Described here are systems and methods for treating fuel injected exhaust streams. In general, the systems comprise a fuel injector, a pre-combustor, and a fuel combustor. The methods described herein include methods for regenerating a NO.sub.x trap or a DPF, and methods for generating a substantially uniform fuel air mixture at a fuel combustor inlet, or a substantially uniform temperature at a fuel combustor outlet. The methods of regenerating a NO.sub.x trap typically comprise the steps of injecting fuel into an exhaust stream, passing the stream through a pre-combustor, operating the pre-combustor to at least partially combust the injected fuel, reacting the fuel and exhaust stream mixture within a fuel combustor to generate a reducing gas mixture, and introducing the reducing gas mixture into a NO.sub.x trap, whereby the NO.sub.x trap is regenerated. Similar methods for regenerating a diesel particulate filter are also described. Control strategies are also provided.