Effects of Port-Injection Specifications on Air Fuel Ratio and Emission Behavior under Transient Operation 2018-32-0012
In port injection, the influence of fuel adhesion on intake port wall caused by varying of injection location on exhaust A/F under the transient and the exhaust gas composition was evaluated. Meanwhile, the adhesion was observed to clarify the mechanism that governs these behaviors on the transition process.
When the engine speed was low and the throttle opening degree after rapid opening was low in the upstream injection, the exhaust A/F under and after transient operation was found to rich spike. Conversely, in the downstream injection, although lean spike did occur under transient operation, no rich spike was found under and after transient operation. Superposition of fuel adhesion to the intake port wall and liquid fuel film flow were observed under and after transient operation at low engine speed in upstream injection using intake port visualization. The rich spike in the upstream injection could have been caused by high amount of fuel adhesion to the intake port wall before transient operation, which then flowed into the cylinder due to the increase in intake flow during rapid opening.
Next, the exhaust gas emissions under transient operation were then measured. In the upstream injection in which the unavoidable large rich spike is occurred, CO and THC were observed. On the other hand, in the downstream injection, although small these compositions were observed, relatively high amount of NOx was observed due to lean spike. However, lean spike under transient operation in the downstream injection can be addressed by transient injection control. Thus, it is considered that the downstream injection has advantageous for exhaust gas purification.