Effect of Supercharging on Cycle-To-Cycle Variation in a Two-Stroke Spark Ignition Engine

Fluctuations in the operational output of spark ignition engines are observed from one engine cycle to the other, when an engine is run at technically identical operating condition. These fluctuations known as cycle-to-cycle variations, when high, adversely affect the performance of an engine. Reduction in cycle-to-cycle variation in engines has been noted by researchers as one of the methods of improving engine efficiency and operational stability. This study investigated the combustion performance characteristics of two fuels: E5 (95% gasoline and 5% ethanol) and ULG98 (unleaded gasoline) in a spark ignition engine, operating at varying inlet pressure conditions and ignition timing. A two-stroke, 80mm bore, spark ignition engine was operated at an engine speed of 750 rpm, inlet pressures of 1.6 and 2.0 bar and spark-timings ranging from 2 to 13 bTDC. A top cylinder head with a centralized spark plug was used in all the experiments. The Gross Indicated Mean Effective Pressure (GIMEP), GIMEP’s coefficient of variance (COV) and the Mass Fraction Burned (MFB) were determined. An increase in the intake pressure of the engine gave rise to an increase in the engine’s GIMEP in all the fuels tested. While a decrease in the COV of the engine’s GIMEP with an increase in the engine’s intake pressure was observed, its effect on the crank angle of occurrence of MFB varied for E5 and ULG 98 fuels. The study established that reduction in the cycle-to-cycle variation in spark ignition engines can be achieved by supercharging or turbo-charging these engines.