In the hydrogen explosion at Fukushima Daiichi Nuclear Power Station, the presence of flammable organic compounds together with hydrogen in reactor buildings was suggested. Aiming to elucidate the explosion characteristics, we performed the experiments of spherically expanding hydrogen-methane-air lean premixed flames in a closed chamber, where methane was adopted as a representative of flammable organic compounds. At sufficiently small flame radii, smooth flame surface was observed. The addition of methane to hydrogen-air mixtures generated the increase in the propagation velocity of unstretched flame. At large flame radii, cellular surface induced by intrinsic instability was found, and the flame acceleration was confirmed. The parameters of flame acceleration model were estimated, and then the flame propagation velocity depending on the flame radius was predicted. The normalized increment coefficient became larger at low equivalence ratios, owing to stronger diffusive-thermal instability. Under the same hydrogen concentration, the methane addition generated the increase in the maximum pressure in a closed chamber. The maximum pressure of experiments was lower than that of calculations, which was because of heat loss during premixed combustion. Under the same methane concentration, the pressure ratio of experiments and calculations was lower when the flame propagation velocity was smaller. This was because of larger heat loss. The obtained results were valuable information to elucidate the hydrogen explosion at Fukushima Daiichi Nuclear Power Station.

This study discusses self-driving motorcycles that use front-wheel drive. The ability of the motorcycle to maintain stability at high speeds is owing to the gyroscopic effect. However, at lower speeds, when the gyroscopic effect is reduced, human riders need to shift their weight or steer the motorcycle to prevent it from falling. To ensure the safety of self-driving motorcycles, we simulated an autonomous motorcycle accelerating from 0 to 1.5 m/s without falling. During the acceleration, we controlled only the front-wheel drive and kept the steering angle fixed at 0.52 rad (30 deg). By fixing the steering angle to 0.52 radians, the centrifugal force was generated as the restorative force of the motorcycle, and enabled precise control of the acceleration response of the motorcycle and enhanced its stability against disturbances. The primary goal of this study is to achieve stability while the motorcycle accelerated from 0 to 1.5 m/s. To accomplish this, we introduced a two-stage control design method using Linear Quadratic Regulator (LQR) control. This method enables us to achieve the desired acceleration response and improved stability in the face of disturbances. For our simulations, we employ SPACAR, a program based on the finite element method, to derive the linearly approximated state-space representation. The simulation results demonstrated controlled motorcycle realizing good accelerating performance and stability against disturbances.