Search Results (105)

As a key precursor of tropospheric ozone and secondary particulate matter, nitrogen oxides (NO_x) exert significant impacts on air quality. Traffic emissions represent a dominant source of near-surface NO_x. The widespread adoption of new energy vehicles (NEVs) has progressively transformed the automobile fleet composition, leading to measurable reductions in NO_x emissions. This study developed a NO_x emission inventory model to quantify the impact of NEV penetration on emission trends in Guangdong (2013–2022), under the assumption that the emission shares of internal combustion engine vehicles (ICEVs) and NEVs have no significant change in adjacent years. Results demonstrate that total vehicular NO_x emissions peaked in 2019 at 55.69 × 10⁴ tons (a 16.6% increase from 2018), followed by a consistent decline. ICEVs exhibited a declining emission share from 0.037 × 10⁴ tons/year in 2013 to 0.022 × 10⁴ tons/year in 2019—a 40.5% reduction, attributable to progressive technological advancements. Following a marginal increase (2019–2021), the emission share declined significantly to 0.019 × 10⁴ tons/year in 2022. In contrast, NEVs contributed to emissions reduction, with maximal mitigation observed in 2021 (−0.241 × 10⁴ tons). ICEVs initially demonstrated emission reductions (2014–2017), succeeded by a transient increase (11.7 × 10⁴ tons through 2021) before resuming decline in 2022. The NEV-driven mitigation effect intensified progressively from 2018 to 2021, with modest attenuation in 2022. Full article

A computational fluid dynamics (CFD) numerical simulation methodology was implemented to model transient heating processes in steel industry reheating furnaces, targeting combustion efficiency optimization and carbon emission reduction. The effects of oxygen concentration (O₂%) and different fuel types on the flow and heat transfer characteristics were investigated under both oxygen-enriched combustion and MILD oxy-fuel combustion. The results indicate that MILD oxy-fuel combustion promotes flue gas entrainment via high-velocity oxygen jets, leading to a substantial improvement in the uniformity of the furnace temperature field. The effect is most obvious at O₂% = 31%. MILD oxy-fuel combustion significantly reduces NOx emissions, achieving levels that are one to two orders of magnitude lower than those under oxygen-enriched combustion. Under MILD conditions, the oxygen mass fraction in flue gas remains below 0.001 when O₂% ≤ 81%, indicating effective dilution. In contrast, oxygen-enriched combustion leads to a sharp rise in flame temperature with an increasing oxygen concentration, resulting in a significant increase in NOx emissions. Elevating the oxygen concentration enhances both thermal efficiency and the energy-saving rate for both combustion modes; however, the rate of improvement diminishes when O₂% exceeds 51%. Based on these findings, MILD oxy-fuel combustion using mixed gas or natural gas is recommended for reheating furnaces operating at O₂% = 51–71%, while coke oven gas is not. Full article

A brick kiln was experimentally studied to measure the transient temperature of hot gases and the compressive strength of the bricks, using pine wood as fuel, in order to evaluate the thermal performance of the actual system. In addition, a transient combustion model based on computational fluid dynamics (CFD) was used to simulate the combustion of natural gas in the brick kiln as a hypothetical case, with the aim of investigating the potential benefits of fuel switching. The theoretical stoichiometric combustion of both pine wood and natural gas was employed to compare the mole fractions and the adiabatic flame temperature. Also, the transient hot gas temperature obtained from the experimental wood-fired kiln were compared with those from the simulated natural gas-fired kiln. Furthermore, numerical simulations were carried out to obtain the transient hot gas temperature and NOx emissions under stoichiometric, fuel-rich, and excess air conditions. The results of CO₂ mole fractions from stoichiometric combustion demonstrate that natural gas may represent a cleaner alternative for use in brick kilns, due to a 44.08% reduction in emissions. Contour plots of transient hot gases temperature, velocity, and CO₂ emission inside the kiln are presented. Moreover, the time-dependent emissions of CO₂, H₂O, and CO at the kiln outlet are shown. It can be concluded that the presence of CO mole fractions at the kiln outlet suggests that the transient combustion process could be further improved. The low firing efficiency of bricks and the thermal efficiency obtained are attributed to uneven temperatures distributions inside the kiln. Moreover, hot gas temperature and NOx emissions were found to be higher under stoichiometric conditions than under fuel-rich or excess of air conditions. Therefore, this work could be useful for improving the thermal–hydraulic and emissions performance of brick kilns, as well as for future kiln design improvements. Full article

