May 21, 2024

With the rising gas prices that is not slowing, it’s an appropriate time to reassess whether our cars are insufficiently efficient? Europe has voted to stop the manufacture of new vehicles powered by combustion engines until 2035 however, the majority of the automobiles that are currently in circulation in France and around the world are still in this category.

The engines function by burning diesel or petrol fuel, and then converting the heat into mechanical power that is then used to propel the vehicle. In the majority of cases, 50 percent of the power generated is transformed into mechanical energy however the rest is released in the form of heat. In addition, not all mechanical energy is transferred directly to wheels. In fact, nearly 30% going to waste because of friction.

The amount of energy consumed to move the vehicle is about 30% of total energy generated by fuel. The question is, where does the waste go, how is it possible to cut down on it, and what can be reasonably expected saving on gas?

How does a combustion engine work

Within a engine that burns air and fuel is burnt within “the combustion chamber. This raises the amount of gas that is in the chamber, and the resulting pressure is pushed by the piston downwards. The piston is linked to the crankshaft using the connecting rod, which converts the piston’s horizontal movement into a rotational one. After that, this rotation is transferred from the crankshaft into the mechanical transmission (including the gearbox) and finally to the wheels.

Diagram of the combustion engine, showing motion of the components (red) and areas of friction (yellow). Zephyris/Wikimedia/TCF, CC BY

Many engine valves are then opened and close, letting the waste gases go out and fresh air and fuel into. A small part (40 to 50 percent) of the energy generated by combustion is transformed to energy that can be used for mechanical purposes. The rest is wasted and being released via hot gases that escape from the exhaust pipe and into the radiator that keeps cooling the motor. But, by enhancing the combustion process and implementing energy recovery systems, we could be able to boost the quantity of converted energy, and also reduce the consumption of fuel by around 30 percent.

The loss of fuel is due to friction

It is worthwhile to clarify what exactly it means by “friction”. The word is used to describe the force that creates opposition to the movement between two objects once they come in contact. For instance contact between the shoes we wear and ground lets us walk on the ground without falling. When there is a low friction, like in the case of frozen it is much more difficult for shoes to slip on the ground, making walking very difficult. It is possible to opt to wear skates that use their very low coefficient of friction to allow us to move about sliding.

In essence, when two objects are moved (or rub) to each other, the resulting resistance force is created by the friction. This causes heat loss that we can see when we rub our hands together as an example. In automobiles, the exact same thing happens between moving engine components along with the mechanic transmission. As researchers, we seek to determine the effect on this phenomenon.

“Tribology” is a branch of science that studies friction, contact and the best way to reduce their effects. Research conducted in this area has provided a better understanding of the energy loss due to friction in the combustion engine of cars as well as in the transmission that is connected to the wheels. In the above diagram the areas of contact in which loss is caused by friction are illustrated in yellow. The largest energy losses are found close to the piston (at around 45 percent of the losses) which is followed by connections to the connecting rod the crankshaft, and the the cylinder block (approximately 30 percent) and the valves and the actuating system (approximately 10 percent). The remainder of the energy is loss through other fittings for engines.

The mechanical energy that is useful to an engine’s combustion is further limited due to the loss of mechanical transmission, caused primarily by friction between gears. All of these losses cause the loss of about 30 percent of the energy generated from the engine in typical conditions of operation for the vehicle.

Can we cut down on the use of gasoline by limiting energy losses due to friction?

As about 30% of the gasoline is consumed to counter friction between its mechanical components, reducing the loss can result in substantial reductions in fuel. This is why we need to examine the components that are subject to friction and discuss possible enhancements. The components of the transmission and engine are already lubricated with oil, which is placed between the surfaces to avoid wear and friction.

To further cutting down on energy loss from friction, tribology research is a part of two major areas. The first is about the improvement of lubricants. This research seeks to understand the ways in which specific properties of lubricant like viscosity affect the temperature. The general rule is that friction is likely to diminish when lower viscous lubricant has been used however, its oil film might appear too thick, which can lead to greater contact between uneven surfaces and more wear. To prevent this, a area of research is to discover new additives for lubricant which can be used to coat surfaces with high-quality, non-friction protective layers.

Solutions that minimize wear and friction in contact areas with mechanical parts. Zephyris/Wikimedia/TCF, CC BY

The other research area is making the surfaces more attractive by constructing novel (particularly carbon-based) coatings, which shield these surfaces from coming in contact with one another and results in less friction. Additionally, surfaces could be textured by a system of holes that have the proper dimensions to ensure efficient fluidization.

We have recently completed an investigation in the Institut Pprime in Poitiers (led by CNRS, University of Poitiers and ISAE Ensma), which has demonstrated that the friction of certain types of contact can be reduced by 50% with the use of texturing on surfaces.

Additionally, in the context of vehicles powered by combustion engines numerous studies have established that this technology could reduce energy loss caused by friction by between 50 and 60% in the long time, which is around 15% lower fuel use. When paired with improved engines and lighter, smaller vehicles and, eventually tyres that are narrower, this seemingly tiny amount of fuel saved could eventually be able to reach amounts of up to 50 percent. The growing SUV market within the auto market however, suggests that this method of savings on fuel has not been used by car manufacturers in recent times.

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So, what are the quick solutions to cut costs? Except for purchases of new vehicles The use of better-performing fluids could reduce the amount of fuel used by a small amount which is a tiny amount given increasing fuel costs. Additionally it is often difficult for people to determine what type of lubricant they should choose from since comparative research is generally only found in scientific literature, and thus restricted to a specific audience.

But, we shouldn’t overlook the fact that cars were designed to carry a number of passengers. If fuel consumption is divided by multiple passengers, carpooling could reduce the amount of fuel consumed by two, three, or four times more and even more. When you’re trying to reduce your fuel expenses, driving less is the most effective and easy method.

In the long run what do you think the electric car which is now widely praised be more efficient in cutting down on energy losses due to friction? Since there are fewer mechanical components that are subject to friction the energy losses of electric vehicles have been rated as less than five percent. However, before it’s touted as a breakthrough solution we need to think about the rest of the bolts and nuts to consider, such as the car’s weight, battery’s price, and the cost of extraction and recycling of the production materials.

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