Improvement of thermal efficiency in natural gas fueled engine by applying Miller cycle

摘要

In the future, automotive engine should satisfy the more stringent CO{sub}2 emission regulation without trading off the higher thermal and combustion efficiencies. Miller cycle could be one of the solutions in this context, which can be realized in automotive engines by making the expansion period longer than compression period. In this work, numerical analysis was carried out for both Otto and Miller cycle before the experimental work, and high thermal efficiency was obtained for the case of Miller cycle. Then the natural gas was applied as a fuel and more detailed experimental work was carried out. To realize Miller cycle in engines, intake valve timing was varied by applying several camshafts with different cam profiles. Also a supercharger was adopted to increase the power. Compared to Otto cycle, 10% increase of thermal efficiency was obtained in the Miller cycle due to increased expansion work and decreased pumping work. Also, it was evident that the effect of supercharger on the engine power is much bigger for Miller cycle.