As Diesel engines continue to find favor amongst automakers, two aspects common to all Diesel engines remain at the center of all research activity. While reduction of Diesel emissions, such as NOx, Particulate Matter (PM) and smoke continues to be the more serious challenge, the issue of acceleration performance remains to be fully resolved. If the diesel engine is to find acceptance amongst the US passenger car users, it must perform at the level of the Spark Ignition (SI) engine in terms of brisk acceleration response. It is imperative that the Diesel engine shakes off the image of “the sluggish machine”. Technically this amounts to either reducing turbo-Lag to an indiscernible level or eliminating it completely. Since turbo-Lag is linked directly to turbocharger (T/C) inertial dynamics, several techniques have been tried over the years to reduce this effect. In this paper we present a model-based evaluation of four techniques, namely:

1. Variable Geometry turbocharging (VGT).

2. Electrical Assist of turbochargers.

3. Hyperbar (HB) turbocharging.

4. External Air assist.

Variable Geometry turbocharging has already found wide application and is now considered an essential feature on all modern Diesel engines. Electrical assist of turbochargers for automotive application is still in its developmental stages but holds great promise. Hyperbar T/C and external air assist are unconventional techniques but offer possibilities of improvement for the T/C.

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