First and Second Law Analyses of a Large Bore Two Stroke Spark Ignition Engine Fueled with Natural Gas

Abstract

A zero dimensional thermodynamic model with no spatial resolution has been developed to analyze the effectiveness of energy and exergy utilization in a large bore, single cylinder, two-stroke engine. Exergy analysis was performed to supplement energy analysis to gain deeper insights into the exploitation of the essence of energy during engine operation. The closed and the open portions of the cycle were modeled in this study using theory of gas dynamics and thermodynamics. Suitable forms of the first and second laws of thermodynamics were applied to a two zone (burned and unburned) control mass during the closed portion of the cycle and control volume during the open portion of the cycle, respectively. A Wiebe function describes the fuel burning rate and was used to simulate combustion. All simulated results were validated using experimental data. Exergy transfers in and out of the system accompanying chemical reactions, work, heat transfer and flows were traced and the major sources of exergy destruction (irreversibilities) identified. Major findings from the analysis were that 14% of the fuel’s exergy was destroyed because of combustion and almost half (46%) of the initial exergy is lost with exhaust gases. Compared to four stroke engines the percentage exergy destruction is relatively less because of lower cylinder temperatures. These findings highlight shortcomings in the thermodynamic design of the engine and help direct future research efforts.