Nakao, Y., Sakurai, Y., Hisano, A., Saitou, M. et al., "Effects of Port Injection Specifications on Emission Behavior of THC," SAE Int. J. Engines 9(4):2427-2433, 2016, doi:10.4271/2016-32-0065.
In port injection, it is difficult to control in-cylinder fuel supply of each cycle in a transient state as cold start (in this paper, cold start is defined as several cycles from cranking at low engine temperature). Hence, THC, which is one of regulated emission gases, is likely to increase at cold start. As one of THC emission reduction approaches at cold start, the optimization of fuel injection specifications (including injection position and spray diameter) is expected to reduce THC emission. Setting injection position as downstream position is expected to secure the in-cylinder fuel supply amount at cold start because of small fuel adhesion amount on an intake port wall and a short distance between the injection position and in-cylinder. The position injection contributes to reduction of THC emission due to elimination of misfire. Additionally, fuel atomization is also expected to effective at cold start because mixing promotion caused by fuel atomization is dominant in low engine temperature. On the other hand, the effect of injection specifications under warm-up (in this paper, the engine temperature is relatively lower than hot condition) is also evaluated in this paper. Additionally, the spray behavior in intake port is observed by visualization in intake port. In this paper, fuel atomization method is injection pressure increasing. In comparison with the upstream position injection, downstream position injection improves engine startability and reduces THC emission. Furthermore, the spray diameter at cold start decreases with increases in injection pressure. On the other hand, the fuel adhesion amount on intake valve surface under warm-up becomes less than that at cold start. The THC emission remains approximately the same, regardless of fuel atomization.