CFD modelling was conducted to investigate the influences of low-pressure fire suppression systems on tunnel fires. The main purpose of this study is to evaluate whether CFD is capable of predicting the development of solid fuel fires in tunnels with and without the low-pressure fire suppression systems. To make the assessment, both small-scale and full-scale tests are selected for CFD modelling, including both free burn tests and fire suppression tests. In these two test series, wood cribs (small scale) and wood pallets (full scale) were used as the fire sources, respectively. In CFD modelling, both the simple ignition model and the Arrhenius pyrolysis model were used for the small-scale tests. For the large-scale tests, the fuel geometry was too complicated and thus simplifications using scaling correlations and the simple ignition model was used in CFD modelling. For the simple ignition model, the key empirical coefficient (Ecoefficient) that accounts for the suppression effects was assessed. The impacts of water surface spread velocities were also analysed.