analysis of flaws in European Union fuel econ test
#1
10-11-2007, 06:57 AM
analysis of flaws in European Union fuel econ test
http://www.telegraph.co.uk/motoring/...t/mffuel06.xml
sample quote:
"The same car can double or halve its consumption depending on how and where it is driven," says de Nayer. But the devil lies in the detail. In small cars, cold starts and high-speed driving have a catastrophic effect on fuel consumption. Automatics are more frugal on motorways than when driven gently on country lanes, yet manuals are the opposite. A hatchback is more economical than its MPV or SUV equivalent. There's plenty of lore in fuel consumption testing. Ford's Tim Howard is aware of the problems, and explains the factors behind the variable gap between EU figures and real life. Petrol engines are not efficient on light loads, suffering pumping losses, internal friction and air resistance past the throttle butterflies in the inlet ports. At high engine speeds not covered in the EU tests, many engines (especially turbocharged ones) use over-rich air/fuel mixtures to cool the pistons and valves. Engines differ in these respects, affecting their real-world consumption. Many car makers will also use a higher gear ratio to improve their test-cycle CO2 emissions. But, as Howard says, "there are plenty of studies to show that improvement doesn't always happen in real life, especially in urban driving". There is also the massive influence of temperature. Howard reckons that there is a difference of seven to 10 per cent between the CO2 emissions of a fully warmed-up car and one running at the 20C required by the EU test. What's more, some warm up faster than others. "Vehicles vary enormously on these sorts of things," he says.
sample quote:
"The same car can double or halve its consumption depending on how and where it is driven," says de Nayer. But the devil lies in the detail. In small cars, cold starts and high-speed driving have a catastrophic effect on fuel consumption. Automatics are more frugal on motorways than when driven gently on country lanes, yet manuals are the opposite. A hatchback is more economical than its MPV or SUV equivalent. There's plenty of lore in fuel consumption testing. Ford's Tim Howard is aware of the problems, and explains the factors behind the variable gap between EU figures and real life. Petrol engines are not efficient on light loads, suffering pumping losses, internal friction and air resistance past the throttle butterflies in the inlet ports. At high engine speeds not covered in the EU tests, many engines (especially turbocharged ones) use over-rich air/fuel mixtures to cool the pistons and valves. Engines differ in these respects, affecting their real-world consumption. Many car makers will also use a higher gear ratio to improve their test-cycle CO2 emissions. But, as Howard says, "there are plenty of studies to show that improvement doesn't always happen in real life, especially in urban driving". There is also the massive influence of temperature. Howard reckons that there is a difference of seven to 10 per cent between the CO2 emissions of a fully warmed-up car and one running at the 20C required by the EU test. What's more, some warm up faster than others. "Vehicles vary enormously on these sorts of things," he says.