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To research the quality of the hydrogen–air mixture formation and the combustion characteristics of the hydrogen fueled engine under different hydrogen injection timings, nozzle hole positions and nozzle hole diameter, a three-dimensional simulation model for a PFI hydrogen internal combustion engine with the inlet, outlet, valves and cylinder was established using AVL Fire software. In the maximum torque condition, research focused on the variation law of the total hydrogen mass in the cylinder and inlet and the space distribution characteristics and variation law of velocity field, concentration field and turbulent kinetic energy under different hydrogen injection parameters (injection timings, nozzle hole positions and nozzle hole area) in order to reveal the influence of these parameters on hydrogen–air mixture formation process. Then the formation quality of hydrogen–air mixture was comprehensively evaluated according to the mixture uniformity coefficient, the remnant hydrogen percentage in the inlet and restraining abnormal combustion (such as preignition and backfire). The results showed that the three hydrogen injection parameters have important influence on the forming quality of hydrogen–air mixture and combustion state. The reasonable choice of the nozzle hole position of hydrogen, nozzle hole diameter and the hydrogen injection time can improve the uniformity of the hydrogen–air mixing in the cylinder of the hydrogen internal combustion engine, and the combustion heat release reaction is more reasonable. At the end of the compression stroke, the equivalence ratio uniform coefficient increased at first and then decreased with the beginning of the hydrogen injection. When hydrogen injection starting point was with 410–430°CA, equivalence ratio uniform coefficient was larger, and ignition delay period was shorter so that the combustion performance index was also good. And remnant hydrogen percentage in the inlet was less, high concentration of mixed gas in the vicinity of the inlet valve also gathered less, thus suppressing the preignition and backfire. With the increase of the distance between the nozzle and the inlet valve, the selection of the hydrogen injection period is narrowed, and the optimum hydrogen injection time was also ahead of time. The results also showed that it was favorable for the formation of uniform mixing gas when the nozzle hole diameter was 4 mm. [ABSTRACT FROM AUTHOR]

Abstract: Preignition or backfire occurs easily in hydrogen internal combustion engines (HICE) of manifold injection type, especially, the bigger equivalence ratio is, the more serious backfire happens. And decreasing equivalence ratio will reduce engine''s power output. So to analyze and resolve the contradiction between abnormal combustion and power output in HICE is the key of promoting the progress of research on HICE. Postponing ignition timing is helpful to reducing the occurrence degree or inclination of pre-ignition, and water injection of intake manifold can be used to eliminate backfire. But postponement of ignition has a lesser effect on power output and brake thermal efficiency than water injection of intake manifold, That is to say water injection would bring power output to drop obviously, and water injection will also has many disadvantages, such as, the worse corrosion degree of cylinder and deteriorated lubrication performance. It is necessary to combine postponing ignition timing with water injection of intake manifold to give full play to their advantages, and avoid their disadvantages to the greatest extent. In the paper, the concept of pre-ignition strength and backfire strength were presented, and the inhibition degree of pre-ignition and the elimination degree of backfire was introduced. The functional relationship between inhibition degree of pre-ignition and ignition timing was established, and the functional relationship between the elimination degree of backfire and water injection rate was also established for quantitative analysis and research into inhibiting pre-ignition and eliminating backfire. A optimal control method was put forward about resolving contradiction between eliminating backfire and improving performance of HICE, which not only eliminates backfire, but also take into account the power output and economy. [Copyright &y& Elsevier]

Abstract: With its obvious advantages, hydrogen is expected to be greatly used as a new energy, which can reduce vehicle emissions effectively and efficiently. Besides, it can be adopted as an alternative fuel for petroleum fuel of internal combustion engine. However, due to its unique physical and chemical characteristics, hydrogen often leads to abnormal combustion and decay of power, which can be effectively dealt with by optimal control. In this paper, thermodynamic analysis methods, like mass transfer and energy transfer, is combined with state space analysis methods of nonlinear control system, so that an optimal control model of nonlinear combustion control system for hydrogen fueled engines can be established. Through illustrating the inner relations between combustion and energy transfer of hydrogen fueled engines and operating parameter, state parameter and performance index, this paper provides theoretical analysis and found experimental research for promoting abnormal combustion and performance index after controlling operating parameters optimally and changing state parameters of the cylinder. Based on nonlinear programming theory and multi-objective genetic algorithm, the methods of establishing the optimal control model and carrying out the optimal value of operating parameters are shown in this paper. What’s more, some new ways are proposed to integrate the optimal control aspects of multi-variate, multiple targets and multiple constraints for hydrogen fueled engines by changing the multi-objective and multi-constraint optimal control into the single-target integrated optimal control. [Copyright &y& Elsevier]

When hydrogen internal combustion engine works using the intake manifold injection mode to provide the hydrogen, it has to face a contradiction between the abnormal combustion (preignition, backfire, etc.). Currently, most researches on abnormal combustion in hydrogen internal combustion engines have focused primarily on backfire and detonation, with limited investigation of pre-ignition, particularly when initiated by in-cylinder hot spots. In order to explore the relationship between the hot spot and the pre-ignition of hydrogen internal combustion engine, the influence of characteristic parameters of hot spot, such as hot spot area, initial temperature, duration of hot spot and temperature change rate, on pre-ignition of hydrogen internal combustion engines were analyzed. On the basis of using the isolated factor method to research the influence of each characteristic parameter on the occurrence time of pre-ignition of hydrogen internal combustion engines, the comprehensive effect of these characteristic parameters on the occurrence moment of pre-ignition in hydrogen internal combustion engines was also investigated with the orthogonal test method. It is found that the occurrence of pre-ignition of hydrogen internal combustion engines is the result of multi-factor interaction. Pre-ignition is most affected by hot spot area, and when the hot spot area is the same, the order of influence of pre-ignition timing is initial temperature > temperature change rate > duration of hot spot. The research results can promote the practical application of hydrogen fuel in internal combustion engines and provide guidance for the structural design of hydrogen internal combustion engines. • Hydrogen engine pre-ignition results from combined effects of several parameters such as the area, initial temp. • Strategies to control temp change rates could mitigate pre-ignition risks and optimize combustion performance. • Compared to initial temp, the moment of pre-ignition is more sensitive to changes in the area of the hot spot. • With equal hot spot area: initial temp > temp change rate > duration influence hydrogen engine pre-ignition. [ABSTRACT FROM AUTHOR]