Homogeneous conversion of NO_x and NH₃ with CH₄, CO, and C₂H₄ at the diluted conditions of exhaust‐gases of lean operated natural gas engines

Abstract

Understanding gas-phase reactions in model gas mixtures approximating preturbine heavy-duty natural gas engine exhaust compositions containing NO, NH 3 , NO 2 , CH 4 , CO, and C 2 H 4 is extremely relevant for aftertreatment procedure and catalyst design and is thus addressed in this work. In a plug-flow reactor at atmospheric pressure, five different model gas mixtures were investigated in the temperature range of 700-1 200 K, using species analysis with electron ionization molecular-beam mass spectrometry. The mixtures were designed to reveal influences of individual components by adding NO 2 , CH 4 , CO, and C 2 H 4 sequentially to a highly argon-diluted NO/NH 3 base mixture. Effects of all components on the reactivity for NO x conversion were investigated both experimentally as well as by comparison with three selected kinetic models. Main results show a significantly increased reactivity upon NO 2 and hydrocarbon addition with lowered NO conversion temperatures by up to 200 K. Methane was seen to be of dominant influence in the carbon-containing mixtures regarding interactions between the carbon and nitrogen chemistry as well as formaldehyde formation. The three tested mechanisms were capable to overall represent the reaction behavior satisfactorily. On this basis, it can be stated that significant gas-phase reactivity was observed among typical constituents of pre-turbine natural gas engine exhaust at moderate temperature. K E Y W O R D S ammonia, exhaust gas aftertreatment, gas-phase kinetics, natural gas engines, nitric oxide This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Exploring NH3 and NOx Interaction Chemistry With CH4 and C2H4 at Moderate Temperatures and Various Pressures

“…By examining Figure 3 one can see that the profile of NO with temperature in GM4 has a distinct difference from that in other mixtures, and is also different from the result observed in the work of Schmitt et al (Schmitt et al, 2021). To clarify the kinetics (Sun et al, 2021) 1 6,000 0 1,000 500 500 0.06 0.932 GM4 (Sun et al, 2021) 1 behind it, ROP analyses were performed at low-to hightemperatures (860, 1,162 and 1316 K).…”

“…Numerous previous studies (Miller and Bowman, 1989;Glarborg et al, 2018;Okafor et al, 2018;Schmitt et al, 2021) have concluded that reactions R1-R5 are the major reactions in the oxidation of NH 3 /NO x . Figure 3 summarizes the reaction pathways of NH 3 in the oxidation of GM1-5.…”

“…Meanwhile, lean-operated natural gas engines are considered as a promising technology because of their high thermo-efficiency and comparably low pollutant emissions (Lott and Deutschmann, 2021). Alternative concepts like biomethane and power-to-gas technologies will endow gas engines with outstanding potential on the way towards carbon neutrality (Schmitt et al, 2021). Nevertheless, the excessive engine-out emissions of methane, known with potent greenhouse potential and liable to produce carcinogenic formaldehyde by partial oxidation, bring new challenges to natural gas engines (Hutter et al, 2018).…”

“…Hemberger et al (Hemberger et al, 1994) investigated the selective non-catalytic reduction (SNCR) of NO by ammonia with the addition of methane and ethane in a flow reactor over the temperature range 800-1300 K. Gasnot et al (Gasnot et al, 2012) performed an experimental and kinetic study of the effect of several additives such as CH 4 , C 2 H 4 , C 2 H 6 , C 2 H 2 , CH 3 OH, C 2 H 5 OH and CO on ammonia-based SNCR process at temperatures of 900-1200 K. Torkashvand et al (Torkashvand et al, 2019) investigated hydrocarbon abatement from the exhaust of lean-burn gas engines under ambient pressure and pre-turbine conditions. Most recently, Schmitt et al (Schmitt et al, 2021) conducted flow reactor experiments in the temperature range of 700-1200 K at atmospheric pressure to reveal influences of individual components by adding NO 2 , CH 4 , CO, and C 2 H 4 sequentially to a highly argon-diluted NO/ NH 3 base mixture.…”

Combustion, Chemistry, and Carbon Neutrality

“…The importance of SCR with NH 3 for lean-burning engines, the need to avoid NO x and NH 3 slip, and the potential formation of HCN in the catalytic reactions when using different catalysts has been mentioned before (Section ). , For lean-burning engines fueled by natural gas or by methane from bioresources or PtG processes, Zengel et al (2020) have analyzed the interplay of CH 2 O, a component from incomplete combustion in the exhaust gases, and the reducing agent NH 3 for four different commercial SCR catalysts . They used catalyst coatings on honeycombs under typical technical conditions with a synthetic SCR gas and alerted to the formation of toxic HCN (up to 30 ppm) as a potential major hazard associated with SCR application .…”