Hydrogen is a promising zero-carbon fuel for internal combustion engines; however, the geometric optimization of injectors for low-pressure direct-injection (LPDI) systems under lean-burn conditions remains underexplored. This study presents a high-fidelity optimization framework that couples a validated computational fluid dynamics (CFD) combustion model with a surrogate-assisted multi-objective genetic algorithm (MOGA). The CFD model was validated using particle image velocimetry (PIV) data from non-reacting flow experiments conducted in an optically accessible research engine developed by Sandia National Laboratories, ensuring accurate prediction of in-cylinder flow structures. The optimization focused on two critical geometric parameters: injector hole count and injection angle. Partial indicated mean effective pressure (pIMEP) and in-cylinder NO_x emissions were selected as conflicting objectives to balance performance and emissions. Adaptive mesh refinement (AMR) was employed to resolve transient in-cylinder flow and combustion dynamics with high spatial accuracy. Among 22 evaluated configurations including both capped and uncapped designs, the injector featuring three holes at a 15.24° injection angle outperformed the baseline, delivering improved mixture uniformity, reduced knock tendency, and lower NO_x emissions. These results demonstrate the potential of geometry-based optimization for advancing hydrogen-fueled LPDI engines toward cleaner and more efficient combustion strategies. Full article

Some of the popular and successful atmospheric pressure fuel/air plasma-assisted combustion methods use repetitive ns pulsed discharges and dielectric-barrier discharges. The transient phase in such discharges is dominated by transport under strong space charge from ionization fronts, which is best characterized by the streamer model. The role of the nonthermal plasma in such discharges is to produce radicals, which accelerates the chemical conversion reaction leading to temperature rise and ignition. Therefore, the characterization of the streamer and its energy partitioning is essential to develop a predictive model. We examine the important characteristics of streamers that influence combustion and develop some macroscopic parameters. Our results show that the radicals’ production efficiency at an applied field is nearly independent of time and the radical density generated depends only on the electrical energy density coupled to the plasma. We compare the results of the streamer model to the zero-dimensional uniform field Townsend-like discharge, and our results show a significant difference. The results concerning the influence of energy density and repetition rate on the ignition of a hydrogen/air fuel mixture are presented. Full article

This study presents a comprehensive finite element investigation into the design optimization of an ultra-high temperature ceramic matrix composite thruster for green bipropellant systems. Focusing on ZrB₂–SiC–Cfiber composites, it explores their thermal and mechanical response under realistic transient combustion conditions. Two geometries, a simplified and a complex full-featured model, were evaluated to assess the impact of geometric fidelity on stress prediction. The complex thruster model (CTM) offered improved resolution of temperature gradients and stress concentrations, especially near flange and convergent regions, and was adopted for optimization. A parametric study with nine wall thickness profiles identified a 2 mm tapered configuration in both convergent and divergent sections that minimized mass while maintaining structural integrity. This optimized profile reduced peak thermal stress and overall mass without compromising safety margins. Transient thermal and strain analyses showed that thermal stress dominates initially (≤3 s), while thermal strain becomes critical later due to stiffness degradation. Damage risk was evaluated using temperature-dependent stress margins at four critical locations. Time-dependent failure maps revealed throat degradation for short burns and flange cracking for longer durations. All analyses were conducted under hot-fire conditions without cooling. The validated methodology supports durable, lightweight nozzle designs for future green propulsion missions. Full article

This article reviews the physical and chemical mechanisms associated with unsteady swirl-stabilized partially or fully lean premixed combustion. The processes of flame stabilization, mode conversion, swirl number oscillation, equivalence ratio oscillation, and vortex rollup are described. The key challenges associated with flow-flame dynamics for several sources of perturbations are presented and discussed. The Rayleigh criterion is discussed. This article summarizes the scientific knowledge gained on swirling flames dynamics in terms of modeling, theoretical analysis, and transient measurements with advanced diagnostics. The following are specifically documented: (i) the effect of the swirler on swirling flames; (ii) the analytical results, computational modeling, and experimental measurements of swirling flame dynamics; (iii) the influence of flow features on flame response of swirling flames for combustion instabilities studies; and (iv) the identification and description of the combustion dynamics mechanisms responsible for swirl-stabilized combustion instabilities. Relevant elements from the literature in this context for hydrogen fuel are included. Full article

