Improvement of Repeatability in Tailpipe Emission Measurement with Direct Injection Spark Ignition (DISI) Vehicles

The effects of engine and after-treatment control conditions on emissions fluctuation were evaluated and the technical idea for improving the repeatability in tailpipe emission measurement from DISI vehicles was provided. To improve measurement repeatability, low emissions analyzers with dilution air refining system were employed for this research. In addition, a new device that enabled monitoring of signals from the Engine Control Unit (ECU) was developed. A novel approach using these devices was applied to DISI gasoline engine vehicles equipped with de-NOx catalyst to clarify emission characteristics in the Japanese 10.15 test cycle emission tests. Through the tests, it is found that NOx emissions most correlated with the temperature at the de-NOx catalyst. CO and HC reaching the de-NOx catalyst played an important role in the temperature increase of de-NOx catalyst by exothermic reactions. Lean combustion at the early stage of the Japanese 10.15 test cycle results in higher tail-pipe NOx emissions by increasing the amount of NOx in de-NOx catalyst. In order to control de-NOx catalyst conditions, optimum vehicle preconditioning and accurate driving using the automatic driving unit were applied. Testing demonstrated repeatable emission measurements.