The world’s first mass-produced ethanol car, the Fiat 147, motored onto Brazilian roads in 1979. The vehicle crowned decades of experimentation in the country with sugar-cane (and later, corn-based and second-generation sugar-cane waste) ethanol as a homegrown fuel. When Chinese automaker BYD introduced a plug-in hybrid designed for Brazil in October, equipped with a flex-fuel engine that lets drivers choose to run on any ratio of gasoline and ethanol or access plug-in electric power, the move felt like the latest chapter in a long national story.
The new engine, designed for the company’s best-selling compact SUV, the Song Pro, is the first plug-in hybrid engine dedicated to biofuel, according to Wang Chuanfu, BYD’s founder and CEO.
Margaret Wooldridge, a professor of mechanical engineering at the University of Michigan, in Ann Arbor, says the engine’s promise is not in inventing entirely new technology, but in making it accessible.
“The technology existed before,” says Wooldridge, who specializes in hybrid systems, “but fuel switching is expensive, and I’d expect the combinations in this engine to come at a fairly high price tag. BYD’s real innovation is pulling it into a price range where everyday drivers in Brazil can actually choose ratios of ethanol and gasoline, as well as electric.”
BYD’s Affordable Hybrid Innovation
BYD Song Pro vehicles with this new engine were initially priced in a promotion at around US $25,048, with a list price around $35,000. For comparison, another plug-in hybrid vehicle, Toyota’s 2026 Prius Prime, starts at $33,775. The engine is the product of an $18.5 million investment by BYD and a collaboration between Brazilian and Chinese scientists. It adds to Brazil’s history of ethanol use that began in the 1930s and progressed from ethanol-only to flex-fuel vehicles, providing consumers a tool kit to respond to changing fuel prices, ongoing drought like Brazil experienced in the 1980s, or emissions goals.
An engine switching between gasoline and ethanol needs a sensor that can reconcile two distinct fuel-air mixtures. “Integrating that control system, especially in a hybrid architecture, is not trivial,” says Wooldridge. “But BYD appears to have engineered it in a way that’s cost-effective.”
By leveraging a smaller, downsized hybrid engine, the company is likely able to design the engine to be optimal over a smaller speed map—a narrower, specific range of speeds and power output—avoiding some efficiency compromises that have long plagued flex-fuel power-train engines, says Wooldridge.
In general, standard flex-fuel vehicles (FFVs) have an internal combustion engine and can operate on gasoline and any blend of gasoline and ethanol up to 83 percent, according to the U.S. Department of Energy. FFV engines have only one fuel system, and mostly use components that are the same as those found in gasoline-only cars. To compensate for ethanol’s different chemical properties and power output compared to gasoline, special components modify the fuel pump and fuel-injection system. In addition, FFV engines have engine control modules calibrated to accommodate ethanol’s higher oxygen content.
“Flex-fuel gives consumers flexibility,” Wooldridge says. “If you’re using ethanol, you can run at a higher compression ratio, allowing molecules to be squeezed into a smaller space to allow for faster, more powerful and more efficient combustion. Increasing that ratio boosts efficiency and lowers knock—but if you’re also tying in electric drive, the system can stay optimally efficient across different modes,” she adds.
Jennifer Eaglin, a historian of Brazilian energy at Ohio State University, in Columbus, says that BYD is tapping into something deeply rooted in the culture of Brazil, the world’s seventh-most populous country (with a population of around 220 million).
“Brazil has built an ethanol-fuel system that’s durable and widespread,” Eaglin says. “It’s no surprise that a company like BYD, recognizing that infrastructure, would innovate to give consumers more options. This isn’t futuristic—it’s a continuation of a long national experiment.”
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