Study of compressed natural gas impact on spark ignition engine performance

Compressed natural gas (CNG) is alternative fuel for internal combustion engines. In diesel engines, compressed natural gas is used by organizing a dual-fuel operation cycle. Spark ignition engines can work both in a mode with CNG only and in dual-fuel mode with gasoline. This paper presents an experimental study of the impact of the use of compressed natural gas as independent fuel, on the effective indexes of a spark ignition engine. The study has been carried out by comparing the engine indexes when operating separately with gasoline and compressed natural gas. The comparison is made both on the basis of the engine load characteristics and the engine speed characteristics at full load. The load characteristics are taken at a constant mean effective pressure dictated by the engine operation with CNG. The speed characteristics at full load are registered at an air-fuel ratio providing maximum braking power when the engine is running on both fuels. A quantitative assessment has been made of the changes in the power indexes, fuel economy parameters and ecological performances of the engine during its operation with both types of fuel. The indicator diagrams of the engine are registered on the studied modes. Based on the indicator diagrams, the changes in some of the burn parameters are analysed.