In-Cylinder Gas Exchange Control Process for Maximizing Fuel Conversion Efficiency

Abstract

The use of exhaust gas recirculation in internal combustion engines, obtained by means of variable valve timing techniques, has represented a good alternative to reduce in-cylinder gas emission and the specific fuel consumption, consequently improving thermal efficiency. The control of valves opening and closing times, especially when keeping some overlapping, may permit the residual gases trapping, what makes the cylinder temperatures lower and reduce engine-out emissions, mainly of nitrogen oxides. Besides that, these techniques allow load control, what can eliminate the necessity of throttling and hence pumping losses. Based on this, this paper presents an analysis of the use of variable valve timing focused on trapping some residual gases in a spark ignition engine. It has been used a four valve Single Cylinder Research Engine-SCRE with direct injection. It was adopted a volumetric ratio equal to 15:1, an engine speed of 2500 rpm and the ethanol as fuel. Valves timing were changed taking into account the maximum fraction of exhaust gases which could be used without compromising mixture inflammability. Changes in performance were analyzed and the importance of controlling the amount of recycled exhaust gases was finally evidenced.