Abstract
Growing interest has arisen to adopt Variable Valve Timing (VVT) technology for automotive engines due to the need to fulfill the pollutant emission regulations. Several VVT strategies, such as the exhaust re-opening and the late exhaust closing, can be used to achieve an increment in the after-treatment upstream temperature by increasing the residual gas amount. In this study, a one-dimensional gas dynamics engine model has been used to simulate several VVT strategies and develop a control system to actuate over the valves timing in order to increase diesel oxidation catalyst efficiency and reduce the exhaust pollutant emissions. A transient operating conditions comparison, taking the Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC) as a reference, has been done by analyzing fuel economy, HC and CO pollutant emissions levels. The results conclude that the combination of an early exhaust and a late intake valve events leads to a 20% reduction in CO emissions with a fuel penalty of 6% over the low speed stage of the WLTC, during the warm-up of the oxidation catalyst. The same set-up is able to reduce HC emissions down to 16% and NOx emission by 13%.
Highlights
During the last years, the emissions legislation in the major automotive regions have established more restrictive limits of the air pollutants released into the atmosphere in order to reduce the environmental impact of the transportation activities
Arnau et al [1] studied the potential that variable valve timing and a second exhaust valve event have in increasing the exhaust gas temperature
Several variable valve timing alternatives have been discussed in this work with the aim of improving the temperature upstream de Diesel catalyst
Summary
The emissions legislation in the major automotive regions have established more restrictive limits of the air pollutants released into the atmosphere in order to reduce the environmental impact of the transportation activities To this end, minimizing fuel consumption and emissions has become one of the major goals of engine developers and manufacturers. Arnau et al [1] studied the potential that variable valve timing and a second exhaust valve event have in increasing the exhaust gas temperature Their results showed that an increment of 50 ◦ C in the exhaust temperature, associated with a fuel penalty of 5%, can be obtained by advancing the exhaust and delaying the intake valve events. Luján et al [2] studied the possibility of placing the after-treatment system, a DOC (Diesel Oxidation Catalyst) coupled to a DPF (Diesel Particle Filter), before the turbine to ease the pollutants oxidation and DPF passive regeneration
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