What is a TDI engine

What is a TDI engine?

What is a TDI engine: a general analysis, the pros and cons of the motor

The abbreviated name of the diesel engine TDI stands for Turbocharged Direct Injection. The creation of the engineers of the Volkswagen company at the automobile concern.

The development of this engine began in the late 70’s. The concern has exclusive rights for the name TDI, as the name is protected by patent, so you can always without error determine the origin of such engines.

The entire subsidiary range of vehicles of German origin is equipped with such power units, regardless of the type of vehicle, which includes vans, trucks, cars and SUVs.

TDI engines are also entitled to some other companies with which Volkswagen has signed a cooperation agreement. In order to understand, it is necessary to characterize this power unit.

General analysis of TDI engines

The main characteristic advantages of such engines, to which you need to pay attention are:

All these positive characteristics did not appear immediately. Even after the arrival of the Audi 80 with the TDI engine on the market, the prevalence of such engine characteristics was not observed. Only after painstaking work and various kinds of modifications in 1989, the manufacturers released a powerful turbodiesel, which was completely inferior to gasoline engines.

Experts confirm that TDI engines are the best in modern times. Their efficiency is determined from the proportion of initial power and torque per 1 cylinder volume and fuel consumed.

Variable geometry turbine function

Along with the direct injection system, the main indisputable advantage of the engine is the variable geometry turbocharger, this makes such engines competitive not only among diesel engines, but also among gasoline engines.

In this turbocharger, the distribution and performance of the exhaust gas flow is subject to adjustment. This makes it possible to achieve the desired turbine speed, which has a positive effect on performance. A simple turbine does not have this option.

If we consider a VNT turbine, it is designed with guide vanes, a control system and a vacuum drive. As they move around their axis, the blades are at the correct angle and this changes the channel cross-section. On this basis it is possible to correct the speed and the vector of the exhausts.

The actuating mechanism controls the rotation of the vanes at all times. It is equipped with a ring and a lever that takes the influence of the vacuum actuator, which is regulated by an independent linkage.

The valve is the actuator control, it enters the engine ECU and is responsible for changing the boost pressure with signals that come from the temperature and boost pressure sensor.

The exhaust flow energy metering valve is a kind of turbine on the TDI engine. The metering unit provides the necessary air pressure under all engine operating conditions.

TDI technical differences

Technical differences of TDI engines

Respectable efficiency and fuel economy shows on the AUDI v12. Due to the increased injection pressure, which reaches 2050 bar, there is a high efficiency of the unit. If you compare with other models, their performance does not exceed 1350 bar.

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It is common knowledge that the fuel injector is responsible for maintaining the total pressure in the line. At the signal of the electronic control unit, the piezoelectric injectors produce metered injection at a time of less than 0.2 ms.

The common rail accumulator injection system has realized a way of increasing the efficiency of diesel engines. Thanks to it the injection mechanism becomes independent of the crankshaft angle and the operating mode of the engine.

With increased pressure and low-load operation the requirements for injection are met, enabling fuel to be injected into the cylinder. Compared with a simple fuel system, the common rail system is superior in terms of its maintainability. It places high demands on the quality of the fuel, which the simple system loses out to.

A number of atypical features of TDI engines can be corrected in a few points:

Comprehensive control of the fuel injection device originated by linking the injector to the pump. This has resulted in higher torque when modifying the operating mode.

High shock loads are absent during fuel combustion, this is due to the low noise level of the engine.

In the exhaust concentrations of nitrogen oxide are low. In this regard, the index of toxicity is acceptable, which is not the case with other types of engines. Among its peers, this unit is rightly considered the most environmentally friendly.

Faults of TDI engines

The reliability of TDI engines is quite high, according to the specialized resources. With the right quality organized maintenance it can be operated for millions of kilometers.

The degree of reliability of modern compressors has also increased and sometimes reaches at least the life of the engine itself. 150,000 to 200,000 km is the average life of most turbines.

Such service life is achieved due to the high exhaust gas temperature, which can reach 1000 degrees and the high rotational speed, which approaches to two hundred thousand revolutions per minute.

The service life of the injectors depends directly on the correctness of the feeding system and the quality of the fuel, which is a disadvantage.

The most significant measures that will prolong the life of TDI weak links are:

– Timely oil changes;

– periodic change of air filter;

– systematic diagnosis of boost pressure.

Turbocharged Direct Injection engines are quite difficult to service on their own, so it is always recommended to contact specialized car service centers.

To summarize

The diesel engine managed to rise to a whole new level, thanks to the development and solutions of engineers. The record is set for the fuel efficiency of TDI engines. The Audi 100 TDI accomplished 4,814.4 kilometers on one full tank of fuel.

