Jun Fu

Ammonia is a green zero-carbon fuel, yet its low reactivity poses challenges, including difficult ignition and slow combustion rates. Compared to diesel or biodiesel, dimethyl ether (DME) has no C-C bonds, which means it produces almost no soot and has a high cetane number that helps it ignite easily. So, using the highly reactive DME to help ignite liquid ammonia is a good way to make it burn better. This study uses computer simulations to look at how well liquid ammonia and DME work together as fuel with different injection setups. Results indicate optimal DME ignition enhancement at injector spacing L = 6 cm, injection angle 180°, and ammonia energy share 70%, outperforming cases with spacings of 7–8 cm and angles of 150°, 120°, 90°, and 60°. At the same time, having shorter spacing during DME combustion leads to smaller areas for OH but more NH₂ formation, showing that ammonia is more effective at cooling the flame and that more ammonia is being used as fuel. Additionally, when DME is not burning, both OH and NH₂ areas grow larger at shorter spacings, showing that the fuel mixes sooner, the reaction areas get bigger, and the burning process is more complete. Regarding the bimodal NH₂ peaks, the initial peak reflects partial ammonia oxidation that is flame-entrained during DME combustion, while the secondary peak indicates the onset of autoignition, which is characterized by diminished reaction rates and reduced combustion intensity.

Given the nonlinear and time-varying characteristics of diesel engine speed control, a conventional proportional integral derivative (PID) controller is inadequate for addressing the lag or overshoot in the system response, and it struggles to adapt to complex dynamic changes under load. This study proposes a fuzzy proportional integral derivative (FPID) control,which is based on an improved sparrow search algorithm(ISSA) with the aim of enhancing the system’s adaptability. By refining the algorithm to augment its parameter control capabilities and employing test functions for experimental comparisons, the improved algorithm exhibited accelerated convergence and increased accuracy. The improved sparrow search algorithm is applied to two controllers for experimental comparison, and the results indicate that, in contrast to the traditional PID control algorithm, the FPID control algorithm reduces the adjustment time by 1.4 s and decreases the overshoot by 6.8% when the speed is adjusted to 2000 revolutions per minute (RPM). The duration for speed fluctuation stabilization under load changes of 8 and 10 is decreased by 18% and 30%, respectively, and the fluctuation deviation of the speed is reduced by 7% and 12%, respectively. Consequently, the implementation of FPID parameters tuned by the improved sparrow algorithm provides robust support for the stable operation of a diesel engine during speed fluctuations.

The airflow in the exhaust muffler can affect the sound propagation characteristics. In this work, For a single-cylinder diesel engine, an experimental bench was set up, and the accuracy of the simulation model was verified through the mutual comparison between the experimental data and the simulation results. the transmission loss of exhaust muffler of a single-cylinder diesel engine is analyzed numerically. In addition, the influence of airflow on the acoustic performance of muffler is studied and analyzed in detail. Finally, a finite element method, namely automatic matched layer (AML) is used to simulate the anechoic boundary conditions, and the value of transmission loss of muffler with and without airflow is calculated. Results demonstrate that: Considering the influence of airflow, the transmission loss value of the muffler shows the obvious increase in the low-frequency domain of 0–2000 Hz, particularly below 1000 Hz, with difference up to 50 dB and an average of approx. 30dB. Nevertheless, the airflow has minimal influence on transmission loss in the medium-high frequency of 2000–7000 Hz. The acoustic performance is greatly affected by the internal fluid flow, and the fluid flow is beneficial to improving the acoustic performance of mufflers, especially in the low-frequency domain. Additionally, the change of transmission loss curve is more complex when the influence of airflow is considered. The research results of this work provide a more accurate prediction method on the transmission loss in practical application, and of reference significance for future studies on the acoustic performance of mufflers.

