Search Results (81)

In this study, we comprehensively analyzed material consumption (fuel, hydraulic oil, lubricants, and AdBlue fluid) and estimated carbon dioxide emissions during logging operations. This study was carried out in the northeastern part of Poland. Four harvesters and four forwarders representing two manufacturers (John Deere-Deere & Co., Moline, USA, and Komatsu Forest AB, Umeå, Sweden) were analyzed to compare their operational efficiency and constructional influences on overall operating costs. Due to differences in engine emission standards, approximate greenhouse gas emissions were estimated. The results indicate that harvesters equipped with Stage V engines have lower fuel consumption, while large forwarders use more consumables than small ones per hour and cubic meter of harvested and extracted timber. A strong positive correlation was observed between total machine time and fuel consumption (r = 0.81), as well as between machine time and total volume of timber harvested (r = 0.72). Older and larger machines showed about 40% higher combustion per unit of wood processed. Newer machines meeting higher emission standards (Stage V) generally achieved lower CO₂ and other GHG emissions compared to older models. Machines with Stage V engines emitted about 2.07 kg CO₂ per processing of 1 m³ of wood, while machines with older engine types emitted as much as 4.35 kg CO₂ per 1 m³—roughly half as much. These differences are even more pronounced in the context of nitrogen oxide (NO_x) emissions: the estimated NO_x emissions for the older engine types were as high as ~85 g per m³, while those for Stage V engines were only about 5 g per m³ of harvested wood. Continuing the study would need to expand the number of machines analyzed, as well as acquire more detailed performance data on individual operators. A tool that could make this possible would be fleet monitoring services offered by the manufacturers of the surveyed harvesters and forwards, such as Smart Forestry or Timber Manager. Full article

Ammonia (NH₃) is a promising carbon-free marine fuel that is aligned with the International Maritime Organization’s (IMO) decarbonization targets. However, its high toxicity and flammability pose serious explosion hazards, particularly in confined fuel preparation spaces. This study investigates the influence of the ignition source location on the explosion characteristics of ammonia within an ammonia fuel preparation room using computational fluid dynamics (CFD) simulations via the FLACS platform. Nineteen ignition scenarios are established along the X-, Y-, and Z-axes. Key parameters, such as the maximum overpressure, pressure rise rate, reduction rate of flammable gas, ignition detection time, and spatial–temporal distributions of temperature and combustion products, are evaluated. The results show that the ignition location plays a critical role in the explosion dynamics. Ceiling-level ignition (Case 19) produced the highest overpressure (4.27 bar) and fastest pressure rise rate (2.20 bar/s), indicating the most hazardous condition. In contrast, the forward wall ignition (Case 13) resulted in the lowest overpressure (3.24 bar) and limited flame propagation. These findings provide essential insights into the risk assessment and safety design of ammonia-fueled marine systems. Full article

Natural gas hydrate (NGH hereafter), commonly known as combustible ice ((CH₄)n·mH₂O), is an abundant non-conventional clean energy resource. It is mainly located in permafrost areas and submarine sediment layers at depths of 0–200 m and 300~3000 m underwater. Submarine NGH accounts for about 97%. Its commercial mining may be a solution to mankind’s future energy problems, as well as the beginning of a series of geological risks. These risks can be divided into two categories: natural geological hazards and secondary geological accidents. Based on the viewpoints of Earth system science researchers, this paper discusses the main potential geo-hazards of submarine NGH mining: stratum subsidence, seafloor landslides, the greenhouse effect, sand piping, well blowout, and wellbore instability. To minimize the potential catastrophic impacts on the Earth’s ecosystem or mechanical accidents, corresponding technical precautions and policy suggestions have been put forward. Hopefully, this paper will provide a useful reference for the commercial mining of NGH. Full article

The solid-fuel scramjet has become a potential power device for hypersonic missiles in the future and has important military application prospects due to its advantages in gas flow regulation, flame stability, and blended combustion efficiency. This paper summarizes the research progress of three types of solid-fuel scramjet, including a large number of landmark numerical and experimental results. At the same time, the research progress of supersonic steady combustion and combustion enhancement technology, thermal protection technology, and the improvement of solid-fuel and combustion performance are reviewed. On this basis, the key technologies of the solid solid-fueled scramjet are summarized, and several internal scientific problems are summarized, such as the combustion organization strategy of the wide velocity domain solid rocket scramjet, efficient combustion chamber loading and thermal bulking technology, combustion instability, etc. Finally, some suggestions for the future development of the solid-fuel scramjet are put forward. Full article

