HONDA Insight - Manual (Page 89)

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The insight is designed to operate at a very lean air fuel ratio during light throttle cruise conditions. The
mixture can be as lean as 22:1 if conditions allow. This provides very good fuel economy, and low HC and
CO emissions. However, the lean mixture also causes a rise in combustion temperature, and high NOx
production is the result.
In order to prevent high NOx tailpipe emissions during lean burn operation, the Insight uses a dual
catalyst system that includes an extra NOx storage/NOx reduction catalyst.
The 3-way catalyst is closely coupled to the exhaust manifold to minimize heat-up time, thus reducing
emissions after a cold start.
The lean NOx catalyst is in the conventional location, underneath the car.
Lean NOx Catalyst Functioning
The lean NOx catalytic converter is
comprised of a ceramic A1203 substrate, a
platinum (Pt) catalyzing surface, and a titanium-
sodium (Ti-Na) NOx storage surface.
During lean burn operation, the exhaust gas
contains a larger percentage of oxygen (O2) and
NOx, the NOx being primarily nitrogen
monoxide (NO). The platinum catalyzes the O2
and NO to produce nitrogen dioxide (NO2), which is able to be stored on the Ti-Na surface.
When it determines that the Ti-Na surface is saturated, the Insight temporarily richens the mixture. This
action decreases the NOx and O2 in the exhaust, and raises the levels of hydrocarbons (HC) and carbon
monoxide (CO). The platinum is then able to use the HC and CO to catalyze the NO2 (that has been stored)
into harmless nitrogen gas (N2), carbon dioxide (CO2) and water vapor (H20).