Several countries, consortia and industries are increasingly publicizing in the press their willingness to consider ammonia as one of the zero carbon footprint fuels of the future. In the case of internal combustion engines, it was previously concluded that the ammonia as fuel can be used alone if boosted operating conditions or high compression ratio [1]. But most of the cases, the addition of small hydrogen amounts is needed [2] to match all operating conditions. Even if ammonia has a low laminar flame speed and high auto-ignition temperature, the addition of hydrogen can induce knock phenomena. To predict the occurrence of knock by models, kinetics mechanisms must be improved with auto-ignition delays in similar conditions to these engine conditions, i.e., at high pressure and middle temperature in order to well dimension engines. Until now, only a few of studies have been focused on the ignition delay measurement for ammonia and ammonia with small amount of H2, in these conditions, by means of a Rapid Compression Machine (RCM) or a Shock Tube (ST). He et al. [3] explored the pressure range from 20 to 60 bars with initial temperature varying from 950 K to 1150 K for NH3/H2 from until 20% of H2 in volume. Dai et al. [4,5] explored the IDs at 70 bars for NH3 only at an equivalence ratio of 3 and at 60 bars, for 0.5 to 2 of equivalence ratio, but without any temperature condition under 1050 K. Pochet et al. [6] explored the 1000 K to 1100 K temperature range at two pressures, 43.4 and 65.5 bars, but lean mixtures as 0.2, 0.35 and 0.5 of equivalence ratio. More recently Liao et al. [7] determined NH3’s IDT at 30 bars between 1200 K and 1450 K. Faced with this lack of data, the objective of this study is to provide experimental IDT obtained in a Rapid Compression Machine for 40 bars to 70 bars of pressure range with 10 bars steps, for 950 K to 1150 K with 50 K steps, and an equivalence ratio variation from lean to rich mixtures from 0.5 to 2.5 with 0.2 steps, and to evaluate the different available kinetics mechanisms to predict NH3 alone or blended with H2 (until 20% in vol.) under knock engine conditions. Numerical simulations were done by using the ANSYS Chemkin PRO’s Closed Homogeneous Batch Reactor. Numerous kinetic mechanisms were tested in order to find the most appropriates ones. From the first experimental dataset, the best predictive mechanisms are those proposed by Keylab 2019 [10] and Polimi 2021 [16].