To address challenges of high ignition energy and slow combustion propensity in marine natural gas engines, this study proposes a dual-fuel combustion strategy using port fuel injection natural gas and centrally gasoline direct-injected (GDI). Through integrated computational fluid dynamics (CFD) simulations and experimental validation, the thermodynamic impacts of gasoline-induced active stratification near the spark plug are systematically evaluated. Results demonstrate that the GDI-natural gas (NG) configuration significantly enhances combustion performance compared to pure NG operation. Optimized ignition timing and fuel stratification elevate the peak heat release rate by 11.9%, increase indicated thermal efficiency (ITE) by 1%, raise peak cylinder pressure by 1.1 MPa, and reduce combustion duration by 6.2%. Kinetic analysis confirms that gasoline reactivity accelerates flame propagation, suppresses cycle variability, and extends the stable ignition window. This work provides a practical framework for implementing stratified combustion in marine engines to achieve higher efficiency.
Through the utilization of the CoFlame code, this study examines the impact of CO2/H2O on the generation of soot in high-pressure ethylene laminar diffusion flames. The computational predictions show good consistency with the experimental measurements. The soot yield escalates with increasing pressure, whereas both the flame temperature and its associated peak values exhibit a gradual decline across all oxygen-rich conditions. Under increasing pressure, the maximum rates of soot production and oxidation increase, and the nucleation rate shifts from a single peak to a double-peak profile in the same oxygen-rich environment. At elevated pressures, the atmosphere of O-2/H2O has the most inhibiting influence on soot formation, followed by O-2/CO2, while O-2/N-2 displays the weakest suppression. Quantitatively, the O-2/N-2 atmosphere yields the highest peak rates for both soot formation and oxidation: the formation rate reaches 1.25 & times; 10(-3) g/cm(3)/s, and the O-2 oxidation rate attains a maximum of 0.35 & times; 10(-3) g/cm(3)/s. Conversely, the O-2/CO2 atmosphere results in the lowest soot generation rates. Under the O-2/H2O atmosphere, soot generation is slightly higher than that under O-2/CO2; however, oxidation is predominantly governed by OH radicals, with a peak value of 0.25 & times; 10(-3) g/cm(3)/s, rather than by O-2. Notably, this OH-driven peak exceeds the O-2 oxidation peak observed in the O-2/CO2 case. Furthermore, the mole fractions of C6H6, C16H10, and C2H2 are found to decrease monotonically with increasing pressure. Finally, a sensitivity analysis of the key elementary reactions is also presented to elucidate the underlying chemical kinetics.
Al2O3 nanoparticles serve as a potential additive to improve engine characteristics, shortening ignition time, earlier combustion initiation, and reducing heat release in diesel engines run on vegetable oil-based fuels. Injection pressure (IP) is also one vital parameter that influences atomization and spray characteristics of fuel, affecting engine characteristics. This article embodies the injection pressure adjustment effects on diesel engine characteristics for Al2O3 nanoparticle-seeded Nahar vegetable oil-diesel blend. The N20D80 (20% Nahar vegetable oil + 80% diesel) blend seeded with 50 ppm Al2O3 nanoparticles at IPs of 170 bar, 200 bar, and 230 bar has been investigated. Compared to diesel, the N20D80 blend achieved 2.03% higher brake thermal efficiency (BTE) at 230 bar, whilst the N20D80A50 (N20D80 + 50 ppm Al2O3 nanoparticles) blend exhibited almost identical BTE to diesel. The test blends exhibited almost similar brake-specific fuel consumption (BSFC) to diesel. At 230 bar, the N20D80 blend reduces up to 18.95% in carbon monoxide (CO) and 10.11% in carbon dioxide (CO2), while the corresponding emissions reduce up to 25% and 34.15% for the N20D80A50 blend. The reduction in the emissions of oxides of nitrogen (NOx) were recorded up to 31.72% for the N20D80 blend at 230 bar, while N20D80A50 recorded 47.18% at 170 bar.
Based on the theory of finite-time thermodynamics, a model of the reversible ground-source heat pump cycle accounting for heat transfer losses is established. Research shows that when the flow rate on the evaporator side and the condenser side is in the effective range 20-100 m(3)/h, the theoretical limit unit coefficient of performance (COP) of the ground-source heat pump under the refrigeration condition can reach the extreme value of 10.7, while the theoretical limit unit COP based on the reverse Carnot cycle is 20.1. The theoretical limit unit COP of the ground-source heat pump under heating conditions can reach the extreme value of 9.8, while the theoretical limit unit COP based on the reverse Carnot cycle is 12.9. Under the refrigeration condition, in order to improve the unit COP, the flow rate on the evaporator side can be properly reduced, and the flow rate on the condenser side can be increased. Under the heating condition, in order to improve the unit COP, the flow rate on the condenser side can be properly reduced, and the flow on the evaporator side can be increased. The unit COP improves by 11.3% after optimization during the cooling season compared with the benchmark COP. The unit COP improves by 5.4% during the heating season after optimization, compared with the baseline.
Abstract Transpiration cooling through sintered metallic porous media is a promising active thermal-protection strategy for high-heat-flux aerospace and propulsion applications, yet the relative influence of the solid material, the pore architecture, and the pore diameter on cooling performance has not been established within a single, internally consistent framework. This study presents a combined experimental and numerical investigation that decouples and ranks these three parameters. Four sintered porous specimens—comprising a titanium powder, a sintered SS316L powder, and SS316L wire mesh at pore diameters of 80 and 100 µm—were tested in a rectangular channel over a Reynolds-number range of 38,000–70,000, with cooling effectiveness, surface temperature, and pressure drop measured across a nine-point thermal-imaging grid. A two-dimensional local thermal nonequilibrium (LTNE) Darcy–Forchheimer model employing physically based inertial coefficients, with no calibration against the thermal data, was developed to interpret the measurements. The results establish a clear sensitivity hierarchy in which solid thermal conductivity exerts the dominant influence, pore architecture exerts a secondary influence, and pore diameter exerts a comparatively minor influence: the titanium specimen attained cooling effectiveness values of 0.77–0.88 against 0.567–0.677 for the SS316L wire mesh, the isotropic sintered powder outperformed the anisotropic wire mesh, and the difference between the 80 µm and 100 µm meshes was limited to approximately 2.3%. The model reproduced the measured cooling effectiveness with a root-mean-square error of 0.090 while recovering physically consistent injection velocities and revealed that the classical Kozeny–Carman relation over-predicts the permeability of consolidated woven meshes by up to two orders of magnitude—identifying the effective permeability as the principal source of residual model uncertainty. The combined findings yield validated design guidance for transpiration-cooled components, prioritizing high-conductivity matrices and isotropic pore architectures, and identify direct permeametry as the key measurement required to render the flow closure fully predictive.
