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News Release from: International Iron and Steel Institute | Subject: Aluminium vs steel - which is greener
Edited by the Manufacturingtalk Editorial
Team on 20 August 2007
Steel versus aluminium - which is
'greener'?
In response to an article on aluminium, it is erroneous to claim that aluminum-intensive vehicles produce less greenhouse gas emissions than steel-intensive vehicles, explains Ed Opbroek.
Reducing greenhouse gases emitted from the vehicles we manufacture, drive, and ultimately dispose of, is highly visible topic for the automotive industry But how do we know if we're correctly evaluating the amount of greenhouse gases (GHGs) created? The answer to that complex question may well drive the direction of future government environmental regulation and consumers' vehicle purchase choices, not to mention the welfare of our planet
This article was originally published on Manufacturingtalk on 3 May 2001 at 8.00am (UK)
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While various academic and industry studies may vary in their approach and application, they are governed by one of two schools of thought when evaluating GHGs, as follows.
* One method is to focus predominantly on quantifying the tailpipe emissions from a particular vehicle over the course of its on-road use.
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* A second, and more comprehensive technique for GHG evaluation, is focusing on the entire life cycle.
To fully assess a vehicle's carbon footprint, all phases of a vehicle's life must be considered.
This includes the GHG emissions resulting from the production of the materials used to make the vehicles, the manufacturing of the vehicles themselves, and the end-of-life phase - in addition to the use phase.
In the same way an all-electric car that doesn't emit C02 from its tailpipe can't be truly considered 'emissions free' if the electricity used to power it was created by burning coal, evaluating a vehicle's GHG impact by its use phase alone is too narrow a metric for an accurate assessment.
Using a life cycle assessment technique is critical for material selection and design decisions to achieve vehicle mass reduction because changes in the product system, such as using aluminum instead of steel structure applications, may decrease the use phase global warming potential at the expense of increasing the material production phase global warming potential.
A 2007 study and GHG calculation methodology developed by Dr Roland Geyer at the University of California, Santa Barbara (UCSB), USA, is a more comprehensive tool.
This model utilizes the mass reduction and fuel consumption change data, scientifically comparing differences in life cycle GHG emissions resulting from different material choices and vehicle design assumptions.
The UCSB model thoroughly analyses the total vehicle life cycle GHG emissions on a comparative basis - evaluating the effect of using today's advanced high strength steel (AHSS) or aluminum.
This model calculates the familiar GHG reductions that occur from fuel economy improvement, as well as the emissions from fuel production and combustion over the total distance driven during the vehicle's lifetime.
Equally as important, the UCSB model also calculates the impact of material production - a stage where steel has much lower GHG emissions than aluminum - as well as the effect of recycling prompt scrap during the vehicle manufacturing phase and end-of-life scrap at the vehicle disposal phase.
This model has been well tested and it reproduces results from other life cycle assessment studies.
One important case study involves a C-Class vehicle with a gasoline internal combustion engine (ICE).
The model compared an optimised aluminum design with the AHSS design.
Although some additional mass savings can be achieved with aluminum, the increase of CO2 equivalent emissions from the material production phase more than offsets the reductions generated in the use phase.
The vehicle's total life cycle emissions are, in fact, increased by 2% above that of the vehicle designed with AHSS.
Thus, when we truly compare 'apples to apples', an optimised aluminum design does not have an environmental advantage over the AHSS designs in the total life cycle analysis.
In conclusion, from a rigorous scientific point of view, it is erroneous to claim that aluminum-intensive vehicles produce less greenhouse gas (GHG) emissions than steel-intensive vehicles.
To add insult to injury, aluminum's increased environmental burden also comes with a significant cost increase compared with AHSS.
* About the author - Ed Opbroek is the director of 'WorldAutoSteel', the automotive group of the International Iron and Steel Institute.
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