Are Diesels Being Unfairly Targeted?

By Edward A. Sanchez — Jan. 4, 2024

The majority of topics and discussion on The Watt Car EV blog and podcast are about battery electric and PHEV vehicles. But occasionally, topics pop up related to the broader transportation ecosystem that are comment-worthy. In Episode 152 of The Watt Car EV Podcast, Phil Royle and I discussed the U.S. Department of Justice’s fine against diesel engine manufacturer Cummins. To be fair, Cummins has diversified beyond just diesels to include a portfolio of alternative fuel propulsion technologies. A prescient pivot considering regulatory trends globally.

I’m not usually one to be an apologist for “Big Oil” or ICE powertrains, but it seems like companies that sell diesel engines and vehicles have become an especially juicy target for regulators lately. Although hard to conceive of in the post-Dieselgate world we now live, for decades, diesel engines were considered somewhat of an environmental hero, at least relative to gasoline engines, for their higher overall efficiency and lower CO2 emissions. For more than 20 years, diesel engines had more than 50% market share in many European markets. Diesel fuel was often subsidized to be cheaper than gasoline, and diesels were implicitly encouraged by a combination of marketing and tax policy.

Diesels’ halo of environmental friendliness crumbled under the harsh spotlight of the Volkswagen “Dieselgate” scandal, which went on to directly or indirectly implicate Tier 1 suppliers such as Bosch, and other OEMs such as Mercedes-Benz, Stellantis (at the time FCA) subsidiary VM Motori, and others.

The Dieselgate scandal starkly highlighted how difficult controlling NOx emissions was, and has resulted in nearly universal application of urea-based fluid selective reduction catalysts (SCR) in most markets. Yet despite this glaring Achilles’ heel, there are few technologies that can effectively compete with diesel right now for workhorse applications such as towing and long-haul freight.

That’s not to say technologies aren’t on the horizon that may ultimately displace diesel engines as the technology of choice, but nothing has yet emerged as a “no-brainer” replacement across the board. Hydrogen? Expensive, unreliable, inconsistent, and hard-to-find fueling infrastructure. Natural Gas? Somewhat greater availability, but slightly less power than diesel. Electric? Shows promise, but requires massive batteries that can affect trailer load capacity. Also, megawatt charging is still in its infancy, and until it is ubiquitous as diesel filling stations, will not totally replace diesels for heavy road freight.

As Phil and I discussed in Episode 152, a series hybrid concept such as the Ramcharger could gradually replace conventional diesels in the three-quarter to one-ton truck market, and potentially Class 8. But battery technology is not yet at a point where it can fully compete with diesel in time-of-fueling and ubiquitous availability (especially taking into account the need for pull-through charging).

I am not saying diesels are without their issues, as starkly demonstrated by Dieselgate, and the associated investigations and cases that have followed. But the more than century-old technology has persisted as long as it has by being one of the most effective, efficient combustion propulsion technologies discovered. Global regulations are acting as a slow-moving boa constrictor around diesels, with ever more stringent NOx requirements, a specific emissions component that diesels struggle with.

Over the next several decades, we’re likely to see diesel trucks forced off the road in most major developed markets, likely replaced by some combination of EVs, hydrogen, natural gas, and hybrid powertrains. But diesels will likely remain in developing markets such Africa, Latin America, and possibly India for decades to come.

Is this fair? Environmental and socioeconomic justice is a whole other discussion. But despite diesel’s dirty reputation, Rudolf’s technology should be given its due for powering and enabling global commerce and construction over the last century, for better, or for worse.

(Image courtesy Ram)