Is This 3-Cylinder Diesel the World's Cleanest Combustion Engine?

Yesterday, Express Drives brought us a another story about the 10.6-liter, 3-cylinder diesel engine that Achates Power claims is the "World's cleanest combustion unit." The article begins by contrasting the huffing and puffing and smoke generated by an old school high-capacity diesel engine under a heavy load with the new Achates engine. This Achates diesel has all the right stuff. Less smoke, better fuel-efficiency and more power. What's not to like? On the dyno it produces 440 hp and 2372Nm of torque, with a potential for more. 

Engineering a new engine design isn't something that happens overnight. We recently mentioned a new diesel engine design that Ford is undertaking and how it would be three years before we see it in production. So it is that Achates Power initiated this project in 2018, which is just now coming to fruition.

The project has been funded by the petroleum and natural gas company Saudi Aramco. The concept for this engine drew inspiration from aviation designs, resulting in a two-stroke rather than a four-stroke diesel. The engine is currently being tested in a Peterbilt 579 as well as a Walmart delivery truck.

CALSTART, a non-profit dedicated to the adoption of clean energy, has given the 3-cylinder opposed-piston 2-stroke an outstanding emissions rating of 0.02 grams per brake horsepower-hour limit for ultra-low NOx. This statement about the engine was surprising to read. "The engine is designed to take on natural gas, gasoline, diesel as well as hydrogen fuel." There are no emissions coming out of the tailpipe, according to the company's technical officer.

Compared to a conventional engine of the same stroke running at identical rpm (thus same mean piston speed and same piston acceleration), the doubled stroke of an opposed piston engine gives a more compact combustion chamber that provides better thermodynamic efficiency and the highest power density in mass and volume.

It's not surprising to see oil companies pursuing clean energy and low carbon solutions for our future. Many clean energy advocates distrust the motives of oil companies. In reality, the internal combustion engine has a proven track record a a low cost and efficient source of power. If it can be turned into a clean source of power, there's still an abundant supply of this natural resource just below the earth's surface. 

The only natural resource more abundant is air, but hydrogen fuel cell vehicles may be expensive due to the technology. According to the company, internal combustion doesn't require the same level of purity and produces a minimal amount of NOx. There's some very real potential down this path for the future as well. 

The Walmart truck with this engine will be rolling out in July.

The source for this story can be found here at Express Drives.

Our first story about this engine can be found here.