## 1 Introduction
[15] established a numerical model to calculate the thermodynamic performance and work consumption in the compression phase. [PERSON] et al. [16] reported a comprehensive model by considering leakages and frictions to analyze the performance of a semi-hermetic CO\({}_{2}\) compressor. [PERSON] et al. [17] analyzed the effects of natural gas compositions on the thermodynamic process and it was demonstrated that natural gas with lower molar weight consumes more power per cycle than natural gas with higher molar weight. [PERSON] et al. [18] compared various integral correlations of heat transfer inside the cylinder for different settings and fluids. A numerical model that only considered the compressor will result in approximation in the evaluation of compressor performance, ignoring pulsation propagating inside suction and discharge systems. In this view, few linear hybrid models have emerged by coupling the acoustic description of pipelines to the lumped parameter approach. [PERSON] and [PERSON] [19] reported the importance influence of pressure pulsation on the thermodynamic process with a hybrid model by combining acoustic wave theory. This hybrid approach was further employed to investigate the coupling between compressor and the connected pipelines system [20; 21]. Similarly, [PERSON] and [PERSON] [22] developed a hybrid model of a refrigeration reciprocating compressor by simplifying the plenum cavity based on plane wave theory. [PERSON] et al. [23] conducted an iteration scheme to overcome the poor convergence problem of suction pressure. [PERSON] et al. [24; 25] built a comprehensive simulation model of a multicylinder automotive air-conditioning reciprocating compressor. In order to model the complex fluid domain, some authors used the acoustic finite element method (FEM) for geometrieswith single input and single outlet [26; 27; 28] and geometries with multi-ports [29]. However, the main limitation of these linear hybrid models lies in the event of pulsations with large amplitude [30; 31]. A more promising reciprocating compressor model is thus potentially obtained by simultaneously simulating the thermodynamic cycle and the in-pipe unsteady flow. [PERSON] et al. [32] highlighted that the predictions of finite disturbance theory were much more accordance with experimental data than results from acoustic wave theory. [PERSON] and [PERSON] [33] developed a transient gas dynamic mathematical model considering thermodynamics with gas leakage, kinematics, valve dynamics, gas flow through valves and transient unsteady flow in the duct system. [PERSON] et al. [34] revealed that pulsations can be damped by large piping volumes with weak impedances, and conversely amplified by strong impedance systems. The parametric optimization of reciprocating compressors in a CNG refueling station can lead to higher compressor efficiency and increased reliability. As noted before, pressure pulsations have been recognized as having an important impact on compressors. In order to find alternative means to reduce pressure pulsation influence, it is of fundamental importance to understand the interaction between pressure pulsations and thermodynamic processes. The objective of this work is to investigate effects of pressure pulsations on reciprocating natural gas compressor performance thermodynamically by applying the developed hybrid numerical model. This detailed numerical methodology could simultaneously evaluate the compressor performance and the pipeline pulsation. The thermodynamic properties of methane as the working fluid are computed based on ideal and real gas assumptions. For the real gas model, the thermodynamic properties are obtained by means of calling the NIST REFPROP database [35]. Validation of the model has been carried out through comparing the predictions against previous experimental results. The effects of pressure pulsations with or without resonance on the compressor performance have been compared between ideal and real gas models.