Reduction of cold-start emissions from an ammonia mono-fueled spark ignition engine

This article presents the first practical engine system using ammonia (NH3) as a mono-fuel. To address the low flammability and distinctive odor, the system incorporates a four-cylinder spark ignition engine with an onboard reformer applying autothermal reforming to generate hydrogen as a combustion promoter, a three-way catalyst (TWC), and selective catalytic reduction (SCR) catalyst as an NH3 adsorbent. The system successfully reduced nitrogen-based exhaust emissions during cold starts, which was a challenge, by controlling the air-fuel ratio (lambda). Nitrogen oxides were suppressed by rich combustion until the TWC became active, while NH3 passing through the TWC was adsorbed by the SCR catalyst. After TWC activation, simultaneous purification of NH3 and nitrogen oxides was achieved by controlling lambda at 1. The adsorbed NH3 was subsequently purified along with nitrogen oxides via the SCR reaction by lean operation, regenerating the adsorption capacity and achieving near-zero emissions.