## 4 Conclusions  
It is essential to systematically manage DPFs. These are the most effective exhaust after-treatment control systems for reducing the amount of particle emissions (mass/PM,  
Figure 16: DPF diagnosis algorithm developed in this study. number/PN) generated by a diesel-fueled engine. Failure to maintain DPFs can have significant consequences for vehicles. The purpose of this study was to investigate the OBD signal and PN emission characteristics of DPFs with different types of damage and to present an OBD-based algorithm for determining various types of DPF damage from vehicle OBD signals. In this study, three DPF samples with different types of damage (crack, hollow, and melting) were installed on the exhaust system of the test SUV with a 2.0 L diesel-fueled engine. The KD-147 driving cycle was carried out on a chassis dynamometer. An OBD-II monitoring system was used to measure signals from the engine and DPF. In addition, an opacity smoke-meter and an instrument that measures particle number were used to measure the particulate emission. The main results of this study are summarized below:  
1. The three types of DPF damage were identified using X-ray images with a tube voltage of 125 kV. The failures in the crodierite DPF substrates were classified into the following types: cracks in the material inside the DPF, its melting, and hollow fractures. 2. A comparison of the characteristics of the OBD data obtained by the GDS under the KD-147 driving mode with each of the DPF samples revealed that the difference in maximum value of the OBD data was larger than the difference in minimum value. In particular, the maximum values of the three parameters (airflow mass, boost pressure, and VGT actuator) were distinctly different for each of the DPF samples. 3. A comparison of the exhaust temperature at the rear end of the DPF revealed that the exhaust temperature gradient in the case of the normal DPF and crack-damaged DPF followed the KD-147 driving pattern. This was because volume damage had not occurred inside the crodierite DPF substrates. However, in the case of the hollow- and melting-damaged DPFs, the volume inside the crodierite DPF substrates reduced, or the time for the exhaust gas to stay in the DPF substrates decreased. Thereby, these present relatively smooth shape patterns. 4. In the case of the normal DPF device, the emissions were less than 10% of the permissible exhaust emissions for diesel vehicles in Korea. Meanwhile, the emissions with each of the three damaged DPFs exceeded this value. 5. At particle number and size concentration, the normal DPF sample showed the lowest maximum number of total particle emission levels (within 10\({}^{7}\)). Meanwhile, the crack- and hollow-damaged DPF samples showed total PN emission levels within 10\({}^{8}\). The melting-damaged DPF continuously emitted the largest number of nanoparticles (of the order of 10\({}^{9}\) #/cc) regardless of the vehicle driving speed in the KD-147 driving mode. The normal DPF also emitted a significant number of nanoparticles with sizes of at most 23 nm. 6. Finally, the OBD-based algorithm to determine whether a DPF is damaged was developed from the airflow mass, boost pressure, and VGT actuator control duty data measured by the GDS diagnostic as comparable signals. It is anticipated that prior to obtaining an X-ray image to determine whether the DPF is damaged, it can be primarily selected using the algorithm developed in this study. The EURO-7 environmental regulation necessitates the installation of a DPF device for diesel-fueled vehicles. In certain DPF-equipped vehicles, the filter may cause problems depending on the driving conditions and durability. In this case, it is inefficient to perform an X-ray inspection on all vehicles. Therefore, it is more efficient to filter out vehicles with problems in advance by using the DPF device, and to perform an X-ray inspection on only these vehicles. In this respect, the results of this study are highly effective.