Modeling of the turbulent burning velocity considering the effect of fuel composition in EGR condition

抄録

From the viewpoint of CO₂ reduction, it is necessary to improve the thermal efficiency of internal combustion engines and to use carbon-neutral fuels. Recently, it has been reported that an oxygenated component blended fuel can expand the lean operating limit. From the results of the shortening of combustion duration in that fuel, one of the reasons for the expansion of that is presumed increase in turbulent burning velocity. Similarly, increase in turbulent burning velocity may be one of the reasons for an expansion of EGR limit. So, it is important to identify fuel composition that has the potential to expand lean limit or EGR limit by increasing turbulent burning velocity. In addition, given the current situation where various carbon-neutral fuel candidates are being studied, internal combustion engines must achieve high thermal efficiency by combustion that matches any fuels. It is also important to be able to immediately understand the requirements for achieving high thermal efficiency with any fuel. From the above, the purpose of this study is to clarify the effect of fuel composition on turbulent burning velocity under the conditions such as lean or EGR dilution and to establish a model considering that. Markstein number is a dimensionless number that indicates the change of burning velocity when the flame is stretched, and varies with fuel composition. In addition, it is considered an important indicator in combustion under EGR condition. Therefore, a modified model based on Peters’ model focusing on flame stretch and Markstein number was considered. In order to investigate the effect of fuel composition and to verify the modified model, experiments using Rapid Compression Machine (RCM) were performed to measure turbulent burning velocities of some fuels in EGR condition. In this time, from the viewpoint of clarifying the effect of the composition of possible carbon-neutral fuel candidates on combustion and verifying the influence of Markstein number, ethanol blended fuel and ETBE blended fuel were used. As a result of comparison between the turbulent burning velocity obtained from models and experiments, it was confirmed that the modified model reproduced the experimental results more accurately than the base model. Using the modified model, the effect of fuel composition on turbulent burning velocity was investigated. As a result, it was revealed that decrease in Lewis number by ethanol blend made turbulent burning velocity increase.