Navigant Research Blog

Quest for Aerodynamic Vehicles Faces Headwinds

David Alexander — January 8, 2015

Although recent reductions in oil prices have slightly eased demand for more efficient vehicles, national governments are still pushing the rollout of more stringent emissions standards.  Because electric vehicles remain saddled with heavy, bulky, costly batteries,  the automotive industry is now investing in other technologies that improve the fuel economy of vehicles powered by conventional internal combustion engines that run on gasoline or diesel fuel.  Navigant Research has recently released a detailed report on this topic: Automotive Fuel Efficiency Technologies.

The report concludes that there is no single solution, and future improvements will be accomplished via many small changes that will combine to deliver measurable results.  Downsizing engines, adding turbocharging, reducing losses in transmissions, lowering mass, and improving aerodynamics will all make contributions.  The features that offer the largest benefit for the lowest cost will be implemented first.  What makes sense for a luxury vehicle may not be right for an entry-level car.  One of the primary avenues for fuel economy improvements is likely to be making cars more aerodynamically efficient.

Drag Reduction

Manufacturers must balance many factors, such as the customers who want better fuel economy but will not necessarily be willing to sacrifice performance to get it.  Less dense materials are more expensive than steel, and lighter vehicles must still meet all the relevant structural standards.  Ideal shapes for the best aerodynamic performance may be impractical to manufacture and difficult for people to get in and out of.

At an investor day hosted by Fiat Chrysler Automobiles in May 2014, the company outlined its new approach to global vehicle architectures.  In the presentation, engineers outlined their analysis of the relative importance of different factors affecting the amount of energy required to propel the vehicle.  The biggest factor in city driving was the vehicle weight, followed closely by tire drag and then aerodynamic drag.  On the highway, aerodynamics was the biggest factor, followed again by tire drag.

Lose the Mirrors

So it’s likely that aerodynamic performance will be getting plenty of attention for vehicles coming to market in the coming years.  Some features being looked at include active components, such as grill shutters that only open when cooling is needed, a feature that is already available on certain Ford Focus models in Europe.  Smoother airflow over and under the body and reducing the drag coefficient of the vehicle are options under development in both computer-aided analysis software and wind tunnels.

One of the easiest ways to reduce aerodynamic drag by 3% to 6% would be to eliminate external mirrors.  Tesla has been campaigning with the National Highway Traffic Safety Administration (NHTSA) to try to get the U.S. law changed to allow an external camera with an internal video screen as an alternative to an external mirror (as featured on its Model X design) and probably has support from many other original equipment manufacturers (OEMs).  Volkswagen is also pushing for change in Europe to expand the market for its ultra efficient XL1 vehicle that also has this feature.  If governments are serious about fuel efficiency, this would be an easy change to make by modifying the wording to require a rear view rather than specifying a mirror.

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