Powertrain & Energy - January 25, 2012 - 5

Layouts and pressure measurement locations of the analyzed pre(top) and post-turbine exhaust aftertreatment systems. The models were based on a largebore, 30-35-L, V8 diesel engine with one turbocharger per cylinder bank and have been correlated to test data. Aftertreatment systems were then added to the correlated model in the locations identified. ficient oxidation of exhaust pollutants. The higher temperature regime is particularly beneficial during cold starting and at lower engine loads, where exhaust gas enthalpy is lower due to leaner air/fuel ratio operation. Extensive use of exhaust gas recirculation in modern engines further increases the overall gas-to-fuel ratio during part load operation, making catalyst functionality even more challenging than before. Another benefit of PTC usage is a significant reduction in catalyst volume over the post-turbine configuration. This is due to higher gas density prior to expansion through the turbine, allowing the same substrate space velocity to be attained with a
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smaller cross-sectional area. The packaging benefits alone can be quite attractive, particularly if space is a commodity in the application of concern. Despite the clear benefits associated with PTC use, the concept is not without its challenges. The pre-turbine location is a much harsher thermodynamic environment, compared to the post-turbine location. A PTC needs to be robust and durable against higher temperature and pressure gradients, as well as pulsation effects associated with engine firing order. Secondly, it should be noted that any substantial application of aftertreatment in the pre-turbine positions (i.e., anything beyond a very modest pre-catJanuary 25, 2012

Powertrain & Energy - January 25, 2012

Table of Contents for the Digital Edition of Powertrain & Energy - January 25, 2012