Effect of internal and external EGR on cyclic variability and emissions of a spark ignition two-stroke cycle gasoline engine

Abstract

Conventional two-stroke cycle engine suffers from typical drawbacks including lower combustion efficiency and excessive emissions of uHC and CO which are largely due to low in-cylinder average charge temperature at low load and speed regions of engine operating conditions. Utilising the hot burned Exhaust Gas Recirculation (EGR) technique can boost the in-cylinder average charge temperature of the engine. The influence of hot burned gases applied by means of both Internal EGR and External EGR strategies on the combustion stability and exhaust gas emission of a single-cylinder two-stroke cycle engine running at low-load and mid-load of operating conditions was investigated experimentally along with simulation works using 1-D engine simulation code. The results indicated that both In-EGR and Ex-EGR improved the combustion stability (lower misfire cycle) and decreased the concentrations of uHC and CO emissions, specifically at low speed region; however, NOx concentration was increased. At Internal EGR setting of 30%, the Coefficient of Variation for maximum in-cylinder pressure (COVPmax) reached the minimum by 5.64 while when External EGR percentage was 25%, COVPmax approached about 6.67 at the mid-speed (2000 rpm) of engine operating condition.