Transient EGR Control for a Turbocharged Heavy Duty Diesel Engine

EGR system is one of the most useful way to reduce NOx. In order for heavy duty diesel engines to meet more stringent exhaust emission regulations, higher EGR rate should be needed. When higher EGR rate is applied to a turbocharged and intercooled diesel engine, however, spike smoke at rapid acceleration is generated due to delay of boost pressure rise. It is needed to develop new control method of EGR to eliminate smoke spike. Therefore, the closed loop EGR control system was developed and tested. The closed loop control system controls EGR valve as feed-backing estimated air excess ratio(Lambda) by detected air mass flow and engine operation condition. The closed loop control system applied to a diesel engine with displacement of 13L and experimentally evaluated the effects of the control system at the transient test. As the result, smoke spike at rapid acceleration was kept lower and PM was reduced by 40%, compared with the conventional control system, under even high EGR rate condition.