Impact of the Internal Combustion Engine Thermal State during Start-Up on the Exhaust Emissions in the Homologation Test

Due to the increasingly restrictive exhaust emissions requirements from conventional vehicles, the internal combustion engine start-up seems to be most important part of engine operation. The period immediately after starting the engine is the time when the exhaust emissions are highest, thus, this aspect is currently subject to heavy analysis. The article evaluates the impact of the engine thermal state during its start-up for a Euro 5 emission class vehicle type approval test. The engine thermal state during start-up turned out to have a crucial influence (throughout the approval test) on the results of the hydrocarbons road emission (a difference of about 1500%) and the road emission of carbon monoxide (63%). The remaining road exhaust emission values were less sensitive to the thermal state of the engine during start-up—the nitrogen oxides emission value increased by 18% (for a cold start compared to a hot start), and the road fuel consumption (and thus the emission of carbon dioxide) increased by about 6%. In conclusion, the authors refer to technical solutions that may have a significant impact on reducing the exhaust emissions in the considered period of engine cold start