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Tier 4 emissions legislation is emerging as a clear pre-cursor for widespread adoption of exhaust aftertreatment in off-highway applications. Large bore engine manufacturers are faced with the significant challenge of packaging a multitude of catalyst technologies in essentially the same design envelope as their pre-Tier 4 manifestations, while contending with the fuel consumption consequences of the increased back pressure, as well as the incremental cost and weight associated with the aftertreatment equipment. This paper discusses the use of robust metallic catalysts upstream of the exhaust gas turbine, as an effective means to reduce catalyst volume and hence the weight and cost of the entire aftertreatment package. The primarily steady-state operation of many large bore engine applications reduces the complication of overcoming pre-turbine catalyst thermal inertia under transient operation.

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.

Modern powertrain systems, both diesel and gasoline, have achieved an extremely high level of complexity in order to comply with customer demands on performance, fuel efficiency, comfort, as well as regulatory requirements. This leads to relatively high costs of the complete engine and exhaust gas after-treatment system of a vehicle. Therefore, every component needs to be optimized. Metallic substrate catalyst components have been developed and manufactured with optimized fluid dynamic and turbulent flow characteristics leading to smaller components, offering equal or better performance compared to conventional straight channel substrates. The smaller, advanced metal substrate components are easier to package, can be installed closer to the engine, weigh less, and can reduce the necessary precious metal content. This helps in conserving natural resources, and enables original equipment manufacturer to meet their technical targets at lower costs.