Such a small-looking "snail" is one of the most effective ways to increase engine power.
Undoubtedly, each of us at least once in our life noticed a “turbo” nameplate on an ordinary-looking car. Manufacturers, as if on purpose, make these nameplates of a small size and place them in inconspicuous places so that an uninitiated passer-by will not notice and will pass by. And an understanding person will certainly stop and take an interest in the car. Below is a story about the reasons for this behavior.
Automotive designers (since the inception of this profession in the world) are constantly concerned with the problem of increasing the power of motors. The laws of physics state that engine power directly depends on the amount of fuel burned in one working cycle. The more fuel we burn, the more power. And, let's say, we wanted to increase the "number of horses" under the hood - how to do it? This is where problems await us.
The turbocharger consists of two "snails" - exhaust gases pass through one, and the second "pumps" air into the cylinders.
The fact is that oxygen is needed to burn fuel. So it is not the fuel that burns in the cylinders, but the fuel-air mixture. It is not necessary to mix fuel with air by eye, but in a certain ratio. For example, for gasoline engines, one part of the fuel relies on 14-15 parts of air, depending on the operating mode, the composition of the fuel and other factors.
As we can see, a lot of air is required. If we increase the fuel supply (this is not a problem), we also have to significantly increase the air supply. Conventional engines suck it in on their own due to the pressure difference in the cylinder and in the atmosphere. The dependence turns out to be direct - the larger the volume of the cylinder, the more oxygen will enter it at each cycle. This is exactly what the Americans did, releasing huge engines with a mind-boggling fuel consumption. Is there a way to drive more air into the same volume?
There is, and was first invented by Mr. Gottlieb Wilhelm Daimler. Familiar surname? Still, it is she who is used in the name DaimlerChrysler. So, this German was very good at understanding motors and, back in 1885, figured out how to drive more air into them. He figured out how to pump air into the cylinders using a blower, which was a fan (compressor) that received rotation directly from the engine shaft and forced compressed air into the cylinders.
Swiss engineer-inventor Alfred J. Buchi went even further. He was in charge of the development of diesel engines at Sulzer Brothers, and he absolutely did not like that the engines were large and heavy, and they developed little power. He also did not want to take energy from the "engine" to rotate the drive compressor. Therefore, in 1905, Mr. Büchi patented the world's first injection device, which used the energy of exhaust gases as a propellant. Simply put, he came up with turbocharging.
The idea of a smart Swiss is as simple as anything ingenious. As the winds rotate the wings of the mill, so does the exhaust gases turn the wheel with blades. The only difference is that the wheel is very small and there are a lot of blades. A wheel with blades is called a turbine rotor and is mounted on the same shaft as the compressor wheel. So the turbocharger can be conventionally divided into two parts - the rotor and the compressor. The rotor gets its rotation from the exhaust gases, and the compressor connected to it, working as a "fan", pumps additional air into the cylinders. This whole tricky design is called a turbocharger (from the Latin words turbo - vortex and compressio - compression) or a turbocharger.
An analogue of a turbocharger - a drive supercharger - is rigidly connected to the engine and spends part of its power on its work.
In a turbo engine, the air that enters the cylinders often has to be additionally cooled - then its pressure can be increased by driving more oxygen into the cylinder. After all, it is easier to compress cold air (already in the internal combustion engine cylinder) than hot air.
The air passing through the turbine is heated by the compression as well as from the turbocharger parts heated by the exhaust gases. The air supplied to the engine is cooled using a so-called intercooler (intercooler). This is a radiator installed in the path of air from the compressor to the engine cylinders. Passing through it, it gives its warmth to the atmosphere. And the cold air is denser, which means that it can be driven into the cylinder even more.
And this is what the intercooler looks like.
