Abstract: A thermal reactor for reducing exhaust emissions generated by an engine. The thermal reactor preferably includes an outer housing and an inner core mounted within the outer housing. The inner core defines an expansion chamber which receives exhaust gas from the engine. When the exhaust gas enters the expansion chamber, it expands and becomes thoroughly mixed. While in the expansion chamber, at least some of the exhaust gas is oxidized. A single-layered recirculation chamber is located between the outer housing and the inner core. The recirculation chamber receives the exhaust gas from the expansion chamber and recirculates the exhaust gas around the outer surface of the inner core such that the inner core is insulated. By insulating the inner core with heated exhaust gas from the expansion chamber, the expansion chamber maintains a high temperature which facilitates oxidation of the exhaust gases.