## 3 Results
### Regenerations  
Figure 4 compares emissions of one hot start WHTC without regeneration (symbol nR) and two or three subsequent hot start WHTCs that regeneration took place (symbol R) for four diesel engines. For DPF #3 both the \"Golden\" system with the catalytic stripper (CS) and the PMP system with the evaporation tube (ET, bold) were connected to the proportional partial flow dilution system (PD, dark colour columns). For DPF #5 both systems were connected to the tailpipe (TP, light colour columns). For DPFs #4 and DPF #1 the ET system was connected to the PD and the CS system to the tailpipe.  
For DPF #3, the regenerating cycles remained at the same levels as with the non-regenerating one. It is possible that the DPF was quite clean and there was not much soot to be burnt, or the regenerating  
Figure 4: Solid particle number (SPN) emissions during one non-regenerating (symbol nR) and 2 or 3 regenerating (symbol R) hot start WHTCs measured with the “Golden” system with catalytic stripper (CS) and the PMP system with evaporation tube (ET, bold) connected both at the proportional partial flow system (PD, dark colours) for DPF #3, both at the tailpipe (TP, light colours) for DPF #5, one at the tailpipe and the other at the PD for DPF #4 and DPF #1. Numbers give the difference of the CS system compared to the ET system for 23 nm and 10 nm measurements.  
Figure 3: Solid particle number (SPN) emissions with and without the crankcase ventilation connected downstream of the aftertreatment devices, as measured with the “Golden” TP(CS) system for three diesel engines. Numbers give the additional 10–23 nm particles compared to the >23 nm levels. Error bars show one standard deviation of 2–3 tests. The inset compares the sub-23 nm percentages of the TP(CS) and PD(ET) systems with and without the crankcase ventilation connected for DPF #4 and DPF #7. WHTC = World harmonised transient cycle; WHSC = World harmonised stationary cycle; h = hot; c = cold.  
emissions were much lower compared to the levels of the engines (e.g., crankcase emissions levels). For DPF #5 the emissions during the regenerating cycles gradually increased. The differences between the CS and ET systems for the 23 nm CPCs changed from 0% to -6%, while for the 10 nm CPCs from -19% to -1%. These changes have to do with the change of the size distribution and the losses inside the systems. For the non-regenerating cycle the sub-23 nm fraction was very high, thus small particles were emitted and it is possible that the CS system had higher particle losses at small sizes. During the regenerating cycles the majority of particles was >23 nm and consequently the losses were similar. DPF #4 and DPF #1 showed also an increase of the emissions with regenerations. The differences between the CS and ET remained similar with or without regenerations taking place for emissions >23 nm. For DPF #4, where the sub-23 nm data were available, there was a gradual increase of the differences between CS and ET. At the last regenerating cycle the 10 nm CPC connected to the CS measured 41% less than the ET system.  
Figure 5 plots the 10 nm real time signals of the TP(CS) and PD(ET) systems for the last 600 seconds of the first (left panel) and the third (right panel) regenerating WHTC for DPF #4. While the agreement is excellent for the first regenerating cycle, high differences are seen for the third one. The most likely explanation is that volatile particles re-nucleated downstream of the evaporation tube (volatile artefact) [16]. The TP(CS) had PCRF 2000, while the PD(ET) only 100. The system with the catalytic stripper oxidised them so no re-nucleation occurred downstream of the catalytic stripper. Another explanation is that small particles existed during the regeneration that grew to sizes above 10 nm in the evaporation tube system due to condensation of volatile precursors on them, but remained below 10 nm in the catalytic stripper system because the volatile precursors were oxidised.