The PM-Metalit: A PM control technology for Tier 4 Off-Highway Applications 2009-01-2838
Beginning with the interim Tier 4 legislation in the US, off-highway engines with 56 - 560 kW are required to reduce Particulate Matter (PM) emissions to less than 0.02 g/kWh. While this significant reduction in PM emissions represents a great new challenge for off-highway engines, it can be achieved with a combination of engine measures and PM aftertreatment technologies.
An engine with high engine out PM emissions would require a wall flow filter which has to be frequently actively regenerated at temperatures above 600 degree C and requires measures to address ash collection.
On the other hand, an engine with low to moderate engine out PM emissions could be fitted with a passively regenerated partial filter such as the PM-Metalit, with no need for frequent high temperature soot regeneration or ash removal maintenance [1, 2].
A PM-Metalit system is constructed solely from metal and thus is extremely robust against severe mechanical loads that are present in off-highway applications. It relies only on passive regeneration and requires significantly lower exhaust temperatures as well as a much lower degree of engine control measures. These criteria make this technology especially interesting as an aftertreatment solution for off-highway applications.
This paper investigates the applicability of a PM-Metalit for an off-highway engine. An exhaust aftertreatment system (EAS) was designed consisting of a metallic diesel oxidation catalyst (DOC) with LS design [3,4] followed by the filter substrate. This system was evaluated using a modified John Deere 4.5L Tier 3 off-highway engine at the AVL facility in Ann Arbor, MI. The system has been tested under steady-state 8-Mode conditions, as well as in the Non Road Transient Cycle (NRTC), and PM mass and number emissions were recorded.
A total PM reduction of >80% in stationary 8-Mode Tests and >65% in transient NRTC Tests was found, and filtration performance was repeatable and stable during numerous consecutive tests without active regeneration. The PM reduction efficiency of the filter system remained high under artificially loaded conditions as well as under extended low temperature operation without passive regeneration over 30 hours of engine idling.