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Mazda’s Diesel Evolution: Pioneering the e-Skyactiv D Diesel-Hybrid

Mazda Builds The Most Efficient Light-Duty Diesel To Date

Electrification, in one form or another (and for better or worse), is on its way to the automotive world. But instead of ditching internal combustion altogether and diving head first into battery electric vehicle (BEV) technology Mazda is taking a more pragmatic approach. Its new e-Skyactiv D 3.3L inline-six diesel engine will be paired with a 48-volt hybrid system to optimize fuel economy and performance while also lowering tailpipe emissions. We’ve long stated that diesel hybrids are the most logical step toward future low-emission vehicle goals. With proven hybrid technology here already, Mazda’s e-Skyactiv D engine is poised to show the rest of the world just how viable a diesel hybrid will be.

Available in the all-new Mazda CX-60 crossover, unfortunately the e-Skyactiv D option will only be available in European, Australian and Japanese markets, at least for now. But that doesn’t necessarily mean it can never be brought stateside. With fuel efficiency estimates exceeding 44 mpg—in a 4,200-pound CUV, no less—you’re looking at a range of 700 miles per fill up. That’s nearly three times the range of the average EV. Through the use of high-pressure common-rail injection, distribution controlled partially premixed compression ignition (DCPCI), a mild hybrid boost system and modern emissions equipment, Mazda’s e-Skyactiv D promises to deliver one of the cleanest and most efficient diesel packages ever produced.