As the core process of the thermal treatment of municipal solid waste (MSW), incineration process optimization has become a frontier topic in the field of environmental engineering. This study took a 500 t/d incinerator for engineering application as the research object. Based on a two-fluid model, a three-dimensional transient model of a proportional incinerator was established. The effects of primary air proportion and moisture content on the combustion state in the incinerator were verified and discussed using field test data, and the dynamic changes in flue gas temperature were predicted by a BPNN (Backpropagation Neural Network). The results show that the increase in air volume in the drying section promotes water evaporation but inhibits the devolatilization and combustion of fixed carbon. The position where complete devolatilization and fixed carbon combustion begins was delayed by 1.5 m~3 m. The moisture content (M) is negatively correlated with the devolatilization and combustion of fixed carbon. From M = 25% to M = 40%, the flue gas outlet temperature decreased by 140 K. In addition, a dynamic combustion BP neural network model with the movement of the grate under rated conditions was constructed, with the MSE (Mean Squared Error) being 1.629%. The model can learn data characteristics well and has a good prediction effect. This study provides a scientific basis for optimizing the operating parameters of municipal solid waste incinerators, helps to optimize the incineration process, and is of great significance to the thermal treatment of MSW. Full article

Methanol/diesel hybrid−powered vessels represent a significant advancement in green and low−carbon innovation in the maritime transportation sector and have been widely adopted across various shipping markets. However, the dual−fuel power system modifies the fire load within the engine room compared to traditional vessels, thereby significantly influencing the fire safety of methanol/diesel−powered ships. In this study, anhydrous methanol and light−duty diesel (with 0 °C pour point) were used as fuels to investigate the mixed combustion characteristics of these immiscible fuels in circular pools with diameters of 6, 10, 14, and 20 cm at various mixing ratios. By analyzing the fuel mass loss rate, flame morphology, and heat transfer characteristics, it was determined that methanol and diesel exhibited distinct stratification during combustion, with the process comprising three phases: pure methanol combustion phase, transitional combustion phase, and pure diesel combustion phase. Slopover occurred during the transitional combustion phase, and its intensity decreased as the pool diameter or methanol fuel quantity increased. Based on this conclusion, a quantitative relationship was established between slopover intensity, pool diameter, and the methanol/diesel volume ratio. Additionally, during the transitional combustion phase, the average flame height exhibited an exponential coupling relationship with the pool diameter and the methanol/diesel volume ratio. Therefore, a modification was made to the classical flame height model to account for these effects. Moreover, a prediction model for the burning rate of methanol/diesel pool fires was established based on transient temperature variations within the fuel layer. This model incorporated a correction factor related to pool diameter and fuel mixture ratio. Additionally, the causes of slopover were analyzed from the perspectives of heat transfer and fire dynamics, further refining the physical interpretation of the correction factor. Full article

The Particle Image Velocimetry (PIV) Unit in the Combustion Science Experimental System (CSES) aboard the China Space Station (CSS) is designed for flow field measurements in microgravity combustion experiments. However, the lack of a reliable microgravity-compatible tracer particle seeder has hindered its practical application. To address this issue, the cyclone PIV particle seeder was proposed and evaluated through steady and transient numerical simulations using the Reynolds Stress Model (RSM) and Eulerian multiphase model to assess the effects of geometric parameters, gravity, and particle accumulation on flow characteristics and particle seeding performance. Ground-based cold jet and premixed combustion PIV experiments were also conducted. Results show that while the flow field of the cyclone particle seeder is generally similar to conventional cyclone separators, localized differences exist. Traditional optimization strategies of cyclone separators may not be applicable, while a longer vortex finder improved particle seeding performance compared to the shorter configuration and the guide vane design. By combining numerical simulations and experiment results, this study demonstrates the feasibility of using the cyclone particle seeder under microgravity conditions, provides key theoretical support for optimizing cyclone seeders, and enables flow field measurements in future microgravity combustion experiments aboard the China Space Station. Full article

This paper presents research concerning simulating the thermal firebrand effect due to its accumulation in exterior construction wall elements by developing a 3D finite element model (FEM) via ABAQUS (2022) software to analyze the exterior walls commonly applied to the exterior of dwellings in southern Europe and South America. A non-linear thermal transient analysis is undertaken, in which the results are directly compared with a previous experimental campaign, in which firebrands are deposited on localized surfaces of construction wall specimens, and the temperature is measured in the several layers of the construction elements. The walls are composite elements, made of different layer combinations of masonry brick and wood, varying the type of thermal insulation in the internal core from cork to classical rigid rockwool and polystyrene foam (XPS). It can be summarized from the results that the FEM effectively simulates the thermal response of brick, normal wood (NW), and cross-laminated timber (CLT) walls when insulated with materials like cork or rockwool coated with mortar against firebrand accumulation. However, the lack of accounting for uncontrolled combustion leads to inconsistent results. Additionally, for walls using XPS as the insulation material, the model requires further refinement to accurately simulate the melting phenomenon and its thermal impact. Full article

