ARI SHAPIRO, HOST:
The epic scope of the Volkswagen scandal brings this question into focus. Is there a viable future for diesel cars in the United States? NPR's Sonari Glinton took that question to some experts.
SONARI GLINTON, BYLINE: For this story about diesel cars, we have to talk as much about science as business. But don't worry. You don't have to be an engineer. We got plenty.
MARGARET WOOLDRIDGE: Hi. I'm Margaret Wooldridge, and I'm a professor at the University of Michigan in mechanical engineering.
GLINTON: To be more specific, Wooldridge studies and tests engines. So first, she's going to help us understand some of the basics about diesel engines.
WOOLDRIDGE: The primary advantage of a diesel engine versus a gasoline engine is the efficiency. So it's fundamentally higher efficiency than your gasoline engine.
GLINTON: It also has greater low-end torque, which means you have more power at low speeds, but that higher efficiency comes at a cost. The higher efficiency means higher pressure, and the higher pressure results in higher temperatures. So the hotter the burn, the more byproducts you get - things like soot or nitrogen oxide or NOx which are bad for air quality. So the fundamental challenge is...
WOOLDRIDGE: The things that we do to increase the efficiency intrinsically make more air toxic emissions.
GLINTON: Wooldridge says while some of the science to make diesel clean and perform well is difficult, it is still doable.
WOOLDRIDGE: It's a good technology. It really is a good technology from a fundamental, thermodynamic standpoint. The diesel image is what we have to overcome.
RICH JOSWICK: They're not the diesel cars that I remember from 1980 that were these sputtering, black-smoke-spilling things. They really are efficient and powerful.
GLINTON: Rich Joswick is with the PIRA Energy Group. They consult car companies, oil companies, governments - you name it - about energy, especially oil and diesel. He says the extra cost of diesel cars puts it at a disadvantage. And with low gas prices that look to be staying low for a while, that's an extra hit. He says there are just fewer and fewer compelling reasons today to buy a diesel.
JOSWICK: It doesn't look like it's saving you money. Or you want to do it for green reasons, in which case, you might want to buy an electric car instead. An electric car is cleaner than a diesel. Or you are just, you know - you like the lure of some of these powerful European cars.
GLINTON: Joswick says demand for diesel is already very, very low, and growth - if there's any - will be slow. He says he expects diesel to remain niche.
So much of the problem with Volkswagen's diesels is that they were sold as environmentally friendly. Roland Hwang is in charge of transportation at the Natural Resources Defense Council, an environmentalist group.
ROLAND HWANG: When people ask me personally, should I buy that diesel vehicle, I've told them that you should go ahead and buy that vehicle; drive that vehicle because those vehicles meet our standards. I've told that to acquaintances of mine, given that advice to acquaintances of mine in the past.
GLINTON: Hwang says it's clear VW wasn't meeting standards. The Environmental Protection Agency announced today that it will revamp the way they test for emissions and fuel economy across the board - gas and diesel, a move Hwang applauds. But...
HWANG: I think we do have to question whether diesel engines or any other internal combustion engine vehicle really can get us to where we need to be in meeting our air quality and energy goals.
GLINTON: Hwang says gasoline engines are getting more efficient, and there are plenty of other clean and efficient options.
HWANG: We don't care if - whatever that technology is - whether its diesel, whether it's running on gasoline or peanut butter - we don't care what it's running on as long as it's clean.
GLINTON: Hwang says the real challenge is not just to make sure diesel is clean but that all cars are clean and that we can rely on the manufacturers. Sonari Glinton, NPR News. Transcript provided by NPR, Copyright NPR.