Availability analysis of using iso-octane/n-butanol blends in spark-ignition engines

The current work presents a detailed energy and exergy analysis of an iso-octane/n-butanol blend-fueled spark-ignition (SI) engine to investigate exergy loss mechanisms and understand how the exergy destruction changes with different iso-octane/n-butanol blend fuels. Energy and exergy analysis was applied to a quasi-dimensional two-zone SI engine model, including Wiebe function to model the actual combustion process based on fuel types and operating conditions. Results were obtained for an SI engine at 3000 rpm by changing spark timing, volume fraction of n-butanol, and load. When sweeping spark timing, it was found that the location of maximum first and second-law efficiency appear at around −31 °CA ATDC for iso-octane, BU10, BU20 and BU30, and approximately −28 °CA ATDC for n-butanol. Increasing butanol fraction in the blends increases the percentage of total irreversibility in total availability at either MBT or constant spark timing, while has slight influence on availability transferred by heat transfer. At the MBT spark timing and WOT condition, the first-law efficiency increases slightly with increase of n-butanol, while the second-law efficiency for blended fuel decreases slightly. However, with decreasing engine load, the percentages of total irreversibility and availability transferred by heat transfer increase, the first and second-law efficiencies both decrease.