Turbocharged internal combustion engines offer efficient power-to-weight ratios, aiding in fuel-saving efforts within the automotive industry. However, when the flow is low, compressors show various instabilities, i.e., stall and inlet recirculation, which have a negative influence on their performance. This paper uses transient numerical simulations to explore the inlet recirculation phenomenon in a turbocharger compressor. The Reynolds-Averaged Navier–Stokes equations and k-ω SST turbulence model were solved using ANSYS CFX. The numerical model was verified using the experimental data for the design speed line. Analysis of mesh independence was performed to assess the discretization uncertainty near the design and surge line points. The results indicate that the inlet recirculation appears for moderate flows lower than design conditions. It shows significant radial and streamwise growth as the flow decreases. The reversed flow area increases more intensely in the radial direction at medium mass flow rates, whereas the streamwise growth is more substantial at low mass flow rates. The reversed flow reached 27% of the total inlet area at the point on the surge line. It was accompanied by a 15.7% drop in efficiency between the points with weak and strong inlet recirculation. The presented research indicates significant changes in the size of the inlet recirculation zone in the circumferential direction. It reaches its highest intensity close to the angular position of the volute tongue. Full article

Xinjiang is a region of China that suffers severe energy resource loss and air pollution resulting from long-term coalfield fires in near-surface inclined coal seams. Beneath these fire areas, abandoned mined-out goaf is common. Accidents easily occur during the treatment of such fire areas owing to the instability of strata overlying the goaf. Here, we carried out non-destructive exploration of the goaf below a fire area using the airborne transient electromagnetic method, accurately identifying the locations and sizes of 21 goaf areas. We then established a stratigraphic model using the thermal-solid coupling function in UDEC software. Our simulations showed that under the combined action of high temperature generated by coal combustion and high pressure generated by fire-fighting machinery, the maximum displacement and vertical stress in strata overlying the goaf were 1.42 m and 36 MPa, respectively. Such large displacement and stress values inevitably lead to the destabilization of overlying strata via turning, sliding, and tipping, seriously threatening the safety of mining personnel and machinery. In the field, the rock layer above the goaf was first accurately blasted, and then fire extinguishing was carried out after the overlying rock had collapsed and compacted. Full article

Vehicle system models can be roughly divided into two categories, dynamic and steady-state (or quasi-steady-state) models, and can be applied to evaluate vehicle transient performance such as vehicle longitudinal and lateral dynamics, as well as energy economies like fuel or electricity consumption. This paper reviews various energy consumption models for automotive systems, focusing on component- and vehicle-level models. As the foundation to calculate the energy consumption, powertrain component models of three main vehicle types (internal combustion engine (ICE) vehicles, electric vehicles (EVs), and hybrid vehicles) are reviewed with their key components, including internal combustion engines, electric motors, and batteries. Three types of vehicle energy consumption models are explored according to their interpretability: white-box, black-box, and grey-box models. Optimizing vehicle energy usage based upon a vehicle energy consumption model is reviewed from the aspects of eco-driving and eco-routing problems at the end of the paper. Eco-driving research primarily selects models focusing on transient performance; whereas eco-routing focuses on steady-state or quasi-steady-state conditions to balance the needs of model accuracy and calculation efficiency for real-time applications. This review aims to guide model selection and inspire future applications of energy consumption models for advancing sustainable automotive technologies. Full article

Advancements in fuel injection systems have dramatically improved the precision of controlling injected fuel mass or flow rate; a key factor in optimizing internal combustion engine (ICE) performance, emissions control, and fuel efficiency. This review systematically analyzes 145 scientific research papers from the last two decades, including older foundational works, tracing the evolution of injected mass control from early Bosch and Zeuch meters to advanced machine learning or physical models. This study draws upon research collected from the most reputable databases. Through both qualitative and quantitative analyses, the state-of-the-art of these systems is presented, and key innovations are highlighted regarding advanced control algorithms and real-time feedback mechanisms under various operational conditions such as high or transient loads and multi-stage injection strategies. Special attention is given to challenges in maintaining precise control with alternative fuels like biodiesel, hydrogen, or synthetic fuels, which exhibit different physical properties compared to traditional fuels. The findings emphasize the need for further research on injection control, especially in light of stringent emissions regulations. Improving these systems for next-generation ICEs is a key point for achieving cleaner, more efficient combustion and bridging the sustainability gap between traditional and future mobility solutions. Full article