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Tier 4 emissions legislation is emerging as a clear precursor for widespread adoption of exhaust aftertreatment in offhighway 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. Upstream placement of the catalyst packages also offers potential for reducing the overall fuel consumption penalty (associated with the use of aftertreatment) in comparison to the conventional post-turbine placement. This softening of the fuel consumption penalty can be attributed to better light-off and performance of catalyst substrates, as well as a reduction in the impact of aftertreatment pressure drop on engine pumping work. The investigation involved numerical simulation of pre-turbo application of a diesel oxidation catalyst (DOC), partial-flow diesel particulate filter (DPF), and selective catalytic reduction (SCR) catalyst on a 30-35L class diesel engine. The effect of this placement over traditional downstream placement in terms of fuel consumption, package size, weight and cost was examined. The investigation revealed that the inherently higher gas density in the pre-turbine location allows a dramatic reduction in catalyst volume of up to 70%. The fuel consumption penalty associated with the addition of aftertreatment can also be reduced by approximately 1% with upstream placement of the catalyst packages.

In a gasoline engine, the cycle-by-cycle fresh trapped charge, and corresponding unswept residual gas fraction (RGF) are critical parameters of interest for maintaining the desired air-fuel ratio (AFR). Accurate fueling is a key precursor to improved engine fuel economy, and reduced engine out emissions. Asymmetric flow paths to cylinders in certain engines can cause differences in the gas exchange process, which in turn cause imbalances in trapped fresh charge and RGF. Variable cam timing (VCT) can make the gas exchange process even more complex. Due to the reasons stated above, simplified models can result in significant estimation errors for fresh trapped charge and RGF if they are not gas dynamics-based or detailed enough to handle features such as variable valve timing, duration, or lift. In this paper, a new air flow and RGF measurement tool is introduced. The tool is a combination of 1-D gas dynamics modeling and imposed, measured dynamic pressure signals in the intake and exhaust manifolds. With this method, the components to be modeled in the gas exchange system are reduced to a minimum, making it possible to model the gas exchange process with adequate detail and still maintain reasonable tool execution time. In this approach, the accuracy of the air flow and RGF estimation are not influenced by the location of pressure transducers and it is possible to "track" EGR flow from the exhaust to the intake system. The tool is demonstrated on a 4-cylinder gasoline engine powered vehicle with dual intake and exhaust cam phasing. Predictions from the tool are compared to AFR and other real-time signals measured during a variety of different real-world transient drive cycles. The instantaneous fresh trapped charge, RGF across all cylinders, as well as the influence of VCT actuation is discussed.

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