One of the most effective solutions for improving the performance and reducing the emission of spark-ignition engines is
introducing a hybrid fuel with gasoline. Hydroxy gas (HHO) that is generated from the water electrolyzes process has a significant effect in enhancing the thermal efficiency and reducing fuel consumption rate and the resulted combustion emissions of SI engine. Because HHO gas has significant advantages rather than fossil fuels. In this study, a fuel dry cell is constructed and tested in different concentrations of electrolysis water solutions and with alternating the number of neutral plates, to obtain the most economic, safe, and suitable cell for the desired engine operation conditions. The engine used is a 183 CC single-cylinder air-cooled (Robin EY 20-3) without any change in engine construction. The load used for this purpose is a centrifugal water pump with a maximum delivery flow rate of 520 L/min. First, the engine is allowed to run separately without the cell under different speeds of 1200, 1500,2000,2500,3000 and 3500 rpm, then the cell is
connected to the engine. Many different operating parameters are measured such as pump flow rate, fuel consumption rate, water pressure, exhaust temperature, and engine emissions; HC and CO. The experimental results show that increasing the concentration of electrolysis solution or reducing the number of neutral plates increased the production rate of the gas, but it has an undesirable effect on increasing the temperature of the cell. And for engine performance, the average enhancement of engine efficiency, reductions in brake specific fuel consumption, reduction in CO and HC emissions are 5.44%, 16.9%, 4.8%, and 5.5%, respectively