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Downsizing and downspeeding have become accepted strategies to reduce fuel consumption and criteria pollutants for automotive engines. Engine boosting is required to increase specific power density in order to retain acceptable vehicle performance. Single-stage boosting has been sufficient for previous requirements, but as customers and governments mandate lower fuel consumption and reduced emissions, two-stage boosting will be required for downsized and downsped engines in order to maintain performance feel for common class B, C, and D vehicles. A 1.6L-I4 diesel engine model was created, and three different two-stage boosting systems were explored through engine and vehicle level simulation to reflect the industry's current view of the limit of downsizing without degrading combustion efficiency with cylinder volumes below 400 cm₃. Some current engines are already at this size, so downspeeding will become much more important for reducing fuel consumption in the future.

Diesel exhaust aftertreatment systems are required for meeting both EPA 2010 and final Tier 4 emission regulations while meeting the stringent packaging constraints of the vehicle. The aftertreatment system for this study consists of a fuel dosing system, mixing elements, fuel reformer, lean NOx trap (LNT), diesel particulate filter (DPF), and a selective catalytic reduction (SCR) catalyst. The fuel reformer is used to generate hydrogen (H₂) and carbon monoxide (CO) from injected diesel fuel. These reductants are used to regenerate and desulfate the LNT catalyst. NOx emissions are reduced using the combination of the LNT and SCR catalysts. During LNT regeneration, ammonia (NH₃) is intentionally released from the LNT and stored on the downstream SCR catalyst to further reduce NOx that passed through the LNT catalyst. This paper addresses system packaging and exhaust flow optimization for heavy-duty line-haul and severe service applications.