Fuel Efficiency - Fuel Efficiency of Vehicles

Fuel Efficiency of Vehicles

See also: Fuel economy in automobiles

The fuel efficiency of vehicles can be expressed in more ways:

  • Fuel consumption is the amount of fuel used per unit distance; for example, litres per 100 kilometres (L/100 km). In this case, the lower the value, the more economic a vehicle is (the less fuel it needs to travel a certain distance); this is the measure generally used across Europe (except the UK and Denmark - see below), New Zealand, Australia and Canada. Also in Uruguay, Paraguay, Guatemala, Colombia, Japan, China, and Madagascar., as also in post-Soviet space.
  • Fuel economy is the distance travelled per unit volume of fuel used; for example, kilometres per litre (km/L) or miles per gallon (MPG), where 1 MPG (imperial) ≈ 0.354006 km/L. In this case, the higher the value, the more economic a vehicle is (the more distance it can travel with a certain volume of fuel). This measure is popular in the USA and the UK (mpg), but in Europe, India, Japan and Latin America the metric unit km/L is used instead.

Converting from mpg or to L/100 km (or vice versa) involves the use of the reciprocal function, which is not distributive. Therefore, the average of two fuel economy numbers gives different values if those units are used, because one of the functions is reciprocal, thus not linear. If two people calculate the fuel economy average of two groups of cars with different units, the group with better fuel economy may be one or the other. However, from the point of energy used as a shared method of measure, the result shall be the same in both the cases.

The formula for converting to miles per US gallon (exactly 3.785411784 L) from L/100 km is, where is value of L/100 km. For miles per Imperial gallon (exactly 4.54609 L) the formula is .

In Europe, the two standard measuring cycles for "litre/100 km" value are "urban" traffic with speeds up to 50 km/h from a cold start, and then "extra urban" travel at various speeds up to 120 km/h which follows the urban test. A combined figure is also quoted showing the total fuel consumed in divided by the total distance traveled in both tests. A reasonably modern European supermini and many mid-size cars, including station wagons, may manage motorway travel at 5 L/100 km (47 mpg US/56 mpg imp) or 6.5 L/100 km in city traffic (36 mpg US/43 mpg imp), with carbon dioxide emissions of around 140 g/km.

An average North American mid-size car travels 21 mpg (US) (11 L/100 km) city, 27 mpg (US) (9 L/100 km) highway; a full-size SUV usually travels 13 mpg (US) (18 L/100 km) city and 16 mpg (US) (15 L/100 km) highway. Pickup trucks vary considerably; whereas a 4 cylinder-engined light pickup can achieve 28 mpg (8 L/100 km), a V8 full-size pickup with extended cabin only travels 13 mpg (US) (18 L/100 km) city and 15 mpg (US) (15 L/100 km) highway.

The average fuel economy is higher in Europe due to the higher cost of fuel. In the UK, a gallon of gas without tax would cost $1.97, but with taxes cost $6.06 in 2005. The average cost in the United States was $2.61. Consumers prefer "muscle cars" but choose more fuel efficient ones when gas prices increase.

European-built cars are generally more fuel-efficient than American vehicles. While Europe has many higher efficiency diesel cars, European gasoline vehicles are on average also more efficient than gasoline-powered vehicles in the USA. Most European vehicles cited in the CSI study run on diesel engines, which tend to achieve greater fuel efficiency than gas engines. Selling those cars in the United States is difficult because of emission standards, notes Walter McManus, a fuel economy expert at the University of Michigan Transportation Research Institute. “For the most part, European diesels don’t meet U.S. emission standards,” McManus said in 2007. Another reason why many European models are not marketed in the United States is that labor unions object to having the big 3 import any new foreign built models regardless of fuel economy while laying off workers at home.

An interesting example of European cars' capabilities of fuel economy is the microcar Smart Fortwo cdi, which can achieve up to 3.4 l/100 km (69.2 mpg US) using a turbocharged three-cylinder 41 bhp (30 kW) Diesel engine. The Fortwo is produced by Daimler AG and is currently only sold by one company in the United States. Furthermore, the current (and to date already 10 year old) world record in fuel economy of production cars is held by the Volkswagen Group, with special production models (labeled "3L") of the Volkswagen Lupo and the Audi A2, consuming as little as 3 L/100 km (94 mpg; 78 mpg).

Diesel engines generally achieve greater fuel efficiency than petrol (gasoline) engines. Passenger car diesel engines have energy efficiency of up to 41% but more typically 30%, and petrol engines of up to 37.3%, but more typically 20%. That is one of the reasons why diesels have better fuel efficiency than equivalent petrol cars. A common margin is 25% more miles per gallon for an efficient turbodiesel. For example, the current model Skoda Octavia, using Volkswagen engines, has a combined European fuel efficiency of 41.3 mpg for the 105 bhp (78 kW) petrol engine and 52.3 mpg for the 105 bhp (78 kW) — and heavier — diesel engine. The higher compression ratio is helpful in raising the energy efficiency, but diesel fuel also contains approximately 10% more energy per unit volume than gasoline which contributes to the reduced fuel consumption for a given power output.

In 2002, the United States had 85,174,776 trucks, and averaged 13.5 miles per US gallon (17.4 L/100 km; 16.2 mpg). Large trucks, over 33,000 pounds (15,000 kg), averaged 5.7 miles per US gallon (41 L/100 km; 6.8 mpg).

Truck fuel economy
GVWR lbs Number Percentage Average miles per truck fuel economy Percentage of fuel use
6,000 lbs and less 51,941,389 61.00% 11,882 17.6 42.70%
6,001 – 10,000 lbs 28,041,234 32.90% 12,684 14.3 30.50%
Light truck subtotal 79,982,623 93.90% 12,163 16.2 73.20%
10,001 – 14,000 lbs 691,342 0.80% 14,094 10.5 1.10%
14,001 – 16,000 lbs 290,980 0.30% 15,441 8.5 0.50%
16,001 – 19,500 lbs 166,472 0.20% 11,645 7.9 0.30%
19,501 – 26,000 lbs 1,709,574 2.00% 12,671 7 3.20%
Medium truck subtotal 2,858,368 3.40% 13,237 8 5.20%
26,001 – 33,000 lbs 179,790 0.20% 30,708 6.4 0.90%
33,001 lbs and up 2,153,996 2.50% 45,739 5.7 20.70%
Heavy truck subtotal 2,333,786 2.70% 44,581 5.8 21.60%
Total 85,174,776 100.00% 13,088 13.5 100.00%

The average economy of automobiles in the United States in 2002 was 22.0 miles per US gallon (10.7 L/100 km; 26.4 mpg). By 2010 this had increased to 23.0 miles per US gallon (10.2 L/100 km; 27.6 mpg). Average fuel economy in the United States gradually declined until 1973, when it reached a low of 13.4 miles per US gallon (17.6 L/100 km; 16.1 mpg) and gradually has increased since, as a result of higher fuel cost. A study indicates that a 10% increase in gas prices will eventually produce a 2.04% increase in fuel economy.

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