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The Shell Eco-Marathon is an annual competition sponsored by Shell, in which participants build special vehicles to achieve the highest possible fuel efficiency. The Eco-Marathon is held around the world with events in Europe, the Americas and Asia. Entrants come from several backgrounds including enthusiastic amateurs, university teams and staff of major motor manufacturers.
In 1939, a group of Shell scientists based in a research laboratory in Wood River, Illinois, USA, had a friendly bet to see who could drive their own car furthest on one gallon of fuel. The winner managed a distance of 21.12 km/L (59.7 mpg-imp; 49.7 mpg-US). A repeat of the challenge yielded dramatically improved results over the years:
- 149.95 MPG with a 1947 Studebaker in 1949
- 244.35 MPG with a 1959 Fiat 600 in 1968
- 376.59 MPG with a 1959 Opel in 1973.
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A world record was set by a French team in 2003 called Microjoule with a performance of 10,705 mpg-imp (0.02639 L/100 km; 8,914 mpg-US). The current record is 12,665 mpg-US (0.018572 L/100 km; 15,210 mpg-imp), set in 2005 by the PAC-Car II. The world record in diesel efficiency was achieved by a team from the Universitat Politècnica de Valencia (Politechnical University of Valencia, Spain) in 2010 with 1396.8 kilometres per litre. In contrast, the most efficient production diesel passenger cars achieve 60 mpg-US (4 L/100 km; 72 mpg-imp), and some high-powered sports cars achieve as little as 8 mpg-US (29 L/100 km; 10 mpg-imp).
The current European Shell Eco-marathon  record for a combustion engine entry was set in 2004 by the team from Lycée La Joliverie (France) at 3,410 km on the equivalent of a single litre of fuel. Prototype vehicles using fuel cells are capable of greater energy efficiency. In 2005, a hydrogen-powered vehicle built by Swiss team ETH Zurich achieved a projected 3,836 km on the equivalent of a single litre of fuel. This is equivalent to the distance between Paris and Moscow.
The Eco-Marathon has different classes of competition according to the energy source used: Fuel cells, solar cells, gasoline, diesel fuel and LPG. During the competition, cars must attain an average speed of at least 15 mph (23 km/h) over a distance of 10 miles (16 km). The course is typically a motor racing track or closed off city streets. The fuel is strictly measured out for each entrant at the start and end of the course. The difference is used to calculate the vehicle's average fuel consumption. Solar-powered vehicles are not eligible for the grand prize for fuel efficiency.
The top performing vehicles are purpose designed for high efficiency. Some vehicles use a coast/burn technique whereby they briefly accelerate from 10 to 20 mph (from 16 to 32 km/h) and then switch the engine off and coast until the speed drops back down to 10 mph (16 km/h). This process is repeated resulting in average speed of 15 mph for the course. Typically the vehicles have:
- Automobile drag coefficients (Cd) below 0.1
- Rolling resistance coefficients less than 0.0015
- Weight without driver under 45 kg
- Engine efficiency under 200 specific fuel consumption (cc/bhp/hr)
The vehicles are highly specialized and optimized for the event and are not intended for everyday use. The designs represent what can be achieved with current technology and offer a glimpse into the future of car design based on minimal environmental impact in a world with reduced oil reserves. The work of the participants can be used to show ways manufacturers could redesign their products.
- Simpson, Richard (2003-07-18). "Running on empty". The Daily Telegraph (London: Telegraph Media Group). Retrieved 2008-10-20.
- "Lowest Fuel Economy Models: 2010 Model Year". United States Environmental Protection Agency. October 19, 2009. Retrieved 1 March 2010.
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