The Effect of Mixing Cyclopentane, Nitromethane, or Furan with Gasoline on the Performance of Lean Burn SI Engine
Because of recent environmental problems, there is a demand for improving the thermal efficiency of automobiles. Lean-burn engines are one method for improving thermal efficiency. Some previous studies have reported that the mixing of furan and nitromethane with high octane gasoline reduced the knocking occurrence and extended the lean limit, and thus increased the thermal efficiency. Therefore the purpose of this research was to understand the changing engine performance by mixing some fuels to high octane surrogate gasoline. Four types of fuels were prepared for experiments: high octane surrogate gasoline 100 vol. %, high octane surrogate gasoline 50 vol.% + cyclopentane 50 vol.%, high octane surrogate gasoline 95 vol.% + nitromethane 5 vol.%, high octane surrogate gasoline 50 vol.% + furan 50 vol.%. Experiments were performed by varying the excess air ratio from 1.0 to the lean limit of each fuel. The mixing of cyclopentane or furan with high octane surrogate gasoline extended the lean limit and thus increased the thermal efficiency. On the other hand, the mixing of nitromethane could not extend the lean limit. In fuel-lean conditions, exhaust components also differed, the mixture of nitromethane emitted more NOx than the mixture of cyclopentane or furan. Furthermore, knocking occurrences were also changed by the mixing of fuel. Especially in fuel-lean conditions, the mixing of cyclopentane, nitromethane, or furan made knocking more likely, therefore the ignition timing had to be retarded. Those results were discussed based on ignition delay time and laminar flame speed estimated from zero-dimensional detailed chemical reaction calculations using CHEMKIN-PRO.