Research on optimum method to eliminate backfire of hydrogen internal combustion engines based on combining postponing ignition timing with water injection of intake manifold

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.

► Relation between inhibition degree of pre-ignition and ignition time is established. ► Relation between elimination degree of backfire and water injection rate is created. ► A optimal control method is developed. ► The method eliminates abnormal combustion, and take performance of HICE into account. ► The method is to change both ignition time and water injection of intake manifold.