Assessing environmental impacts of two-stroke outboard motor lubricants using tank testing and simple dispersion model

摘要

Each year vessels impact the world's waterways by releasing one million tonnes of oil annually, resulting in significant environmental pollutant impacts. Simple, carburetted, two-stroke engines, such as those used for small outboard engines have been shown to emit up to l/3rd of their raw fuel/oil mix into the ocean, unburnt and are a significant contributor to total vessel pollution. Results obtained from laboratory measurements of the mixing action of propellers are presented. The results show that the propeller of a boat mixes more extensively than that of a simple jet. Traditionally pollutant levels have been expressed in units of mass per unit time or per unit of fuel. In the current work the engine performance of a typical outboard motor has been assessed to enable the emission to be expressed in units of mass per unit of engine output energy. This is a form which is particularly useful for comparisons between vessels with different sizes of two stroke engines, which are the most common form of engine in current use. The objective of the current work is to combine existing measurements of the pollutants emitted in terms of engine performance with dispersion measurements by propellers. This will enable predictions of pollutant levels to be made. A simple estimate of the emission level of an outboard motor is presented to show the usefulness of the results for predicting the levels of emissions. Further development and validation of models using the present results is necessary to understand mixing process by propellers and for full environmental assessments of vessel pollutants to be made.