In the last decades the impact of wildfires on forest ecosystem and human assets has steadily increased. Forest operations can help to reduce the spread rate and intensity of wildfires by limiting the biomass available for combustion. Fuel removal is mainly done with preventive silviculture works which, in the Mediterranean basin, typically feature a negative economic balance. The introduction of small-sized forest machines may enhance efficiency and safety of such operations. The study compares the performance of the common motor-manual work system with an innovative machine performing both harvesting and forwarding of biomass. The study took place in a post-fire regenerated Pinus halepensis Mill. area with high fuel accumulation. Three plots were selected to represent the main development stages of this type of forest, respectively with a density of about 1700, 5000 and 9600 trees∙ha⁻¹. The machine showed a clear advantage over the manual system with the lower and intermediate trees density, where the capacity to valorize the biomass reduced the overall balance per hectare respectively to 19% and 50% of the alternative. This allows to cover the whole operation with the local public subsidy, unlike the manual system. With the higher density, the overall balance is unfavorable for both work systems and different solutions should be tested. Full article

Phenolic aerogel is one of the most widely used lightweight thermal protective materials at present. With changes in the application environments, higher requirements are put forward for the heat resistance and mechanical properties of phenolic aerogel. In this paper, boric acid was used to modify phenolic resin, and then boron-modified phenolic aerogel was prepared. The chemical structure of modified phenolic resin was studied by infrared spectroscopy (FTIR). The microstructure, thermal stability, heat resistance in air, and compression resistance of phenolic aerogel were studied by volume shrinkage, scanning electron microscope, thermogravimetric analysis, high-temperature combustion test, and mechanical test. The results showed that the modification introduced boron oxygen bonds on the phenolic main chain. The compatibility difference between boron and phenolic resin with different content has a significant impact on the performance of phenolic aerogel. When boron content is 5–10% of phenolic resin, the network structure and thermal stability of phenolic aerogel can be significantly improved, and the maximum compressive strength of phenolic aerogel can also be improved. Boron-modified phenolic aerogel is expected to play an important role in the field of thermal insulation. Full article

The speed of the engine–propeller directly determines the power output for Unmanned Aerial Vehicles (UAV) with internal combustion engines. However, variable air pressure can impact the engine’s air exchange and combustion processes, causing minor changes that affect the engine speed and result in variations in propeller thrust. A single-loop control strategy was proposed incorporating a feed-forward air-intake model with throttle feedback for small UAVs equipped with a two-stroke scavenging internal combustion engine and propeller. The feed-forward model was built with a simplified model of the airpath based on the scavenging measurement, which combined the tracer gas method and CFD simulation by a two-zone combustion chamber model. The feed-forward control strategy was built by a simplified crankcase–scavenging–cylinder model with CFD results under different air pressures, demonstrating a 1% error compared with CFD simulation. An iterative method of feed-forwarding was suggested for computing efficiency. A feedback controller was constructed using fuzzy PID for minimal instrumentation in engine control for small aircraft. Finally, the single-loop control strategy was validated through simulation and experimentation. The results indicate an 89% reduction in average speed error under varying air pressure and an 83.7% decrease in average speed overshoot in continuous step speed target experiments. Full article

Numerical and experimental approaches are conducted to investigate the flow features and secondary combustion performance induced by different air–fuel ratios in a boron-based solid-ducted rocket engine. The results indicated that the afterburning chamber flow features become more complicated owing to the multiple nozzles of the gas injector, and a number of recirculation zones are generated. Because of this, the mixing of the fuel gas and incoming air is enhanced. When the air–fuel ratio decreases, the heat release in the afterburning chamber increases continuously, which causes the pre-combustion shock train to continue to propagate upstream in the subsonic diffuser of the inlet isolator, along with the boundary layer separation zone also moving forward, and the stability margin of the direct-connect inlet decreasing gradually. Furthermore, the direct-connect inlet works at a critical state with an air–fuel ratio of 11.5. As the mass flow rate of the fuel-rich gas rises gradually, the engine thrust gradually increases, and the number of vortexes in the afterburning chamber and the corresponding region affected by the vortexes generally decrease. Meanwhile, the mixing and combustion of the fuel-rich gas and incoming flow were not substantially changed. Additionally, the combustion efficiency and specific impulse are proportional to the air fuel ratio. Full article

