In September 2017, the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) came into effect for the EU and Japan. How does it work? The WLTP uses various tests to measure fuel consumption, vehicle CO2, and pollutant emissions. Engineers run these tests at specialized facilities where wind tunnels help determine the aerodynamic load for each vehicle, for example, and climatic chambers assist in testing emission rates.
The WLTP is a vast improvement compared to the prior NEDC (New European Driving Cycle) regime, providing a more accurate basis for calculating a vehicle’s fuel consumption and emissions. This is because the WLTP is based on real driving data, ensuring that any lab-based measurements better reflect the on-road performance of a vehicle.
Compared to the NEDC, the WLTP also takes a more comprehensive approach to emissions testing, using longer cycle times, greater cycle distances and average speeds, and tripling the number of tested driving phases. However, there are still many shortcomings that the WLTP must address to meet the needs of today’s automotive industry.
The most important contribution to emissions is the aerodynamic drag of the vehicle. Under the WLTP regulation, OEM’s must physically test every vehicle type and variant under real conditions to calculate the emissions that will be reported with the vehicle.
Let’s explain what this means in real terms. OEMs often produce multiple vehicle types, including sedans, SUVs, hatchbacks, and so on. For each vehicle type, you can also change the parts used where, for example, different side mirrors, rims, front and rear spoilers, etc. could be added to the final design. Experts estimate that the number of vehicle customizations will keep rising in the near future to help OEMs stand out in a crowded marketplace, further exacerbating this issue. When you add together every potential vehicle iteration, that’s a lot of physical emissions tests. What’s more, the WLTP also requires far more testing than the previous NEDC system did. The resulting time commitments for these tests will place considerable pressure on the limited number of available testing facilities.
From a logistical standpoint, it’s difficult to imagine how OEMs can run all the extensive physical tests required by the WLTP for every vehicle iteration. As these testing facilities reach full capacity, this has a knock-on effect, leaving manufacturers with an impossible choice – should they prioritize testing of their existing vehicles to promote customization or new vehicle designs to promote innovation?
Unless a different approach is taken, the WLTP will significantly restrict the automotive industry, creating a testing bottleneck where OEMs cannot keep pace with consumer demand and struggle to innovate. It’s time for a change.
In 2017, the WLTP CFD sub-working group was created, bringing together OEMs, CFD software vendors, like ESI, and legal authorities from the EU to discuss how to address these challenges. The group agreed that simulation is a viable alternative to physical tests to determine emissions rates, under certain circumstances. These simulations must operate within a specified error range, and with approval from the responsible authority.
With a certified CFD process, OEMs can replace expensive and time-consuming physical tests with CFD results to evaluate deltas in aerodynamic performance between a reference shape and the design iteration, and apply the same delta to the experimental measurement of the reference case.
To that note, ESI Group produced a streamlined and robust solution so that OEMs can predict aerodynamic performances with less than 24 hours of manpower with 256 CPUs. The solution is fully automated from CAD to PDF reporting, allowing aerodynamicists to invest their time in vehicle engineering and innovation. This reduces the need for wind tunnel testing mandated by the WLTP, freeing up valuable industry resources and reducing costs for manufacturing and innovation.
The CFD methodology can be certified for WLTP in two different ways. The first procedure enables certification based on a single baseline. Here, a baseline vehicle is tested and compared with the same baseline modified by change of parts (vehicle design iterations). To validate the accuracy of the applied CFD method, at least two different design iterations per part on the same common vehicle baseline must be tested. In this case, the CFD methodology can be certified for the baseline type of car, for the two-part variances tested.
The second procedure enables certification based on multiple baselines. Here, a single part is tested with a range of different vehicles. To validate the accuracy of the CFD methodology, at least eight tests must be run with the different vehicle types for the common baseline part.
Of course, this does not negate the need for physical tests altogether. It does, however, reduce many of the pain points manufacturers face under the WLTP regime and frees up a significant proportion of the industry’s overstretched testing facilities.
The WLTP CFD sub-working group submitted its proposals to the EU on October 21, 2019. If these proposals are accepted, the discussion moves to include other countries as we push to introduce WLTP certification by CFD at the United Nations. We’re facing a difficult road ahead, where the Ministry of Land, Infrastructure, Transport and Tourism in Japan has, until now, opposed these changes.
However, the automotive industry must overcome the challenges of real-world emissions testing to provide both vehicle customization and innovation. With many of the world’s biggest manufacturers implementing the WLTP, now is the time to move emissions testing into the digital domain using Cloud applications.
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