Effects of Intake and Exhaust Continuously Variable Valve Duration on Fuel Consumption and Emission Characteristics in Engine and Vehicle Tests

An experimental study was conducted on a multi-cylinder engine equipped with both intake and exhaust continuously variable valve duration (CVVD). Due to CVVD and continuous variable valve timing (CVVT), valve closing and opening timings of both intake and exhaust sides became decoupled, so that four valve timings (opening and closing timings of intake as well as exhaust sides) can be optimized under each engine condition. Theses independent valve timings allowed reductions of fuel consumption as well as particle number (PN) and stoichiometry combustion under full-load condition without compromise of performance. In addition, to reduce raw gaseous emissions and shorten light-off time of catalyst under catalyst heating condition, various valve timings were tested in the engine test bench. As results, nitrogen oxides (NOx) – total hydrocarbon (THC) trade-off relation was relieved by optimal valve timings including negative valve overlap duration compared to the base engine. As the last part of this study, FTP-75 and US-06 driving cycle tests were carried out in order to verify the positive effects of CVVD shown from the engine test. As results, both of fuel economy and emissions characteristics were improved compared to the base vehicle.