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An appropriate test procedure, based on a duty cycle representative of real in-use operation, is an essential tool for characterizing engine emissions. A study has been performed to develop and validate a snowmobile engine test procedure for measurement of exhaust emissions. Real-time operating data collected from four instrumented snowmobiles were combined into a composite database for analysis and formulation of a snowmobile engine duty cycle. One snowmobile from each of four manufacturers (Arctic Cat, Polaris, Ski-Doo, and Yamaha) was included in the data collection process. Snowmobiles were driven over various on- and off-trail segments representing five driving styles: aggressive (trail), moderate (trail), double (trail with operator and one passenger), freestyle (off trail), and lake driving. Statistical analysis of this database was performed, and a five-mode steady-state snowmobile engine duty cycle was developed.

The purpose of this project was to modify existing small off-road engines to meet ARB's originally proposed 1999 emissions standards. A particular point was to show that compliance could be attained without the need to redesign the base engines. Four high-sales volume, ARB-certified 1997 model engines were selected from the following categories: 1) handheld two-stroke engine, 2) handheld four-stroke engine, 3) non-handheld side-valve engine, and 4) a non-handheld overhead-valve engine. Engines were selected, procured, and baseline emission tested using applicable ARB test procedures. Appropriate emission control strategies were then selected and applied to the four engines. Emission reduction strategies used included air/fuel ratio optimization, and catalytic aftertreatment. Following the development of the four emission-controlled engines, final, certification-quality emissions tests were performed. All four engines met ARB's original 1999 Tier 2 emission standards after development.

One of the central points of debate in the discussion of whether oxidation catalysts are capable of working with leaded-fuel is the simulation of in-use mileage accumulation. Various catalyst ageing cycles have been proposed. Some engine cycles have been shown to only slightly deactivate catalysts, while road ageing experience typically produces significant catalyst deactivation. This paper will report the influence of three different engine ageing cycles on oxidation catalyst durability when a typical 0.15 g Pb/liter European fuel is used. Steady-state ageing at either 370°C or 590°C inlet temperatures were compared to a multi-mode cycle with a maximum catalyst inlet temperature of 760°C. The multi-mode cycle was developed as a simulation of the CCMC cycle requirements based on information obtained from characterizing a vehicle driven according to the recommendations of the CCMC.