Of all the construction waste, the building interior decoration and renovation waste (D&R waste) is difficult to dispose of and recycle due to its complex components and varied producers. The goal of this study is to reveal the current situation of D&R waste disposal through case studies and put forward the correlation proposal to improve standards of D&R waste recycling. This study investigated the various stages of the D&R waste management process, including generation, collection, transportation, sorting, recycling, and landfilling. Detailed studies were conducted for (i) the composition of D&R waste and (ii) the material flow analysis (MFA) of D&R waste recycling in different cases with different sorting technology. The results show that (i) concrete, stone, and other hard inorganic materials accounted for about 35–55% of the total. Soft inorganic materials such as aerated concrete and gypsum made up 5–25%, slag 15–20%, timber 5–10%, combustible matter such as plastic, rubber, and paper 9–12%, and glass and metal 1–5%, and (ii) artificial intelligence (AI) sorting offers better sorting performance and economic advantages over manual sorting, promoting the application of artificial AI sorting equipment as important solutions to face the key challenges of D&R waste recycling. Full article

Currently, in the two technological approaches for using diesel pilot injection to ignite methanol and partially substituting diesel fuel with methanol, neither can fully achieve carbon neutrality in the context of internal combustion engines. Compression-ignition direct-injection methanol marine engines exhibit significant application potential because of their superior fuel economy and lower carbon emissions. However, the low cetane number of methanol, coupled with its high ignition temperature and latent heat of vaporization, poses challenges, especially amidst increasingly stringent marine emission regulations. It is imperative to comprehensively explore the impacts of the engine geometry, intake boundary conditions, and injection strategies on the engine performance. This paper first investigates the influence of the compression ratio on the engine performance, subsequently analyzes the effects of intake conditions on methanol ignition characteristics, and finally compares the combustion characteristics of the engine under different fuel injection timings. When the compression ratio is set at 13.5, only an injection timing of −30 °CA can initiate methanol compression ignition, but the combustion is not ideal. For compression ratios of 15.5 and 17.5, all the injection timings studied can ignite methanol. Reasonable increases in the intake pressure and intake temperature are beneficial for methanol compression ignition. However, when the intake temperature rises from 400 K to 500 K, a decrease in the thermal efficiency is observed. Particularly, at an injection timing of −30 °CA, both the peak cylinder pressure and peak cylinder temperature are higher, the ignition occurs earlier, the combustion process shifts forward, and the combustion efficiency and indicated thermal efficiency are at higher levels. Furthermore, the overall emissions of NO_X, HC, and CO are relatively low. Therefore, selecting an appropriate injection timing is crucial to facilitate the compression ignition and combustion of methanol under low-load conditions. Full article

Electric and hybrid vehicles are known for their significant reduction in road noise. However, concerns have emerged regarding their silent operation, potentially increasing risks for other road users. To mitigate this, the Acoustic Vehicle Alert System (AVAS) has been mandated by regulations such as R138 by UNECE in the USA and Europe. This regulation dictates the generation of sound in electric vehicles of categories M and N1 during normal, reverse, and forward motion without the internal combustion engine engaged. Compliance involves meeting specific sound requirements based on vehicle mode and condition. This paper introduces a Python-based approach to designing digital horn sounds, leveraging music theory and signal processing techniques to replace traditional mechanical horns in electric vehicles equipped with AVAS devices. The aim is to offer a practical and efficient means of generating digital horn sounds using this software. The software includes an application capable of producing and customizing horn sounds, with the HornSoundGeneratorGUI class providing a user-friendly interface built with the Tkinter library. To validate the digital horn produced sounds by the software and ensure compliance with AVAS regulations, comprehensive electrical and acoustic tests were conducted in a fully equipped quality laboratory. The results demonstrated that the sound levels achieved met the required 105–107 dB/2 m standard specified by the regulation. Full article

