A Convenient Technique for Determining Two-Stroke Emission Measurement Accuracy and A/F Ratio

This paper describes a method of using the total emission concept for conveniently assessing the accuracy of emission measurements. The measured total HC emissions are treated as unburned fuel (C₈ basis) plus burning zone HC (C₁ basis). Statistical analysis shows that the emission test data may be questionable if the total emission calculation exceeds the range of 100 +/- 2σ*. This paper also describes a technique to determine the Air to Fuel (A/F) ratio for two-stoke engines. This method may be used to calculate the overall A/F and burning zone A/F for DI two-stroke engines and for engines using oxygenated fuel.

Twenty-five OMC engines have been tested by following EPA emission test procedure. The total emission and A/F analysis for these tests indicate that the new method is a very useful tool for assessing A/F and the accuracy of emission measurements. This technique reduces the emission test errors and shortens engine calibration and development time.