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The aim of this work is to investigate the possibility of heat insulation by “Temperature Swing”, that is temperature fluctuation, on combustion chamber walls coated with low-heat-conductivity and low-heat-capacity materials. Adiabatic engines studied in the 1980s, such as ceramic coated engines, caused constantly high temperature on combustion wall surface during the whole cycle including the intake stroke, even if it employed ceramic thermal barrier coating methods. This resulted in increase in NOx and Soot, decrease in volumetric efficiency and combustion efficiency, and facilitated the occurrence of engine knock. On the other hand, “Temperature Swing” coat on the combustion chamber walls leads to a large change in surface temperature. In this case, the surface temperature with this insulation coat follows the transient gas temperature, which decreases heat loss with the prevention of intake air heating, and also which is expected to prevent NOx and Soot from increasing.

A concept of dual-fuel, Premixed Compression Ignition (PCI) combustion controlled by two fuels with different ignitability has been developed to achieve drastically low NOx and smoke emissions. In this system, isooctane, which was used to represent high-octane gasoline, was supplied from an intake port and diesel fuel was injected directly into an engine cylinder at early timing as ignition trigger. It was found that the ignition timing of this PCI combustion can be controlled by changing the ratio of amounts of injected two fuels and combustion proceeds very mildly by making spatial stratifications of ignitability in the cylinder even without EGR, as preventing the whole mixture from igniting simultaneously. The operable range of load, where NOx and smoke were less than 10ppm and 0.1 FSN, respectively, was extended up to 1.2MPa of IMEP using an intake air boosting system together with dual fueling.

Free Piston Engine linear Generator (FPEG) that is thin and compact and has high efficiency and high fuel flexibility has been developed. The developed FPEG consists of a two-stroke combustion chamber, a linear generator, and a gas spring chamber. This paper focuses on the control logic of the linear generator, where the generator can be changed instantly to act as a driving motor, according to demand. Both the position and velocity of the piston are selected as feedback parameters for the control logic. The proposed feedback method realizes stable and robust control behavior with respect to abnormal combustion conditions, such as pre-ignition. In addition, the control logic must satisfy the following requirements. First, in order to achieve stable two-stroke combustion, the position of the piston is precisely controlled, especially near the top dead center (TDC) and the bottom dead center (BDC).