| abstract |
A compression ignition internal combustion engine for a heavy-duty diesel vehicle comprising an exhaust system comprising a composite oxidation catalyst (12, 42) upstream of a soot filter substrate (44, 50), the composite oxidation catalyst comprising: a substrate (5) having a length L and extending axially between an inlet end (I) and an outlet end (O) and two catalyst washcoat zones (1, 2), wherein the first catalyst washcoat zone (1) having a length LI wherein L1<L, is defined at one end by the inlet end (I) and at a second end by a first end (15) of the second catalyst washcoat zone (2) having a length L2, wherein L2<L, wherein the second catalyst washcoat zone (2) is defined at a second end thereof by the outlet end (O), and wherein the first catalyst washcoat zone (1) comprises a first refractory metal oxide support material and supported thereon both platinum and palladium at a Pt/Pd weight ratio of <1; and the second catalyst washcoat zone (2) comprises a second refractory metal oxide support material and one or more platinum group metal components supported thereon; and a washcoat overlayer (G) extending axially from the inlet end (I) comprising a particulate metal oxide having a loading of >48.8 g/l, wherein a total platinum group metal loading in the first catalyst washcoat zone (1) is greater than a total platinum group metal loading in the second catalyst washcoat zone (2) and wherein the first catalyst washcoat zone (1) comprises one or more alkaline earth metal components supported on the first refractory metal oxide support material. |