The laminar and turbulent flame speed of methanol/ammonia/air, ethyl-acetate/ammonia/air, and dimethoxymethane/ammonia/air under atmospheric and elevated pressures

Experiments of the laminar and turbulent flame speed of typical E-fuels blended with ammonia: methanol/ammonia/(CH₃OH/NH₃)/air, ethyl-acetate/ammonia/(EA/NH₃)/air, and dimethoxymethane/ammonia/(DMM/NH₃)/air under atmospheric and elevated pressures (1 and 3 atm) are conducted in a fan-stirred constant volume combustion chamber, with initial temperature of 373 K. The results show that turbulent flame speed (S_T) follow the same ranking order as laminar flame speed (S_L) at fuel-lean side from high to low as: DMM, CH₃OH, and EA; while with ammonia addition, CH₃OH/NH₃ and EA/NH₃ have similar S_L and S_T values; and at fuel-rich side, DMM and EA show increasing S_T and S_T/S_L values than at fuel-lean side Meanwhile, the measured Markstein length (L_b) is decreasing towards the fuel-rich side and even becomes negative for EA. Ammonia addition enhances the turbulent flame wrinkling and deformation from the morphology analyses, and this leads to E-fuel/NH₃ blends always having higher normalized turbulent flame speed (S_T/S_L) than pure E-fuel. Next, we test several different turbulent flame speed correlations composed of (u'/S_L) and (l_T/l_F), it is found that the power exponents of (u'/S_L) and (l_T/l_F) do not necessarily have to be equal; they change as the turbulent regime varies in different zones. S_T/S_L/Ka = a(Da/Le)^b performs best among all correlation types with 0.5 ≤ b ≤ 1 corresponding to the Damköhler's two limits. Comparing three types of Lewis number, it is found that volume based Le_V has the best fitting goodness in the correlation of S_T/S_L/Ka = a(Da/Le)^b. Taking into account the developing flame brush thickness, wrinkling ratio and integral length scale as a function of radius, the flame radius based Da_R correlations are proposed: S_T/S_L/γ = a(Da_R/Le)^b where 0.5 ≤ b ≤ 1 which can unify present experimental data with Lewis number larger than unity and previous data with Lewis number less than unity.