The design and simulation of a two-stroke free-piston compression ignition engine for electrical power generation

Abstract

Free-piston engines are under investigation by a number of research groups worldwide due to their potential advantages in terms of fuel efficiency and engine emissions. Some prototypes have emerged, mainly aimed for vehicle propulsion, and have reported favourable performance compared to conventional technology. This paper describes the design of a modular compression ignition free-piston engine generator, applicable to electric power generation in large-scale systems. The development of a full-cycle engine simulation model is described, and extensive simulation results are presented, giving insight into engine operating characteristics and performance. The operating characteristics of the free-piston engine was found to differ significantly from those of conventional engines, giving potential advantages in terms of fuel efficiency and emissions formation due to fast power stroke expansion. Effects of varying engine stroke length and compression ratio were not found to give any large advantages.

Dimensionless Parametric Analysis of Spark Ignited Free-Piston Linear Alternator

“…The modeling of the heat release in free-piston engine is one of the factors with the highest degree of uncertainty in the simulation model [11]. The piston motion of free-piston engines differs significantly from that of conventional engines and very little research exists on how this influences the combustion process.…”

“…The stroke to bore ratio is one of the core design variables in internal combustion engines, relating combustion chamber surface area to its volume and piston area to stroke length [11]. In order to predict the performance of FPLA with various sizes and dimensions, seven cases of dimensionless effective stroke length were chosen as the basic variable to investigate the performance of the FPLA in wide operating ranges.…”

“…Exhaust blown down is modeled to be a polytrophic expansion process while the exhaust port is opening and the scavenging ports are still covered by the piston [11].…”

“…When the prototype was running with frequency of 27Hz and compression of 9, the average power output was approximately 350W, but the efficiency had not been reported [10]. Mikalsen and Roskilly proposed a design of a single cylinder free-piston engine generator with gas-filled bounce chamber, simulated its working process and discussed the effects of parameters in a wide operating range to the engine's performance [11]. A novel approach of modeling the free-piston engines through the introduction of solution-dependent mesh motion in an engine CFD toolkit OpenFOAM was also presented [12].…”

Approach to Electromagnetic Control of the Extreme Positions of a Piston in a Free Piston Generator

“…Part 2: engine dynamics and piston motion control., 2010). The othershighlighting simulation approach (Pohl & Graf, 2005), (Li, Luan, Wang, & Deng, 2010), (Larmi, Isaksson, Tikkanen, & Lamiila, 2001), (Shourky, Taylor, Clark, & Famouri, 2002), (Goldsborough & Van Blarigan, 2001), (Mikalsen & Roskilly, 2008).…”