Ignition delay times of NH3 /DME blends at high pressure and low DME fraction: RCM experiments and simulations

Autoignition delay times of ammonia/dimethyl ether (NH3/DME) mixtures were measured in a rapid compression machine with DME fractions 0, 2 and 5 100% the fuel. The measurements performed at equivalence ratios φ=0.5, 1.0 2.0 pressures range 10–70 bar; depending on fuel composition, temperatures after varied from 610 K to 1180 K. Admixture is seen have dramatic effect ignition time, effectively shifting curves vs. temperature lower temperatures, up ~250 compared pure ammonia. Two-stage observed φ=1.0 2% 5% fuel, despite pressure being higher than that which shows two-stage ignition. At reproducible pre-ignition rise for both fractions, not components. A novel NH3/DME mechanism was developed, including modifications NH3 subset addition NH2+CH3OCH3 reaction, rate coefficients calculated ab initio theory. Simulations faithfully reproduce rise. While also exhibits mixtures, qualitative quantitative improvement recommended. overall ammonia/DME are predicted well, generally within 50% experimental values, although reduced performance ammonia φ=2.0. Simulating process, we observe oxidized much more rapidly Analysis indicates this ‘early oxidation’ generates reactive species initiate oxidation ammonia, turn begins heat release raises accelerates process towards reaction path analysis low-temperature chain-branching reactions important early while sensitivity several DME, cross between presented here, critical ignition, even