Despite the positions many OEM’s around the world have apparently taken, Mazda refuses to abandon internal combustion. The Japanese automaker has long been a proponent of diesel propulsion—once upon a time trying, in vain, to bring a compound turbocharged 2.0L Skyactiv D four cylinder to the American car market prior to 2019 (though it did succeed in bringing a 2.2L version that was used in the CX-5). Mazda’s e-Skyactiv D 3.3L six cylinder is of an inline design, sports high-pressure common-rail injection, and makes use of an advanced combustion technology coined Distribution Controlled Partially Premixed Compression Ignition (DCPCI), which the company says provides for a thermal efficiency higher than 40 percent. More on DCPCI in a bit.
The e-Skyactiv D is part of Mazda’s catalog of “Multi-Solution Scalable Architectures,” which consists of mild hybrid models, plug-in hybrid models and EV models. It’s all part of the manufacturer’s strategy to offer a powertrain that meets differing emissions standards from country to country and locality to locality. Mazda’s official target for the e-Skyactiv D 3.3L was “both high output and high environmental performance.” The 200 cubic inch, dual overhead cam, four valve per cylinder, revvy inline-six does deliver on the output front, producing 251 hp in all-wheel drive (AWD) CX-60’s, along with 406 lb-ft of torque.
Variable geometry turbocharging, high-pressure common-rail injection and a compact exhaust aftertreatment system are all along for the ride with the e-Skyactiv D, but so is water-to-air intercooling. The water-to-air unit (upper right) is tied in with the engine coolant circuit and is highly effective at lowering intake air temperature and EGT. Also notice the composite intake manifold, as well as where EGR makes its way back into the intake stream.
In terms of exhaust aftertreatment, it looks as if Mazda has taken an approach similar to what GM did with its 3.0L Duramax. On the exhaust side of the e-Skyactiv D engine you can see that there is no downpipe to speak of. Rather, the VGT turbo feeds exhaust gases straight into what appears to be a combination of DPF and SCR components. This design makes passive regeneration cycles virtually unnoticeable to the driver. This type of compact packaging is made possible thanks to the inline-six configuration.
Complementing the DCPCI advanced combustion system are low compression pistons that feature dual zone, egg-shaped combustion chambers. The oblong combustion chambers divide the pre-mixed air and fuel mixture into two separate regions within the fuel bowl. This results in ultra-clean combustion across all engine speeds and also yields exceptional fuel economy.
Here you can see the separate regions of air/fuel mixtures at work within the piston. A spin-off of Premixed Charge Compression Ignition (PCCI), Distribution Controlled Partially Premixed Compression Ignition (DCPCI) is similar in that it’s a form of low temperature combustion (LTC). One of the biggest benefits of LTC is that it’s very effective at reducing NOx, and when combined with EGR an engine’s in-cylinder combustion temperature is lowered even more (and lower temps mean decreased NOx).
DCPCI’s big advantage over PCCI is that it makes ignition timing more controllable and precise. This precision leads to increased thermal efficiency, which is the reason DCPCI yields the kind of fuel economy it does. A higher than normal thermal efficiency (40-plus percent in this case) means that heat can better be converted into mechanical work than it can be in a traditional turbocharged diesel engine.
A common-rail injection system utilizing lightning-quick piezoelectric injectors makes Mazda’s highly-efficient, distribution controlled partially premixed compression ignition (DCPCI) possible. The verdict is still out on who Mazda uses as its fuel system supplier for the e-Skyactiv D engine, but the company has a history of using both Denso and Bosch components.
Of course an engine cover obstructs your view of Mazda’s e-Skyactiv D masterpiece under the hood of the CX-60. It’s the modern age, right? In all seriousness, the e-Skyactiv D has been seamlessly integrated into the new CUV. Engine clatter is faint, if audible at all, in the cabin. And thanks to the inherent perfect balance of the inline-six design, vibration is all but non-existent.
The supporting act for the e-Skyactiv D only makes the diesel-powered CX-60 more efficient. Mazda’s “mild hybrid” system (or M Hybrid Boost system) means there is no electric-only means of propulsion. Rather, the hybrid-electric arrangement simply provides aid to the internal combustion engine. In this case, a 48-volt lithium-ion battery is part of the system. There is no plug-in hybrid technology present here.
The primary purpose of Mazda’s mild hybrid system is to support the engine at low rpm and low load “to improve environmental performance.” What that means is curbing the emissions that are created when a diesel is operated in low rpm conditions, the point where it’s most likely to producing excess particulate matter (PM) and NOx. The hybrid system is advantageous throughout the 3.3L e-Skyactiv D’s power range, but the system really shines in off-idle acceleration.
Though some mild hybrid systems integrate the electric motor (also referred to as a generator or e-machine) up front via belt-drive or on one of the axles, Mazda designed its powertrain with the motor positioned between the engine and transmission. In hybrid speak, this location is known as P1.
Key components in Mazda’s M Hybrid Boost system include the engine, electric motor, transmission, inverter, battery, and DC/DC converter. This is arguably the most straightforward form of a hybrid system, and also why it’s referred to as a mild system. Mild hybrid technology (especially in this case) is geared toward maximizing the fuel efficiency—and to some extent the performance—of a vehicle with an internal combustion engine.
We’re told the electric motor within the mild hybrid system contributes 17 hp to the CX-60’s bottom line. However, the 113 lb-ft of torque it brings to the equation explains why it’s so effective in low rpm operation. Even in diesel applications, where torque is produced quickly in the power band, electric can serve a vital purpose in meeting emissions at low engine speeds.
An all-new eight-speed, multi-plate clutch, automatic transmission accommodates the electric motor within the bellhousing. In all wheel drive applications, it will work in conjunction with Mazda’s i-Activ All Wheel Drive system. The hybrid system’s inverter, which converts DC from the battery into AC for the electric motor, is positioned on top of the transmission case.
A DC/DC converter (arrow) is used to convert high voltage into lower DC voltages, which in this case is to supply the CX-60’s 12-volt onboard electrical system. These components are constantly evolving in order to keep pace with all of the state-of-the-art infotainment systems and advanced driver assist technologies (which the Mazda CX-60 will no doubt be equipped with), not to mention the fact that they help power headlights, provide interior illumination, and even power windshield wiper motors.
Mazda’s M Hybrid Boost system also uses regenerative deceleration (i.e. regenerative braking) to recharge the hybrid system’s 48-volt battery. Called a regenerative-friction brake coordination system, it repurposes the otherwise wasted energy used during braking and stores that energy until it’s needed.
As is the case with any hybrid vehicle, surplus electricity is always generated. In Mazda’s M Hybrid Boost system this surplus is used to power in-vehicle electrical components, which includes a plethora of late-model accessories. The rest is stored in the battery for later use.
Impressively, the 3.3L e-Skyactiv D is no heavier than Mazda’s four-cylinder 2.2L Skyactiv D (the engine previously used in the CX-5). The automaker’s use of aluminum and composite materials where possible account for much of the weight savings. Depending on trim level and options, the diesel hybrid CX-60 tips scales between 4,189 and 4,299 pounds. Its lightweight powertrain is said to help prevent body roll, as does the midship placement of the battery unit.
With 406 lb-ft of torque on tap beginning at 1,500 rpm and holding flat until 2,400 rpm you can bet the Mazda CX-60 has significant towing capability. In fact, Mazda gives diesel-hybrid CUV’s a 5,500-pound tow rating—an impressive stat given its vehicle class. Of course, that table-top torque curve provides more than sufficient off-idle acceleration and strong passing power at highway speeds.
The subtle, unique badging on this European CX-60 says it all. Long-rumored to have been in the works, Mazda fans the world over are wholeheartedly welcoming the arrival of the inline-six diesel engine. Can this diesel-hybrid make oil burners popular once again in Europe? And can it sway European Union policy makers to reconsider their fossil fuel ban that’s set to go into effect in 2035? We can only hope.
Didn’t know about Mazda’s love for diesels? Back in 2013, the auto maker campaigned a 2.2L Skyactiv-D engine in a race car built for Grand-Am GX racing. The move was a way to showcase what its then soon-to-be-brought-to-market 2.2L Skyactiv-D platform was capable of in a high-rpm, high load endurance environment.
Fuel efficiency is a major point of appeal for car buyers, especially those driving in Europe where diesel and gasoline (petroleum) outpace U.S. prices substantially. Thanks to the e-Skyactiv D engine and hybrid technology, a CX-60 is capable of achieving up to 57.6 mpg (in rear-wheel drive form) according to the WLTP test procedure—a more optimistic way of measuring new vehicle fuel economy than our own EPA ratings. But even when WLTP numbers are converted to EPA figures, the aforementioned RWD configuration still returns a respectable 48 mpg.

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Designed to challenge competitors like BMW’s X3 and Audi Q5, Mazda’s CX-60 checks all the boxes for anyone looking for an upscale crossover utility vehicle. And, as was Mazda’s plan, it’s a great long-range option in a world where BEV’s may one day dominate the passenger car, CUV and light-truck segment. Our only hope is that it’s given a chance to stick around overseas (i.e. consumers buy them) so that Mazda might one day consider bringing them to the U.S.

CX-60 E-SKYACTIV D

QUICK FACTS

CONFIGURATION: Inline-six
DISPLACEMENT: 3.3L (200 ci)
BORE: 3.39-inch (86 mm)
STROKE: 3.71-inch (94.2 mm)
HORSEPOWER: 251 hp (AWD models), 197 hp (RWD models) at 3,750 rpm
TORQUE: 406 lb-ft at 1,500 to 2,400 rpm
0-62 MPH: 7.3 seconds
TOP SPEED: 137 mph
CURB WEIGHT (EST): 4,200 lbs
WLTP FUEL ECONOMY (EST): 53.3 mpg (AWD), 57.6 mpg (RWD)
EPA FUEL ECONOMY (EST.): 44.3 mpg (AWD), 48 mpg (RWD)
EMISSION STANDARD: Euro 6d

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