Environmentally harmful species in the exhaust gas emitted from an internal combustion engine, such as hydrocarbons (HC), carbon monoxide (CO), PM, and nitric oxides (NOx) are regulated species that need to be removed from the exhaust gas. In lean combustion engines, e.g. diesel engines, determined by their lean combustion nature, PM and NOx are two major emissions. In controlling these emissions, DPF has become the most effective technology in decreasing PM emissions, including both particle mass and numbers, while a number of technologies, including LNT (Lean NOx Trap) and SCR (Selective Catalytic Reduction) have been used for reducing NOx emissions.
In a DPF system, PM information is important in controlling DPF regeneration processes and detecting anomalies in the DPF system. Normally DPF systems need to be regenerated from time to time to remove accumulated PM. In triggering a DPF regeneration process, PM deposit quantity is required to be accurately detected to avoid late regeneration which may cause damage to the DPF due to that a large amount of extra heat can be generated in self-sustained combustion of PM in the DPF. In running a DPF system, in addition to PM deposit quantity, the effectiveness of the DPF, which is indicated by a filtering efficiency, also needs to be monitored. A low filtering efficiency suggests a DPF failure, which is required to be detected to satisfy On Board Diagnostic (OBD) requirements.
The PM deposit quantity can be detected directly or calculated with a PM concentration in exhaust gas flow upstream from the DPF, while a low filtering efficiency can be detected by monitoring PM concentration downstream from the DPF. A variety of sensors, such as capacitive sensors and microwave sensors can be used in directly detecting PM deposit amount in a DPF, while resistive sensors and charge transient sensors are used in detecting PM concentration in an exhaust flow. Among these sensors, PM deposit sensors normally are not appropriate for diagnosing DPF failures, while PM concentrations sensors are sensitive to particulate size and their poor accuracy limits their applications in controlling DPF regenerations.
To increase control and diagnostic performance whilst lower system complexity, it is then a primary object of the present invention to provide a multifunctional PM sensing device that is insensitive to particulate size and other influencing factors, such as exhaust gas temperature and exhaust gas species, and can be used for both triggering DPF regeneration and detecting DPF failures.
A further object of the present invention is to provide a PM sensing device that is able to regenerate by itself, so that a PM concentration in a shorter period of time can be obtained.
Another object of the present invention is to provide a diagnostic apparatus with a PM sensing device to detect anomalies in a DPF system and a DPF device.