The TDI engines are a line of diesel powertrains, produced by German car giant Volkswagen. Diesel engines, marked with the abbreviation TDI (from English. Turbocharged Direct Injection) are turbocharged units and equipped with a direct fuel injection system. These engines can be found on various diesel car models, whose manufacturers are part of the WAG concern (Audi, Volkswagen, Skoda, etc.)
We also recommend reading the article about it, what is the EGR system. In this article you will learn about the purpose and principles of the exhaust gas recirculation system of gasoline and diesel engines.
History of the TDI engine
The diesel engine has always attracted various companies with its untapped potential. The main task, which was put before the engineers, was the transformation of the noisy, low-speed and low-speed unit in such a motor, which could be easily installed in cars. The result was the creation of a powerful, economic and environmental diesel, which in its performance characteristics was as close as possible to the gasoline power unit.
Audi has become a pioneer in this direction, which in the far 1980s installed a 1.6-liter diesel 54-horsepower under the hood of its popular Audi model 80. Further improvement and development of technology has led to this, that already in 1989 Audi was the first in the world to set up and launch into mass production compact, traction and powerful turbodiesel, which received the well-known today TDI designation.
The first TDI was a diesel engine from 5 cylinders, had a working volume 2.5 liters, equipped with turbocharging with intercooler (intermediate air cooling system, inflated). The maximum power of this motor was 120 c.. The torque indicator was on the mark 256 Nm and was achieved when exiting 2250 about / min.
Since its appearance on the market, this power unit has become quite popular, since it was a worthy alternative not only to diesels from other manufacturers, but was quite capable of competing with gasoline engines. Audi's TDI provided excellent dynamics, while fuel consumption was significantly lower compared to other analogues.
Features and benefits of the TDI engine
After Audi joined WAG, Volkswagen Group took first place in the list of manufacturers of diesel engines. Innovative engineering solutions and advanced production technologies have provided TDI engines:
- low noise level at work;
- high torque;
- low fuel consumption;
- reducing the toxicity of exhaust gases;
Today, the TDI diesel engine has a number of advantages over its counterparts, among which fuel efficiency and efficiency are singled out. One of the main advantages is deservedly considered to be the higher injection pressure compared to the performance of other systems. The injection pressure in TDI motors is marked 2050 there is, while analogues issue only 1350 there is.
In the TDI, the injector is combined with a pump, that allows to realize the maximum control over all processes of fuel injection. This solution provides the TDI engine with high torque, as well as the elastic operation of this diesel in different modes. Thanks to this fuel supply system, the process of combustion of diesel fuel in TDI engines is more uniform and occurs "delicately", ie with minimal shock loads. For this reason, the noise level during diesel operation was significantly reduced, and the content of nitric oxide in the exhaust gases decreased. In other words, The diesel TDI engine is powerful, quiet, the least harmful to the environment and the most economical engine among the diesel power units available on the market.
Reliability of diesel TDI
The turbocharger installation allowed the diesel engine to develop more power, and increased diesel efficiency. As for TDI motors, then these engines are quite reliable if operated properly. The serviceability of these internal combustion engines is most strongly influenced by the quality of fuel and timely maintenance. With proper care, the engine itself can be even a "millionaire".
The weak point of the TDI are the injectors and turbocharger. The life of the injectors directly depends on the quality of diesel fuel and the general condition of the diesel TDI power supply system. Turbine life may vary, the average resource is 120-160 thousand. Km.
Fuel injection in TDI engines
In the early stages of development of diesel engines, the pressure in the system, which involves the presence of a pump in connection with simple mechanical nozzles, there were some 20-40 Bar. Modern diesel has a pressure at the minimum mark 1600 Bar and above. The tendency to increase the fuel injection pressure is related to this, that diesel engines differ in a very short time, which is allocated to the process of mixing.
If the crankshaft rotates on 2000 about / min, then only a portion of diesel fuel and air is released for mixing 3-4 milliseconds. Increasing the crankshaft speed further shortens this time interval. Also, the preparation of a homogeneous fuel-air mixture becomes possible only by increasing the injection pressure. In the case of low pressure, the fuel mixture will be of poor quality, the combustion process is low efficiency. The result is increased diesel toxicity and low efficiency.
Previously, for fuel injection on diesel was responsible for fuel injection, which works in pair with mechanical nozzles, Today, common rail systems are used for diesel engines. Since the combustion process in a diesel engine is an explosion from the contact of a portion of diesel fuel with air heated to the compression stroke, then the injection time is very limited.
TNVD in modern diesel simply creates pressure in the general highway, and piezo injectors (piezoelectric nozzles) TDI is able to inject a clearly defined amount of diesel fuel into the cylinders of a diesel engine in a very short period of time (less than 0,2 milliseconds) on the command of the ECU.
