Experimental analysis of engine out emissions of a light-duty diesel engine during warm-up under cold start conditions

Abstract

Emission targets of diesel engines are achieved by high-performance exhaust gas aftertreatment systems (EATS). Due to the light-off temperature, the system does not work as desired under cold operating conditions. This is especially challenging with the introduction of Euro 7 because engine warm up is getting more critical, as not only emission limits are getting tighter, but also the range of ambient temperatures is widened. Especially cold start conditions will be challenging: On one hand engine out emissions cannot be converted by the EATS before light-off which is extended by a greater temperature deficit. On the other hand, engine out emissions are affected by poor combustion boundary conditions. This paper focuses on the impact of temperature on emission formation by carrying out the first five km of three different driving cycles under cold start conditions. Based on these cycles, representative stationary operating points for each emission species were defined. A method was developed to reproduce thermal boundary conditions from engine warm up. This method allows to investigate the impact of thermal conditions on emission formation in steady state. Therefore a light-duty diesel engine was instrumented with a high number of temperature sensors in the cylinder liner wall and cylinder head as well as in the oil, gas, fuel and coolant path. The results were analyzed using 0D/1D simulation models to isolate the thermal impact on the emission formation. The obtained results serve as a basis for following measures on a similar single-cylinder research engine to develop innovative cold start measures.