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Design Features of DOC
The catalyst volume is typically equal to the engine swept volume. A DOC although, may appear similar to the oxidation catalysts used for gasoline vehicles but the following differences in the design features are incorporated;
- Ceramic monoliths of a lower cell density having 200 to 400 cpsi are normally used to keep it free of clogging by soot.
- As alumina is more readily gets converted to Al2 (SO4)3, different washcoat materials like titanium oxide, silicon dioxide, or mixtures of 50 % CeO2 and 50% γ-Al2O3 are used.
- Mainly platinum is used in DOCs with metal loading varying from 0.5 to 2.0 g/l.
- The diesel oxidation catalyst is placed downstream of the turbocharger and experiences much lower temperatures (100-550º C) compared to the gasoline engine catalyst (300-1100º C). The thermal deactivation of DOC is not a major problem.
- Diesel engines burn more lubricating oil in the cylinder and the engine oils have a higher metal additive content than the gasoline engines. The pore structure of washcoat must be formed to tolerate larger amounts of these inorganic oxides
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