D-CAT ( D iesel- C lean A dvanced T echnology) is the marketing name of an emission control technology from Toyota , the application in Toyota and Lexus - diesel engines place. The system lowers soot particle emissions to a level comparable to particle filters, does not require fuel additives like many other systems and is declared maintenance-free.
In order to meet the legal environmental requirements, exhaust gases are post-treated using thermochemical processes. However, such procedures have been standard for diesel engines since the early 1990s. In order to stand out from the competition, which has long been established in this area, the after-treated exhaust gases in the D-CAT models from ( Avensis , Corolla Verso, Auris , RAV-4 and Lexus IS) are significantly below the Euro 4 emissions limit values - by 80 % for particle emissions and 50% for nitrogen oxides NO x . The process in D-CAT 2.2 makes it one of the cleanest diesel engines in the world.
For example, according to the Certificate of Conformity , the Avensis D-CAT is characterized by NO x emissions of 110 mg / km (Euro 4/5/6 value: 250/180/80 mg / km) and a particle Emissions of 2 mg / km (Euro 4/5/6 value: 25/5/5 mg / km).
The engine can generate an output of 130 kW (177 hp) and a maximum torque of 400 Nm .
In contrast to soot particle filters already on the market , the system reduces both soot particles and nitrogen oxides. Like other systems, it is maintenance-free and does not require any additives . The effect is achieved through internal engine measures and the downstream installation of a special storage catalytic converter.
The core of the D-CAT system is the cleaning system for diesel soot particles and the reduction of nitrogen oxides as well as the second generation of the high-pressure common rail diesel injection system. There are also other control systems and technologies.
Storage catalytic converter
The cleaning system for diesel soot and the reduction of nitrogen oxides of the untreated exhaust gases ( D iesel P articulate N Ox R eduction, DPNR) operates at the same time, thus reducing pollution emissions from diesel engines. Like many other particle filters, the DPNR catalytic converter is maintenance-free, but is twice as expensive to manufacture due to the combined operation.
Second generation common rail system
With the D-4D high-pressure common-rail diesel engine, Toyota was among the pioneers in this field in 1995, along with a number of other manufacturers. The D-4D system belongs to the latest generation. The injection system works with piezo technology. The system is similar to that of VDO Automotive and Bosch , but is manufactured by Denso and can generate an injection pressure of 1,800 bar regardless of the engine speed . This system offers a short time interval of 0.4 milliseconds between the end of the pilot injection and the start of the main injection . With the introduction of the third generation of the Toyota Avensis (Germany launch: January 24, 2009), the maximum injection pressure increases to 2,000 bar .
With the D-CAT system, up to five injections per work cycle are possible to control the combustion speed. An injection shortly before the main injection reduces the nitrogen content as well as the noise level and possible vibrations . Particle residues are burned by an injection shortly after the main injection.
Injection into the exhaust port
The DPNR catalyst works by varying the air-fuel ratio in the exhaust gases through the engine control system. For this purpose, a fifth injection nozzle is located in the exhaust port to improve the operating conditions for the DPNR catalytic converter. This brief enrichment of the fuel-air mixture enables the DPNR catalytic converter to trigger and reduce the stored nitrogen oxides. At the same time, the injection into the exhaust port prevents the catalytic converter from being contaminated with sulfur , which can otherwise accumulate inside with nitrogen oxides (NO x ). If the stored nitrogen oxides reach a certain value, the temperature of the catalyst bed is increased to over 600 ° C by the injection into the outlet channel in order to thermally decompose the nitrogen oxides.
Exhaust gas recirculation
The D-CAT system works with an exhaust gas recirculation valve (EGR valve / for Toyota EGR valve) and an exhaust gas recirculation cooler.
Depending on the load conditions, a different proportion of the exhaust gas flows through the EGR valve and the EGR cooler back into the intake tract. This system can lower the combustion temperature, which means that significantly fewer nitrogen oxides are produced. The cooling effect is based on the fact that the recirculated exhaust gas no longer contains oxygen and thus does not take part in the combustion. Since part of this effect would be compensated by the high exhaust gas temperature, an exhaust gas recirculation cooler is used in order to keep this compensation effect as low as possible.
A low combustion temperature directly reduces the formation of nitrogen oxides.
Gradual fuel injection (Uniform Bulky Combustion System)
This technology enables largely silent combustion (elimination of nailing ) at low temperatures. This is done by dividing the fuel injection into stages. This initially creates a preliminary mixture with a high excess of air, while the injection time is delayed for the combustion of the remaining fuel.
Toyota's D-CAT system is based on the continuous supply of data to the engine control system. The data is provided by sensors that detect changes in the air-fuel ratio, exhaust gas temperature and pressure.
Although the system is considered to be very reliable, defects can occur which are difficult to localize due to the complicated structure. Another disadvantage is the higher fuel consumption (0.2 to 0.45 liters per 100 km).
As can be read in the long-distance test (2006) by AutoBild magazine, the complicated Toyota D-CAT often has the unpleasant effect that white or blue clouds of smoke billow out of the exhaust, so that other road users suspect a vehicle fire. These clouds of smoke occur when cleaning the DPNR storage catalytic converter. In the case of newer D-Cat models (from around 2007) the system has been revised so that this effect should no longer occur. However, if white smoke does occur in D-CAT models, be it in models before 2007 or after 2007, the deficiency can be remedied by the relevant Toyota dealer by updating the programs and control parameters of the engine control unit .
- Jürgen Pander: Toyota Avensis D-CAT: Clean performance. In: Spiegel Online . July 1, 2005 .
- Practical test: Toyota RAV4 2.2 D-CAT - fun mobile in off-road optics. In: FTD.de . September 27, 2007, archived from the original on February 11, 2013 .
- Dirk Branke, Manfred Klangwald: This is where Toyota goes to the laundry. In: Auto Bild . June 22, 2006 (long-term test Toyota Avensis D-CAT).