Truck Encyclopedia (16): The best turbocharging technology in history

This issue of Kajia Encyclopedia will talk about the technical development of turbochargers and the layout form of turbochargers.

▎Technological development of turbochargers

Since 1905, Swiss engineers proposed the concept of turbocharging, and more than 100 years have passed since the official birth of turbocharging technology. During this period, turbocharger technology has also continued to advance, let's take a look at the technological development of turbochargers.

● Twin-scroll turbine

The early ordinary turbine has a large or small turbo lag, which brings the driver the feeling that the car does not go by stepping on the accelerator lightly, stepping on a little deeper, the car is like being kicked out, the engine power output is extremely non-linear, the sense of abruptness is strong, and the driving experience is very poor.

Due to the low exhaust gas volume of the engine at low speed, the kinetic energy generated by the lower exhaust gas flow rate is not enough to drive the operation of the turbine, and the turbine can only start when the engine speed is increased and the exhaust gas force is large, which is the turbine hysteresis phenomenon.

The greater the turbo hysteresis, the higher the speed required for the engine to exert force, and the less available engine speed. With the engine displacement unchanged, the larger the diameter of the supercharger, the more severe the turbo hysteresis.

To solve the turbine hysteresis, engineers came up with ways to modify the exhaust pipes to increase the exhaust gas flow rate.

The exhaust manifold of the engine is divided into two or more streams of airflow, and the flow rate of the exhaust airflow is increased by reducing the interference of the exhaust airflow between two adjacent cylinders, so that the turbocharger can enter the working state earlier.

Compared with ordinary turbocharged engines, single-turbo twin-scroll engines can effectively alleviate lag at low speeds, making the peak torque of the engine burst earlier and better fuel economy.

● Variable cross-section turbocharging technology

Variable Geometry Turbine technology is abbreviated as VGT, which is Variable Geometry Turbine.

VGT was also born to reduce turbo lag.

At the heart of the variable section turbocharger system are the deflector vanes with adjustable vortex cross-section. By adding a ring of angle-adjustable deflector blades on the outside of the turbine. By adjusting the angle of the diversion blade, the flow rate and flow rate of the gas flowing through the turbine blade are controlled, thereby controlling the rotation speed of the turbine.

When the exhaust pressure of the engine is low at low rpm, the angle of opening of the deflector blade is smaller, and the air flow rate at the turbine will be accelerated, increasing the pressure at the turbine, so that it is easier to push the turbine to rotate, thereby effectively reducing the phenomenon of turbo hysteresis, and also improving the response time and acceleration ability of the engine at low rpm.

With the increase of rotation speed and the increase of exhaust pressure, the blades also gradually increase the opening angle, and in the full load state, the blades remain fully open, reducing the exhaust back pressure, so as to achieve the pressurization effect of general large turbines.

In addition, since the rotational speed of the turbine can be effectively controlled by changing the blade angle, it is also possible to achieve overload protection against the turbine, so turbochargers using VGT technology do not need to be equipped with exhaust pressure relief valves.

Diesel engines with variable turbine cross-section technology are significantly more efficient at all speed ranges than the standard bleed-valve turbochargers currently used. This makes the engine have smoother power output at both low and high speeds.

● Electric turbocharger

Due to the physical limitations of the exhaust gas turbine, the exhaust pressure must reach a certain value to push the blades to rotate. In order to solve the turbo hysteresis, engineers modified the exhaust pipe to give birth to a twin-scroll turbine, and added a more complex VGT variable section turbine, but this was still not enough, and the electric turbine was born.

Electric turbines are turbines powered by electricity as an energy source. Compared with the traditional exhaust gas turbine, the electric turbine structure is simpler and the size is smaller, because the motor directly drives the impeller to work, and does not need engine exhaust gas to push, so there is no turbine hysteresis.

