Our Turbocharged Direct Injection (TDI) diesel engines are responsive and fun to drive, as well as being very efficient. They offer more power, with great fuel economy, which all helps to lower emissions.
Why drive a TDI?
- You'll enjoy the savings. Economical fuel consumption, long service and maintenance intervals, plus low emissions, all combine to keep costs low.
- You'll love the drive. Our turbodiesel engines offer exceptional torque even at low revs. This results in tremendous fun at the wheel, thanks to their effortless acceleration and sparkling performance.
- You'll feel the power. High levels of pulling power over a wide rev range offer real driving pleasure.
What do we mean by TDI?
TDI identifies all our advanced diesel engines using direct injection and a turbocharger. TDI engines are economical and smooth with high levels of torque (pulling power) and good energy efficiency.
Fuel needs oxygen to burn and the engine has to be supplied with huge quantities of air to be effective. You can solve this problem with a bigger engine - or you can solve it with a turbocharger - as in the TDI. Driven by the exhaust gases, it squeezes air more tightly into the cylinders.
The air is then cooled (cool air takes up less space than hot air) and diesel is injected directly into the cylinders at very high pressure through a nozzle. It's this intensive mixing of highly atomised fuel with the compressed air that leads to better, more efficient combustion.
Your driving experience is quiet and refined because effective sound insulation keeps noise to a minimum, while hydraulic engine mounts ensure smooth, low-vibration running.
The great advantage of TDI engines is that they are very powerful, even at low revs, and economical across the entire speed range. This efficiency also means that you save on fuel costs and emit less CO2, so helping to minimise your impact on the environment.
The turbocharger. To boost power output and torque, we fit our TDI engines with exhaust turbochargers featuring variable turbine geometry. They compress the air required for combustion, letting the engine draw in more air while its displacement and revs stay the same.
A turbocharger is powered by the energy in the exhaust gas. It has two connected turbines. The turbine wheel in the exhaust stream drives the intake compressor, which sucks in air through the intake system. The compressed air is cooled by a charge air cooler before entering the combustion chamber. Because cool air is denser than hot air, more oxygen can be fed into the cylinder boosting the efficiency of the combustion process.
Overcoming turbo lag. The main disadvantage of a turbocharger is that it needs a certain gas pressure to work, only available when engine revs are high enough. To avoid 'turbo lag' - a delay in available power - the turbocharger needs to be able to control the exhaust pressure at low engine revs.
A variable turbine geometry (VTG) turbocharger does this with a system of mechanical guide vanes. These vanes move to adjust the cross-section area to maximise the air flow into the exhaust turbine. Thus at lower speeds, a higher flow can be maintained, increasing the pressure to the compressor and therefore increasing power output.
Our injection systems. We are one of the leaders in developing advanced efficient diesel engines with lower emissions. Our innovative engines are progressively meeting the new EU 5 standard, ahead of legislation. Our range of three to ten-cylinder turbodiesel engines are based on unit injector systems, and common rail injection.
How injection works. The pressure at which the diesel is injected into the cylinder is the key factor in diesel direct injection. The fuel has to mix swiftly with the compressed air in the cylinder. The higher the pressure, the more finely the diesel is atomised for an intensive mixing of the fuel and air particles. This, in turn, leads to a better and more efficient combustion process. The energy from the fuel is used more effectively and emissions are reduced.
We use 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 and a main injection. Pilot injection achieves smooth combustion, ensuring that the extremely high pressures necessary for combustion to take place are reached more gradually. This significantly reduces combustion noise and cuts emissions.
Common rail - third-generation diesel direct injection. Common rail is the latest diesel engine technology and is used in all ŠKODA vehicles already. The common rail system stores the injection pressure in a high-pressure fuel reservoir referred to as the ‘common rail’ as it supplies all the injectors. In this system the generation of pressure and the fuel injection processes are separate.
Lines connect all the cylinder injectors to the common rail in parallel, ensuring they all have an uninterrupted supply of constant pressure. The injection quantity and timing are controlled using solenoid valves.
The advantage of common rail is that fuel can be delivered at higher pressure, giving better mixing with air for a more efficient and cleaner combustion. This gives you higher performance combined with improved fuel consumption.
The ever-higher injection pressures that make diesel engines cleaner and more efficient than before place big demands on the common rail system. Our latest generation of diesel engines reach injection pressures as high as 1,800 bar. For this reason we make the rail ourselves, and we are the first car maker to do so.
The diesel particulate filter. Legislation is continually driving car manufacturers to produce cleaner and more environmentally friendly vehicles. Our advanced diesel engines meet this challenge and are cleaner than ever before. One important factor is their diesel particulate filters (DPF), which are very effective in cutting particulate emissions, trapping even the finest soot particles that are produced as the engine burns diesel fuel.
The latest generation of filters operate without additives. This makes them maintenance-free for an exceptionally long time: an initial inspection is usually carried out only after 150,000 km. The filter's lifespan is dependent on factors such as fuel quality, driving style, use and oil consumption.