Hybrid power systems are now widely utilized in a variety of vehicle platforms due to their efficacy in reducing pollution and enhancing energy utilization efficiency. Nevertheless, the existing vehicle hybrid systems are of a considerable size and weight, rendering them unsuitable for integration into 25 kg compound-wing UAVs. This study presents a design solution for a compound-wing vertical takeoff and landing unmanned aerial vehicle (VTOL) equipped with an improved series hybrid power system. The system comprises a 48 V lithium polymer battery(Li-Po battery), a 60cc internal combustion engine (ICE), a converter, and a dedicated permanent magnet synchronous machine (PMSM) with four motors, which collectively facilitate dual-directional energy flow. The four motors serve as a load and lift assembly, providing the requisite lift during the take-off, landing, and hovering phases, and in the event of the ICE thrust insufficiency, as well as forward thrust during the level cruise phase by mounting the variable pitch propeller directly on the ICE. The entire hybrid power system of the UAV undergoes numerical modeling and experimental simulation to validate the feasibility of the complete hybrid power configuration. The validation is achieved by comparing and analyzing the results of the numerical simulations with ground tests. Moreover, the effectiveness of this hybrid power system is validated through the successful completion of flight test experiments. The hybrid power system has been demonstrated to significantly enhance the endurance of vertical flight for a compound-wing VTOL by more than 25 min, thereby establishing a solid foundation for future compound-wing VTOLs to enable multi-destination flights and multiple takeoffs and landings. Full article

The present work intends to make a scientific contribution to future drive technology in medium-duty road freight transportation that is as objective and fact-based as possible. In cooperation with a medium-sized forwarding company, 1-day transports, previously driven with diesel trucks, were examined. Using a physically based model, which was first validated by comparing simulated CNG drive data with real-world diesel data, the findings were transferred to battery electric trucks (BETs) and fuel cell trucks (FCETs) and extrapolated to 2050 based on expected technological developments. The model makes statements based on the results of the investigated application regarding specific consumption, greenhouse gas (GHG) emissions, consumption shares and recuperation. The CNG combustion technology (ICET-CNG) serves as a reference. BETs in this application have the lowest emission and consumption values: BET₂₀₅₀ will consume a third of the energy and emit a fifth of the GHGs of ICET-CNG₂₀₂₄. The weight of the battery leads to higher consumption values. FCETs have higher fuel consumption due to their longer drive trains. This is partially compensated by their lower weight: FCET₂₀₅₀ will consume 40% of the energy and emit a third of the GHGs of ICET₂₀₂₄. In long-distance traffic, aerodynamic drag is the dominant consumption factor, accounting for 40%, which should be addressed in further truck development. Recuperation extends the range by 3–7%. Full article

The flashover mechanism in an aircraft cargo compartment under low pressure was investigated in this study. A series of fire experiments were conducted in a scale model of a one-quarter volume FAA standard aircraft cargo compartment at 96 kPa and 60 kPa. The ignition of single-walled corrugated cardboard was chosen as the criterion of the flashover. The influence of different fire sizes and fuel types on the flashover was studied by comparing the average temperature of the smoke layer, the radiation heat flux at the floor level, and the heat release rate of the fire source. The critical condition and behavior of the flashover were analyzed. The results show that under low pressure, the flashover occurs at a higher temperature and radiation heat flux. Increasing the fire source size brings the flashover forward. At 60 kPa and 96 kPa, the cardboard ignites under a flashover when the average temperature of the smoke layer reaches 551 °C and 450 °C, and the average radiant heat flux at the floor level reaches 19.6 kW/m² and 14 kW/m², respectively. In addition, the minimum fire size for a flashover is directly proportional to the heat of evaporation and inversely proportional to the heat of combustion. Full article

When a motor is accidentally started, the solid particles produced by fuel combustion have impact and erosion effects on the surrounding structure via gas ejection, and the structure of the bulkhead is damaged. Therefore, in this paper, the effect of solid particle phase motion on a bulkhead was investigated. A two-dimensional SST k-ω model was used for the analysis. The grid size of the core area of a supersonic jet was selected as R_N/24 by the calculation accuracy, and the resources and time consumption of the calculation were comprehensively considered. Based on the simulation of supersonic impact jets, the influence of the phase motion of solid particles was introduced, and the impact of a two-phase jet field on a wall was investigated. The addition of a particle phase created a hysteresis effect on the airflow, changing the shock structure of the pure gas-phase flow field. The rebound of the particle phase at the wall caused the waves in front of the wall to move forward and the stagnation bubble structures to disappear in some cases. The particle aggregation degree and collision angle would affect the particle erosion rate of solid bulkheads. The increase in particle jet impingement distance would change the distribution of particle aggregation and would influence the distribution of wall particle erosion rate and deposition rate. This paper would provide theoretical and engineering guidance for the safety protection design of magazines, which is of great significance for the safety assurance of ship magazines. Full article