Numerical investigation of the oblique detonation initiation in ammonia/hydrogen/air mixtures

In this paper, two-dimensional numerical simulations of oblique detonation waves at the altitude of 30 km are carried out using Navier-Stokes equations coupled detailed chemical reaction. We investigated the characteristic parameters and the morphology of oblique detonation induction region with different Mach number in ammonia/hydrogen/air mixtures and the effect of the hydrogen percentage on the initiation characteristics. The numerical simulation results show that, in pure ammonia, the transition from oblique shock wave to oblique detonation wave changes from abrupt to smooth type, and the length of induction region decreases by more than a factor of ten, as the Mach number increases from 10 to 12. While, the flow field structure of the oblique detonation wave induction region is more complex due to the presence of compression waves. When Ma = 10, a long induction region is detrimental to the initiation of oblique detonation. Hydrogen addition is a potential solution. As the hydrogen content increases from 0 % to 100 %, the characteristic length of the induction region is significantly reduced. In blended fuels with higher hydrogen content and lower ammonia content, the characteristic length becomes even shorter than that of pure hydrogen fuel. After adding hydrogen, the intensity of the compression waves decreases, and a smooth transition structure is formed. Additionally, the oblique detonation wave in ammonia can achieve higher pressure than that in hydrogen at the same equivalence ratio, and this effect is particularly significant under high Mach numbers. In summary, ammonia is more suitable as a fuel for oblique detonation engines at high Mach numbers, while adding hydrogen at low Mach numbers can improve detonation performance.