Life cycle energy and environmental evaluation of downsized vs. lightweight material automotive engines

• Two alternatives were evaluated for meeting the new fuel economy regulations.
• The environmental impacts of downsized vs. lightweight engines were compared.
• Downsized engines use direct fuel injection and turbocharging.
• Lightweight engines employ materials such as magnesium.
• Analysis favors engine downsizing combined with light-weighting the entire vehicle.

New, stringent fuel economy and emissions regulations are putting increasing pressure on automobile manufacturers to come up with technologies that will help reach those targets. Reducing the weight of the car is one way of achieving better fuel economy during the use stage of the automobile's life cycle. This can be done by replacing the cast iron and steel in the engine with other lighter weight metals such as aluminum and magnesium. However, this change does not come without associated tradeoffs involving cost, performance, and environmental impact. Another way of increasing the fuel efficiency while maintaining the same power output is by going to a lower displacement (essentially a smaller) engine, employing direct fuel injection and turbocharging. This paper reports on a study comparing the life-cycle environmental impacts associated with the two alternatives, along with a cost analysis of the two competing technologies. A combined approach of downsizing the engine and light-weighting the entire vehicle, including the engine components, wherever feasible, is looked upon as the most preferred path to achieving greater improvements in overall lifetime energy consumption and further reductions in environmental impacts.