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Average fuel consumption was 1.7 liters per 100 kilometers and the average speed was 60 km/h. The TDI engines, are leading the way compared to petrol engines not only in the city, but also in racing events. The Audi R10 TDI diesel wins regularly even on the toughest tracks.

With faultless selection and timely change of engine oil, with competent operation and of course using specialized service, the engine TDI will live a long carefree life. At observance of the simplest measures and conditions these engines will keep their performance for many thousands of kilometers.

TDI engine

The TDI engines are a range of diesel power units produced by the German car giant Volkswagen. Diesel engines, designated by the abbreviation TDI (Turbocharged Direct Injection) are turbocharged units equipped with a direct fuel injection system. These engines can be found in different diesel models of cars manufactured by WAG (Audi, Volkswagen, Skoda, etc.).

History of TDI engine

The diesel engine has always attracted various companies with its untapped potential. The main task for the engineers was to turn a noisy, slow-speed and low-speed unit into a motor that could be easily installed in passenger cars. The result was the creation of a powerful, economical and environmentally friendly diesel engine, which by its performance characteristics was as close as possible to the gasoline power unit.

A pioneer in this direction was Audi, which in the distant 1980 has installed a 1.6-liter diesel 54 hp atmobiles under the hood of its popular model Audi 80. Further refinement and development of technology has led to the fact that in 1989, Audi was the first in the world to adjust and put into mass production a compact, efficient and powerful turbodiesel engine, which received the now widely known designation TDI.

The first TDI was a five-cylinder diesel engine with a displacement of 2.5 liters and was equipped with a turbocharger with intercooler (a system for intercooling of pressurized air). Maximum power of this engine was 120 hp. The torque was 256 Nm at 2250 rpm.

Since its introduction to the market, this power unit has become quite popular, as it was a worthy alternative not only to diesel engines from other manufacturers, but was quite able to compete with gasoline engines. TDI from Audi provided excellent dynamics, while fuel consumption was significantly lower compared to other counterparts.

Features and benefits of the TDI engine

After Audi became part of WAG, the Volkswagen concern took the first positions in the list of diesel engine manufacturers. Innovative engineering solutions and proven production technologies have provided TDI engines with:

– low noise level during operation; – high torque figure; – low fuel consumption; – reduced exhaust emissions;

Today, the TDI diesel engine has a number of advantages compared to its counterparts, among which fuel efficiency and efficiency are singled out. One of the main advantages is deservedly considered a higher injection pressure compared to the performance of other systems. The TDI engines have an injection pressure of 2050 bar, compared to counterparts with an injection pressure of only 1350 bar. In the TDI the injector is combined with a pump for maximum control over the entire fuel injection process. Such a solution provides the TDI engine with high torque, as well as elastic operation of this diesel engine in different modes. Thanks to this fuel injection system the combustion process in the TDI engines is more uniform and “gentle”, i.e. with minimal shock loads. For this reason, the noise level during operation of the diesel has been significantly reduced, as well as the nitrogen oxide content in the exhaust gases. In other words, the TDI diesel engine is powerful, quiet, the least harmful to the environment and the most economical engine among diesel powertrains available on the market.

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Reliability of TDI diesels

Installing a turbocharger has allowed the diesel engine to develop more power, and the efficiency of the diesel has increased. As for the TDI engines, these engines are quite reliable if properly operated. The most strongly on the serviceability of these engines affects the quality of fuel and timely maintenance. With the proper care the engine itself can be even a “millionths” engine. The weak point of the TDI is the injectors and the turbocharger. The life of the injectors is directly dependent on the quality of the diesel fuel and the overall condition of the diesel TDI power system. The service life of the turbine may vary, the average life is 120-160 thousand km.

Fuel injection in TDI engines

In the early stages of the development of diesel engines, the pressure in the system, which implies the presence of an HPI in conjunction with simple mechanical injectors, was only 20-40 bar. Modern diesel engines have pressures at a minimum of 1,600 bar and higher. The trend toward higher fuel injection pressures is related to the fact that diesel engines are characterized by a very short time to mix. If the crankshaft rotates at 2,000 rpm, then only 3 to 4 milliseconds are allocated for mixing a portion of diesel fuel with air. Increasing the speed of the crankshaft further reduces 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 characterized by low efficiency. The result is a higher toxicity of the diesel exhaust and lower efficiency.

Earlier for the fuel injection on diesel was responsible for the fuel injection, which works in tandem with mechanical injectors, today diesel engines are equipped with Common Rail systems. Since the combustion process in the diesel is an explosion from the contact of a portion of fuel with heated air during the compression stroke, the injection time is very limited.

