Navigant Research Blog

New Technologies Boost Fuel Economy

David Alexander — March 26, 2013

While battery electric and hybrid vehicles are slowly gaining in popularity, they show no signs of becoming a significant portion of vehicle sales in the next several years.  Automakers, meanwhile, are busy exploring other aspects of vehicle design that will improve fuel efficiency.  Below is an update on some of these approaches:

Better Aerodynamics.  At speeds of 30 mph or less, aerodynamic performance has a minor impact on fuel efficiency.  Once freeway speeds are achieved, though, the energy needed to push the vehicle through the air dominates other factors.  Because drag is proportional to the vehicle cross-sectional area, the coefficient of drag (Cd), and the velocity squared, less energy is needed to maintain speed of smaller and smoother cars.  Significant improvements were measured on VW’s new XL1 hybrid when the conventional door mirrors were replaced with tiny cameras that projected the rear side view on to a small screen on the door where the mirror would normally be.

Reduced Mass. The energy required to overcome inertia and accelerate a vehicle is a function of its mass, so heavier vehicles need more energy to get them moving.  They also have to dissipate more energy to slow down and stop, which means bigger and more powerful brakes.  Electric vehicles with large and heavy battery packs suffer particularly in this department.  Automakers seeking to produce lighter vehicles face two big problems: alternative, lighter materials such as aluminum and carbon fiber are more expensive and often harder to work with, and lighter vehicles have to be stronger to keep the occupants safe from impact with heavier vehicles.

ICE Technology. The internal combustion engine continues to get incrementally more efficient.  Turbocharging and supercharging are now used for economy as well as performance, and features such as direct injection and higher compression have migrated from diesel engines to gasoline.  Downsizing the engine’s volumetric capacity without sacrificing performance is now a realistic option, and cylinder deactivation allows fuel saving when cruising while maintaining full power for acceleration when needed.

Stop-Start. Sometimes labeled “micro-hybrid,” the ability to eliminate idling while the vehicle is stationary has the potential to save a lot of money for drivers in heavy traffic.  Stop-start technology requires other vehicle systems to be electrified, which in itself can improve fuel efficiency.  New stop-start systems in development will add an electric “crawl” mode to extend the fuel savings in slow-moving traffic jams.

All these technologies are being introduced as new models come to market, but the challenge for automakers is to incorporate features that offer customer benefits without the steep price premiums that hamper EV sales.

Some of these innovations face regulatory hurdles.  To launch its XL1 hybrid in Germany and Austria, Volkswagen had to get special government dispensation because it lacks conventional external mirrors. The XL1 is illegal to drive in other European countries and in North America.  For some new technologies to take hold, lawmakers must revisit certain existing restrictions on vehicle design.

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