A study of mixture formation and flame speed in a hydrogen direct injection SI engine

In order to study instationary hydrogen combustion in a hydrogen fueled direct injection SI engine, high speed schlieren experiments were performed. The influence of internal and external mixture formation to the combustion (flame speed, lean limit of combustion) was investigated. The flame speeds obtained with internal mixture formation were significantly higher. The lean limit of combustion was found to be smaller with external mixture formation. To study the influence of the flow field to the flame propagation Laser Doppler Velocimetry (LDV) measurements were performed. In order to investigate the mixture formation, a technique for the quantitative two - dimensional determination of the hydrogen-air ratio was developed. The technique is based on the spontaneous Raman scattering of the hydrogen molecules (Stokes Q-branch) and the simultaneous measurement of the pressure inside the combustion chamber. From these data the local partial pressure of the hydrogen and, therefore, the hydrogen-air ratio can be calculated.