Road cars are usually evaluated in a general motorsport environment, because this composes all emission stories and the general management. Aerodynamics is one of the fields in which car constructors try to match all the constraints. In a global view of the aerodynamic application in the automotive field, the road car is not a small part of this. Even though the approach is completely different from the motorsport one, it helps to have a holistic and complete overview of the aerodynamic approach in the car development. Another point is more practical, actually being an aerodynamicist will be a huge job in the next future. In terms of environmental causes, after diesel gate (2015), the automotive industry had changed its focus. However, the diesel gate itself had more political reasons instead of more technical ones. The worst point about diesel gate was the mismatch of the legal homologation relative to what the constructor were selling. In any case, this single event was the trigger of a big reaction. Now the period has too many doubts, since the planning for a road car production is usually bigger than the motorsport ones, and the investment is much higher. Hence, the decisions which are being proposed will exhibit their impacts in the next 8 years.

The general environment is the CO₂ emission story. These black points are the legal targets that all the car constructors must obey in 2015, 2025 and 2030 (Figure 2). The blue line represents the real performance of the manufacturers at this moment (2021). It is possible to observe that at the actual period the first discrepancy appears, because this period represents this inconsistency. It seems that the compliance mechanism is the tool to be legal. This period was very difficult to keep the line under the homologation target. Very likely the car constructor will be out of this target, because there are some compliance mechanisms that help them to stay under the technical limit.

Figure 2 illustrates a regional comparison between different countries. As can be seen, there is no country in which the cars sold inside them are under the proposed target.

Figure 3 illustrates the correlations between the average CO₂ emission and the average weight. The important point of it is how CO₂ emissions are calculated. These are based on the following equation:

S_AVE = (Σ_i=1ⁿS_i)/n < Σ_i=1ⁿ[95 + a∙(M_i – M₀)]/n

It takes into account the mass of the variables. The 95 number is the legal limit of that period. M₀ is the average mass of the car under homologation, M_i is the mass of the car under inspection of that manufacturer and a is the correction factor. The logic behind the “a” meaning is that since the CO₂ emission is, in some way, linked to the mass of the car, there are some constructors that are in a better position than others. Hence, the logic of “a” is that it is considering the fact that there is a spread between the manufacturers and different constructors and their cars. However, this is something that is going to be featured over the years. Hence, “a” is progressively reduced so that this line will be flat. The constructor of heavy cars must optimize their projects in order to stay inside the legal limits. If there is not a compliance or tolerance tool, the car companies at Figure 3 would be out of the limit. More or less all legal constructors just thanks to these compliance mechanisms, basically the phase-in provision. This does not consider the full production of CO₂ emissions, but 95% of the vehicles. For instance, if there is a sporty car which is out of the legal limits, this can be considered inside of 5% CO₂ emission which is not accounted for.

Super-credit system

There are some rewards when it is demonstrated that all technologies in order to reduce internal emission are being used. This reward comes in the form of CO₂ higher rule. There is also the super-credit system, which is basically underway. For road cars that are lower than 50 g/Km emission “n” is not 1, it is lower than 1. This decreases the calculated value of the CO₂ emissions. However, this factor is for 2021 legal limits, n-value is not 1, it was 2 in 2020, 1.67 in 2021, 1.33 in 2022 and 1 in 2023. These coefficients have some influence in the positioning of the construction on the legal graph. It is possible to understand the importance of having some part of the production that legally can re-enter within this limit. An example is Porsche. For this brand, the production is high and the average emission is also high. Hence, the hybrid technology became important for Porsche to reduce CO₂ of all its production cars, except the sports cars.

However, the real scenario is the one from the last 20 years, the CO₂ emissions increased more and more, becoming far from the legal rules. The gap between the stated and measured values increased from 7% and 37%, respectively. Hence, there was a quite good correlation between the real and the homologated value. As can be seen the story is completely critical (Figure 5), because the results have evident mismatch. The clash between these situations results in decisions to go with electric and hybrid cars. This considers all the environments, not the real sustainability of these choices, because the starting point was this great mismatch.

References

• International Council on Clean Transportation (ICCT) – August, 2021;
• International Council on Clean Transportation (ICCT), January 2019;
• International Council on Clean Transportation (ICCT), November 2016.