Coefficients of friction in the tribocontacts were estimated based on available information in the literature on the average passenger car in use today, a car with today’s advanced commercial tribological technology, a car with today’s best advanced technology based upon recent research and development, and a car with the best technology forecasted in the next 10 years.

Among the study’s conclusions are:

• Annual friction loss in an average car worldwide amounts to 11,860 MJ: of this, 35% is spent in overcoming rolling resistance in the wheels, 35% in the engine itself, 15% in the gearbox and 15% in braking. With current technology, only 21.5% of the energy output of the fuel is used to actually move the car; the rest is wasted.

• Of the energy output of fuel in a car engine, 33% is spent in exhaust, 29% in cooling and 38% in mechanical energy, of which friction losses account for 33% and air resistance for 5%. By comparison, an electric car has only half the friction loss of that of a car with a conventional internal combustion engine.

• Worldwide, 208,000 million liters of fuel (gasoline and diesel) was used in 2009 to overcome friction in passenger cars. This equals 360 million tonne oil equivalent per year (Mtoe/a) or 7.3 million TJ/a. Reductions in frictional losses will lead to a threefold improvement in fuel economy as it will reduce both the exhaust and cooling losses also at the same ratio.

• Globally, one passenger car uses on average of 340 liters of fuel per year to overcome friction, which would cost €510 (US$654) according to the average European gas price in 2011 and corresponds to an average driving distance of 13,000 km/a (8,078 miles).

• By taking advantage of new technology for friction reduction in passenger cars, friction losses could be reduced by 18% in the short term (5–10 years) and by 61% in the long term (15–25 years). This would equal worldwide economic savings of €174,000 million and €576,000 million (US$223,277 million and US$739,125 million), respectively; fuel savings of 117,000 million and 385,000 million liters, respectively; and CO₂ emission reduction of 290 million and 960 million tonnes, respectively.

The VTT and ANL study shows that friction in cars can be reduced with new technologies such as new surface coatings, surface textures, lubricant additives, low-viscosity lubricants, ionic liquids and low-friction tires inflated to pressures higher than normal.

Friction can be reduced by 10% to 50% using new surface technologies such as diamond-like carbon materials and nanocomposites. Laser texturing can be employed to etch a microtopography on the surface of the material to guide the lubricant flow and internal pressures so as to reduce friction by 25% to 50% and fuel consumption by 4%. Ionic liquids are made up of electrically charged molecules that repel one another, enabling a further 25% to 50% reduction in friction.

A driver can significantly influence the fuel consumption of his or her car. A reduction of 10% in driving speed, e.g. from 110 km/h to 100 km/h (68 mph to 62 mph), translates into a 16% saving in fuel consumption. Slower speeds also allow for higher tire pressures; an increase from 2 bar to 2.5 bar (29 psi to 36 psi) can translate into a 3% saving in fuel consumption.

The study was conducted at the Metal Products and Mechanical Engineering strategic competence cluster in the DEMAPP programme, co-ordinated by FIMECC Oy, where practical solutions for minimizing friction loss are also being developed. The study was funded by the Finnish Funding Agency for Technology and Innovation (Tekes), VTT and FIMECC Oy, and the Argonne National Laboratory, Department of Energy.

Resources

• Kenneth Holmberg, Peter Andersson, Ali Erdemir (2011) Global energy consumption due to friction in passenger cars, Tribology International, doi: 10.1016/j.triboint.2011.11.022