Mazda e-Skyactiv D powerful diesel hybrid engine: technology, fuel economy, emissions

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Mazda says its new e-Skyactiv D engine is one of the cleanest diesels and has more than forty percent thermal efficiency.

Published on Nov 13, 2022 08:00:00 AM

Mazda’s new diesel combustion chamber design has separate fuel injection and combustion areas.

Given the controversy surrounding diesel engines over the past few years and the inevitable public conclusion that the fuel itself is the problem, rather than the way it’s used, it’s surprising that manufacturers are still developing them. They did, however, with Japanese automaker Mazda’s announcement of e-Skyactiv D, a new electrically assisted 3.3-liter straight six for its CX-60 SUV, the latest example.

Diesel engines have a natural advantage in terms of fuel consumption, because they have a high level of compression to reduce fuel, rather than using a spark, and that is similar to high thermal efficiency. On that note, Mazda has pushed the boat out with an advanced technology it calls Distribution-Controlled Partially Premixed Compression Ignition (DCPCI).

Although it gives little on how the DCPCI works, it does reveal that each combustion chamber contains egg-shaped combustion chambers to improve air flow and fuel mixing. In general, however, partially premixed compression ignition (PPCI) is not a new concept, having been the subject of research for years around the world.

PPCI is a type of low temperature combustion (LTC) somewhere between conventional diesel combustion, where fuel and air are not mixed evenly through the cylinder, and homogeneous charge compression ignition (HCCI), where they are.

The advantage of LTC is that it is good at reducing NOx and particulate emissions at the same time (something not easy to do in a combustion engine) and improving fuel economy. So it’s just a question of who to choose.

Compared to HCCI, PPCI makes it easier to control the ignition timing, mixes fuel and air better and, when used properly with exhaust gas recirculation (EGR), keeps temperatures down. That reduces NOx and efficiency, which, along with improved fuel economy, is the name of the game.

Improving fuel economy goes hand in hand with turning more heat produced from fuel combustion into mechanical work, rather than losing it to the atmosphere (thermal efficiency).

Mazda says the Skyactiv D is one of the cleanest diesels out there and is more than 40 percent more thermally efficient, so it scores points across the board.

Although we still do not know exactly how Mazda arrived at the design of the new engine, research often involves the use of optical single-cylinder research engines (such as Ricardo’s Hydra 1, which makes it possible to examine the behavior of the fuel-air mixture and combustion using special photographs and lasers).

Will engines like the new e-Skyactiv D be able to reverse the damage to the diesel name after the scandals of the past few years? It’s a steep hill to climb. But it is worth remembering that diesel engines are the main candidates for synthetic fuels and biofuels, and the PPCI design will still produce the same benefits by using them.

In the meantime, they should help ease the burden on drivers’ pockets due to current fuel prices, and tick all the boxes on reducing emissions.

Light and power

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