For some years now, hybrid or electric vehicles have been built and sold to comply with EU standards, though there are still some unresolved issues like those related to their manufacturing, the disposal of the batteries and, above all, questions about the main energy source used to obtain electricity for charging them.

That said, some manufacturers and designers are still studying ways to try and improve the efficiency of existing internal combustion engines, conscious of the modest theoretical performance of petrol engines which, in principle, exceeds 30% while, on the road, it is reduced to approximately 20%.

Diesel engines are more efficient. The 38-40% theoretical performance drops to about 30%, on the road.

There are manufacturers who believe it is possible to build more efficient engines in terms of performance.

Improvements can be applied to every phase of engine operation; many experts still focus on combustion, while a handful study mechanical modifications which, by varying the compression ratio and/or reducing the displacement of a running engine, can increase efficiency.

Following are some of the solutions and research currently under way:

The variable-compression thermal engine is a reality

HeraldScotland: 2017 Paris Motor Show

Infiniti QX50  the world's first variable compression ratio production engine

Variable compression ratio from 8:1 up to 14:1

Engine displacement with minimal variations from 1997cc to 1970cc


Other engines tested but still not in production.


MCE-5 The ratio varies but the engine displacement remains unchanged

DIESOTTO Mercedes Benz The ratio varies but the engine displacement remains unchanged

SAAB The ratio varies but the engine displacement remains unchanged

Porche Stepcom conrod The ratio and engine displacement both vary

Lotus the compression ratio varies for 8:1 to 40:1

According to many car manufacturers, Variable Compression Ratio –or VCR– engines are one of the most promising solutions for reducing fuel consumption, on which decisive strategies for the future could be based.


How to vary engine displacement.


Ford: the EcoBoost 1.0 is the world's first application, on a 3-cylinder engine with cylinder deactivation technology.

Honda: a single engine with 15 available displacements thanks to pistons with different strokes.

Hyundai: the engine has different displacements thanks to the use of different cylinder pairs.

Lamborghini uses it for the V12 of the Aventador with the name of Cylinder Deactivation System.

Mercedes e Volkswagen: have, very recently, used cylinder deactivation.

The vast majority of internal combustion engines consist of cylinders, a crankshaft and pistons that determine equal unit displacement but, due to constant capacity, have one downside: an insufficient margin for controlling the operating point.

Furthermore, to obtain smooth idling a great deal of mechanical energy is consumed.


What is the future of the combustion engine?

Some combustion engine manufacturers believe that, in order to reduce consumption and pollution, the engine of the future must have a variable compression ratio (VCR).

Others think that, when running, reducing the engine displacement increases its efficiency in terms of consumption and pollution.

These two technical solutions, put together, could make it possible for the combustion engine to prosper in the future.

This “ideal” engine would increase efficiency, reduce consumption, and CO2 emissions and pollution.


Is MoMi Control, perhaps, the “ideal” engine?

In 2019, researchers from Sapienza University of Rome worked on and studied MoMi for more than six months. Having seen the results, in 2020 and 2021, other researchers from ENEA, one of Italy’s major public research organisations, also located in Rome, investigated, analysed and tested, for over nine months, the performance of a new crank mechanism: “MoMi Control”.

The report following the latter research was published in March 2021. The data are the result of more than five years of studies and calculations by an inventor/design engineer based in Vicenza Italy, with the help of a mathematician.

MoMi Control, therefore, makes it possible to vary the engine's displacement while simultaneously varying, independently, the compression ratio (VCR) as well. Calculations showed that it is mathematically possible to widen the spectrum of the CR. Data with a CR ranging from 6.8 to 36.8 have already been generated. Any value in between is possible.

For the comparative study, both investigations chose the Gordon P. Blair engine, a 4-cylinder, 4-stroke, spark-ignition engine, with 2000 cm3 capacity, for which extensive literature is available.


FINAL data for the second study

processed by ENEA between July 2020 and March 2021

Following are some improvements found in MoMi crank mechanisms.

  • Unlike standard engines, the MoMi Control crank mechanism does not have a fixed pair of displacement and compression ratio values.
  • The engine examined (a 2000cc, spark-ignition, naturally aspirated engine) can, with MoMi Control, reduce its displacement up to 1080cc but can also increase it up to 2400cc. In this way you will have available not just one 2000cc engine but an engine that will have all the variable displacement from 1080 to 2400 cc.
  • It will be possible to pair every displacement within the aforementioned range with any compression ratio (CR) from 9.8:1 to 21.8:1.
  • The ENEA study specifies that the MoMi Control crank mechanisms can be sized and used on any type of engine, even the most innovative still in the experimental stage. By optimising the piston movements for controlling, varying and managing both the CR and the displacement, MoMi Control should always increase the efficiency of these engines by pushing it towards 30% (33% is the value that refers to the average increment in the 9 cycles tested).
  • In the WLTC, the top efficiency is 28.53%. Even the reduction of CO2, in this cycle, exceeds 28%. This already seems achievable in 2021.


CO2 emissions

The EU is taking steps to reduce CO2 emissions in cars and vans. The revised standards will contain stricter regulations concerning CO2 emissions for cars and new light commercial vehicles.

On 16 January 2019, Member States endorsed a provisional agreement reached by the Presidency and Parliament representatives, on 17 December 2018.

Average CO2 emissions of new cars registered in the EU will have to be 15% lower in 2025, compared to the emission limits valid in 2021, and 37.5% in 2030.

The CO2 emissions of new vans will need to be 15% lower in 2025 and 31% in 2030.

These are targets for the entire EU vehicle fleet. The commitment to reducing emissions will be distributed among manufacturers based on the average mass of their car fleets.

As the basis for calculating the specific emissions targets for manufacturers, stricter rules have been agreed for the transition from the old NEDC test procedure to the more accurate WLTP test procedure.

HeraldScotland: It appears that the manufacturers have difficultyproducing vehicles with these characteristics.

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It appears that the manufacturers have difficulty

 producing vehicles with these characteristics.