10. Combustion and Reacting Flows

High-pressure turbulent/laminar burning velocities (ST/SL) of ammonia/hydrogen/air mixtures are important to all zero-carbon-emission internal combustion engines for achieving a future net-zero-carbon society. This work measures high-pressure SL and ST for centrally-ignited, outwardly-propagating premixed NH3/H2/air flames in a large dual-chamber, constant-pressure, fan-stirred cruciform burner capable of generating near-isotropic turbulence. At first, values of SL at p=1,3,5 atm are measured at three equivalence ratios (phi=0.8,1.0,1.2), each phi with various blending hydrogen percentages (XH2=0-50%). SL increases with increasing XH2. At XH2=45% and phi=1, SL~p^-0.40, where SL=0.34 m/s at 1 atm. For simplicity, NH3/H2/air mixtures (phi=0.8,1.0,1.2) at XH2 = 45% are selected to investigate the effects of pressure (p=1,3,5 atm) and r.m.s. turbulence fluctuation velocity (u'=0-2.8 m/s) on ST. All values of ST are measured within a range of effective flame radius =25-45 mm at a mean progress variable c ̅=0.5. Six general correlations, i.e. (1) Kobayashi et al. (1998), (2) Bradley et al. (2005), (3) Chaudhuri et al. (2012), (4) Shy et al. (2019), (5) Wang et al. (2020), and (6) Lhuillier et al. (2021), are used to fit present NH3/H2/air ST/SL results together with our previous ST/SL data of CH4/air flames at phi=0.8 and 0.9 and at T=300 and 423 K. It is found that these very scattering data of various pre-mixtures under different conditions can be all merged into single curves by the aforesaid six general correlations. Specifically, (1) (STc=0.5/SL) = 2.27[(u'/SL)(p/p0)Le^-1]^0.41 (R2=0.90), (2) (STc=0.5/u') = 0.71(KLe)^-0.3 (R2=0.98), (3) (STc=0.5/SL) = 0.31(ReT,flameLe^-1)^0.5 (R2=0.98), (4) (STc=0.5/u') = 0.3(DaLe^-1)^0.5 (R2=0.97), (5) (STc=0.5/SL)-1 = 0.21(ReT,flameLe^-2)^0.54 (R2=0.94), and (6) (STc=0.5/SL)Da^-1 = 0.11(KaLe^-1)^0.95 (R2=0.99), where R2 is the coefficient of determination and Le, K, ReT,flame, Da and Ka are Lewis, Karlovitz factor, turbulent flame Reynolds, turbulent Damköhler and turbulent Karlovitz numbers, respectively.

Mr.

Hsun Yang