A Qualitative Evaluation of Mixture Formation in a Direct-Injection Hydrogen-Fuelled Engine

In an optically-accessible single-cylinder engine fuelled with hydrogen, OH* chemiluminescence imaging and planar laser induced fluorescence (PLIF) are used to qualitatively evaluate in-cylinder mixture formation. The experiments include measurements for engine operation with hydrogen injection in-cylinder either prior to or after intake valve closure (IVC). Pre-IVC injection is used to produce a near homogeneous mixture in-cylinder to establish a baseline comparison for post-IVC injection. To assess the effects of injection pressure on mixture formation, two injection pressures are used for post-IVC injection. For post-IVC injection with start of injection (SOI) coincident with IVC, mixture distribution is similar to pre-IVC injection and there are little differences between the two injection pressures. With retard of SOI from IVC, mixture inhomogeneities increase monotonically for both injection pressures. However, the spatial and temporal development of the mixture distribution differs significantly between the two injection pressures. With late injection and for both injection pressures, hydrogen is predominately concentrated in small volumes that are spatially located close to the cylinder wall. This suggests that the injector tip geometry (or injector location) used in the present study is not ideal for late injection strategies due to an expected increased heat-loss due to combustion of locally-rich regions near the cylinder wall.