Free-piston engines have been under extensive investigation in recent years, however have not yet seen commercial success in modern applications. This paper reviews some of the recently reported commercial developments in free-piston engine systems particularly aimed for use in hybrid electric vehicle powertrains and discuss these in light of published research. By looking at recent publications, and in particular patent documents, from major industrial players, insight into the less widely reported commercial research efforts on free-piston engines is obtained. Further, these publications provide a useful indication as to what these developers see as the main technical challenges for this technology.

Free-piston engine generators (FPEGs) have huge potential to be the principal energy conversion device for generating electricity from fuel as part of a hybrid-electric vehicle (EV) powertrain system. The principal advantages lay in the fact that they are theoretically more efficient, more compact, and more lightweight compared to other competing EV hybrid and range-extender solutions (internal combustion engines, rotary engines, fuel cells, etc.). However, this potential has yet to be realized. This article details a novel dual-piston FPEG configuration and presents the full layout of a system and provides technical evidence of a commercial FPEG system’s likely size and weight. The work also presents the first results obtained from a project which set-out to realize an operational FPEG system in hardware through the development and testing of a flexible prototype test platform. The work presents the performance and control system characteristics, for a first of a kind system; these show great technical potential with stable and repeatable combustion events achieved with around 700 W per cylinder and 26% indicated efficiency.

The objective of this paper is to investigate the properties of oil-based nanofluids and produce stable and biodegradable oil-based nanofluids by metal oxide nanoparticles. The cooking oil was used as a base for the nanofluid preparation. Titanium oxide was embedded as the nanoparticles, mixed with cooking oil volume concentration of nanofluids specimens, and labelled as 0.01, 0.03, 0.05, 0.07, and 0.09. The study explained the analysis techniques applied to determine the enhancement of thermal properties of nanofluids. The thermal conductivity of nanofluids was studied by heat transfer rate and the overall heat transfer coefficient gained. The metal oxide nanomaterials were mixed with the oil-based fluids in order to prepare the specimens. This research focused on the usage of vegetable oil and titanium oxide nanoparticles mixture to form nanofluids. The results obtained indicated that the nanofluid gave better thermal conductivity than oil-based fluids. The results significantly increased the thermal properties limitation and improved the product reliability. The enhancement of heat transfer rate for 0.09% of nanofluid volume concentration was increased by 36.25%