Sunday, January 15, 2012

Vehicular fuel consumption: it's significantly affected by friction losses

I didn't know this, but apparently up to 1/3 of vehicular fuel consumption is wasted on friction. Yep, based on estimates of European drivers in a story over at PhysOrg:
There are 612 million cars in the world today. The average car clocks up about 13,000 km per year, and in the meantime burns 340 litres of fuel just to overcome friction, costing the driver EUR 510 per year.
What's more, here's the tally for where all the fuel is being consumed in an average internal combustion engine (ICE) setting:
  • 33%: exhaust
  • 29%: cooling
  • 38%: mechanical energy (33% friction + 5% air resistance)
Woah. To put that in terms in context:
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.
What? Out of the $4/gallon that people are spending to fill up their cars, they are squandering $3/gallon to just get their ICE car to a point where it is capable of movement? But technology is (potentially) on the way to help!
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.
Well, so... improvements in friction reduction can help reduce fuel consumption by 4% through laser texturing and an additional 4% through using ionic liquids. So technology helps with reducing fuel consumption by up to 8%!

Of course, drivers can drive slower, and thus reduce fuel consumption even further than what is proposed through friction-reduction technology alone:
A reduction of 10% in driving speed, e.g. from 110 km/h to 100 km/h, translates into a 16% saving in fuel consumption.
And that's dropping from 68mph to 62mph, which is far below most states' highway speed limits. Dropping one's speed from 80mph to 55mph (what many people drive at on MI highways vs. the speed at which cars are rated for their fuel economy) will translate into a 28% saving in fuel consumption.

The killer line (at least for the greenie in me) is actually toward the beginning of the article:
By comparison, an electric car has only half the friction loss of that of a car with a conventional internal combustion engine.
Why? Because an electric car doesn't have all those moving parts in its engine that an ICE has. Every moving part creates friction losses, which add up. In addition, the vibrations of the engine itself creates friction losses. Furthermore, every moving part in an ICE has the potential of having crud build up in it, thus diminishing its smooth running. In comparison, an electric engine has ... no moving parts.

But I don't own a car, and I don't drive very often, so what do I care? Well, friction is also an important thing to consider when riding a bike and purchasing components. I've been lucky to be able to afford good components that allow for really low friction at the pedal and the wheel, and I (usually) keep my chain well-oiled to ensure that I don't lose too much power in overcoming the friction there.

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