Over time, environmental protection standards have become more strict and complex. Nitrogen oxides (NOx) are regulated pollutants produced by combustion in a diesel engine. In this project, camshaft timing modifications were studied as a way of reducing NOx emission levels while using low cost hardware. Different valve timing strategies were proposed and modelled using engine simulation. This project was based on two concepts. The first was to open the intake valve during the exhaust stroke, thus expelling burnt gases from the cylinder into the intake manifold and then later re-admitting these gases into the cylinder during the intake stroke of the next cycle. The second was to open the exhaust valve during the intake stroke, allowing burnt gases from the exhaust manifold to enter the cylinder at the same time as the fresh charge enters. Both technologies studied were able to recirculate the exhaust gases without an external EGR system. The EGR amount was controlled by either an intake throttle or an exhaust throttle. The amount of EGR was predicted using engine simulation. The brake-specific fuel consumption (BSFC) and brake-specific NOx (BSNOx) trade off was the main criterion used to select the best technology, although other features such as predicted manifold pressures and engine-out soot were also considered.
The results indicate that, by using increased amounts of EGR while varying the intake or exhaust throttle position, NOx emissions can be reduced with a slight BSFC penalty. These methods are thus a low cost means of reducing engine-out NOx emissions.