VVA-strategier för avgastemperaturhöjning på en HD-Dieselmotor

Sammanfattning: Regulations on the exhaust emissions of HD-diesel engines are becoming more and more stringent, and therefore, emission after-treatment systems are commonly used. These systems rely on catalytic conversion of NOx,CO , and HC emissions, and are thus dependant on temperature. At low load of the engine, exhaust temperatures are not sufficient for the after-treatment components. Therefore, means to increase the exhaust temperature while maintaining low emissions and fuel consumption are needed. The focus of this project has been to develop strategies for the lift profiles of exhaust and intake valves in the engine, with the goal to raise exhaust temperature in combination with low emissions and fuel consumption. The strategies have been tested in a single-cylinder research engine equipped with a hydraulic variable valve actuation system. Conventional strategies used to raise the exhaust temperature were also tested and compared to the valve strategies developed in this project. The results show that all strategies tested increased the exhaust temperature at low loads, but by different magnitude, different emissions, and fuel consumption. The exhaust brake showed highest potential for heating the exhaust after-treatment system quickly, and opening of the exhaust valve during the intake stroke in combination with intake throttle was most efficient for maintaining the temperature with low fuel consumption. It also proved that this lift height can be kept constant at different loads by the use of throttle, exhaust brake, or Miller late intake valve closing. The strategies of Miller, valve lift during the intake or exhaust strokes, and valve phase shift also proved to reduce NOx emissions at loads up to 50% . It can be concluded that variable valve actuation can be used to increase exhaust temperature at low load, and that there is also a great potential of reducing emissions at the same time.