Test The Limits

Fuel Economy : Keep it Real

By Exa

March 28 2016

The disparity between published test figures and real-world fuel economy has long been a topic of discussion, and in Europe, the average gap between the two has reportedly risen to 40%. The current figure in the USA isn’t as high, but is rising, and the push for compliance testing to better reflect real-world operation was recently given further impetus by Volkswagen’s admission of a ‘cheat device’ to ensure some diesel models met NOx limits during laboratory testing.


The future of fuel economy performance and vehicle emissions testing dominated the agenda at the recent Fuel Economy Detroit conference, where OEMs, supplier companies, regulators and other interested parties met to debate the regulations, technologies and other factors that will shape the next decade of vehicle development. In particular, the challenge of meeting tougher regulations such as the US CAFE 2025 targets – which represent a 54% improvement on 2014 levels – was addressed.


It’s not just powertrain engineers that are working on the problem, however. The conference also heard from lightweight materials specialists such as Ford’s Matt Zaluzec, as well as our very own Ales Alajbegovic, VP for ground transportation at Exa.


“We need to stop designing cars to pass laboratory tests and make sure they perform as well as possible on the road,” Alajbegovic commented during his presentation at the conference. “The diesel emissions scandal was an extreme example, but there are plenty of other changes automakers make for the benefit of the lab rather than the road, and in the end it’s the customer that loses out.


“You can’t really blame the carmakers for the situation they’re in,” he expanded. “Selling cars is a competition and there are financial incentives to get the best numbers possible within the system, so they fully take advantage of the  rules as they exist. Aerodynamics is a good example – if you’re lab testing, you’re assuming no crosswinds and no turbulence from other vehicles. As a consequence, aero devices developed in a wind tunnel – like the blade air-dams you see on the front chin of US trucks and SUVs – are really most effective in idealized conditions. In the real world they could potentially make the car less fuel-efficient.”


At the Exa booth outside the conference room, delegates and media representatives were able to meet with Alajbegovic and technical director, Kevin Golsch, a former GM aerodynamicist who was able to provide real-world examples of how Exa’s PowerFLOW software had been used to improve the C7 Corvette. The ’Vette was also the subject of one of the 3D software demonstrations being shown on Exa’s big screen, which sparked some interesting discussions throughout the day.


Exa believes that CFD will be essential to achieving the further reductions in aerodynamic drag required to meet future fuel economy targets. Aside from its ability to model turbulent air and varying environmental conditions such as wind strength and direction, it’s able to balance the often-conflicting demands of aerodynamic performance, thermal management and styling in a way that wind tunnels are not. But until regulators agree to incorporate simulation data into compliance testing – as happens in the heavy truck market with the EPA’s Greenhouse Gas Emissions Model (GEM) – the OEMs’ focus is likely to remain on wind-tunnel numbers.


Back in the conference, the attention turned to some of the powertrain technologies that will bring emissions figures down. According to Honeywell, the current trend for downsized turbocharged engines is set to continue, with the market share of turbos in North America expected to rise from 23% in 2015 to 39% by 2020. They will be joined by new emissions-reducing innovations, too, such as the Rankine heat-to-power converter from Faurecia, which is due to be launched in 2018.


“It’s always interesting to see what other companies are doing and hear expert opinions,” concluded Alajbegovic. “The questions after my presentation were thought-provoking and the feedback from our conversations at the booth has been very helpful. For sure, we’re not the only ones in favor of using CFD technology to improve real-world fuel economy.”