Influence of Catalyst and Exhaust System on Particulate Deposition and Release from an IDI Diesel Passenger Car under Real World Driving

The influence of a diesel oxidation catalyst and a practical exhaust system with two silencers on the storage and release of particulates during cold start real world driving was investigated using a Ford 1.8 litre IDI Mondeo diesel passenger car. Particulates were sampled simultaneously at three points in the exhaust using an on-board gravimetric filter paper method. The test was carried out on two different on-road driving cycles: a simulated ECE 15 cycle to represent free moving low power city driving conditions, and a traffic jam and high speed suburban driving cycle. The results showed that the particulate matter was deposited in the oxidation catalyst during cold start and deposited in the exhaust system downstream of the catalyst throughout the test period. The particulate deposition and release downstream of the catalyst were influenced by the previous operational history of the vehicle. The exhaust pipe deposition was of a similar magnitude to the tailpipe particulate emissions. The particulate release or ‘blow-out’ also played a role in the tailpipe emissions. The particulate release from the final silencer occurred out-of-phase from the oxidation catalyst release. Most of the particulate blow-outs took place under low and medium speed driving conditions. However, only a few net particulate releases from the whole exhaust system were observed in the warm up period. This was due to the reduction/deposition and release of the particulate matter in different parts of the exhaust system, which cancelled out each other. During the simulated ECE 15 cycle tests, the particulate release from the catalyst had an increase with higher speed and acceleration. The particulate release downstream of the catalyst was greater under low speed and acceleration.