Flame Area Correlations with Heat Release at Early Flame Development of Combustion Process in a Spark-Ignition Direct-Injection Engine Using Gasoline, Ethanol and Butanol

As the vehicle emission regulations become stricter worldwide, one way to meet the emission requirements is to engage the use of alternative fuels in engine combustion. In this investigation, the early combustion processes of regular gasoline and alternative fuels, including ethanol and butanol, were studied by simultaneously recording both the in-cylinder pressure and the crank angle-resolved high-speed flame images in a single-cylinder spark-ignition direct-injection engine. The engine was equipped with a quartz insert in the piston which provided an optical access to its cylinder through the piston. The effects of engine coolant & oil temperatures and intake air swirl ratio on the early flame development were also studied. The heat release was derived from the in-cylinder pressure measurements and the corresponding flame area characteristics were extracted from the images. Experimental results show a reasonable correlation between the heat release and the area of the flame at the early combustion stage. The flame area correlations with heat release of gasoline, ethanol, and butanol can also be distinguished by the properties of each type of fuel. The correlations are also influenced by different operating coolant & oil temperatures and swirl ratios. In addition, a new link between CA05 (5% of total heat release) and CAarea5% (flame size reaching 5% of the piston area) has been established, thus providing a better understanding of the relationship between heat release process and flame area properties. Overall, this study has demonstrated that high-speed in-cylinder combustion imaging could be a viable diagnostic to reveal the combustion quality, especially at the early stage of the combustion process where the pressure transducer might not provide reliable results.