Effects of natural gas compositions on CNG (compressed natural gas) reciprocating compressors performance

The aim of the current work is to investigate the effects of natural gas compositions on reciprocating compressor performance numerically. A numerical model has been built based on first law of thermodynamics, mass balance, AGA8 EOS (Equation of State) and thermodynamics relationships. The model could predict compressor parameters (pressure, temperature, mass flow rate, mass and valves motions) at various crank angles and cylinder volume. For validation, the numerical results are compared with previous experimental values and good agreement is encountered. The impact of key parameters such as: clearance, angular speed and molecular weight of natural gas have been investigated on the compressor performance. The results show that, for natural gas with higher molecular weight, suction valve opening time is less than natural gas with lower molecular weight. Also, the consuming indicated work per cycle for natural gas with lower molar weight (Khangiran composition with 98% methane) is approximately 50 kJ/kg more than higher molar weight (Ghasoo gas with 79% methane). - Highlights: • Effects of natural gas compositions on reciprocating compressor performance are investigated thermodynamically. • AGA8 equation of state and thermodynamic relations are employed. • In-cylinder thermodynamic properties have been calculated numerically. • A good agreement with previous measured values is obtained. • Effects of various parameters investigated deeply.