Combining Early Intake Valve Closure and Exhaust Throttling to Achieve Rapid Exhaust After-treatment Warm up in Diesel Engine Systems

Nowadays, the thermal management of exhaust after-treatment (EAT) units is a paramount concern for diesel automotive vehicles to meet the stringent emission regulations. In general, EAT temperatures above 250oC are favorable for effective emission conversion efficiency. At low-loaded operations, it is difficult to achieve that since exhaust temperature remains much below 250oC. Therefore, this numerical work aims to elevate exhaust temperature at a light-loaded diesel engine model through adopting two different engine- base techniques, namely early intake valve closure (EIVC) and exhaust throttling (ET). Both individual and combined modes of EIVC and ET are examined for high exhaust temperatures in the system. ET enhances exhaust temperature over 250oC with high exhaust flow rate, which is desirable for rapid EAT warm up. However, it causes up to % 15 fuel penalty, which highly impairs its practicality. Unlike ET, EIVC is thermally efficient and can raise exhaust temperature above 250oC. Yet, it has the disadvantage of significantly lowered exhaust flow rates, which is inconsistent with fast EAT warm up. Simultaneous application of ET and EIVC, as EIVC+ET, can still keep exhaust temperature above 250oC with reduced fuel penalty (down to % 8.8). It also has the benefit of increased exhaust flow rates compared to EIVC mode, which substantially heightens heat transfer rates to the EAT unit (up to % 101). Thus, it can sustain accelerated EAT warm up in the system. EIVC+ET method is also seen to be effective to improve EAT stay-warm performance (delaying EAT cool off) as it enables high exhaust temperature and high exhaust rates, which is not possible with other methods examined in the analysis.