|Improvement in fuel consumption in India of a hybrid vehicle over a conventional vehicle. Click to enlarge.|
In a pair of studies using real-world driving conditions, scientists at the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) found that hybrid cars are significantly more fuel-efficient in India and China than they are in the United States due to traffic and driving conditions in those countries.
They found that driving a hybrid would achieve fuel savings of about 47 to 48% over a conventional car in India and about 53 to 55% in China. In the United States, hybrids are rated to produce a fuel savings of about 40% over their conventional counterparts. Currently hybrid and electric vehicles have a tiny share of the market in India and China and are seen as a higher-end product.
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. The studies are believed to be the first of their kind.
These findings could have an important impact in countries that are on the brink of experiencing an explosion in the sales of personal vehicles; the government of India has already taken note of the findings.
Currently greenhouse gas emissions from the transportation sector in India and China are a smaller piece of the pie compared with other sectors. 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.—lead researcher Anand Gopal
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.
China study. To represent typical Chinese driving conditions, the researchers selected drive cycles from 11 Chinese cities of different size, with the drive cycles capturing on-peak and off-peak driving times, and road types including freeways, major arterials, sub-arterials, and residential roads. Comparing the characteristics of the different drive cycles against US drive cycles, they found that Chinese driving often involves lower speed driving, a moderate stop frequency and more sudden acceleration and deceleration.
They used the drive cycles as inputs for powertrain models for a conventional engine-only vehicle, a mild parallel hybrid with integrated starter/generator, a power–split hybrid, and a conventional gasoline vehicle with start–stop functionality, then compared the fuel savings potential from each vehicle architecture against the conventional vehicle in US and Chinese driving conditions.
The results show that the driving conditions in China enable hybrid vehicles to achieve significantly greater fuel savings as compared with hybrids in the US, with parallel hybrids producing 25.5% fuel savings in China versus 13.2% fuel savings in the US and power–split hybrids producing 53.6% fuel savings in China versus 32.6% fuel savings in the US.
The fuel savings benefits from parallel and power–split hybrids significantly exceed the fuel savings from conventional gasoline vehicles with start–stop functionality for both the US and China. These results suggest that the increased cost of deploying hybrids will have significantly greater impact in Chinese driving conditions, and hybrid vehicles in China should be seriously considered for incentive programs (perhaps as part of the recently announced 2012–2020 China automotive industry development plan) to accelerate their deployment, they concluded.
India study. 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. Here also they used the US drive cycle as a basis for comparison.
|Estimated fuel savings in China from three types of hybrid vehicles over conventional vehicles. Click to enlarge.|
Gopal describes the traffic in India as “pretty slow, pretty crazy, always congested.” 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.—Samveg Saxena, lead author
The engineering results were a little surprising, Saxena said, as they went into the study thinking regenerative braking would make for very unique fuel-saving opportunities.
The authors also carried out a parametric analysis of battery size on fuel savings mechanisms, and found that hybrid vehicles for Indian driving conditions should ideally have a power capacity between 15 and 20 kW, with 10 kW as a lower limit.
The government of India, which launched a national plan last year with the goal of getting 6 to 7 million hybrid and electric vehicles (EVs) on the road by 2020, is already working with the Berkeley Lab researchers to further analyze their results. India is a member country of the Electric Vehicles Initiative (EVI) of the Clean Energy Ministerial, a global forum of governments focused on accelerating the transition to clean energy technologies. Through EVI, Berkeley Lab’s research will guide India in moving forward with its EV plan.
EVs in India. A third paper by Gopal, Saxena, and Phadke also looked at electrical consumption of all-electric vehicles in India. The study lays the groundwork for their next project, which is to analyze how EVs can be integrated into the existing electrical grid and how to minimize grid emissions.
This study uses detailed vehicle powertrain models to estimate per kilometer electrical consumption for electric scooters, 3-wheelers and different types of 4-wheelers in India.
They validated the powertrain modeling methodology against experimental measurements of electrical consumption for a Nissan LEAF. They then used model to predict electrical consumption for several types of vehicles in different driving conditions.
The results show that in city driving conditions, the average electrical consumption is:
- 33 Wh/km for the scooter
- 61 Wh/km for the 3-wheeler
- 84 Wh/km for the low power 4-wheeler
- 123 Wh/km for the high power 4-wheeler
For highway driving conditions, the average electrical consumption is: 133 Wh/km for the low power 4-wheeler and 165 Wh/km for the high power 4-wheeler. The impact of variations in several parameters are modeled, including the impact of different driving conditions, different levels of loading by air conditions and other ancillary components, different total vehicle masses, and different levels of motor operating efficiency.
Samveg Saxena, Amol Phadke, Anand Gopal (2014) “Understanding the fuel savings potential from deploying hybrid cars in China,” Applied Energy, Volume 113, Pages 1127-1133 doi: 10.1016/j.apenergy.2013.08.057
Samveg Saxena, Amol Phadke, Anand Gopal, Venkat Srinivasan (2014) “Understanding Fuel Savings Mechanisms from Hybrid Vehicles to Guide Optimal Battery Sizing for India,” International Journal of Powertrains
Samveg Saxena, Anand Gopal, Amol Phadke (2014) “Electrical consumption of two-, three- and four-wheel light-duty electric vehicles in India,” Applied Energy, Volume 115, Pages 582-590, doi: 10.1016/j.apenergy.2013.10.043