AUTONEWS

M 252: the new diesel-powered petrol engine that will make its debut in the 2026 Mercedes CLA 

There is nothing else being talked about but electric cars, so it may come as a surprise that Mercedes-Benz is preparing to introduce a completely new combustion engine at this “stage of the championship”, the M 252. The justification for this decision is easy. The manufacturer itself recognizes that electrification will not happen at the same speed everywhere: “the mobility desires and needs of customers in different regions of the world determine the pace of this transformation”.

New modular family... The question of the M 252's raison d'être has been settled and, from what Mercedes-Benz suggests, it won't be the only one. The new engine belongs to a new family of modular engines, with the curious acronym FAME (Family of Modular Engines).

This family was developed by Mercedes-Benz, but also involved Horse. Yes, that one. It is the joint venture between the Chinese company Geely and the Renault Group for the development and production of combustion and hybrid engines, and this company will be responsible for the production of the new engine in China.

Being part of a new family, there are a series of characteristics that will be common to all its members. Starting with the aluminum block with NANOSLIDE technology (guarantees a finish with less friction on the cylinder walls), through to the cylinder head with partially integrated manifold.

Also noteworthy is the compact intake duct and an exhaust system placed close to the engine in what Mercedes calls a one-box design.

The turbocharger will also be common to all, here with a new segmented turbine technology with switchable scroll connection. Without going into details — that would be enough for another article — the objective of this technology is to improve engine response at low revs and improve efficiency, reducing consumption and emissions.

As you would expect, efficiency drove many of the decisions about this family of FAME engines. Furthermore, it will comply with future emissions standards (Euro 7, for example).

M 252 in detail...In the case of the M 252, the efficiency of this 1496 cm3 four-cylinder in-line block is also seen in its operation according to the Miller cycle, a more efficient combustion cycle than the traditional Otto, from which it derives.

To put it simply, it is the equivalent of the Atkinson cycle that we are used to seeing in so many hybrid engines, but which appears here associated with supercharging (in this case, a turbocharger).

The Miller cycle allows you to reduce fuel consumption, especially at partial loads, which is the most common driving style in everyday life. In this case, the intake valves close earlier than they would in the Otto cycle, reducing throttling losses and allowing the M 252 to have a compression ratio of 12:1. This is quite a high value for a supercharged engine and is also synonymous with greater efficiency.

In addition to the Miller cycle, the M 252 will also be a mild hybrid. This means that associated with the combustion engine will be a 48 V electrical system consisting of an electric motor integrated into a new eight-speed dual-clutch gearbox (8F-eDCT) — the only one available —; and a 48 V battery (lithium-ion) with 1.3 kWh capacity.

This new generation of mild-hybrid systems guarantees wider use, potentially reducing consumption, especially in low-speed scenarios, such as urban driving. Mercedes-Benz indicates that when driving at constant speed, the 20 kW (27 hp) electric motor will take over, eliminating the operating inefficiencies of the combustion engine.

It will also be possible to coast or freewheel at speeds of around 100 km/h and this mild-hybrid engine features energy recovery when decelerating or braking. Mercedes-Benz says it can recover up to 25 kW of energy, regardless of the gear ratio.

Diesel Consumption...The increased efficiency of this new petrol engine, in conjunction with the electric motor, is what will allow for low consumption, at the level of a Diesel engine, according to Karsten Krebs, who led the development of this unit (source: Autocar). In the case of the CLA, consumption of around five liters per 100 km was mentioned.

We'll have to wait to confirm this claim: there are no official consumption figures and a test in real conditions is still further away in time.

What we do know is that when the M 252 hits the market, it will start being offered in three power levels: 100 kW (136 hp), 120 kW (163 hp) and 140 kW (190 hp). Mercedes does not deny the possibility of there being more variants in the future.

These power figures can be temporarily increased — for 20 seconds at 3,000 rpm — if necessary, thanks to the 20 kW (27 hp) electric motor.

Refined... Last but not least, the German manufacturer highlights the refinement (NVH or Noise, Vibration and Harshness) of the new M 252. The fact that it has four cylinders and not three, like some competitors (BMW, for example), gives it an initial advantage. But Mercedes reinforces the argument with the addition of various foams and covers to reduce noise.

Furthermore, it brought over from its higher-segment models the same double bulkhead solution to better isolate the cabin from the engine compartment. The bulkhead's soundproofing, furthermore, has been extended to the side area of ​​the A-pillar and floor.

When will it arrive?...The third generation of the Mercedes-Benz CLA will hit the market in early 2025. However, priority will be given to the launch of the 100% electric version, which also promises very high levels of efficiency.

The M 252-equipped CLA isn't scheduled to arrive until late 2025 or early 2026.

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