Effects of Stroke to Bore Ratio on Exergy Balance in Spark Ignition Engines

This study aims to investigate theoretically the effects of stroke to bore ratio on exergy balance in spark ignition (SI) engines. For this purpose, a two–zone quasi–dimensional cycle model was developed for SI engines without considering the complex calculation of fluid dynamics. The combustion process is simulated as turbulent flame entrainment model in the cycle simulation. Principles of the second law of thermodynamics were applied to the developed model in order to perform the exergy (or availability) analysis. The variations of exergetic terms and irreversibilities throughout the investigated part of the cycle were analyzed depending on stroke to bore ratio. The results of the study showed that variation of stroke to bore ratio have significant effects on the variation of the exergetic terms, irreversibilities and efficiencies. Exergy transfer with work increases, while exergy transfer with heat decreases with increasing of stroke to bore ratio. The maximum increment in exergy transfer with work is about 12.5% and maximum decrement in exergy transfer with heat is about 11.25% for the stroke to bore ratio of 1.3 compared to stroke to bore ratio of 0.7. Irriversibilities and exergy transfer with exhaust decrease with the increasing of stroke to bore ratio. The maximum decrements are about 3.1% in the irriversibilities and 4.9% in exergy transfer with exhaust for the stroke to bore ratio of 1.3 compared to stroke to bore ratio of 0.7. The first and second law efficiencies are increase, while brake specific fuel consumption decreases with the increase of the stroke to bore ratio. The maximum increments are about 12.3% in the first and second law efficiencies and the maximum decrement is about 11.3% in brake specific fuel consumption for the stroke to bore ratio of 1.3 compared to stroke to bore ratio of 0.7.