The more exhaust gases enter the turbine, the faster it rotates and the more additional air enters the cylinders, the higher the power. The efficiency of this solution in comparison, for example, with a drive supercharger, is that very little engine energy is spent on "self-service" of the boost - only 1.5%. The fact is that the turbine rotor receives energy from the exhaust gases not due to their deceleration, but due to their cooling - after the turbine, the exhaust gases still go quickly, but colder. In addition, the free energy expended on air compression increases the efficiency of the engine. And the ability to remove more power from a smaller displacement means less frictional losses, less weight of the engine (and the machine as a whole). All this makes turbocharged cars more economical than their naturally aspirated counterparts of equal power. It would seem that this is it, happiness. But no, it's not that simple. The problems have just begun.
Firstly, the speed of rotation of the turbine can reach 200 thousand rpm, and secondly, the temperature of the hot gases reaches, just try to imagine, 1000 ° C! What does all this mean? The fact that it is very expensive and difficult to make a turbocharger that can withstand such heavy loads for a long time.
Exhaust gases heat both the exhaust system and the turbocharging to very high temperatures.
For these reasons, turbocharging became widespread only during the Second World War, and even then only in aviation. In the 50s, the American company Caterpillar was able to adapt it to its tractors, and craftsmen from Cummins designed the first turbodiesels for their trucks. Turbomotors appeared on serial passenger cars even later. It happened in 1962, when the Oldsmobile Jetfire and Chevrolet Corvair Monza were released almost simultaneously.
But the complexity and high cost of the design are not the only drawbacks. The fact is that the efficiency of the turbine is highly dependent on the engine speed. At low speeds, the exhaust gases are few, the rotor spins up weakly, and the compressor almost does not blow additional air into the cylinders. Therefore, it happens that up to three thousand revolutions per minute the motor does not pull at all, and only then, after four or five thousand, "shoots". This fly in the ointment is called turbo lag. Moreover, the larger the turbine, the longer it will spin up. Therefore, motors with very high power density and high-pressure turbines, as a rule, suffer from turbo lag in the first place. But turbines that create low pressure have almost no thrust dips, but they also do not raise power very much.
There are more sophisticated designs. For example, engineers came up with the idea of installing not one, but two turbines on the engine. One works at low engine speeds, creating traction at the "bottom", and the second turns on later. This solution was called twin-turbo and allowed to kill two birds with one stone - both the turbo lag and the problem of lack of power. At the end of the last century, cars with a sequential turbine connection scheme had some popularity; they were produced by Nissan, Toyota, Mazda and even Porsche. However, due to the complexity of the design of the eyelids of such devices, it turned out to be short-lived, and other ideas were spread.
For example, parallel turbocharging, or biturbo. That is, instead of one turbine, two small identical turbines are installed that work independently of each other. The idea is that the smaller the turbine, the faster it spins, the more "responsive" the engine is. Typically, two small turbines were installed on V-shaped engines, one for each half.
Another option is turbines with two "snails", or twin-scroll. One of them (slightly larger) receives exhaust gases from one half of the engine cylinders, the second (slightly smaller) from the other half of the cylinders. Both supply gases to one turbine, effectively spinning it up both at low and high speeds.
The twin-scroll turbine has a double “volute” of the turbine - one efficiently operates at high engine speeds, the other at low speeds.
But the designers did not rest on this either. Naturally, rather than blocking two turbines, it is much easier to get by with one. You just need to make sure that the turbine works equally efficiently over the entire speed range. This is how variable geometry turbines appeared. This is where the fun begins. Depending on the speed, special blades rotate and the shape of the nozzle varies. The result is a "super turbine" that performs well across the entire rev range. These ideas have been in the air for more than a dozen years, but they were successfully implemented relatively recently. Moreover, at first turbines with variable geometry appeared on diesel engines, fortunately, the temperature of the gases there is much lower. And from gasoline cars, the first to try on such a turbine is the Porsche 911 Turbo.
The design of turbo engines has been brought to mind for a long time, and recently their popularity has increased dramatically. Moreover, turbochargers turned out to be promising not only in terms of forcing engines, but also in terms of increasing the efficiency and purity of the exhaust. This is especially true for diesel engines. A rare diesel engine today does not carry the "turbo" prefix. Well, the installation of a turbine on gasoline engines allows you to turn an ordinary-looking car into a real "lighter". The one with a small, barely noticeable "turbo" nameplate.