Characteristics of CNG fuel engine

In CNG vehicle, usually there are two types of fuel supply method; premixed ignition and gas-jet ignition. In premixed ignition, the fuel is introduced with intake air so that homogeneous air-fuel mixture may form. The ignitability of this method depends on the global equivalence ratio. Differently, in gas-jet ignition, CNG is introduced directly into the engine combustion chamber. The overall mixture is stratified by retarded fuel injection (close to ignition timing). This method relies on local combustible mixture near the ignition position, resulting in high ignitability. In this study, a visualization technique is employed to obtain fundamental properties regarding overall mixture formation and combustion characteristics of direct injected CNG fuel inside a constant volume chamber and engine. For gas-jet visualization, Schlieren high speed imaging is used with the effects of ambient pressure and impingement wall on mixture formation being investigated.