The Achates: A New Old Engine

You’d be forgiven for thinking that the diesel engine is dead. The relentless electric hype has become just a little hard on the eyes and the eardrums, especially now with the recent launch — I think — of the Tesla Semi. And a little earlier we heard Navistar say its new S13 is the last internal combustion engine it will ever design from the ground up.

But hey, relax. That company also said that by 2030 50% of its new vehicle sales will be zero-emission models, expanding to 100% by 2040, but it allowed that “…internal combustion engines will be required for many years until the electric vehicle can be fully adopted and when we have available cross-country infrastructure in place.”

Battery-electric, eh? That implies that hydrogen won’t have a place in heavy trucks and I’m definitely not so sure about that. And not necessarily by way of fuel cells.

Nor do I believe that new diesel designs, or revivals of old ones, are not in the cards. Case in point: the Achates engine. And there are good reasons why it stands an excellent chance of moving us forward while retaining the diesel’s advantages.

As an industry we’re going to face some serious challenges in the next couple of decades if we’re going to keep diesels in the realm of respectability. The next round of EPA regulations is demanding some mighty significant emissions improvements as of 2027. California will take those regs a step or two further, and we all know how influential that state is when it comes to what other jurisdictions do. Engine makers, albeit with some mighty flubs that put nasty financial pressures on truck owners, have always managed to meet the increasingly stringent emissions mandates. They’ll meet that 2027 standard too, I have no doubt.

Trouble is, they’ll have to do so with what I’d guess will be wildly complicated and seriously expensive engines that nobody will really want to own and operate. The pre-buy in advance of that date will be like nothing we’ve ever seen. And used-truck prices are bound to go through the roof at that point.

One of the effects of that may be that battery-electric and fuel-cell electric trucks get a hefty boost up the market ladder, which may well be inevitable.

Opposed-Piston Achates Engine

But wait, there really is another option, or at least there should be -- the 10.6-litre, 2-stroke, 3-cylinder, opposed-piston Achates engine. It already meets those tough 2027 regs while being lighter and a claimed 30% more fuel-efficient compared to an equivalent conventional diesel. Producing 1750 lb ft of torque and about 400 hp, it comes from Achates Power of San Diego, California, a company formed in 2004 to exploit a very old design that’s seen use in ships, locomotives, and military vehicles like tanks since the 1930s. I believe that some Russian tanks still use such engines, many of which are now resting peaceably in Ukraine, many others turned around to attack the invaders.

Some Russian tanks still use such engines, many of which are now resting peaceably in Ukraine.

Opposed-piston engines have two pistons per cylinder, facing each other, and a central combustion chamber. Explosive fuel burn pushes the pistons apart, and their connecting rods twist separate crankshafts at each end of the cylinder. Through pulleys and gears, the crankshafts transfer their power to a single output shaft. Ports in the cylinders allow entry of air and expulsion of exhaust gases, and pistons compress and fire every time they meet.

It's been a slow road for Achates since 2004, with various projects funded by the likes of the American military along the way and involvement with Cummins and other big players like oil company Aramco. Back in 2015 Achates was awarded $9 million by the U.S. Department of Energy to develop a new "disruptive" internal-combustion engine in partnership with Argonne National Laboratory and Delphi Automotive.

That time it was running gasoline, not diesel, and a compression-ignition design at that. It was claimed to yield fuel-efficiency gains of more than 50% compared to a downsized, turbocharged, direct-injection gasoline engine while reducing the overall cost of the powertrain system.

And by the way, it can run on hydrogen too. In fact, Achates says that hydrogen opposed-piston engines have an inherent efficiency advantage over conventional internal-combustion engines with an efficiency approaching or exceeding that of fuel cells. They’re also “much less complex and have a cost advantage over fuel cells.

"The OP Hydrogen engine should be developed and evaluated as a zero-emission long-haul solution,” Achates says.

For now diesel will have to do, and one such Achates engine is in revenue service with Walmart in a project funded by the California Air Resources Board and several partners. Peterbilt adapted the engine for use in a 579 tractor. It meets CARB’s 2027 regulation, which requires a 90% reduction in emissions of nitrogen oxide compared to current standards, and has been demonstrated to reduce carbon dioxide by 10%. Not only that, but it’s engineered to achieve superior fuel efficiency because of its lower heat losses, improved combustion, and reduced pumping losses, according to the company.

“It is particularly noteworthy that we were able to achieve the extremely stringent state NOx limits without any additional emissions control devices, reducing cost, complexity, and compliance risk of ultralow NOx powertrain solutions,” said Dave Crompton, president and CEO of Achates Power.

It took a while, but now the case for this engine is stronger than ever. Has its time come?