The control of a free-piston engine generator. Part 2: Engine dynamics and piston motion control

Abstract

Free-piston engines are under investigation by a number of research groups due to potential fuel efficiency and exhaust emissions advantages over conventional technology. The main challenge with such engines is the control of the piston motion, and this has not yet been fully resolved for all types of free-piston engines. This paper discusses the basic features of a single piston free-piston engine generator under development at Newcastle University and investigates engine control issues using a full-cycle simulation model. Control variables and disturbances are identified, and a control strategy is proposed. It is found that the control of the free-piston engine is a challenge, but that the proposed control strategy is feasible. Engine speed control does, however, represent a challenge in the current design.

A review of free-piston linear engines

“…However, freepiston motion in the cylinder does lead to variation in combustion pressure at each engine cycle [14,15]. Also, in FPLE operation, which is mainly controlled by an electronic system, the piston crown can hit the cylinder head if the piston motion is not controlled correctly [16,17], though that possibility can be eliminated by installing a damping device in the cylinder [18].…”

A Free-Piston Linear Generator Control Strategy for Improving Output Power

“…Due to that increasing fuel mass is an effective way to increase the output power [7,23,28,29], the relationship between the output power and the electromagnetic force profile is seldom noticed. In the previous research most researchers only pay attention to the stable operator of the piston.…”

“…This brings the ability to accommodate multi-fuel by easily controlling the compression ratio without modifying the mechanical structure. The energy conversion efficiency can be increased with optimizing the compression ratio [6][7][8][9]. Furthermore, the key performances of FPLG, the output power and system efficiency could be improved by controlling the motion state of the piston [10,11].…”

“…The second one is specifying a reference current profile to generate an appropriate electromagnetic force for stable operation [5,[18][19][20]. Another one is to achieve the balance of energy flow by regulating the load factor and combustion parameters [7][8][9][21][22][23][24].…”

Study of the Injection Control Strategies of a Compression Ignition Free Piston Engine Linear Generator in a One-Stroke Starting Process

“…Due to its unique structure and working principle, the free piston engine has the advantages of mechanical simplicity, low frictional losses, high efficiency, high suitability for multi-fuel or homogeneous charge compression ignition (HCCI) operation, and low emissions [1][2][3][4][5][6][7][8]. The history of the research and development on free piston engines can be divided into two phases [2].…”