This paper presents the analysis which is based on the parameters of the real device for producing a mixture of hydroxyl (HHO) and similar parameters to the real 2.0 SDI VW Golf MK V engine. Theoretical analysis has been made to principles of cooperation the engine with HHO’s generator. The effects of the gas on the engine and operating economy were established. The analysis was divided into quantitative and qualitative. Quantitative analysis was contained the theoretical and economic calculation of the thermodynamic cycle taking into account the HHO gas. Qualitative analysis was concerned to the quality of combustion in the engine and the impact generator HHO to the quality of the combustion.