What does TSI engine mean?

TSI is a set of double supercharging technology developed by Volkswagen Group. In fact, it can be understood literally. The front T and S stand for turbo and supercharger respectively, that is, the combination of turbo and supercharger. Domestic media used to call it double pressurization. This twin turbocharging is quite different from the twin turbocharging of Volkswagen Audi Group, which can be said to be completely two concepts. So why use mechanical supercharging and turbocharging at the same time to provide high-pressure intake for the engine? Now that Volkswagen has extended this technology to production cars, it must have its own advantages in performance. To understand the advantages of dual turbocharging, we must first understand the advantages and disadvantages of turbocharging and mechanical turbocharging. In fact, the purpose of any kind of pressurization is the same, that is, to compress the air before it is introduced into the cylinder for combustion. The benefits are obvious. The density of compressed air is higher, which means that there are more oxygen molecules per unit volume. Under the condition of constant engine displacement, the more oxygen molecules inhaled, the more gasoline provided by the fuel injection system, and the higher the power that can be output. Turbocharging and mechanical supercharging are both to achieve this goal, but the means to achieve it are different. Turbocharged engines use an intake turbine to compress air, and the other end of the intake turbine is connected with an exhaust turbine. We know that the exhaust of the engine is high temperature and high pressure, which means that there is still huge energy in the exhaust. When the exhaust turbine is installed in the exhaust pipe, the exhaust energy can be used to drive the turbine to rotate at a high speed, so as to drive the intake turbine to rotate at a high speed to obtain the energy for compressing the intake air. Therefore, the turbocharger does not need to consume additional engine energy. Moreover, the higher the engine speed, the greater the exhaust gas emission speed and energy, which makes the turbine speed higher, so the intake turbine has stronger ability to compress air.

For turbocharged engines, the higher the speed, the higher the intake efficiency and the greater the power that can be exerted. Therefore, the turbocharger is very beneficial to the high-speed operation of the engine. But we know that turbines have mass, and objects with mass have inertia. We know that the engine speed is often only a few hundred revolutions at idle speed, and the turbine cannot participate in the work at idle speed. In addition to the low engine speed and insufficient exhaust energy to drive the turbine to run at high speed, there is another more important reason that the engine load is low at idle speed. If the turbine works at this time, the engine will overheat and consume more unnecessary gasoline. Therefore, when idling, the intake and exhaust bypass valves will automatically open. At this time, the intake and exhaust air do not pass through the turbine, fresh air is directly sucked into the cylinder, and waste gas is directly discharged into the atmosphere. Because the compression ratio of supercharged engine is relatively low (generally below 8.0, the low compression ratio is because the air will give off heat after being compressed by supercharger, and if the compression ratio is too high, the mixture will continue to give off heat in the compression stroke, resulting in natural mixture), the dynamic performance of the engine is very poor before turbine intervention. Even for low-value supercharging, the turbine will take effect at least at 1800 rpm (the turbine intervention speed of Passat 1.8T is 1800 rpm -2000 rpm). Although the engine can exert strong power after 2000 rpm, it has full stamina, but it can also be said that there is no power at the beginning. Even a V8 turbocharged engine like Porsche Cayenne TURBO can't compete with natural aspiration at first. This is the common problem of turbocharged engines: turbo lag.