With the continuous development of industrial automation, diesel engines play an increasingly important role in various types of construction machinery and power generation equipment. Improving the dynamic and static performance of the speed control system of single-cylinder diesel engines can not only significantly improve the efficiency of the equipment, but also effectively reduce energy consumption and emissions. Particle swarm optimization (PSO) fuzzy PID control algorithms have been widely used in many complex engineering problems due to their powerful global optimization capability and excellent adaptability. Currently, PSO-based fuzzy PID control research mainly integrates hybrid algorithmic strategies to avoid the local optimum problem, and lacks optimization of the dynamic noise suppression of the input error and the rate of change of the error. This makes the algorithm susceptible to the coupling of the system uncertainty and measurement disturbances during the parameter optimization process, leading to performance degradation. For this reason, this study proposes a new framework based on the synergistic optimization of the untraceable Kalman filter (UKF) and PSO fuzzy PID control for the speed control system of a single-cylinder diesel engine. A PSO-optimized fuzzy PID controller is designed by obtaining accurate speed estimation data using the UKF. The PSO is capable of quickly adjusting the fuzzy PID parameters so as to effectively alleviate the nonlinearity and uncertainty problems during the operation of diesel engines. By establishing a Matlab/Simulink simulation model, the diesel engine speed step response experiments (i.e., startup experiments) and load mutation experiments were carried out, and the measurement noise and process noise were imposed. The simulation results show that the optimized diesel engine speed control system is able to reduce the overshoot by 76%, shorten the regulation time by 58%, and improve the noise reduction by 25% compared with the conventional PID control. Compared with the PSO fuzzy PID control algorithm without UKF noise reduction, the optimized scheme reduces the overshoot by 20%, shortens the regulation time by 48%, and improves the noise reduction effect by 23%. The results show that the PSO fuzzy PID control method with integrated UKF has superior control performance in terms of system stability and accuracy. The algorithm significantly improves the responsiveness and stability of diesel engine speed, achieves better control effect in the optimization of diesel engine speed control, and provides a useful reference for the optimization of other diesel engine control systems. In addition, this study establishes the GT-POWER model of a 168 F single-cylinder diesel engine, and compares the cylinder pressure and fuel consumption under four operating conditions through bench tests to ensure the physical reasonableness of the kinetic input parameters and avoid algorithmic optimization on the distorted front-end model.

The acoustic performance of exhaust mufflers is a crucial metric for evaluating their effectiveness, with the inlet configuration significantly influencing sound attenuation. This study employs finite element analysis to numerically analyze side‐mounted and bottom‐mounted models at the inlet. Results indicate that within the low‐frequency range, the side‐mounted model exhibits notably superior sound attenuation compared to the bottom‐mounted model, with the internal baffle model showing a particularly significant improvement, averaging 25 dB higher in transmission loss. Conversely, in the high‐frequency range, the bottom‐mounted model outperforms the side‐mounted model. Increasing the number of air intakes will not increase low‐frequency noise reduction performance, but it will increase high‐frequency noise reduction performance. These findings provide empirical support for inlet design in mufflers and offer insights into the structural design’s impact on acoustic performance.

Blending gasoline with hydrogenated catalytic biodiesel has the potential to improve combustion problems of gasoline direct-injection compression combustion, and the spray characteristics of the blending fuel can directly affect the combustion effect. In order to understand the spray characteristics of a gasoline–hydrocatalyzed catalytic biodiesel mixture, a numerical spray model of constant volume combustion chamber was established, and the accuracy of the model was verified by experimental data in the literature. Based on this model, the spray penetration, sauter mean diameter, spray velocity field and concentration field of gasoline–hydrocatalyzed catalytic biodiesel at different blending ratios were studied. The results show that under the conditions of 850 K ambient temperature, 5 MPa ambient pressure, and 80 MPa injection pressure, as the proportion of hydrogenated catalytic biodiesel in the blending fuel increases, the spray penetration increases, the sauter mean diameter decreases slightly, and the area of high velocity and high concentration at the spray center increases. The results of this study will contribute to the development of blended fuels for superior combustion performance and reduced pollutant emissions at appropriate blending ratios.

