Comparative autoignition and NOx characteristics of NH3/DME and NH3/MeOH blends under temperature, pressure, and equivalence-ratio variations

Abstract

A comparative chemical-kinetic assessment of dimethyl ether (DME) and methanol (MeOH) as ammonia ignition promoters was performed under identical reactor and mixture constraints. Blends containing 70% NH 3 and 30% DME or MeOH were simulated in an adiabatic constant-pressure reactor over 900–1200 K, 5–10 atm, and equivalence ratios (φ) of 0.7–1.3. The mechanism was assessed against independent ignition-delay measurements under literature-specific conditions, and ignition-state rate-of-production analysis was used to interpret promoter-dependent chemistry. Promoter ranking reversed with temperature: at 900 K, NH 3 /DME ignited substantially earlier (4.465 versus 23.692 ms), whereas NH 3 /MeOH ignited earlier at 1000–1200 K. At 1000 K, 10 atm, and φ = 1.0, the corresponding ignition delays were 4.421 and 3.946 ms. Despite earlier MeOH-assisted ignition above 900 K, NH 3 /DME produced higher maximum temperatures, peak OH mole fractions, and peak heat-release rates, the latter exceeding NH 3 /MeOH by approximately 33–44%. Enrichment from φ = 0.7 to 1.3 shortened ignition delay by approximately 20–22% but reduced final NO by more than 93% in both blends. NH 3 /MeOH retained lower final NO while producing larger transient HNO, NO 2 , and N 2 O maxima. The ROP results linked these differences to stronger instantaneous H/O/OH turnover in NH 3 /DME and promoter-dependent competition among HNO–NO and NO–NO 2 recycling pathways. Promoter selection is therefore condition-dependent and cannot be based on ignition delay or final NO alone.