Impacts of different exhaust thermal management methods on diesel engine and SCR performance at different altitude levels

Abstract

Exhaust thermal management is important for efficient operation of the diesel engine aftertreatment system to meet emissions requirements at low speed and low load conditions. In order to study the impacts of exhaust thermal management strategies on diesel engine performance and SCR conversion efficiency at different altitudes, the effects of the altitudes (2000, 1000, and 0 m), intake throttling, exhaust throttling, and post injection were experimentally studied with a high-pressure common-rail diesel engine that consisted of a diesel oxidation catalyst (DOC) and a selective catalytic reduction (SCR) aftertreatment device. The results showed that the exhaust temperature and the SCR conversion efficiency were improved by intake or exhaust throttling or post injection at any altitudes. However, the intake or exhaust throttling resulted in engine air flow rate reduction, combustion deterioration, brake specific fuel consumption (BSFC) increase, and NOx emissions decrease. When the intake throttling and the exhaust throttling were compared with the same pressure change amplitude, the intake throttling provided better effects on exhaust temperature enhancement, SCR conversion efficiency increase, while the exhaust throttling provided worse effects on BSFC. As the altitudes increased, the impacts of the intake or exhaust throttling on the SCR conversion efficiency and the BSFC became more prominent. Moreover, increasing post injection fuel quantity or retarding post injection timing made combustion worse, BSFC higher, and NOx emissions lower with benefits of exhaust gas temperature increase and SCR conversion efficiency increase. Therefore, post injection is an effective method of exhaust thermal management and should be adopted first. Then, intake throttling should be used. Finally, exhaust throttling can be considered.