G070031 Influence of Compression Ratio on Combustion in a Homogeneous Charge Compression Ignition Engine

HCCI combustion has attracted considerable interest as a new combustion concept for internal combustion engines in recent years because of their potential for high efficiency and clean combustion. And thermal efficiency will be as good as higher compression ratio has been known. However, knowledge about compression ratio change of the HCCI engine is less. Therefore in this study, influence of compression ratio on combustion in an HCCI engine was investigated by using spectroscopic measurements and chemical kinetic simulations. And two stroke engine was used for the test engine. The cylinder head of a four-stroke engine has a complex valve train system, making it difficult to obtain optical measurements inside the combustion chamber. Compared with a four-stroke engine, a two-stroke engine has a simpler cylinder head construction that allows greater freedom for making optical measurements in the combustion chamber. Since the purpose of the present study was to investigate HCCI combustion mechanisms on the basis of optical measurements, it was decided to use a two-stroke test engine. The results revealed that combustion can be suppressed steep by controlling the ignition timing also high compression ratio. And the results of chemical kinetic simulations that the ignition delay period tended to differ at different compression ratios when EGR was applied. It is because temperature and pressure histories by piston compression were changed by the changing compression ratio.