Effects of Port Injection Specifications on Air-Fuel Ratio and Emission Behavior under Transient Operation 2018-32-0012
When an electronically controlled fuel injection device is located at downstream in intake port (hereinafter defined as downstream injection, on the other hand, upstream injection is defined as that fuel injection device is located at upstream in intake port), the possibilities of an improvement in the engine startability, increase in maximum power, and decrease in THC during warming have been reported in visualizations of the intake port. In addition, the amount of wall adhesion decreased with downstream injection in previous paper . In this paper, we examine the influence on the amount of wall adhesion due to the difference in injection position on fuel transport in the intake port during transient operation and the obtained exhaust A/F and the amount of exhaust gas emitted during transient operation are evaluated. In addition, regardless of the injection position, we also grasp the general trend of the transient A/F behavior according to the transient operation such as engine revolution, the engine load, and the throttle opening after transient.
Using the same intake port visualization system reported in the previous paper, we observe the fuel behavior during the transient for the different injection positions and elucidate the mechanism.
First, we observe the behavior of the exhaust A/F during the transient operation with respect to the fuel injection position, the engine revolution and the throttle opening after rapid opening of the throttle (hereinafter defined as “throttle opening after transient”, on the other hand, “throttle opening before transient” is defined as throttle opening before rapid opening of the throttle). Although there was no lean spike during the transient operation at low engine revolution and small “throttle opening after transient” in upstream injection, the exhaust A/F after the transient operation tends to arise richer shift. As engine revolution is large and the “throttle opening after transient” is also large, the lean tendency is both during and after the transient operation. On the other hand, for downstream injection, although the tendency for a lean spike during the transition operation to upstream injection becomes stronger but the rich shift after the transient operation is not observed, the tendency of the exhaust A/F with respect to the engine revolution and “throttle opening after transient” was similar to that during the upstream injection.
We confirmed the above phenomena with the intake port visualization system, revealing that the superimposition of wall adhesion onto the intake port and the flow of the fuel film occurred after the transient operation at low engine revolution in upstream injection. In upstream injection, it is considered that wall adhesion occurred upstream of the intake port, and the fuel film flowed into the cylinder due to an increase in the intake air flow rate during the transient operation, causing a rich spike. For downstream injection, it is considered that the tendency for a lean spike occurs since the flow of wall adhesion during the transition is small.
Next, exhaust gas after catalyst was measured for all rich spikes, the A/F flat zones, and the lean spikes during the transient in the exhaust system with a catalyst. The emission of NOx in the lean spike and the emissions of CO and THC in the rich spike are large. We found that the purification of CO and THC in the exhaust gas declined since a rich spike can’t be avoided physically in upstream injection.
From the above, it is possible that the purification of CO and THC in the exhaust gas may deteriorate because of rich spike, which are physically unavoidable during the transient in upstream injection. In contrast, downstream injection is considered to be advantageous for exhaust gas purification since lean spike is expected to be eliminated depending on the injection control of the transient.