Experimental study on the explosion characteristics of ammonia-hydrogen-air mixtures.

• The maximum explosion pressures and maximum rates of pressure rise of the ammonia-hydrogen-air mixture linearly increase as the initial pressure increases. • The explosion characteristic parameters vary monotonously as the equivalence ratio increases, and the peak value is obtained at the equivalence ratio of 1.1. • The improvement of the explosion intensity slightly reduces as the hydrogen concentration approaches 50%. • Hydrogen addition reinforces the explosion characteristics of the ammonia-air mixture by prominently improving the hydrodynamic instability and thermal-diffusion instability. Ammonia-hydrogen blended fuel has drawn substantial attention as an environmentally friendly, carbon-free fuel because it effectively overcomes the inherent disadvantages of pure ammonia in combustion performance, such as a high ignition energy, slow combustion rate, and low combustion efficiency. While recent research on the combustion performance of hydrogen-ammonia blends has advanced, there remains a scarcity of studies addressing the explosion characteristics of these fuels. In this paper, a series of experiments conducted within a standard 20-L spherical combustion chamber to investigate the explosion characteristics of ammonia-hydrogen-air premixed gases under diverse conditions, spanning from low to high pressures (0.02–0.3 MPa) and from fuel-lean to fuel-rich scenarios (0.7–1.5), are discussed. The results reveal that the explosion characteristics are pronouncedly enhanced by hydrogen addition. The maximum explosion pressure (P max) and maximum pressure rise rate ((d P /d t) max) increase, while the explosion time (t exp) decreases with increasing hydrogen concentration. P max and (d P /d t) max exhibit linear increases as the initial pressure rises and reach their peaks at an equivalence ratio of 1.1; t exp displays nonmonotonic variations with increasing initial pressure and equivalence ratio. Hydrogen addition remarkably increases the hydrodynamic instability and thermal-diffusion instability of the reactive mixture, enhances the thermal-mass diffusion on the flame front, and promotes flame deformation and cellular structure formation, resulting in an improvement of the flame propagation and compression effect on the unburnt reactant before the flame. Research into the explosion characteristics provides valuable insights for the safe storage and transportation of ammonia-hydrogen blended fuels. These results indicate avenues for further enhancing the detonation characteristics and explosion performance of ammonia-hydrogen blended fuels. [ABSTRACT FROM AUTHOR]