Describe the specific process by which diesel particulate filters (DPFs) remove particulate matter from exhaust gas and explain what happens when this process fails.

Diesel Particulate Filters (DPFs) remove particulate matter, also known as soot, from diesel engine exhaust gas through a process called filtration. The DPF is a device containing a ceramic monolith with many small channels. These channels are alternately plugged at each end, forcing the exhaust gas to flow through the porous walls of the filter. As the exhaust gas passes through the filter walls, the particulate matter is physically trapped within the pores of the ceramic material. This is similar to how an air filter removes dust from the air. Over time, the accumulated particulate matter increases the backpressure in the exhaust system. To prevent the DPF from becoming completely blocked, a process called regeneration is used to burn off the accumulated soot. During regeneration, the exhaust temperature is raised to approximately 600 degrees Celsius (1112 degrees Fahrenheit). This high temperature causes the particulate matter to oxidize (burn) into ash and carbon dioxide, which are then expelled from the exhaust. There are several methods to increase exhaust temperature for regeneration, including post-injection of fuel, using a diesel oxidation catalyst (DOC) to create heat, or using an electric heater. If the DPF fails, several problems arise. First, the DPF can become completely blocked with soot, causing excessive backpressure in the exhaust system. This reduces engine performance, increases fuel consumption, and can damage the engine. Second, if regeneration fails, the accumulated soot can ignite uncontrollably, causing a thermal runaway event that can damage or destroy the DPF. Third, a failed DPF will release excessive amounts of particulate matter into the atmosphere, violating emissions regulations. For example, if a faulty sensor prevents the exhaust temperature from reaching the required level for regeneration, the DPF will become clogged with soot, leading to reduced engine power and increased smoke. Therefore, proper functioning of the DPF and its regeneration system is crucial for maintaining engine performance, fuel efficiency, and emissions compliance.