In this work, a predictive model has been developed in order to investigate the dual-fuel diesel engine operating on different gaseous fuels. A thermodynamic single zone modeling of the engine in dual-fuel (DF) mode was carried out to understand the characteristics of combustion and to predict the cylinder pressure. Tow primary fuels were tested, natural gas (NG) and biogas. The biogas fuel is composed of 60% methane (CH4) and 40% carbon dioxide (CO2). They are introduced into the intake manifold in order to be mixed with the air. Diesel fuel is the pilot fuel. A single zone model was coupled with a double-Wiebe function and was adopted to simulate the heat release rate. The double-Wiebe function includes six parameters, determined by using the least squares method, based on the experimental values obtained on a single cylinder test bench engine. Also, this predictive model is based on sub-models such as the ignition delay, the heat losses through walls and the flow rate through the intake and exhaust valves. The simulated results were compared with experimental results under different engine loads. The present model reproduces the cylinder pressure with high precision. Moreover, the calculation of other engine parameters such as indicated thermal efficiency and indicated power shows a satisfying and good agreement between both experimental and simulated results with a relative error lower than 5%.