An internal combustion engine system is described herein. The system uses an additive added to the exhaust of the internal combustion engine to maintain a range of NO2 to NO within a range that provides for a fast SCR reaction in a selective catalyst reduction unit. The additive and the exhaust enter a diesel oxidation catalyst (DOC), whereby the NO2 undergoes a two-stage process. In the first stage, the NO2 from the exhaust is adsorbed onto the precious metal catalyst of the DOC and an atomic oxygen is removed from the NO2, reducing the NO2 to NO. Because of the higher reactivity of the additive, the additive scavenges a portion of the atomic oxygen from the catalyst. During the second stage of the DOC process, the NO is oxidized over the catalyst to form NO2.