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A three dimensional model of 2.0L, turbocharged gasoline direct injection (GDI) engine was established using AVL-Fire. The mixture formation process and spray impingement were analyzed with various injection strategies. The results showed that, as the injection timing delay, the amount of spray impingement reduces and the mixture at the ignition timing is less homogeneous. Compared with the single-stage injection, the dual-stage injection could reduce the amount of spray impingement. The intakeports were designed to obtain high tumble ratio, then the formation of mixture in cylinder was simulated to study the effect of tumble ratio on spray impingement and mixture formation process. It turned out that the intakeports with higher tumble ratio could get better mixture formation and less amount of spray impingement.

Gasoline-fueled small engines have been developed predominantly for power by using fuel-rich combustion, and unburned HC is usually a consequence of inadequate mixing and combustion of the charge. In principle, a straightforward way to reduce HC emissions is to run at an almost stoichiometric air-fuel ratio while NOx emission become problematic, namely a tradeoff exists between the amount of HC and NOx emission, especially at high engine loads. Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NOx production when burning stoichiometric or even leaner mixture. In this paper, experimental investigations were conducted on a small off-road gasoline engine to study the effect of EGR system on the engine-out emission especially the unburned HC and NOx.

Some motorcycles, such as 3 wheels and scooters, have dual high exhaust characteristics on CO and NOx. A mechanical exhaust gas recirculation (EGR in brief) system has been developed for motorcycles and attempt to reduce NOx exhaust emission as a valuable method. Mechanical control valve are driven by intake vacuum of the engine. Appropriate amount of exhaust gas are return to engine intake system during acceleration process and high speed condition. This system also can shut down EGR at deceleration and idling speed condition. Then, NOx and fuel consumption reduction performance was confirmed by means of experimental methods.