Volkswagen Cars

                  The TDI engine uses direct injection, where a fuel injector sprays atomised fuel directly into the main combustion chamber of each  cylinder, rather than the pre-combustion chamber prevalent in older diesels which used indirect injection.
                  The engine also uses forced induction by way of a turbocharger to increase the amount of air which is able to enter the engine cylinders and most TDI engines also feature an intercooler to lower the temperature (and therefore increase the density) of the 'charged', or compressed air from the turbo, thereby increasing the amount of fuel that can be injected and combusted. These, in combination, allow for greater engine efficiency, and therefore greater  power  outputs (from a more complete combustion process compared to indirect injection), while also decreasing emissions and providing more torque than its non-turbo and non-direct injection petrol engined counterpart.

                  Similar technology has been used by other automotive companies, but "TDI" specifically refers to these Volkswagen Group engines. Naturally aspirated direct-injection diesel engines (those without a turbocharger) made by Volkswagen Group use the Suction Diesel Injection (SDI) label.

                The reduced material volume of the direct injection diesel engine reduces heat losses, and thereby increases engine efficiency, at the expense of slightly increased combustion noise. A direct injection engine is also easier to start when cold, due to more efficient placing and usage of glowplugs.

                 Direct injection turbodiesel engines are frequent winners of various prizes in the International Engine of the Year Awards. In 1999 in particular, six out of twelve categories were won by direct injection engines: three were Volkswagen, two were BMW, and one Audi.

                The TDI engine is a turbocharged and intercooled diesel engine with "direct injection" - that is, the fuel injector nozzle sprays directly into the main combustion chamber, rather than into a separate prechamber as was done with previous automotive diesel engines.  This is similar to the way that bigger diesel engines have worked for many years, but with countless improvements to refine the process and make it suitable for a passenger car engine. The result is an engine which is so refined in comparison to older passenger car diesel engines, that there really is no comparison.

* TDI " State Of The Art Diesel Technology "
                  The term TDI is often seen as a synonym for a diesel engine offering bountiful torque delivery, outstanding power output and low fuel consumption figures. From a technical standpoint, however, Volkswagen uses the name TDI to designate all of its highly sophisticated diesel engines featuring direct injection and turbocharging.

                 The fundamental characteristics shared by all TDI engines are high-pressure fuel injection and variable turbine geometry for excellent cylinder charging and an efficient combustion process. At the same time, Volkswagen is increasingly deploying innovative common-rail technology. The fundamental characteristics shared by all TDI engines are high-pressure fuel injection and variable turbine geometry for excellent cylinder charging and an efficient combustion process. At the same time, Volkswagen is increasingly deploying innovative common-rail technology.

               Diesel direct injection currently offers a higher degree of engine efficiency – up to 45 percent – than any other technology. Consequently, a large part of the energy stored in the fuel is transformed into kinetic energy and, as a result, engine power. This is dependent on extremely efficient combustion of the fuel. The geometry of the combustion chamber and the atomisation of the fuel play a decisive role here.

* Advantages at a glance :

(1) All TDI engines stand out for their excellent cost efficiency. Economical fuel consumption, long service and maintenance intervals, as well as low emissions combine to keep costs low.

(2) Turbodiesel engines from Volkswagen offer refined power delivery from low engine speeds all the way up the rev scale. This results in tremendous fun at the wheel, thanks to the excellent acceleration and above-average performance figures.

(3) High torque levels over a wide rev range and a high maximum output combined with minimal fuel consumption generate a sense of refined driving pleasure.

* COMBINED RAIL – THIRD GENERATION DISEL DIRECT INJECTION :

             In the common rail system, the components for pressure generation and fuel injection are separate from one another. An independent pump maintains a constant fuel pressure at all times. This pressure is stored in a single distribution rail, the common rail, which is so called because it is shared by all the cylinder heads. The injectors which feed the fuel to the engine’s cylinders are connected to the common rail by short feed lines in a parallel arrangement.

