§ 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]