Parametric Studies of the Impact of Turbocharging on Gasoline Engine Downsizing

The internal combustion engine and associated powertrain are likely to remain the mainstay of mobility over the next twenty years and to remain a significant portion of the portfolio of technologies employed over a much longer period of time. Efficient combustion of all fuels (petroleum based or alternative) requires copious amounts of air particularly with downsized engines. Turbocharging technology thus becomes an even more critical part of reducing both global warming gas and urban pollutant emissions from IC engines.

Gasoline engine downsizing and turbocharging have been shown to improve fuel economy by ∼20% in production vehicles. In addition to data over a wide range of engines/vehicles, the results of a simple analysis done on vehicles/engines/drive cycles are presented to show the benefits of turbocharging and downsizing in a parametric variation of downsizing in combination with other technologies. The analysis shows that 40% downsizing with turbocharging to restore the baseline torque curve gives about 21% reduction in fuel consumption. Fuel cut off during idling and coasting is estimated to give an additional 9% improvement, yielding a total of 30% reduction in fuel consumption. However, conventional turbocharging has been unable to supply enough air to maintain high torque at low speeds. Advances in turbo technology such as twin scroll turbine housing together with exhaust manifold design and direct injection have gone a long way towards meeting this need. In this paper, more advanced turbo technologies such as a parallel flow double sided compressor are presented that show promise in addressing this issue as well as reducing turbo inertia and improving turbo efficiency at low speeds.