* Technology :

              The ever higher injection pressures being generated for boosting the efficiency of diesel engines and lowering their emission levels place acute demands on the common rail system. For this reason, Volkswagen manufactures the rail itself, the first automotive manufacturer to do so. Our latest generation of diesel engines attains injection pressures as high as 1,800 bar. The resulting operating requirements mean that surface finish, fatigue strength, seal tightness and cleanliness must all be of an exceptionally high standard. Consequently, every component must first come through ten million load cycles at alternating pressures without developing a single flaw.

* Common Rail in the New Golf :

             In the new Golf, common rail technology makes a significant contribution to reducing noise levels too: while the injection pressure of up to 1,800 bar and specially designed eight-hole injector nozzles guarantee extremely fine atomisation of the diesel fuel, latest-generation piezoelectric inline injectors are responsible for controlling the nozzles. The piezoelectric technology enables more flexible fuel injections with smaller quantities of fuel that can be metered more precisely. The advantages of this are very quiet and pleasurably smooth engine running, remarkably spontaneous response, as well as particularly low fuel consumption and emissions figures.

* TURBOCHARGER :

            To further increase power output and torque, Volkswagen equips its TDI engines with exhaust turbochargers featuring variable turbine geometry. They compress the air required for combustion, thus enabling the engine to draw in a greater quantity of air while its displacement and revs remain the same. The engine power output is consequently higher.

               A turbocharger is powered by the energy contained in the exhaust gas. It consists of two turbines. The turbine wheel is located in the exhaust stream and drives a compressor wheel connected by a shaft. This is where the air is compressed. The air heated by the compression process is usually cooled by means of a charge air cooler, and then fed to the combustion chamber. Cool air takes up less space than hot air. Charge air cooling thus allows more oxygen for combustion to enter the combustion chamber.

               The main disadvantage of a turbocharger is that it needs a certain gas pressure in order to work, but this pressure is only available when the engine revs are sufficiently high. This is the origin of the expression “turbo lag”. To achieve optimum efficiency at lower engine revs, too, the turbocharger needs a means of controlling the exhaust pressure.
               In a VTG turbocharger (VTG = variable turbine geometry), a system of mechanical guide vanes alters the cross-section of the exhaust flow inlet on the powertrain side. If the gas pressure declines at slower engine revs, the control system adjusts the guide vanes to a position that narrows the cross-section, thus accelerating the exhaust flow and increasing the pressure.As the exhaust gas pressure rises with increasing engine revs, the control system makes the inlet cross-section larger by altering the position of the guide vanes.

              Turbochargers with variable turbine geometry are especially effective at increasing power in the part-load range – “turbo lag” is no longer a problem. They result in an engine with a higher power output and improved responsiveness. Moreover, they can have a positive impact on emissions.


* DIESEL PARTICULATE FILTER :

             Modern diesel engines emit substantially less particulate matter than older engines. Diesel particulate filters are very effective in minimising particulate emissions. The filters are capable of trapping even the finest soot particles produced by the combustion of diesel fuel.

          The latest generation of diesel particulate filters at Volkswagen operates without additives and is therefore completely maintenance-free for a long time. An initial inspection is usually carried out after 150,000 km. The filter’s lifespan is dependent on factors such as fuel quality, driving style, use and oil consumption.

                   The coated filter consists of a porous ceramic component with a coating containing precious metal. As the exhaust gas passes through the filter material, particulate matter is detained while the gases flow on unhindered. To ensure the filter’s long-term permeability, it needs to be cleaned of the trapped particles.

                     To clean the filter, the trapped particulate matter is periodically removed. In passive regeneration, the soot is slowly and gently converted to CO2. This process requires an exhaust temperature of over 630 °C and takes place without the need for special measures, e.g. on the motorway. Only when the vehicle is driven for long periods at low load, e.g. in urban traffic, is the filter actively cleaned.

