Scholl, F., Gerisch, P., Neher, D., Kettner, M. et al., "Development of a NOx Storage-Reduction Catalyst Based Min-NOx Strategy for Small-Scale NG-Fueled Gas Engines," SAE Int. J. Fuels Lubr. 9(3):734-749, 2016, doi:10.4271/2016-32-0072.
One promising alternative for meeting stringent NOx limits while attaining high engine efficiency in lean-burn operation are NOx storage catalysts (NSC), an established technology in passenger car aftertreatment systems. For this reason, a NSC system for a stationary single-cylinder CHP gas engine with a rated electric power of 5.5 kW comprising series automotive parts was developed. Main aim of the work presented in this paper was maximising NOx conversion performance and determining the overall potential of NSC aftertreatment with regard to min-NOx operation.The experiments showed that both NOx storage and reduction are highly sensitive to exhaust gas temperature and purge time. While NOx adsorption rate peaks at a NSC inlet temperature of around 290 °C, higher temperatures are beneficial for a fast desorption during the regeneration phase. Combining a relatively large catalyst (1.9 l) with a small exhaust gas mass flow leads to a low space velocity inside the NSC. This enabled long storage periods up to 40 min with purge times of around 40 s. At constant engine power, the NSC system allows reducing tailpipe NOx emissions by up to 92 % (NOx ≈ 22.5 ppm) compared to lean-burn operation at MBT spark timing, while showing a fuel penalty of < 2 %. An oxidation catalyst positioned upstream of the NSC only proved beneficial to reducing HC emissions, while not affecting neither NOx and CO output but increasing fuel penalty due to reduced NOx storage capacity.