Taking a brand of electric turbine as an example, relying on a 48V power supply, the rated power of the electric turbine is 5kW, the maximum instantaneous power is 6.2kW, the continuous working power is 2-3kW, the maximum speed is 72,000 rpm, and 90% of the maximum speed can be achieved within 230 milliseconds. Turbocharger arrangement form

Turbochargers can be divided into twin turbocharging, mechanical supercharging plus turbocharging, turbocharging plus electric turbine, etc. Here is an example of a twin turbo:

● Good things come in pairs – twin-turbo

Twin turbocharging is one of the ways of turbocharging, for the turbo hysteresis phenomenon of exhaust gas turbocharging, two turbines in series, one large and one small, or two identical turbines in parallel, when the engine speed is low, less exhaust can drive the turbine to rotate at high speed to generate sufficient intake pressure and reduce turbo hysteresis.

MAN D3876 with dual-stage turbocharging system and dual-stage charge air cooling system:

(1) Low-voltage supercharger; (2) Pressurized air intercooler; (3) High-voltage booster; (4) Pressurized air cooler

The famous Mann D38 engine adopts a series double supercharging method. This 15.2L inline 6-cylinder engine supercharging system consists of two turbochargers of different sizes connected in series. Small-sized high-voltage superchargers intervene when the speed is low, and as the speed and load increase, large-size low-voltage superchargers gradually intervene.

Thanks to the twin-turbo system, the D38 engine has a maximum horsepower of 640 horsepower and can output a maximum torque of 3,000 Nm at 930 rpm and continues until 1,350 rpm.

MC07.35-40

A09C

In addition, Sinotruk's MC07.35-40 engine and Hino's A09C engine also use a similar dual-supercharging method.

● Sanyang Kaitai - triple turbocharging

Audi 4.0TDI diesel engine

At the 2016 Paris Motor Show, Audi showcased the triple-turbo 4.0TDI diesel engine powered by the Audi SQ7. The engine is equipped with both an electric turbine and an exhaust gas turbine, and the two exhaust valves of the engine cylinders are independent of each other and connected to the two exhaust gas turbines, which are available in series and parallel modes.

At idle or low to medium rpm, only one exhaust gas turbine and electric turbocharger work.

At medium to high speeds, the two exhaust gas turbines work in tandem.

At high speeds, the two exhaust gas turbines are in parallel operation mode.

● Four flat and eight stable - four turbos

In 2016, Volvo built an "Iron Knight" truck based on the D13 engine, in order to meet the air intake, this D13 engine is equipped with four turbochargers, and after tuning, the engine has an astonishing power of 2,400 horsepower and 6,000 Nm. ● The least business-oriented turbo "supercharger"

On February 27, 2020, Volvo released the new FH and other models in Sweden, along with the latest D13TC engine. If you want to say that you are not doing your job, it is still an exhaust gas turbine equipped with this engine.

On the D13TC, this exhaust gas turbine is not used as a supercharger, but uses the exhaust gas capacity to drive the crankshaft in turn. Therefore, this turbine technology is called turbo composite technology.

Volvo's turbo compound technology is called Turbo Compound, that is, the turbo composite supercharging system or mechanical heat recovery system, which is one of the waste heat utilization. It captures wasted energy from engine exhaust and converts exhaust energy into mechanical energy, which is turbo-driven flywheel.

According to Volvo, the D13TC engine's Turbo Compound technology can increase the power output of the crankshaft by 50 horsepower and improve fuel efficiency by 6.5%.

Let's briefly talk about how Volvo's Turbo Compound technology works.

This set of turbo composite assemblies is located between the turbocharger and the engine crankshaft flywheel.

The exhaust gas pushes the turbine impeller, passes through a set of reduction gears, reduces the high speed of the turbine, and then stabilizes the rotational speed change through the hydraulic clutch, and then further decelerates to adapt the rotation speed to the crankshaft speed, and finally the power is transmitted to the crankshaft flywheel through the gear.

Simply put, the turbine pushes the hydraulic clutch, and then transmits power through the gears to help the crankshaft rotate.

If the turbine is connected not to the crankshaft flywheel, but to the generator, the technology is called an electric turbine compound.

Mechanical turbine compounding began to be applied to aircraft engines in the 50s of the 20th century, and then began to be applied to vehicle engines in the 60s. At present, it is very mature in well-known foreign commercial vehicles, but domestic engines are still blank in this regard.

For more than 100 years, it has continued to develop and progress, and every progress is the heartfelt heart of human beings in pursuit of efficient use of energy.