Experimental and kinetic modeling study on ammonia/polyoxymethylene dimethyl ether 2 oxidation in a jet-stirred reactor

The oxidation of ammonia/polyoxymethylene dimethyl ether 2 (NH3/PODE2) was investigated in a jet-stirred reactor with ammonia addition of 10 %, 25 %, and 50 % in mole fraction. Atmospheric experiments were conducted at an equivalence ratio of 1.0, within the temperature range of 500-1100 K. The initial fuel mole fraction and residence time were fixed at 0.5 % and 2 s, respectively. PODE2 and NH3, along with other intermediates and products such as C1-C2 hydrocarbons and permanent gases, were analyzed using gas chromatography and Fourier transform infrared spectroscopy. The experimental results demonstrate that the addition of NH3 has little impact on the consumption of PODE2, primarily influencing the mole fraction of hydrocarbon intermediates. All three blends exhibited negative temperature coefficient (NTC) behaviors. However, NTC behavior was weakened as the NH3 blending ratios increased due to the competition for O2 at low temperatures. A detailed kinetic model for PODE2/NH3 blends was constructed, incorporating updated rate coefficients from the recent literature and analogy methods. The model also considers the interaction between PODE2 and NH3, which was investigated through reaction pathway analysis and sensitivity analysis. Simulated results show that the mole fraction profiles are reasonably predicted by this model at the test conditions. The interaction between PODE2 and NH3 is facilitated by CH3, NH2 radicals, and NO-NO2 cycle. The rapid reversible reaction between NO and NO2 alters the reaction pathway of radicals in the blends. At low temperatures, PODE2 in blend follows the same oxidation pathway as pure PODE2, while NH3 oxidation is affected by the introduction of additional HO2 and H from PODE2. New OH formation pathways involving NH2, NO, and NO2 occur, while the decomposition of H2O2 is inhibited, thereby affecting the oxidation of PODE2 at intermediate temperatures. Additionally, a notable decrease in the intermediates with carbon-carbon double bonds is observed, due to the consumption of CH3 through the reaction NO2 + CH3 = NO + CH3O. This important reaction also promotes the oxidation of CH3 and the NO-NO2 cycle, resulting in an improvement in system reactivity.