         This is achieved by raising the exhaust temperature through alterations to specific engine parameters. The detained soot particles are burnt off every 1,000 to 1,200 km. The positioning of the filter close to the engine means that the exhaust gas temperature is sufficient to convert the soot particles while the engine is running. This results in low component stress and good filter efficiency.

* Diesel High-Pressure Injection Systems – more Power, Less fuel :

                For many years now, Volkswagen has been one of the leading makers of advanced diesel engines. Volkswagen’s innovative unit injector engines, for instance, met the limits of the EURO-4 emissions standard long before its introduction. This demonstrated the leading position of Volkswagen engine technology in the development of efficient and eco-friendly diesel engines. Today, Volkswagen offers a broad range of three to ten-cylinder turbodiesels with reliable and economical diesel engineering based on unit injector systems or common rail injection.

                  The pressure at which the diesel is injected into the cylinder is the key factor in diesel direct injection. The diesel fuel has only an extremely short time in which to mix with the highly compressed air in the cylinder. The higher the injection pressure, the more finely the diesel is atomised in the engine combustion chamber. This ensures an intensive mixing of the fuel and air particles. A higher mixing intensity leads to better and more efficient combustion. The energy stored in the fuel is then used more effectively and, in addition, pollutant emissions are reduced.

                To further optimise the combustion processes, Volkswagen implements various injection stages within one power stroke – referred to as multiple injection. Depending on the engine design, revs and load, modern diesel engines use a pilot or double pilot injection, a main injection and a post injection. Pilot injection has proved the ideal solution for achieving smooth combustion by ensuring that the extremely high pressures that occur in the combustion chamber are reached not instantly, but more gradually. This considerably reduces combustion noises and cuts nitrogen oxide emissions. The objective of post injection is to further optimise the combustion process and thus achieve even lower exhaust emissions.

* COMMON RAIL :

               In the common rail system, the components for pressure generation and fuel injection are separate from one another. An independent pump maintains a constant fuel pressure at all times. This pressure is stored in a single distribution rail, the common rail, which is so called because it is shared by all the cylinder heads. The injectors which feed the fuel to the engine’s cylinders are connected to the common rail by short feed lines in a parallel arrangement.

              The ever higher injection pressures being generated for boosting the efficiency of diesel engines and lowering their emission levels place acute demands on the common rail system. For this reason, Volkswagen manufactures the rail itself, the first automotive manufacturer to do so. Our latest generation of diesel engines attain injection pressures as high as 1,800 bar. The resulting operating requirements mean that surface finish, fatigue strength, seal tightness and cleanliness must all be of an exceptionally high standard. Consequently, every component must first come through ten million load cycles at alternating pressure without developing a single flaw.

                 The classic pump-injector system will be replaced by modern common rail technology in the future.

* PIEZO INJECTORS :

           To achieve maximum precision in controlling the injection process and thus substantially reduce fuel consumption and emissions, Volkswagen uses piezo inline injectors instead of solenoid valves. For instance, in the 2.0 TDI® PD producing 125 kW and in the 3.0 V6 TDI® the injectors are actuated by means of piezo crystals. The injectors contain several piezo crystals connected in series (inline), in order to achieve the required needle or valve lift. Piezo crystals have the property that the structure of their crystal lattice changes when an electric current is applied to them, causing the crystal to expand or contract.

                   Piezo elements are significantly lighter and respond twice as fast as conventional solenoid valves. This enables the injector valve to switch five times more quickly and therefore meter the fuel and control the injection curve far more precisely. This represents an important factor in achieving efficient and smooth combustion with low emissions. To express its capabilities compared with previous systems in figures, diesel injection with piezo injectors offers the potential, depending on the design concept, to reduce fuel consumption by roughly three percent, to lower pollutant emissions by up to 20 percent, to increase the achievable engine power by up to five percent and to approximately halve engine noise with a reduction of up to three decibels.