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The fuel injection system in modern diesel engines simply creates pressure in the common line, and piezo injectors (piezoelectric injectors) TDI are capable of injecting a well-defined amount of diesel fuel into the diesel engine cylinders in a very short period of time (less than 0.2 milliseconds) on command of the ECU. Also in some designs of diesel engine power systems you can find the so-called pump-injectors. This means that each injector injector is equipped with its own high-pressure pump. It turns out that the development of diesel technology today is reduced to increasing the injection pressure and maximum efficiency of the turbocharging system. Thus it is possible to solve the main tasks: to increase power and reduce the toxicity of exhaust gases.

TDI turbocharging: variable geometry turbine

Not only does the performance of a TDI turbocharger to a large extent determine the car’s dynamics, but also its economy and environmental compatibility. The correct supercharging has to be realised within the widest possible range. For this reason, TDI engines are equipped with variable turbine geometry turbochargers. The leading turbine manufacturers in the world use the following names:

– VGT turbine (from Variable Geometry Turbocharger, which means variable geometry turbocharger). It is produced by BorgWarner. – VNT (Variable Nozzle Turbine) turbocharger for diesel engines. This name is used by Garrett.

A variable geometry turbocharger differs from a conventional turbine in that it has the ability to adjust both the direction and magnitude of the exhaust gas flow. This feature allows the most suitable turbine speed to be achieved for a specific engine operating mode. The performance of the compressor is then greatly improved. The VNT turbine, for example, is based on special guide vanes. In addition, there is a control mechanism, as well as noted the presence of a vacuum drive. These turbine blades make a turn at a desired angle around its axis, thereby are able to change the speed and direction of the exhaust flow. This is done by changing the size of the channel cross-section. The control mechanism is responsible for turning the blades. Structurally, the mechanism has a ring and a lever. The lever is actuated by a vacuum actuator, which controls the operation of the mechanism through a special link. The vacuum actuator is controlled by a separate valve that limits the boost pressure. The valve is an integral part of the electronic control system of the internal combustion engine and is triggered depending on the boost pressure value. This is measured by separate sensors:

– temperature sensor, which measures the temperature of the air at the intake; – supercharging pressure sensor;

In other words, the turbocharger on the TDI works so that the charge air pressure is always optimal at different engine speeds. In fact, the turbine is metering the energy of the exhaust gas flow.

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1. As you know, at low engine speeds the exhaust flow rate (energy) is quite low. In this mode, the guide vanes are usually closed, thus achieving a minimum cross-section in the channel. As a result of passing through such a channel, even a small amount of gas will spin the turbine more efficiently, causing the compressor wheel to spin noticeably faster. As a result, the turbocharger provides more output at low rpm.

2. If the driver sharply presses the gas, then a conventional turbine has the effect of the so-called “turbo lag”. Turbine sluggishness should be understood as a delayed response to the accelerator pedal, i.e. not an instantaneous increase in power, but a pickup after a short pause. This peculiarity is caused by the inertia of the turbocharger system, as a result of which the gas flow is insufficient at the moment of a sharp increase in crankshaft rpm. In variable geometry turbines, the guide vanes turn with a delay, so that the desired boost pressure is maintained and the turbo lag is virtually eliminated.

3. At high and near maximum engine speeds, the exhaust gases have maximum energy. To prevent overpressurization, the blades in variable geometry turbines are pivoted so that the forceful flow of gases travels in a wide duct with the largest cross-sectional area.

The relatively short service life of the turbocharger is due to the fact that TDIs are exclusively equipped with variable geometry turbines. During engine operation, the turbocharger is spun up to 200,000 rpm and is constantly interacting with the flow of exhaust gases heated to 1,000 degrees Celsius. Such temperature and mechanical stresses, as well as the individual design features of these turbines relatively quickly lead to the need to repair or replace the turbocharger.

To recap

Thanks to the developments and engineering solutions of Audi, the diesel engine managed to rise to a new stage of its evolution. The efficiency of TDI engines is a kind of a record. The Audi 100 TDI model covered 4,814.4 kilometers on just one full tank of fuel. The average speed was about 60 kilometers per hour, with an average fuel consumption of just over 1.7 liters per 100 kilometers. Also TDI engines closely to the gasoline units, not only on the streets, but also on the race tracks. An excellent example can be considered a diesel Audi R10 TDI, which regularly wins victories on the most difficult tracks. In conclusion we would like to add that the key to long life of both TDI engine and any other engine is correct choice and timely replacement of engine oil, correct exploitation and driving on high-quality fuel as well as professional service. Observance of these conditions will allow the engine and other related systems to keep working properly for more than one hundred thousand kilometers.

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