Investigation research of gasoline direct injection on spray performance and combustion process for free piston linear generator with dual cylinder configuration

Gasoline direct injection (GDI) properties, including injection pressure (IP), injection timing (IT) and injection angle (IA), have critical impacts on the cycle to cycle combustion variation that directly determines the long term stable operation for free piston linear generator (FPLG) with dual cylinder configuration. Therefore, in this present paper, the spray characteristics and combustion process of FPLG were explored through 9 cases that were designed by adopting orthogonal experimental method at different IP, IT and IA. Furthermore, the spray numerical model at different IP were validated with the spray experiment rig. The results displayed that, when at IT130°CA BTDC, the maximum cylinder pressure is 4.1 MPa and the mixture concentration is 0.98. However, at IT120°CA BTDC, the maximum cylinder pressure is 3.6 MPa and the mixture concentration is 0.94. Meanwhile, at IT100°CA BTDC, the maximum cylinder pressure only reaches 3 MPa and the mixture concentration is 0.86. The results indicated that the increase of IT can make the fuel take advantage of strong airflow movement, so as to improve the mixture uniformity. Thus, the combustion quality and power performance are enhanced. Moreover, at IP12MPa, when we define the maximum mixing uniformity as 1, the mixture uniformity reaches 0.98, 0.94 and 0.86 with IT130°CA BTDC, 120°CA BTDC, 100°CA BTDC, correspondingly. It is much higher than IP15MPa and IP7MPa, individually. It is can be explained by the interaction of high IP that can make fuel evaporation to form a mixture, thus reducing the fuel evaporation with the increase of penetration distance. In addition, IA has no obvious influence on the mixture uniformity, but reasonable IA could improve combustion quality within a certain range.