ilPistone.com: Toyota D-CAT ? a breakthrough in clean diesel

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1. DPNR catalytic converter

DPNR (Diesel Particulate NOx Reduction system) represents another ?world first? for Toyota in the development of advanced automotive technologies. It can simultaneously and continuously reduce both particulate matter (PMs) and nitrogen oxides (NOx) in diesel exhaust gas, greatly reducing exhaust emissions Unlike other particle filters, the DPNR catalyst is maintenance free, and does not require the use of any fuel additive.

2. Second generation common-rail system

The current high pressure, common-rail D-4D diesel engine, was pioneered by Toyota back in 1995 and Toyota is now introducing the second-generation system. It has the ability to produce an injection pressure of 1800 bar, irrespective of engine speed - the highest value among second generation common rail systems. Moreover, the interval between end of pre-injection and start of the main injection in this system is the shortest available on any engine today: 0.4 milliseconds.

3. Multiple fuel injection

Toyota D-CAT can use up to five injections during each combustion stroke to control the burn rate. For example, a pilot injection occurs a fraction of a second before the main injection in order to reduce the generation of NOx, noise and vibration, whilst a post-injection is initiated a split second after the main injection to help re-burn particulate residues.

4. Exhaust port injection

The effective operation of the DPNR catalyst relies on the engine management system being able to vary fuel/air ratios in the exhaust gases. For this purpose a fifth injection nozzle has been added and placed in the exhaust port. At the critical moment, fuel is injected downstream of the exhaust manifold in order to create better operating conditions in the DPNR catalyst. This ?rich spike? allows the DPNR catalyst to release and reduce the stored NOx. The exhaust port injection is also used to control sulphur contamination of the catalyst. Sulphur in fuel is one of the problems for the DPNR catalyst because it starts building up in its interior in the form of Sulphur Oxide (SOx). When the stored SOx reaches a certain amount, Exhaust Port Injection is used to increase the catalyst?s bed temperature to values above 600°C to remove the Sulphur Oxide.

5. Large capacity Exhaust Gas Re-circulation

Toyota D-CAT uses a high-response exhaust gas re-circulation (EGR) valve and a large capacity, high-efficiency EGR cooler. The purpose is to cool down the exhaust gases that are re-used and injected again into the combustion chamber. The cooler the exhaust gases are, the greater is their density, allowing a larger mass of EGR gases to be fed into the combustion chamber each time.

6. Low Temperature Combustion

Low temperature combustion (LTC) is used to avoid the formation of smoke, to decrease the air/fuel ratio, and to reduce NOx emissions. In addition LTC helps maintain the optimum catalyst bed temperature, allowing the DPNR catalytic converter to work most efficiently.

7. Uniform Bulky Combustion System (UNIBUS)

This technology enables rapid combustion at low temperatures by dividing fuel injection into different stages, first creating a preliminary air-fuel mixture and then delaying the injection timing for the remaining fuel to be burned.

8. Sophisticated sensors

The operation of Toyota D-CAT relies on a constant stream of accurate data being supplied to the engine management system. This data is provided by sensors, which monitor air/ fuel ratio, gas temperature, and pressure.