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Analysis of Transient HC, CO, NOx and CO2 Emissions from a GDI Engine using Fast Response Gas Analyzers
Abstract:
A study has been conducted to measure the transient HC, NOx, CO, CO2 and particulate emissions from a modern 1.6-liter, Euro IV-stage turbocharged Gasoline Direct Injection (GDI) passenger car engine. The tests were conducted using ultra-fast-response analyzers with millisecond response times so that the real-time effects of the individual combustion events and the ECU's start strategy could be studied.
The results show that through the use of an aggressive cold start calibration strategy, the catalyst is very efficient after light-off at about 30s. However, during this same period, there are signs of partial misfires and rich AFR excursions, both of which contribute to the overall tailpipe emissions. The data from the fast-response analyzers allowed clear discrimination between rich events and partial misfires and would allow appropriate calibration actions to be taken.
NOx conversion was seen to be highly transient, with very big changes in tailpipe NOx emissions occurring corresponding to the fuelling control system AFR switching frequency. Under lean AFR bias conditions, particularly after a lean AFR disturbance, significant NOx breakthrough was seen. ECU optimization using fast-response analyzers could further improve this vehicle's emissions calibration.