Also in some designs of power supply systems for diesel engines can be found so-called pump-injectors. This means, that each injector is equipped with its own high pressure pump. It turns out, development of diesel technologies today is reduced to increasing the injection pressure and maximum efficiency of the turbocharging system. This is how the main tasks can be solved: increase power and reduce exhaust toxicity.
Inflated TDI: turbine with variable geometry
Not only dynamics largely depends on the efficiency of the TDI turbocharger, but also efficiency along with environmental friendliness. Proper air boost should be implemented in the widest possible range. For this reason, turbochargers with variable turbine geometry are fitted to TDI engines.
The world's leading turbine manufacturers use the following names:
- VGT turbine (from English. Variable Geometry Turbocharger, which means a turbocharger with variable geometry). Held by BorgWarner.
- Turbocharger for VNT diesel (from English. Variable Nozzle Turbine, which means a turbine with a replaceable nozzle). This name is used by Garrett.
The turbocharger with variable geometry differs from the usual turbine in that, which has the ability to adjust as a direct, and the amount of exhaust gas flow. This feature allows you to achieve the most suitable speed of the turbine in relation to a particular mode of operation of the engine. The performance of the compressor in this case is greatly increased.
Example, the VNT turbine is based on special guide vanes. Additionally, there is a control mechanism, and the presence of a vacuum drive is noted. These turbine blades rotate to the desired angle around its axis, thereby being able to change the speed and direction of exhaust flow. This is due to the change in the cross section of the channel.
The control mechanism is responsible for turning the blades. Structurally, the mechanism has a ring and a lever. The lever is affected by a vacuum drive, which controls the operation of the mechanism with a special traction. The vacuum actuator is controlled by a separate valve, which limits the boost pressure. The valve is an integral part of the electronic control system of the internal combustion engine and works depending on the values of the boost pressure. This value is measured by individual sensors:
- temperature sensor, which measures the inlet air temperature;
- boost pressure sensor;
In other words, turbocharging on the TDI works like this, so that the charge air pressure is always optimal at different engine speeds. Actually, the turbine dispenses the energy of the exhaust gas flow.
- As you know, at low engine speed flow rate (energy) exhaust is quite low. In this mode, the guide vanes are usually closed, than the minimum section in the channel is reached. As a result of passing through such a channel, even a small amount of gas turns the turbine more efficiently, forcing the compressor wheel to rotate noticeably faster. It turns out, turbocharger provides greater performance at low speeds.
- If the driver presses hard on the gas, then the usual turbine has the effect of so-called "turbines". Concerns should be understood as a delay in response to the accelerator pedal, that is, not an instantaneous increase in power, and picking up after a short pause. This feature is due to ??inertia of the turbocharging system, as a result, the flow of gases is insufficient at the time of a sharp increase in crankshaft speed. In turbines with variable geometry, the guide vanes rotate with a certain delay, which allows you to maintain the required boost pressure and virtually get rid of turbines.
- When driving at high and close to maximum engine speeds, the exhaust gases have maximum energy. To prevent overpressure, the blades in variable geometry turbines are rotated as follows., that the powerful stream of gases moved on the wide channel with the largest cross section.
We also recommend reading the article on the service life of diesel turbines. In this article you will learn about the life of this unit compared to gasoline counterparts, and also get the opportunity to read the basic tips and tricks to increase the life of the turbine of a diesel engine.
The relatively low life of the turbocharger is due to this, that only turbines with variable geometry are placed on the TDI. The turbocharger spins up while the engine is running 200 thousand. About / min and constantly interacts with the flow heated to 1000 degrees Celsius exhaust. Such temperature and mechanical loads, as well as individual design features of these turbines relatively quickly lead to the need to repair or replace the turbocharger.
Let's summarize
Thanks to the developments and engineering solutions of Audi, the diesel engine has managed to rise to a new stage of its evolution.. The efficiency of TDI engines is a record. Audi model 100 TDI passed 4 814,4 kilometers on fuel, equal to only one full fuel tank. The average speed was about 60 km / year, while the average fuel consumption was on the mark a little more 1.7 l on 100 km. Also, TDI engines are close to gasoline units not only on the streets, but also on racing tracks. An excellent example is the diesel Audi R10 TDI, which regularly wins on the most difficult tracks.
Finally, let's add, which is the main guarantee of long life as a TDI engine, and any other, there is a correct selection and timely replacement of engine oil, competent operation and riding on quality fuel, as well as professional service. Compliance with these conditions will allow the engine and other related systems to maintain performance for hundreds of thousands of kilometers.