Analysis of greenhouse gas emissions related to aluminium transport applications

Background, aim and scope

Climate change is a subject of growing global concern. Based on International Energy Agency (IEA 2004) research, about 19% of the greenhouse gas emissions from fuel combustion are generated by the transportation sector, and its share is likely to grow. Significant increases in the vehicles fleets are expected in particular in China, India, the Middle East and Latin America. As a result, reducing vehicle fuel consumption is most essential for the future. The reduction of the vehicle weight, the introduction of improved engine technologies, lower air friction, better lubricants, etc. are established methods of improving fuel efficiency, reducing energy consumption and greenhouse gas emissions. Continued progress will be required along all these fronts with light-weighting being one of the most promising options for the global transport sector. This paper quantifies greenhouse gas savings realised from light-weighting cars with aluminium based on life cycle assessment methodology. The study uses a pragmatic approach to assess mass reduction by comparing specific examples of components meeting identical performance criteria. The four examples presented in this analysis come from practical applications of aluminium. For each case study, the vehicle manufacturer has supplied the respective masses of the aluminium and the alternative component.

Material and methods

A full life cycle assessment with regards to greenhouse gas emissions and savings has been carried out for different aluminium applications in cars as compared to the same applications in steel or cast iron. The case studies reference real cases, where aluminium is actually used in series production. The studies are based on a greenhouse gas lifecycle model, which has been developed following the ISO standard 14040 framework. For each component, sensitivity analysis is applied to determine the impact of lifetime driving distance, driving characteristics (impact of air friction) and recycling rate.

Results

Life cycle results show that in automotive applications, each kilogram of aluminium replacing mild steel, cast iron or high strength steel saves, depending on the specific case (bumper and motor block of a compact car, front hood of a large family car, body-in white of a luxury car), between 13 and 20 kg of greenhouse gas emissions.

Discussion

The performed sensitivity analysis finds that even with ‘worst case’ scenarios savings are still significant.

Conclusions

The results not only demonstrate significant benefits of aluminium with regard to greenhouse gas savings but also show that these are very sensitive to variations of the recycling rate, the life-time driving distance and the driving behaviour.

Recommendations and perspectives

Good care is needed to gather life-cycle data and to make informed estimates, where no data are available. Furthermore, greenhouse gas savings for additional components should be calculated using this life cycle model to sustain the findings.