The effect of the acoustically absorbing wall on the knocking phenomenon of hydrogen engines. (1st February 2023) - Xu, Han
Highlights: Acoustically absorbing wall is a new method to suppress the engine knock. The function of holes in the wall is to redistribute the energy of shock waves. Once a shock wave is intensified excessively, detonation would be formed. Keeping the balance of the energy of shock waves could eliminate the detonation. The design of holes decides the final effect on the engine knock. Abstract: Hydrogen is a kind of promising alternative fuel applied in engines. However, the severe knock with a detonation onset is a huge obstacle for the application of hydrogen. Acoustically absorbing wall could suppress the detonation onset and thus it is found to be a new method to suppress the severe knock without the extra loss of hydrogen engine performance. Detonation bomb experiments were conducted to explore the effect of two kinds of acoustically absorbing walls on the knocking phenomenon. It's found that the wall with a small number of large holes could inhibit the severe knock, while the wall with a large number of small holes would promote it. Based on numerical simulations, it's found that the intensification of the radial wave is the primary cause to result in a detonation wave leading to a severe knock. The small number of large holes could properly "break up" radial waves into axial waves to avoid the detonation onset. However, the large number of small holes would excessively "break up" radial waves into axial waves. As a consequence, instead of the radial wave, the axial wave would be intensified to cause a detonation onset. Therefore, there should be a proper design of the acoustically absorbing wall to keep the balance of the energy contained in waves to efficiently suppress the severe knock.