Lean-Burn Natural Gas Engines: Challenges and Concepts for an Efficient Exhaust Gas Aftertreatment System

Abstract

High engine efficiency, comparably low pollutant emissions, and advantageous carbon dioxide emissions make lean-burn natural gas engines an attractive alternative compared to conventional diesel or gasoline engines. However, incomplete combustion in natural gas engines results in emission of small amounts of methane, which has a strong global warming potential and consequently makes an efficient exhaust gas aftertreatment system imperative. Palladium-based catalysts are considered as most effective in low temperature methane conversion, but they suffer from inhibition by the combustion product water and from poisoning by sulfur species that are typically present in the gas stream. Rational design of the catalytic converter combined with recent advances in catalyst operation and process control, particularly short rich periods for catalyst regeneration, allow optimism that these hurdles can be overcome. The availability of a durable and highly efficient exhaust gas aftertreatment system can promote the widespread use of lean-burn natural gas engines, which could be a key step towards reducing mankind’s carbon footprint.

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1−xZrxO2−δ by a Resonant Nanobalance Approach

“…Cerium oxide (ceria, CeO 2−δ ) and its derivatives are of great technological interest for a variety of applications, of which the catalytic control of automobile emissions prevails [1][2][3][4]. In particular, the operation of three-way catalytic converters (TWC), which was used for the exhaust gas aftertreatment of most gasoline-powered vehicles, relies on the capability of ceria-based catalyst to store and release oxygen.…”

Comparison of the electrical conductivity of bulk and film Ce1–xZrxO2–δ in oxygen-depleted atmospheres at high temperatures

“…Ceria/zirconia mixed oxides Ce 1-x Zr x O 2-d (CZO) are crucial components of state-of-the-art technologies to minimize hazardous emissions of combustion engines in the environment. The most known devices to rely on CZO are the three-way catalytic converters (TWC) used for after treatment of the exhausts of most gasoline-powered vehicles [1][2][3][4][5][6]. The interest in CZO is motivated by its outstanding catalytic properties due to its much lower reduction enthalpies and higher levels of attainable oxygen non-stoichiometry d and, hence, its superior oxygen storage or release capacity, in contrast to pure CeO 2-d [4][5][6][7][8][9][10][11][12][13][14][15][16].…”

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

“…Modern combustion engine technologies have increasingly focused on the reduction of carbon dioxide emissions owing to the globally tightening legislation (Johnson, 2015;Börnhorst and Deutschmann, 2021), whereas the highly optimized engine structures and emission control measures render it extremely difficult to further make a breakthrough on decreasing raw emissions. 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).…”

“…Also, the presence of nitrogen oxides (NO x ) in exhaust gas deserves special attention given its particular environmental hazard in engendering photochemical smog and acid rain (Gasnot et al, 2012;Piumetti et al, 2016). Hence, a highly efficient and durable exhaust gas abatement system, commonly containing both catalytic oxidation of unburned hydrocarbons (UHC) and NO x reduction sections, was considered imperative (Lott and Deutschmann, 2021). The ammonia-based selective catalytic reduction (SCR) technology is currently widely applied for NO x removal from gas engines benefiting from its higher DeNO x efficiency and relatively moderate cost.…”

“…The ammonia-based selective catalytic reduction (SCR) technology is currently widely applied for NO x removal from gas engines benefiting from its higher DeNO x efficiency and relatively moderate cost. However, it must be pointed out that despite the whole DeNO x process integrating simultaneously complex gas-phase and surface chemistry (Vassallo et al, 1995;Tamm et al, 2009), the probability of the gas-phase reactions between hydrocarbons, NO x and NH 3 in SCR was exclusively ignored among most of the studies regarding exhaust gas abatement (Mejía-Centeno et al, 2013;Wang et al, 2019;Lee et al, 2020;Jia et al, 2021;Savva et al, 2021), especially given the recently proposed post-treatment measures allowing the catalytic converters to be positioned closer to the engine thus featuring much higher pressure and temperatures (Lott and Deutschmann, 2021).…”