*3.4. Comparison with Results of Previous Studies*

In this section, simple comparisons with previous studies are proposed in order to evaluate the obtained energy consumption values. Our results were compared with the values calculated in previous life-cycle approaches that were conducted by Nemry et al. [3] and Schweimer et al. [33]. The first study is a report for the European Union, which analyzed the potential ways of reducing the life-cycle impact of the transportation sector in Europe. Here, the results of the material and part production processes were included, but the analysis was based on external data. The second study analyzed 1999-year Golf A4 vehicles, centering the analysis on the assembly phase. Here, inventory data of Volkswagen plants were analyzed in detail, including material and energy inputs. However, it did not expand, to the same degree, on the materials and part production processes.

A rough simulation of energy consumption in the use and ELV phase of the studied vehicle was proposed. The energy that is consumed in the use phase can be calculated when considering the fuel economy of the vehicle, as shown in Equation (8).

$$E\_{\rm II} = FE \ast d \ast \delta\_{\rm \rm gas} \ast HHV\_{\rm gas} \tag{8}$$

where *EU* is energy consumed in the use phase, *FE* is fuel economy, e.g., of Honda Accord 2011, 9.046 l/100 km [34], *d* is the total traveled distance, 100,000 km, *HHVgas* is the higher heating value of gasoline, 46.4 MJ/kg [35], and δ*gas* is the density of gasoline, 0.75 kg/l [35].

The energy that is consumed in the disposal process of the ELV is calculated while using Equation (9).

$$E\_{\rm ELV} = ED \ast G\_{\rm vch} \tag{9}$$

where *EELV* is energy consumed in the ELV disposal process and *ED* is disposal energy, 0.602 MJ/kg [36].

The first column of Table 2 shows the life-cycle values that were proposed in this study. The second and third columns compare the obtained results with previous approaches, demonstrating the compatibility between them. It is also worth mentioning that the energy consumption per mass of vehicle in the production phase is slightly lower when compared to previous studies. This can be explained by the fact that the decrease in energy consumption due to the use of recycled materials is included, and that the effects of miscellaneous materials and fluids are not included in our approach.

**Table 2.** Comparison of vehicle life cycle energy consumption.


## *3.5. Application of the Results*

This study presents a whole picture of the energy and material consumption of the automotive industry, allowing for automakers, part makers as well as researchers, and government bodies to comprehensively understand the production phase of the vehicle. Here, productive processes that have the highest effect in the industry can be identified. Efforts could focus on improving the efficiency of those energy-intensive facilities and processes to elevate the energy efficiency of the industry.

Energy-consumption results tha are obtained from this approach are divided into productive processes, but also per energy resources required for each of them. In this sense, future studies could focus on proposing optimal energy supply systems for the industry. The potential for changing the electricity consumed from the grid to renewable energy could be exploited to improve the environmental aspects of the sector.

This approach also allows researchers and the automotive industry to easily calculate the total energy impact of vehicle production, contributing to upcoming vehicle life-cycle studies and material and energy analysis of the automotive industry. When compared to constant embodied energy values proposed by previous studies, the values presented in this approach not only focus on the automotive industry but also clarify the material flow and processes that are considered in it. This allows for an easy recalculation and adjustment of the values, depending on the changes or differences in production technologies. Moreover, understanding the material flow of the industry enables new approaches for the industry, such as the environmental evaluation of closed-loop recycling, which can identify the process where recyclable material comes back for reprocessing.

Finally, evaluating the automotive industry through a material flow approach also allows one to assess the environmental impact of material required in mining and resource-extraction processes (i.e., the devastation of mining sites, disruption of natural habitats, groundwater contamination, and landscape changes at the extraction site [37]). Moreover, the proposed approach can be applied in risk-evaluation analysis of materials that are supplied to the automotive industry.
