Hybrid vehicles more fuel efficient in India
What makes cities in India and China so frustrating to drive in -- heavy traffic, aggressive driving style, few freeways -- makes them ideal for saving fuel with hybrid vehicles, according to new research by scientists at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab).
In a pair of studies using real-world driving conditions, they found that hybrid cars are significantly more fuel-efficient in India and China than they are in the United States.
These findings could have an important impact in countries that are on the brink of experiencing an explosion in the sales of personal vehicles. "Currently greenhouse gas emissions from the transportation sector in India and China are a smaller piece of the pie compared with other sectors," said lead researcher Anand Gopal. "But vehicle ownership is going to skyrocket in these countries. That is why we decided to focus on this area. Hybrid and electric vehicles can significantly reduce carbon emissions and other pollutants."
What's more, hybrids in India are also more fuel-efficient than they are officially rated for. "With the official fuel economy test procedure currently used in India, fuel savings for hybrids are fairly grossly underestimated, showing only a 29 per cent savings over conventional vehicles," Gopal said. "The test cycle is not representative of driving conditions in India, so that's sending the wrong signal to the consumer."
Their results were reported in two papers, Understanding the fuel savings potential from deploying hybrid cars in China, published in Applied Energy, and Understanding fuel savings mechanisms from hybrid vehicles to guide optimal battery sizing for India accepted for publication in the International Journal of Powertrains, also co-authored by Berkeley Lab battery scientist Venkat Srinivasan.
Gopal, working with Berkeley Lab scientists Samveg Saxena and Amol Phadke, used a powertrain simulation model called Autonomie to create a hypothetical hybridized version of the top-selling conventional car in each country -- in China it was the Buick Excelle and in India the Maruti Alto. The reason for creating a hypothetical version was to isolate the improvement from hybridization and measure only that benefit.
For the India analysis the researchers simulated drive cycles in two Indian cities (New Delhi and Pune) taken from published studies and also used the Modified Indian Drive Cycle, the test for the official fuel economy rating. They found that driving a hybrid would achieve fuel savings of about 47 to 48 per cent over a conventional car in India. In the United States, hybrids are rated to produce a fuel savings of about 40 per cent over their conventional counterparts. Currently hybrid and electric vehicles have a tiny share of the market in India and are seen as a higher-end product.
Gopal describes the traffic in India as "pretty slow, pretty crazy, always congested." In technical terms, the frequent starting and stopping, considerable amount of time spent idling, and low percentage of time spent on highways provide hybrids three ways to save additional fuel.
"One is regenerative braking, another is being able to turn off the engine when the car is stopped or in low-power condition, and another is that the hybrid system -- the electric motor, the batteries -- enable the engine to operate at a higher efficiency operating condition," Saxena explained. "We weighed the importance of these three mechanisms against each other for the Indian vehicles, and found that the ability to increase engine efficiency was the most important reason, second was regenerative braking, then engine shutdown."
The engineering results were a little surprising, Saxena said. "We went into the study thinking regenerative braking would make for very unique fuel-saving opportunities," he said.
(Source: Lawrence Berkeley National Laboratory news release)