§ 90.329 - Catalyst thermal stress test.

§ 90.329 Catalyst thermal stress test.

(a) Oven characteristics. The oven used for thermally stressing the test catalyst must be capable of maintaining a temperature of 500 ±5 °C and 1000 ±10 °C.

(b) Evaluation gas composition.

(1) A synthetic exhaust gas mixture is used for evaluating the effect of thermal stress on catalyst conversion efficiency.

(2) The synthetic exhaust gas mixture must have the following composition:

Constituent	Volume percent	Parts per million
Carbon Monoxide	1
Oxygen	1.3
Carbon Dioxide	3.8
Water Vapor	10
Sulfer dioxide		20
Oxides of nitrogen		280
Hydrogen		3500
Hydrocarbon*		4000
Nitrogen = Balance

* Propylene/propane ratio = 2/1.

(c) Phase 2 engines. The catalyst thermal stress test is not required for engine families certified to the Phase 2 standards.

[60 FR 34598, July 3, 1995, as amended at 64 FR 15243, Mar. 30, 1999]