Characterization of stratified fuel distribution and charge mixing in a DISI engine using Rayleigh scattering

Journal article, 2018

The stratified fuel distribution and early flame development in a firing spray-guided direct-injection spark-ignition (DISI) engine were characterized applying optical diagnostics. The objectives were to compare effects of single and double injections on the stratified air-fuel mixing and early flame development. Vaporized in-cylinder fuel distributions resulting from both single and double injections before, during and after ignition were selectively visualized applying Rayleigh scattering. The optical investigation of the in-cylinder fuel distributions and early flame propagation corroborated the better mixing, showing that double injections were associated with more evenly distributed fuel, fewer local areas with high fuel concentrations, faster initial flame spread and more even flame propagation (more circular flame spreading). The results support the hypothesis that delivering fuel in closely coupled double injections results in better mixing than corresponding single injections. The improved mixing is believed to stem from the longer time available for mixing of the air and fuel in double injection events.