Engine efficiency

Modern cars equipped with powerful economical internal combustion engines have an efficiency of 30-35 % for carburetor engines, and 40-43 % for diesel engines. Let's check if the engine efficiency is actually the same.

1 kg of gasoline or diesel fuel emits 46,1 MJ during combustion. A passenger car that has traveled 100 km at an average speed of 40-60 km/h for urban traffic spends 20 MJ on mechanical work. It turns out that with an engine efficiency of about 40%, fuel consumption per 100 km should be about 1 kg! But, if you count, it turns out that the real efficiency of the engine is no more than 10%. What's the matter?

Any heat engine is designed for a certain power, and its efficiency is maximum at a power close to maximum. If a car, for example a passenger car, will consume this power entirely, then it should go at a speed of 150-200 km/h. In this case, almost all the energy will be spent on aerodynamic losses. If you drive at an average speed of 60 km/h, then the engine will not use even a tenth of its power. Here comes such a low efficiency.

If we consider the efficiency of the engine, then the most economical movement of the car is observed at a speed of 40-50 km/h for trucks and 60-70 km/h for cars. In this case, the minimum fuel consumption is even called the control consumption, but the engine efficiency is still below 10 %.

The engine develops maximum efficiency at full or near full power. What if the engine is efficiently running only at its full power, which is almost never needed? Maybe cars don't need such powerful engines? No, we do. A car with a powerful engine becomes dynamic, agile, safe, and therefore prestigious...

Is it possible so that it would be like in a home refrigerator: if he worked, accumulated cold, he turned off, but when it gets warmer, the thermostat will turn on the refrigerator again? A car engine generates mechanical energy, and we know that there are storage devices for it - springs, compressed gas, flywheels. I ran the engine at full power with high efficiency, transferred energy to the storage device - it turned off, and the car runs on this stored energy. Is it real?

Yes, this is real, such hybrids of a heat engine and storage devices exist, and they consume more than 2 times less fuel than a conventional engine. The hybrid drive helps to use energy on descents and brakes, so as not to be damped in the brakes. And this further increases the efficiency of the car.

Despite the fact that there are hybrids with an electric storage device, it is more economical, of course, to accumulate the mechanical energy of motion without transformations, for example, using a flywheel with a variator on an ordinary passenger car. Other accumulators of mechanical energy - pneumatic, hydropneumatic, spring, unfortunately, are not suitable for this business - their accumulative capabilities are too small. But gas - please! Especially with hydraulics - hydro-gas or hydropneumatic accumulators!

For example, when braking a car, a hydraulic machine connected to its transmission, operating in pump mode, would pump oil into the accumulator, compressing the gas. For the subsequent acceleration, the oil from the drive was directed to the hydraulic machine, which this time would work in the engine mode and accelerate the car. At the same time, fuel consumption was reduced by 30-50 % and the toxicity of exhaust gases was significantly reduced.

In part, it can be considered a hybrid installation with gas compressed in cylinders and feeding the car's drive - a pneumocar. The fact is that the air is greatly cooled during expansion, and heating it greatly increases the internal energy of the gas, and, consequently, the mileage of the car. If the gas is heated up enough, then the installation will give out more energy than it was "laid" in it. Thus, it turns out something like a hybrid of a heat engine and a pneumatic storage device.