4 March 2006
At the Geneva Motor Show, Renault unveiled a diesel particulate filter design with exhaust post-injection. This new technology will be introduced in the first half of 2006 on the 85 hp and 105 hp versions of the 1.5 dCi diesel engine that powers the Clio and Modus passenger car models.
The exhaust system includes a close-coupled oxidation catalyst which controls the CO and HC emissions. A piezo-electric injector, installed between the close-coupled converter and the catalytic filter unit, injects diesel fuel into the exhaust pipe when filter regeneration is required. The injected fuel is oxidized over a second catalyst, positioned immediately upstream of the filter, generating heat and increasing the exhaust gas temperature to the level required to oxidize the accumulated soot.
The use of exhaust post-injection allows to conduct filter regeneration in all traffic situations, even when the car is at a standstill with the engine idling, points out Renault. An injector mounted directly in the exhaust pipe enables the regeneration process to operate continuously, making this system particularly suited for urban traffic applications.
Existing particulate filter systems in passenger cars have relied on engine (rather than exhaust) post-injection to enrich the exhaust gas in hydrocarbons and increase the temperature. This approach, while not requiring the additional exhaust injection hardware, has certain limitations in conducting filter regeneration at very low engine loads. Engine post-injection can also have a detrimental effect on engine durability due to the oil dilution effect on cylinder walls during late cycle fuel injection.
It is believed that North American manufacturers of 2007 heavy-duty engines—which will be equipped with particulate filters—will use a combination of in-cylinder and exhaust fuel injection to trigger filter regeneration.