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The swirl port is de signed for lesser swirl ratio to reduce NOx emissions at higher
speeds. But this condition in creases the air fuel mixing time and particulate and smoke emissions in lower speeds. The combustion system of an internal combustion engine is usually designed for a certain working condition, if the engine load or speed changes, then the designed parameters will not match. For example, the combustion system of a diesel engine is de signed basically on full load condition, when it is run under partial load condition, the engine’ fuel economy will be poorer. A variable swirl system can change the situation and meet the combustion needs of swirl in broader operat ing conditions [1]. If a variable swirl system is ap plied, when the engine works under full load condition, the in let swirl will be decreased so that the charging efficiency is in creased, and under the partial load condition, the in let swirl will be enhanced at a little expense of charge. Hence a variable swirl system can improve engine performance.