# A Study on the Impact of DPF Failure on Diesel Vehicles Emissions of Particulate Matter
## 1 Introduction  
Particulate matter in automobile exhaust gas is one of the targets of exhaust gas regulations, and it is the main cause of problems due to air pollution [1]. The government of the Republic of Korea established the \"Basic Plan for Air Quality Management in the Metropolitan Area\" in 2005 to improve the air environment in metropolitan areas, where air pollution is severe [2]. Under this plan, the \"Atmospheric Environment Improvement Project in the Metropolitan Area\" is being executed, and, as part of this project, the \"Emission Reduction Project for Old Diesel Vehicles of Environment\" (2021) has been promoted for diesel vehicles, which have the greatest impact on the atmospheric environment in metropolitan areas. Through the above project, as of 2018, approximately 490,000 old diesel cars were scrapped early, approximately 510,000 were equipped with diesel particulate filters (DPF), and approximately 200,000 were retrofitted with LPG engines. All of these vehicles were pre-Euro 3, but they were either scrapped or upgraded to Euro 4 under the project, which contributed greatly to reducing the particulate matter emissions in metropolitan areas [3]. In a vehicle equipped with a DPF, management through periodic inspection is required to prevent DPF aging. When the substrate is aged, internal damage occurs due to complexreasons, such as local thermal stress generated during the regeneration process, vibration generated during driving, and increased back pressure with the accumulation of particulate matter (PM) [4]. If a DPF is damaged, its performance in filtering particulate matter emissions decreases significantly. When a vehicle equipped with such a damaged filter is driven, excessive amounts of smoke and ash are emitted, resulting in increased air pollution. However, according to recent audit results obtained in the Republic of Korea, exhaust gas from diesel vehicles has increased owing to the poor management of DPF-equipped diesel vehicles. Because the DPF is managed separately without on-board diagnostics (OBD) interlocking, it is not easy to clearly identify the DPF status (crack, melting, plug, and hollow) through regular periodic inspections such as smoke concentration inspection, OBD diagnosis, and removal visual inspection, and visual inspection is a time-consuming endeavor. In this study, the DPF sample comprised 300 units that were attached to various vehicles after being certified by the Republic of Korea's Ministry of Environment but were detached from these vehicles and stored separately owing to reasons such as damage. Various types of studies have been conducted to confirm the state of the substrate inside the DPF using X-rays. For example, research has been conducted to quantify the accumulation of soot and ash by linearly approximating the change in substrate density of a DPF on the basis of differences in X-ray transmittance [5]. In addition, scanning electron microscopy-energy-dispersive spectrometry (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) have been applied to analyze the physicochemical characteristics of crack, melt, hollow, and plug fractures. In one study, the mechanism of DPF failure was investigated and confirmed [6]. Other works include studies aimed at shaping DPF internal substrate images using computed tomography (CT) X-rays and numerical analysis algorithms [7] and CT X-rays conducted by Waseda University and the National Institute of Advanced Industrial Science and Technology in Japan. In another study, the movement and accumulation of ash were investigated using CT X-ray images. However, all the research methods described above have the drawback that the process of removing the DPF from the vehicle and conducting a precise analysis is time-consuming [8]. Therefore, these methods were judged to be unsuitable from the perspective of commercializing DPF damage diagnosis. Non-destructive imaging using computed radiography (CR) X-rays is considered an alternative to solve these problems.