In recent years, the optimization of diesel engine exhaust mufflers has predominantly targeted acoustic performance, while the impact on engine power performance has often been overlooked. Therefore, this paper proposes a parallel perforated tube expansion muffler and conducts a numerical analysis of its acoustic and aerodynamic performance using the finite element method. Then, a Kriging model is established based on the Design of Experiments to reveal the impact of different parameter couplings on muffler performance. With transmission loss (TL) and pressure loss (PL) as the optimization objectives, a multi-objective optimization study is carried out using the competitive multi-objective particle swarm optimization (CMOPSO). The optimization results indicate that this method can simplify the optimization model and improve optimization efficiency. After CMOPSO calculation, the average TL of the muffler increased from 27.3 dB to 31.6 dB, and the PL decreased from 1087 Pa to 953 Pa, which reduced the exhaust noise and improved the fuel economy of the engine, thus enhancing the overall performance of the muffler. This work provides a reference and guidance for the optimal design of mufflers for small agricultural diesel engines.

In order to broaden the muffler frequency band in the low‐frequency range of the exhaust muffler and to achieve the purpose of broadband noise reduction, in this paper, a model of an annular connecting pipe muffler is proposed using the finite element method (FEM) to simulate the nonreflection boundary condition and to solve the transmission loss (TL). In addition, the experimental value is obtained by the spatial five‐point measurement method and compared with the simulated value, and the validity and reliability of the solution model are verified. Compared with a simple expansion muffler, the average TL of the annular connecting pipe muffler is increased by 11.86 dB, and the maximum TL is increased by 18.31 dB, effectively widening the muffler frequency area, and the overall performance is effectively improved. Finally, the influence of structural factors is analyzed, including the width (W) of the annular connecting pipe, the length (L) of the annular connecting pipe, and the length ratio (m) of the front and rear chambers on the TL and on the width of the anechoic frequency band. The results reveal that the width and length of the annular connecting pipe and front‐to‐back cavity length ratio are the most significant factors to influence the TL, muffler frequency band, and elimination or reduction of the passing frequency, respectively.

A numerical model of the micro-free-piston engine was developed and its correctness was verified by the comparison between the simulation and referential experiment results under the same work conditions. Based on this numerical model, the effects of the water vapor blending ratio (α) on combustion thermal performance and emission characteristics of hydrogen (H₂) homogeneous charge compressing ignition (HCCI) were investigated numerically. The water vapor impact on combustion temperature was analyzed as well. The simulation results reveal that when the initial equivalent ratio is 0.5, blending H₂ with water vapor can delay the ignition time and prolong the whole process. At the same time, the addition of water vapor to H₂ decreases the peak combustion temperature and pressure, which will alleviate the detonation phenomenon of the combustion chamber. Moreover, the power output capacity and NO_x emissions decrease with the increase in α. When α increases to 0.8, the mixture gas cannot be compressed to ignite. Finally, the dilution effect, thermal effect, and chemical effect of water vapor all have the potential to lower the combustion temperature and the dilution effect plays the leading role.

In order to improve the performance of a mini-type air-cooled diesel engine in terms of the overall efficiency and engine emissions, a swirl chamber of a variable cross-section dual-channel model was developed. This study proposed nine turbulent swirl chambers with a variable cross-section for a dual-channel combustion solution, which applied a dual-channel cross-section to the insert between the original swirl chamber and the main chamber. Model-based design, simulation and experiments were applied as a feasible approach to address this issue to find out the influence of the dual-channel inclination angle and divergence angle on the swirl rate in the swirl chamber, the power and the emissions performance, including the fuel efficiency. By comparing the tests, the performance of the diesel engine with a variable cross-section dual-channel swirl chamber was superior to the original one with a single channel in terms of the swirl rate, fuel consumption rate and emissions.