The effects of key parameters on the transition from SI combustion to HCCI combustion in a two-stroke free piston linear engine

A review of free-piston linear engines

“…Based on the Otto cycle, he showed that the use of springs can raise system frequency and affect the piston dynamics toward more stable operation. The use of metal springs in a dual-piston FPLE is also mentioned in a study conducted by Hung et al [22], as shown in Fig. 10.…”

“…4 [22,24,38,39]. Of those, the single-piston engine has a simple design with higher controllability than the other FPLEs; however, the dynamic balance is not good because it has only one piston.…”

“…10. Many previous studies have been done for dual-piston FPLEs [14,19,[22][23][24][26][27][28]; however, most of those engines used air-cooling systems, and the lubricant system for those engines has not yet drawn much interest. To commercialize dual-piston FPLEs, their cooling and lubricant problems need to be considered further.…”

“…As mentioned in the introduction, an FPLE can optimize the combustion process through variable compression ratios [13,14,[22][23][24]. Variation of compression ratios in FPLEs allows them to operate with various kinds of fuels and HCCI combustion, which improve thermal efficiency and reduce temperaturedependent emissions [12].…”

“…Such research has been conducted by institutes and universities such as the Korea Advanced Institute of Science and Technology [19], Beijing Institute of Technology [20,21], University of Ulsan [22], National Taiwan University of Science and Technology [23], Shanghai Jiao Tong University [24], Nanjing University [25], Tongji University [26], Stanford University [27], West Virginia University [28], Newcastle University [29], and Sandia National Laboratories [30]. To easily classify and summarize FPLE research results, we here present a review of FPLEs with different designations and operating characteristics.…”