Automotive Life Cycle
Like many other products, the automotive life cycle consists of three main phases. In the following the automotive life cycle is described based on the greenhouse gas emission profile of a Golf VII, 1.6 TDI for an assumed running distance of 20,0000 km. Three phases are differentiated: production phase (20 % of GHG emissions), use phase (79 % of GHG emissions), and end-of-life phase (1 % of GHG emission). The production phase covers the raw material extraction to semi-finished products or components and finally the car's production and assembly. Within the production phase roughly 21 % of a car's production CO2-eq. emissions are emitted at Volkswagen plants. The other 79 % are emitted over the entire supply chain back to the extraction of raw materials like iron ore for steel production or bauxite for aluminum production (Fig. 23.2).
The use phase covers the tailpipe emissions (tank-to-wheel) as well as the emissions for fuel extractions and production (well-to-tank). At the end-of-life phase, the vehicle is partly dismantled and then shredded for the reuse of the materials, which accounts for around 1 % of the total greenhouse gas-emissions.
In accordance with the drivers for environmentally compatible product design, the main effort is put into the reduction of emissions during the use.
This is achieved by developments like the electrification of the car, more efficient combustion engines and complex emission control systems. Furthermore, the lowering of running resistances, like mass and aerodynamic drag, are addressed.
But these measures can also increase the emissions in production. This can result in a shift of the hot spots within a car's lifecycle. The usage of energy-intensive technologies, like lithium ion accumulators or lightweight materials, can lead to a higher burden in the production and recovery phase, combined with a lower burden in the use phase.
Therefore the task for life cycle engineering is to assure that, in total, environmental impacts of cars over their entire life cycle is lower than that of their predecessor.
Fig. 23.2 Life cycle perspective: A car's CO2 equivalents
Lightweight design is one relevant measure for lowering the car's fuel consumption and driving emissions, as the car's mass has the biggest single influence on the running resistances. However, from an environmental life cycle perspective, it is crucial to choose the “right” lightweight concepts and materials in order to avoid the shift of environmental burdens (Warsen and Krinke 2012).
From the environmental point of view, a ground-breaking success factor for lightweight design depends on the realization of secondary weight effects. Reversing the spiral of increasing weight can and should lead to an adaption of powertrain size. For example, the reduction of 100 kg in a car powered by a turbocharged petrol engine results in a reduction of tailpipe-emissions by 3.6 g CO2/km, which is equivalent to a fuel reduction value (FRV) of 0.15 l/100 km. With an adapted powertrain (adapted engine displacement and gear ratio), the improvement more than doubles to 8.2 g CO2/km (Rohde-Brandenburger 2014). At this point it is important to bear in mind that the choice of a powertrain is made on a vehicle perspective and depends on the available powertrain portfolio (Krinke et al. 2010, p. 38).
Example: Hot Stamped Steel
Usually the most common way to assess the environmental impact of lightweight design is the comparison of two materials in the context of a real application. On the one hand the specific constraints and assumptions are set, but on the other hand the assessment is not valid outside these constraints and assumptions.
Fig. 23.3 Carbon footprint comparison: cold stamped steel vs. hot stamped steel
One good example is the analysis of hot stamped steels in comparison to conventional steel. Hot stamped steels are low-alloy steels with a special aluminumsilicon coating that is heated to 900 °C before the forming process. While the steel is formed, it is hardened by cooling it down abruptly. Therefore the forming process is clearly more energy-intensive than the conventional cold stamping process. The advantage of hot stamping is the much higher strength of the steel part. This property enables thinner and lighter steels that still have the same or even better crash performance than conventional steels. All in all, for an exemplary part, this results in a weight reduction of 20 % and a corresponding lower demand for raw materials. After considering the entire life cycle and the realized weight reduction, the hot stamped steel is advantageous in comparison to the conventional steels as shown in Fig. 23.3. Due to lower material demand and the resulting reduction for raw material extraction and steel production, in this case the lightweight alternative is at an advance even before the first meters are driven with the car. With each driven meter the lightweight effect can unfold on top.
Therefore hot stamped steel is a good example for lightweight strategy which offers environmental advantage from the first mile on.