Exhaust catalyst deactivation in small, handheld, 2-stroke engines is an issue that is faced quite frequently in efforts to improve or maintain catalyst performance but reduce cost. Fresh catalyst performance is rarely an issue, however, sustaining this performance for the specified useful life period of 50, 125, or 300 hours is where challenges start to arise. Our program goal was to develop and demonstrate a commercially viable catalyst which is capable of meeting regulatory and internal requirements with a deterioration factor (DF) near or below 1.0 over a 300 hour useful life period. A secondary objective was to utilize decreased quantities of platinum group metals (PGM) to reduce the cost relative to our reference catalyst. To achieve this, our focus was to reduce poisoning caused by exhaust byproducts and exhaust borne contaminants through a collaboration of catalyst advances and exhaust system design.
Testing was performed on a 50cc 2-stroke leaf blower using various cylindrical metallic monolith catalysts. Catalyst configurations varied in terms of PGM loading, PGM ratio, and coating methodology. The catalyst is contained directly within the muffler body, which also underwent modifications including optimization of internal flow configuration to assist in poison mitigation while maintaining fresh catalyst and engine performance. Data from 300 hour engine aging, coupled with model gas reactor, surface chemistry analysis, and computational fluid dynamics (CFD) supports an integrated approach to replacing a 3.5g/L, 5Pt:25Pd:1Rh catalyst with a 2.6g/L, 5Pt:25Pd:0Rh catalyst in the presence of flow alterations to reduce the rate of catalyst deactivation.