Hybrid and natural gas-fuelled cars greener than those running on gasoline

Hybrid cars and those fuelled by natural gas contribute lesser to global warming than equivalent vehicles running on gasoline, thanks to their lower carbon dioxide (CO2) emissions.

Empa has investigated the CO2 emission behaviour of current hybrid cars, as part of a study undertaken on behalf of the Swiss Federal Office for the Environment (FOEN).

A comparison with gasoline and natural gas fuelled vehicles concluded that hybrid vehicles are the cleanest during inner city driving whilst natural gas fuelled cars do best on the motorway.

When driven in rural areas, both types do equally well. Under mixed conditions (that is real, everyday driving) vehicles based on both concepts offer reductions of up to 25% in CO2 emissions compared to conventional gasoline fuelled automobiles.

Hybrid drive systems and natural gas engines therefore represent an important technical measure for reducing CO2 emissions which can be put to use immediately, as do vehicles powered by renewable fuels such as biogas and ethanol derived from waste matter.

During the study, Empa engineer Robert Alvarez and colleagues compared the fuel consumption of three different hybrid cars.

The fuel usage characteristics were measured on a dynamometer, both for the standard driving cycle as well as for "real world" driving profiles, which better simulate everyday driving under inner city, rural and motorway conditions.

In addition, the researchers measured the amount of energy returned to the storage batteries during regenerative braking (known as recuperation) and the current supplied by the batteries to deliver extra torque to the engine when necessary.

The comparison with conventional gasoline engined cars showed that hybrids achieve up to twice the efficiency in city driving, which naturally has a very positive effect on their fuel consumption and CO2 emission levels.