AN EXPERIMENTAL STUDY ON THE EFFECTS OF EGR AND EQUIVALENCE RATIO ON CO AND SOOT EMISSIONS OF DUAL FUEL HCCI ENGINE

Abstract: HCCI engines improvements are challenged with high CO emissions. In this study, effects of EGR and equivalence ratio on CO and soot emissions of a dual fuel HCCI engine are investigated. The experiments were conducted on a variable compression ratio(VCR) single-cylinder research engine with compression ratio of 17.5:1. Premixed gasoline is provided by a carburetor connected to intake manifold and equipped with a screw to adjust premixed air-fuel ratio, and diesel fuel is injected directly into the cylinder through an injector at pressure of 250 bars. Intake charge temperature was increased up to 110-115ºC by using an electrical heater. The higher advanced injection timing (35 BTDC) was used to initiate the gasoline auto-ignition in the HCCI dual fuel engine. The results show that increasing EGR rate increases CO emissions due to dilution effect which reduces combustion temperature, also addition of EGR increases soot emission as a result of decreases the inlet air and its oxygen, which create rich points in the cylinder mixture. Results also show that the CO emission decreases by increasing the equivalence ratio due to formation of more OH radicals in the cylinder and increasing the overall reactivity