With rising gas prices showing no signs of slowing, it seems like a good time to ask ourselves: Are our cars not efficient enough? Europe has decided to ban the production of new internal combustion vehicles by 2035, but the majority of private vehicles currently in circulation in France and worldwide still fall into this category.
Their engines work on the principle of burning gasoline or diesel and converting the resulting thermal energy into mechanical energy that is used to drive the vehicle. A maximum of 50% of the power supplied is converted into mechanical energy, the rest is released as heat. In addition, not all mechanical energy is transferred to the wheels, as almost 30% of the energy is lost through friction.
Ultimately, the actual energy used to move the vehicle is about 30% of the total energy provided by the fuel. So where does all this waste come from, can we reduce it and what reasonable costs can we expect to save on fuel consumption?
How an Internal Combustion Engine Works
In an internal combustion engine, a mixture of fuel and air is burned in a part called the combustion chamber. This causes the gas volume in the chamber to increase and the resulting pressure pushes the piston element downwards. The piston is connected to the crankshaft via a connecting rod, which converts the vertical movement of the piston into rotary motion. This rotation is then transmitted via the crankshaft to the mechanical transmission (including gearbox) and then to the wheels.
A series of valves in the engine open and close, releasing exhaust gases and introducing a fresh dose of air and fuel. A limited part (40 to 50%) of the thermal energy generated during combustion is converted into mechanical energy. The rest is wasted and carried away by hot gases that exit the exhaust and flow through the radiator, keeping the engine cool. However, by improving combustion and installing energy recovery systems, we can increase the amount of usable energy and reduce fuel consumption by almost 30%.
Fuel Wastage Due to Friction
It is worth noting what “friction” means. This term refers to the force that counteracts the sliding movement between two objects when they come into contact with each other. For example, the friction between our shoes and the ground allows us to walk without slipping. When friction is low, for example when the ground is frozen, our shoes slide more easily on the ground and walking becomes significantly more difficult. However, we can choose skates that take advantage of their low friction with the ground to allow us to slide.
Basically: When two objects are moved (or rubbed) against each other, the resulting resistance force is created by friction. This leads to a loss of energy through heat, which can be observed, for example, by rubbing your hands. In a car, exactly the same phenomenon occurs between the moving parts of the engine and the mechanical transmission. As researchers, we try to assess the impact of this phenomenon.
“Tribology” is a scientific field that deals with contact, friction and methods for mitigating their effects. The latest research in this field has made it possible to estimate the energy losses caused by the friction that occurs in the car’s internal combustion engine and in the gearbox connected to its wheels. In the diagram above, contact areas where friction losses occur are marked yellow. The greatest energy losses occur in the piston area (about 45% of losses); then the connections between connecting rod, crankshaft and block (approx. 30%); and around the valves and their actuation system “approx. 10%”. The remaining 10% is lost in other engine components.
The usable mechanical energy of the engine is also limited by losses in the mechanical transmission, which are caused in particular by friction between the gears. Ultimately, all of these losses result in a loss of approximately 30% of the mechanical energy provided by the internal combustion engine under average vehicle operating conditions.
Could we reduce fuel consumption by limiting energy losses due to friction?
Since approximately 30% of a car’s fuel is used to overcome friction between moving mechanical parts, reducing these losses can result in significant fuel savings. Therefore, we need to investigate friction-prone components to discuss possible improvements. The engine and transmission components are already lubricated with oil, which is placed between the surfaces to prevent friction and wear.
In order to further reduce energy losses due to friction, tribological research covers two main areas. The first concerns the improvement of lubricants. The purpose of this test is to examine how temperature affects certain properties of the lubricant, such as viscosity. In general, friction tends to decrease when a less viscous grease is used, but the oil film may be too thin, resulting in more contact between uneven surfaces and faster wear. To counteract this problem, one area of research aims to develop new lubricating additives capable of coating surfaces with low-friction protective layers.
The second direction of research is to improve the surfaces themselves by creating new coatings (especially carbon) that protect the surfaces in contact with each other and cause less friction. Alternatively, surfaces can be textured with a series of optimally sized holes for more effective lubrication.
We recently carried out a research project at the Prime Institute in Poitiers (led by CNRS, the University of Poitiers and ISAE Ensma) which showed that the friction of some types of contacts can be reduced by 50% thanks to surface texturing.
In addition, several studies on vehicles with internal combustion engines have already confirmed that this new technology can reduce energy losses due to friction by 50-60% in the medium term, resulting in lower fuel consumption of around 15%. Combined with improved engines and smaller, lighter vehicles – and ultimately narrower tires – this seemingly small fuel saving could potentially reach levels of around 50%.However, the growing SUV sector in the automotive market shows us that unfortunately, car manufacturers have not resorted to this fuel saving method in recent years.
So what are our direct solutions to reducing costs? With the exception of buying a new car, using more efficient lubricants can reduce fuel consumption by a small percentage, which is minimal given rising fuel prices. Furthermore, the choice of lubricant can be difficult for the individual as comparative studies are currently only available in the scientific literature and therefore only accessible to specialist readers.
However, we must not forget that cars are designed to carry more passengers. When fuel consumption is divided among multiple passengers, traveling together can reduce fuel consumption by two, three or four times. However, when it comes to reducing fuel costs, reducing driving remains the most effective and simple solution.
Could an electric car, now widely appreciated, be a more effective solution in the long term to reduce energy losses due to friction? Since significantly fewer mechanical components are exposed to friction, the energy loss in electric cars is estimated to be less than 5%. But before we think about this miracle solution, we must take into account all the other aspects, especially the weight of the car, the cost of the battery or the extraction and recycling of production materials.