Modelling the effect of intake valve closing timing on exhaust thermal management of a turbocharged and intercooled diesel engine

Özet

Emissions from diesel engines have become recently a significant problem due to their positive effect on global-warming. There are strict restrictions on emissions and low-emission diesel engines nowadays are required to be developed. One of the solution for reduced-emission diesel engines is to utilize exhaust thermal management systems. However; these systems work efficiently mostly at temperatures above 250 oC and for diesel engines, especially at low speed and low load conditions, exhaust gas temperatures are not generally higher than 250 oC. That not only leads to inefficient aftertreatment systems, but also insufficient emission reduction. Variable valve timing (VVT) can be used to achieve those high exhaust gas temperatures by changing the opening and closing timings of the intake&exhaust valves at any speed and any load. Therefore, the aim of this study is to try to increase the turbine exit temperature of a diesel engine above 250 oC at 2.50 bar brake mean effective pressure (bmep) and 1200 rpm engine speed condition by changing intake valve closing (IVC) timings. Diesel engine system is simulated by using Lotus Engine Simulation (LES) program. The model is then validated with experimental results. It is seen that exhaust gas temperatures can be raised higher than 250 oC for the studied particular engine loading case when IVC is advanced or retarded. The method results in fuel consumption saving in comparison to nominal valve timing by decreasing the required fuel injection rate for the constant engine loading. However, earlier and later closing of intake valve also causes exhaust flow rate to drop off.