Optical study on multi-time ignition mixed-mode combustion with gasoline and PODE

Abstract

In this study, multi-time ignition mixed mode combustion (MIMC) strategy is proposed to improve the dual fuel combustion, based on observation of the ignition and flame development in conventional dual fuel combustion. Gasoline and polyoxymethylene dimethyl ethers (PODE) serve as the premixed and pilot fuel through port fuel injection and direct injection (DI). As PODE have good auto-ignition property and extremely low sooting tendency, MIMC strategy can realize multi-time ignition in conditions which should be avoided by conventional dual fuel strategies. Firstly, the combustion of gasoline-PODE in typical single DI mode is investigated under different conditions. It is found that the ignition location in the intermediate region of radius causes the fastest combustion among the test cases. The independent auto-ignition events during the flame development are also discussed. Then, the idea of MIMC mode is proposed, considering both the spatial and temporal aspects of different batches of ignition. Different with the typical reaction-controlled compression ignition (RCCI) strategy, the MIMC strategy can directly controls the ignition time with the in-cylinder DI time, providing more flexibility for the dual fuel combustion. Optical and thermal data indicate that the MIMC strategy can fasten or slowdown the combustion by combining the control of ignition position and ignition time. When the locations of the ignition events are spatially alternated and their heat release are overlapped temporally, the combustion will be the fastest under the same DI mass.