle holes. In addition to reducing the ignition delay, extending the combustion duration, and increasing the peak pressure, the revised injection settings also boosted the heat release rates. At the maximum load, compared to CHNOB B20, JAMNSOB B20 showed a significant rise in the brake thermal efficiency (BTE) by 4.94% and a considerable decrease in smoke emissions (0.8%) with an increase in NOx (1.45%), by varying the injection timing, injection pressure, and nozzle geometry of the common rail direct injection (CRDI) engine. Full article