Diesel Cat

 

Diesel Cat

 

Diesel Cat

CURRENT PRICE$5.00-$588/each

 

30 DAY AVG. PRICE$276.77/each

DESCRIPTION / USES

Taken from a diesel engine.

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Diesel catalytic converters come from diesel engines. A lot of times the diesel engine cats are not worth too much money due to the lack of precious metals inside like platinum, palladium, and rhodium. However, there are some diesel cats that are worth a decent amount of money. You can send pictures of your diesel cats to our team for an accurate quote.

Since the diesel engine is more durable than its gasoline counterpart, the required life expectancy for diesel catalytic converters is also longer than that for gasoline converters. For example, since 2004 the US EPA durability requirement for emission control systems on heavy-duty diesel engines is 10 years/22,000 hours/435,000 miles (700,000 km), whichever occurs first (previously, the requirements were 8 years/290,000 miles or 467,000 km).

In situations where thermal losses from the converter are important, they have to be modeled during the converter design. Double walled designs with either air gaps or ceramic fiber insulation are commonly used on gasoline converters in the close-coupled location, which are optimized for cold start hydrocarbon performance. Since diesel cold start emissions are much less critical, such designs have not been used for diesel converters. However, due to the low temperature of diesel exhaust gases, diesel converters should be placed close to the exhaust manifold or exhaust pipe insulation should be applied to assure satisfactory catalyst performance. The low temperature performance, including cold start, is becoming increasingly important for diesel catalytic converters, especially in light-duty applications.

The geometry of converter headers, especially that of the inlet header, can influence the exhaust gas flow distribution in the catalyst. It is believed that flow maldistribution negatively affects catalyst performance and/or durability. That opinion, although not supported by convincing experimental data, became a widely accepted consensus. Even if the emission performance is not improved, a skillful design of the headers can certainly decrease the total catalytic converter pressure loss.

Catalyst canning technologies have evolved since the 1990s, driven by the demands of California LEV, ULEV and SULEV gasoline applications. Still more development will be needed to satisfy the demands of future exhaust systems, especially for diesel engines. The major factors responsible for the evolution in catalytic converter technology can be summarized as follows:

  • In gasoline applications, the converter was either moved to a close-coupled location, or a second close-coupled pre-converter was introduced in addition to the underfloor converter. The close-coupled converter, installed very close to the exhaust port of the engine, is exposed to high temperatures, high thermal shock conditions, and increased vibration, thus calling for more robust canning.
  • Ultra-thin wall ceramic substrates for gasoline engines have wall thickness on the order of 0.002-0.003″ (0.050-0.075 mm). Example commercial configurations introduced in the late 1990s include 600/3 and 900/2 substrates. These parts are weaker than the older, thicker wall substrates (e.g., 400/6.5, of 0.0065″ or 0.17 mm wall thickness). New materials and/or packaging methods were necessary to accommodate these parts.
  • Widespread use of catalytic converters on diesel vehicles, such as on Euro 3/4 cars, created specific challenges related to the low temperature operation.
  • Exhaust systems on heavy-duty engines, especially those incorporating diesel particulate filters (DPF), require very robust packaging. While monolithic DPF substrates are packaged using essentially the same methods as catalytic converters, they are much heavier and larger, thus creating new challenges.

Diesel Catalysts

The first thing to say about diesel engines is that they always run ‘lean’.

One outcome of this is that the catalytic converter can only operate in a ‘two-way’ mode which means that it can oxidise carbon monoxide and hydrocarbons but will not be able to reduce Nox.

For this reason, a catalytic converter used on a diesel engine is often known as a ‘diesel oxidation catalytic converter’.

Another important characteristic of diesel engines is that the exhaust gas is cooler than that of spark-ignition engines, in some cases falling to a temperature of barely 100 C at idle.

Since catalytic reactions are temperature dependant, it is a good idea to find out the exhaust gas temperature for a particular application at an early stage.

Coatings on diesel catalytic converters can be varied to give ‘light-off’ at different temperatures, as illustrated on the following graph:

graph-diesel-oxidation

Diesel Catalysts

Users and manufacturers of diesel engines are often keen to reduce particulate emissions, and although catalytic converters are not designed for this purpose, they do in fact have a small beneficial impact for the following reason.

Diesel particulate matter largely comprises carbon (soot) but around the outside of the carbon particles there is a layer of hydrocarbons which add to the mass of particulate matter. Since a diesel oxidation catalytic converter can oxidise hydrocarbons, it can reduce diesel particulate matter to a certain extent, but usually only 10-20%.

Achieving greater reductions than this will necessitate reducing the carbon component and this requires the fitment of a filter.

As described above, the main benefits of a diesel oxidation catalytic converter are its ability to oxidise toxic carbon monoxide and hydrocarbons into non-toxic carbon dioxide and water. Unfortunately they also tend to oxidise the slightly toxic nitrogen oxide into rather more toxic nitrogen dioxide, especially at higher temperatures.

The more active a catalyst is at achieving the beneficial reactions, the more it will produce this undesirable side effect. A common approach to this problem is to reduce nitrogen oxide emissions at source through a technology such as exhaust gas recirculation, but if this is not practicable then it will be necessary to find the coating which gives the best trade off for a given application.

Another consideration when specifying catalytic converters for diesel engines is the sulphur content of the fuel.

Sulphur disagrees with catalytic converters for two reasons – firstly the catalytic converter will oxidise it into a solid which adds to the diesel particulate matter, and secondly the sulphur will gradually deactivate the catalytic coating.

As catalytic converters have become ubiquitous on road vehicles, the sulphur content of forecourt diesel has been progressively reduced. In order to allow exhaust gas after treatment technology to be fitted to off-highway engines, the sulphur content of off-highway fuels such as gas oil or red diesel has also been cut in markets such as the European Union and USA.

Outside these regions, or if there is any doubt, it is essential to check that the sulphur content of fuel used in conjunction with catalytic converters is no more than 50 parts per million.