Comparative assessment of the performance and combustion attributes of a free piston linear generator fuelled with CNG and CNG-CO2

Abstract

A free-piston linear generator (FPLG) is an energy conversion device that can generate electrical energy utilizing different types of fuel. Natural gas fields with high carbon dioxide (CO 2 ) content are being simulated for study, knowing that the presence of CO 2 in natural gas contributes to a reduction in NOx emission while improving the compression ratio. This paper presents a comparative analysis of the performance and combustion characteristics of a spark ignition (SI) FPLG fuelled with two different fuels, namely compressed natural gas (CNG) and a mixture of CNG and CO 2 (CNG-CO 2 ). A test was conducted on the FPLG to study the engine performance and combustion at various lambda ratios. It is clarified that lambda variation significantly affects the piston motion and combustion of CNG and CNG-CO 2 , resulting in a variation in FPLG engine stability. When a lambda tends toward a rich mixture, the translator attains a peak velocity of 5.0 and 6.25 m/s, for the CNG-CO 2 and CNG, respectively, resulting in output power (rms) of 257.2 and 295.7 W at λ = 0.86 and 0.85. Also, the presence of CO 2 in CNG increases the compression ratio. The engine could attain ITE of 22.8% and 15.1% for CNG-CO 2 and CNG, respectively. • The effect of CNG and CNG-CO 2 on the FPLG combustion and performance characteristics are discussed. • The CNG-CO 2 decreased the FPLG combustion stability limits. • The effect of lambda variation on the in-cylinder pressure, heat release rate, and mass fraction burned are analyzed. • The presence of CO 2 in CNG negatively affects the heating value of the mixture while improving the CR and efficiency. • The CNG-CO 2 increases the engine operating stability with increases in lambda ratio and vis versa for pure CNG.