One of the new cars touching down in South Africa in the near future is the Mazda CX-60 Takumi, which has a rather unusual quality.
It has a 3.3-litre engine that receives assistance from a small electric motor, making it a hybrid powertrain, but unlike the vast majority of hybrids, this setup uses diesel rather than petrol.
It is, in fact, the only diesel-hybrid currently available in South Africa, which speaks to a wider topic about why the engine type is so rare to see, given how the two concepts seem like a match made in heaven, at least on paper.
How Mazda’s hybrid engine works
The Takumi’s powertrain consists of a 3.3-litre turbocharged combustion engine, which is aided by 48V mild-hybrid technology that includes a small electric motor that contributes 12.4kW and 153Nm.
Mazda refers to this system as its Mild Hybrid Electric Vehicle (MHEV) engine technology, and like with all hybrids, the goal is to maximize fuel efficiency by leveraging electrical power rather than sipping fuel wherever possible.
The drivetrain encompasses the internal combustion engine (ICE), turbocharger, e-motor, DC/DC converter, inverter, lithium-ion battery, and transmission, all of which play their part in transmitting power to all four wheels.
Like any fossil-fuel car, the propellant is injected into a chamber where it ignites to generate the force needed to push the cylinders and rotate the driveshaft that ultimately spins the wheels.
What differentiates the CX-60 is that it uses fuel injection with a dual egg-shaped combustion chamber, which is able to divide the air-fuel mixture created by the turbocharger, which the company claims results in cleaner and more efficient combustion across all rpm ranges.
As a mild hybrid, the SUV cannot run exclusively off its e-motor; rather, it supports the ICE at low rpm conditions and is powered by a small-capacity battery that is replenished through regenerative braking.
This is because low revs – like in heavy traffic – is an ICE’s least efficient operating mode, as it produces excess carbon and nitrogen dioxide while burning fuel for little gain just to maintain itself without stalling.
Therefore, the torque that the electric motor is quickly able to provide alleviates the burden on the ICE at low speeds until the revs build up again, at which point the combustion power source takes over for longer and faster stretches of driving, making the car as a whole more efficient.
The end result is the Mazda achieves a combined fuel consumption of 4.9l/100km, making the SUV with its gross weight of 2.5 tonnes much more efficient than most city-going hatchbacks.
Why diesel hybrids are so rare
Diesel engines provide greater mileage than petrol units, and hybrids are all about improving fuel efficiency, so the two systems seem like a natural fit for one another, and yet they aren’t very common.
The first reason for this is cost, as diesel engines cost on average 15% more to make and to purchase than an equivalent petrol one, and this is on top of the added spend that a hybrid system brings, making the setup harder to justify both for the manufacturer and the consumer.
Related to this, the inherently efficient nature of diesel drivetrains means there is less of a need (and thus demand) to pair them with hybrids in the first place, especially when you combine this point with the higher purchase cost, as it would take hundreds, if not thousands of miles of driving to start saving money on fuel over the extra that you spent to purchase the car in the first place.
There is also a mechanical reason as to why diesel hybrids aren’t common, which is that they do not complement one another in the same way that a petrol engine would.
Notice the massive difference in power versus torque that an electric motor provides, with the CX-60 producing just 12kW compared to 153Nm.
This same trade-off of torque over power is present in diesel engines and is the reason why the propellant is favoured in working vehicles such as bakkies where torque is much more important for things like towing and low-speed driving (such as when off-roading).
Electric motors work well with petrol plants because they address their main weakness by providing much more torque and improving acceleration, whereas the same setup on a diesel is arguably overkill and contributes less in a comparative sense.