For some Americans, the thought of a diesel engine conjures up images of noisy, lumbering tractor-trailors belching clouds of black smoke. While that may have been an accurate depiction 20 years ago, it’s not anymore. Today’s diesels are clean, quiet, powerful and efficient. In fact, they’re cleaner and more efficient than gasoline engines, causing consumers to take notice. Last year, U.S. sales of diesel-powered passenger vehicles increased 27%. This while overall sales were up just 10%, hybrid market share declined, and electric vehicle revenue fell short of projections. To meet consumer demand for better fuel economy without sacrificing performance, manufacturers are introducing a record number of new diesel models in the U.S., including Audi A8, Cadillac ATS, Chevrolet Cruze, Jeep Cherokee and Porsche Cayenne.
So, why the change of perception when it comes to diesel? And, what makes these engines more efficient than gasoline?
To start, diesel fuel is more energy dense (by volume). More energy density equals better fuel economy (more MPG), which is why diesel is the fuel of choice for commercial vehicles that travel long distances while carrying heavy loads. When compared to a gasoline engine, a diesel engine is roughly 30% more efficient.
In addition, diesel fuel is a lot cleaner than it used to be. With the introduction of ultra-low sulfur diesel (ULSD), the sulfur content in diesel has been substantially reduced, making exhaust control devices more effective and lowering overall emissions. New technologies—such as particulate filters, selective catalytic reduction (SCR) and common-rail fuel injection—provide further emissions reduction.

Chevrolet Cruze
Available in 2013, the Chevrolet Cruze diesel is targeting 50 MPG for models released in the U.S.
Diesels are also more fun to drive. Modern turbochargers have virtually eliminated the sluggish response once associated with these powertrains. Diesels today offer an improved driving experience and better acceleration than their predecessors. This fact was highlighted in a recent report by former U.S. Secretary of Transportation, Norman Mineta. The report tracked revenue from car manufacturers that sold clean diesel and hybrid versions of the same model. While both powertrains offered similar efficiency benefits, the clean diesel version was selected in approximately 39% of cases while the hybrid option was selected in only 5%—suggesting that consumers preferred the “fun-to-drive” nature of diesels.
Mazda with SKYACTIV-D Technology
Mazda's Takeri concept car has been fitted with the company's SKYACTIV-D clean diesel engine.
Although U.S. consumer interest in diesel vehicles is relatively new, turbo diesel engines have already achieved more than 50% market share in Europe and other parts of the world. Some mistakenly attribute this to tax policies that are believed to favor diesel fuel. However, the price difference between diesel and gasoline in Europe is minimal and varies greatly by country (as it does by state in the U.S.). While there is a price difference, it’s not enough to drive diesel sales. Instead, European consumers, like the rest of us, largely base their buying decision on the need to purchase the most fuel efficient vehicle at the most affordable price. And, where fuel prices are high, so are sales of diesels.
As the U.S. finalizes CAFE regulations for 2017-2025, it’s considering offering incentives for clean diesel models—which have historically been ignored in favor of other technologies. Once a decision is reached, Achates Power and other clean diesel engine developers and manufacturers will be well positioned to meet consumer demand. Our opposed-piston, two-stroke diesel engine has already demonstrated fuel efficiency gains of more than 20% (when compared to a leading medium-duty diesel engine) and 55% (when compared to typical gasoline engines) while achieving Euro 6 and EPA 2010 compliance. With fewer parts, it’s also less costly to produce—making it an economically and environmentally sustainable transportation solution.

Clean Diesel Engine Engine Design Fuel Efficiency Standards

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