An experimental study regarding methanol–diesel dual-fuel (DF) engines was conducted on a modified engine to explore the effects of pilot injection timing and period on the two-stage combustion process caused by the pilot injection strategy. In this study, the two-stage combustion process was determined according to the first two peaks of the second derivative of an in-cylinder pressure (d²p/dφ²) curve. The results show that the peak pressure rise rate (PRR) tended to decrease with advancing pilot injection timing at a high co-combustion ratio (CCR), which reduced combustion noise. The start of the combustion of the main injection diesel (SOC2) could be advanced by increasing the pilot injection period or advancing pilot injection timing at a 42% CCR. At an 18% CCR, the pilot injection timing and period had no significant effect on SOC2. With the advancement of pilot injection timing, the start of the combustion of pilot injection diesel (SOC1) advanced, and generally, the coefficient of variation of the PRR (COV_PRR) of the two-stage combustion process increased first and then decreased. However, with the increase in the pilot injection period, SOC1 almost always remained constant and the COV_PRR of the two-stage combustion process generally increased.

The oil-free lubrication seal of a piston rod plays an important role in the application of a Stirling engine. Parallel offset in a piston rod ruins the symmetry of the seal and affects the sealing performance when the seal is worn. In this paper, based on a motion analysis and the finite element method, a three-dimensional model of the Cap-seal was established, and its performance was numerically and experimentally investigated. The results show that parallel offset of the piston rod increases the possibility of seal damage and has no obvious effect on leakage. Under high pressures and low pre-compression ratios, the Cap-seal shows a good sealing capability and exhibits a higher propensity for mechanical damage. A good agreement was obtained between the numerical and experimental results. This study offers guidelines regarding the design and application of oil-free lubrication seals for a Stirling piston rod.

The traditional decomposition–combination wind speed forecasting model has high complexity and a long calculation time. As a result, an ultra-short-term wind speed hybrid forecasting model based on a broad learning system (BLS) that combines improved variational mode decomposition (EPSO-VMD, EVMD) and subseries reconstruction (SR) is proposed in this work. The values of K and α in the EVMD are determined by minimum mean envelope entropy (MMEE) and enhanced particle swarm optimization (EPSO), and EVMD is used to decompose the original wind speed data. SR is applied to recombine the subseries obtained by EVMD to improve the forecasting efficiency. The sample entropy (SE) is used to quantify the subseries’ complexity, and they are then adaptively divided into high-entropy and low-entropy subseries. Adjacent high-entropy subseries of approximate entropy values are merged to obtain a new group of reconstructed high-entropy subseries, while the low-entropy subseries merge into a new subseries as well. Then, the forecasting results of the reconstructed high- and low-entropy subseries are calculated via the BLS and ARIMA models. Numerical simulation results show that the proposed method is more effective than traditional methods.

Oxygen-containing alternative fuels have excellent potential to improve diesel fuel economy and reduce particulate matter (PM) emissions. In this study, a novel mixed dialkyl oxalate (mDAO) as an additive was applied to substitute conventional diesel to investigate the effects of mDAO on the combustion and emission characteristics of a high-pressure common-rail diesel engine. The research conducted suggested that the peak pressure rise rate in the main injection stage and the peak in-cylinder pressure presented the rising tendency with the increased mass fraction of mDAO at most test conditions. With the addition of mDAO, the in-cylinder temperature (T) and brake thermal efficiency (BTE) were higher than that of pure diesel. When the mass fraction of mDAO in the mDAO/diesel blend was 30%, the improvement of BTE was most obvious. The ignition delay was prolonged as the mass fraction of mDAO was increased due to the lower cetane number of the mDAO. In addition, adding mDAO into diesel had an effective impact on the reduction of PM emissions, while the nitrogen oxide (NO _x ) emissions deteriorated. These results indicate that mDAO is a great potential diesel alternative fuel.

The development of green and low-carbon new energy is one of the effective ways to deal with environmental pollution and climate change. Methanol, as an electrocatalytic product, is an excellent energy source and fuel. However, liquid methanol poses issues such as volatility, flammability, and explosiveness during use and long-term storage. This study presented a new methanol–sodium stearate–water-mixed gel. The performance of this mixed gel as a methanol energy storage carrier was evaluated. The results indicated that the gel points of the mixed gel increased with the increased contents of water and gelling agent. The maximum gel point reach approximately 35 °C, which is beneficial for reducing the requirements for the storage temperature. However, an excessive content of the gelling agent would lead to a decrease in the calorific value. The calorific value of the mixed gel containing 10% water is comparable to that of the mixed gel containing 5% gelling agent. Therefore, the scheme of adding water to increase the gel point has a better effect. Additionally, as the content of the gelling agent increased, the three-dimensional network structure formed by the interwoven fibers within the mixed gel became more compact. Meanwhile, the precipitation phenomenon of the gelling agent occurred during the gelation process, resulting in the lower structure of the mixed gel being denser than the upper structure. Therefore, in the large-scale production process of the mixed gel, the gel preparation container should be selected to be flat in shape to improve the uniformity.

To investigate the interaction mechanism between temperature gradients and material temperature dependency in wheel-rail contact behavior, a three-dimensional thermomechanical coupled finite element model was established. Heat flux density, normal/tangential loads, wheel-rail interfacial heat transfer boundary conditions, and surface convective heat transfer coefficients were applied to systematically examine temperature field evolution and its influence on stress-strain characteristics. The results indicated that: (1) Nonlinear temperature growth was observed in the contact patch, with radial temperature gradients significantly exceeding circumferential and axial gradients; (2) Temperature field heterogeneity was dominated by frictional heat source spatial distribution; (3) Temperature-dependent elastic modulus variations increased strain magnitudes by 64%–571%, while reduced friction coefficients induced differential evolution of circumferential/axial normal and shear strains; (4) Radial-circumferential shear strain reversal triggered shear instability. Stress field analysis revealed dominance of normal stresses and radial-circumferential shear stresses, with maximum stress offset ratios reaching 11.5% due to temperature gradient-driven strain redistribution. Yield strength and Poisson’s ratio were observed to inversely regulate stress spatial distributions. The coupled mechanism between thermal gradient effects and temperature-dependent material properties was clarified, providing theoretical support for optimizing wheel-rail thermomechanical performance and thermal damage assessment.