Development of a NO _x Storage-Reduction Catalyst Based Min-NO _x Strategy for Small-Scale NG-Fueled Gas Engines 2016-32-0072

One promising alternative for meeting stringent NO_x limits while attaining high engine efficiency in lean-burn operation are NO_x 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 NO_x conversion performance and determining the overall potential of NSC aftertreatment with regard to min-NO_x operation.

The experiments showed that both NO_x storage and reduction are highly sensitive to exhaust gas temperature and purge time. While NO_x 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 NO_x emissions by up to 92 % (NO_x ≈ 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 NO_x and CO output but increasing fuel penalty due to reduced NO_x storage capacity.