First, the validity of the current test procedure for particle measurement adopted in a periodic technical inspection (PTI) was evaluated by comparing test results obtained with the PTI and a type approval test (TAT) procedure using a Euro V level diesel truck with an intentionally damaged diesel particulate filter (DPF). PM and particle number (PN) with the TAT increased with increasing DPF damage ratio, and the PTI results well reproduced those in the TAT. However, the regulation limit of the PTI was so loose that even a 100% damaged DPF resulted in emission well below the PTI limit, although 0.5% and 5% damage ratios resulted in values exceeding the PN and PM limits in TAT, respectively. Then, we evaluated three different techniques for particle detection with the PTI procedure, such as an opacity meter, which is currently used in PTI, laser light scattering photometry (LLSP), and the PN method. For the detecting DPF failure, opacity meters did not have sufficient sensitivity. On the other hand, the LLSP was sensitive enough for detecting DPF failure, but the results varied among LLSP devices. This variation was due to the test procedure of PTI, which is strongly transient (no load racing). The LLSP and PN measurement devices were sensitive enough to detect DPF failure at idle, which was quite steady, and the variation observed in the PTI procedure did not occur. PN counting of particles over 15 nm was more sensitive than LLSP and was sensitive enough to detect DPF failure, which did not result in the PM limit in TAT being exceeded.
