US Patent 9657626 Emissions reduction system

An exhaust system for a diesel engine is disclosed. The exhaust system may include a diesel oxidation catalyst (DOC) configured to receive exhaust gases from the engine and oxidize hydrocarbons in the exhaust gases and a passive NOx adsorber (PNA) downstream from the DOC and configured to store NOx from the exhaust gases at temperatures up to 150° C. A selective catalytic reduction (SCR) system may be downstream from the PNA and configured to reduce NOx in the exhaust gases. The PNA may be configured to release the stored NOx at temperatures above 200° C. The DOC upstream of the PNA may reduce the amount of N2O that is generated by the PNA by oxidizing hydrocarbons before they reach the PNA.