A multi-stage emissions treatment system is disclosed for non-road, medium-speed, large-displacement dual fuel, diesel or natural gas (LNG or CNG) generator applications. The system integrates an onboard in-cylinder exhaust gas recirculation system with a downstream low temperature selective catalytic reduction unit that utilizes aqueous ammonia as a reductant agent. The combination enables ultra-low nitrogen oxide (NOx) emissions performance at exhaust temperatures below those required for urea-based SCR systems. The engine operates at medium speeds (300-1,200 RPM) and supports both emergency and non-emergency use cases, including compliance with EPA Tier 4 Final standards. The system provides inducement resilience by maintaining such compliance in the event of SCR failure. High torque and inertia characteristics allow the generator to effectively respond to transient loads typical of artificial intelligence workloads. The invention enables the first viable use of medium-speed, large-displacement diesel engines in emissions-constrained, multi-engine stationary power sites such as data centers.