Effect of Ammonia on Laminar Combustion Characteristics of Methane–Air Flames at Elevated Pressures

Abstract

In this paper, laminar combustion characteristics of methane/ammonia/air flames are numerically investigated using the Chemkin/Premix code. The initial temperature is set as 298 K; the initial pressures are set as 1, 2, 5, 10, and 20 atm; and the equivalence ratios are set as 0.8–1.6. Laminar burning velocity (LBV); adiabatic flame temperature (AFT); net heat release rate (NHRR); and the mole fractions of H, NH 2 , NO, NO 2 , and HCN at stoichiometric ratio are studied with ammonia (NH 3 ) addition. Meanwhile, temperature sensitivity and rate of production (ROP) are analyzed. The results show that with the increase of the initial pressures, LBV decreases and AFT and NHRR increase. With the increase of ammonia doping ratios, LBV, AFT, and NHRR decrease. From temperature sensitivity analyses, the main reactions that promote temperature rise are R39 (H + O 2 < = > O + OH), R100 (OH + CH 3 < = > CH 2 (S) + H 2 O), R102 (OH + CO < = > H + CO 2 ), and R122 (HO 2 + CH 3 < = > OH + CH 3 O). The main reactions that inhibit temperature rise are R53 (H + CH 3 (+M) < = > CH 4 (+M)), R36 (H + O 2 + H 2 O < = > HO 2 + H 2 O), and R46 (H + HO 2 < = > O 2 + H 2 ). For the rate of production of the free radical pool, the trends of H and NO are consuming first and then producing, and the trends of NH 2 , NO 2 , and HCN are the opposite. The pathway from methane to carbon dioxide is CH 4 → CH 3 → CH 3 O → CH 2 O → HCO → CO → CO 2 , and the pathway from ammonia to nitrogen is NH 3 → NH 2 → NH/HNO → NO/NO 2 → N 2 .

Ammonia Can be Currently Considered as one of the Best Green Energy Ally

“…This study opens a door for opportunities regarding the use of ammonia for reducing CO2 emissions since it is expected that the problem of NO formation will be resolved. However, the increase in pressure also causes a decrease in the laminar flame speed, and the presence of ammonia causes a decrease in temperature and net heat release rate [128], thus requiring modifications intended to attain flame stabilization under such peculiar fuel characteristics.…”

Ammonia Can Be Currently Considered One of the Best Green Energy Allies

“…This study opens a door for opportunities regarding the use of ammonia for reducing CO 2 emissions since it is expected that the problem of NO formation will be resolved. However, the increase in pressure also causes a decrease in the laminar flame speed, and the presence of ammonia causes a decrease in temperature and net heat release rate [156], thus requiring modifications intended to attain flame stabilization under such peculiar fuel characteristics.…”

Laminar Burning Velocity Measurement of CH4/NH3/H2–Air Premixed Flames under Engine Relevant Conditions

“…Strong ignition enhancement effect is incorporated for NH 3 flames with CH 4 addition even under lean mixture conditions. 37 Jin et al 38 investigated the NH 3 effect on CH 4 −air flames numerically at steep pressures of 1−20 atm and 298 K. With a rise in pressure, a decrease in LBV and adiabatic flame temperature was observed along with a reduction in the peaks for H, NH 2 , NO, NO 2 , and HCN radicals. Bao et al 39 numerically investigated and optimized a reduced GRI 3.0 mechanism for NH 3 fuel chemistry.…”