Japan

Renewable energy is free abundant clean and could contribute towards a significant reduction of the global warming emissions. It is massively introduced as a source of electricity production across the globe and is expected to become the primary source of energy within the following decades. However despite the naturally replenished energy the supply is not always available. For this reason it is necessary at times of excess energy any surplus quantity to be sufficiently captured stored and later used when a deficit occurs. In this paper an overview of a backup power system operating with a hydrogen-biodiesel dual-fuel internal combustion engine is provided. The system is utilizing the organic chemical hydride method for safe hydrogen storage and transportation. The high energy content of hydrogen stored in the form of an organic hydride under ambient conditions makes it an ideal energy backup medium for large-scale and long-term applications. The research work focusses on the operation and emissions output of the dual-fuel internal combustion engine running on fully renewable fuels and the results are compared with the conventional petroleum-derived diesel engine. Biodiesel-hydrogen operation shows significant benefits in the reduction of carbon and soot emissions but deteriorates the NOx formation compared to the conventional diesel-powered engines. The operation of the engine at high loads can provide high exhaust thermal energy while alternative combustion strategies are necessary to be implemented at low load conditions for the optimum operation of the backup power system.

Fuel cell vehicles and some compressed natural gas vehicles are equipped with carbon fiber reinforced plastic (CFRP) composite cylinders. Each of the cylinders has a pressure relief device designed to detect heat and release the internal gas to prevent the cylinder from bursting in a vehicle fire accident. Yet in some accident situations the fire may be extinguished before the pressure relief device is activated leaving the high-pressure fuel gas inside the fire-damaged cylinder. To handle such a cylinder safely after an accident it is necessary that the cylinder keeps a sufficient post-fire strength against its internal gas pressure but in most cases it is difficult to accurately determine cylinder strength at the accident site. One way of solving this problem is to predetermine the post-fire burst strengths of cylinders by experiments. In this study automotive CFRP cylinders having no pressure relief device were exposed to a fire to the verge of bursting; then after the fire was extinguished the residual burst strengths and the overall physical state of the test cylinders were examined. The results indicated that the test cylinders all recorded a residual burst strength at least twice greater than their internal gas pressure for tested cylinders with new cylinder burst to nominal working pressure in the range 2.67–4.92 above the regulated ratio of 2.25.

A public survey was conducted in March 2015 in Japan asking public awareness knowledge perception and acceptance regarding hydrogen hydrogen infrastructure and fuel cell vehicle adopting the same key questions contained in the public surveys conducted six and seven years ago. Changes in answers between two different times of survey implementation were analyzed by comparing results of current survey to those of the previous surveys. Regression analyses were conducted and revealed influence of respondents’ awareness knowledge and perception about hydrogen hydrogen infrastructure and fuel cell vehicle on their acceptance on hydrogen station. We found a large increase in the awareness and relatively a small improvement on knowledge on hydrogen energy hydrogen infrastructure and fuel cell vehicle from the previous surveys. In contrast we did not find much changes in perception of risk and benefit perception on hydrogen society and hydrogen station and public acceptance of hydrogen infrastructure. Through the regression analyses we found large influences of negative risk perception of hydrogen itself and technology of hydrogen station and perception of necessity of hydrogen station on public acceptance of hydrogen station and the small influence of time background on the acceptance. Through the results of analyses implications to public communication in building public infrastructure are presented.

We conducted a fuelling test with hydrogen gas for a safety evaluation of the nozzle/receptacle at a controlled temperature and humidity. Test results confirmed that the nozzle/receptacle froze under specific conditions. However freezing did not cause apparatus damage nor hydrogen leakage. The nozzle/receptacle is thus able to fuel safely even if the nozzle/receptacle is stuck due to ice. In addition we quantified the water volume that causes freezing.

In the accident of Fukushima Daiichi nuclear power plants hydrogen was accumulated in the reactor buildings and exploded. To prevent such explosions hydrogen venting from reactor buildings is considered. When the gas mixture is released to a reactor building through a reactor containment together with the hydrogen some amount of steam might also be released. The steam condenses if the building atmosphere is below the saturation temperature and it affects the hydrogen behaviour. In this study the condensation effect to the hydrogen venting is evaluated using CFD analyses by comparing the case where a hydrogen-nitrogen mixture is released and the case where a hydrogen-steam mixture is released.

Propagation characteristics of hydrogen-air deflagration need to be understood for an accurate risk assessment. Especially flame propagation velocity is one of the most important factors. Propagation velocity of outwardly propagating flame has been estimated from burning velocity of a flat flame considering influence of thermal expansion at a flame front; however this conventional method is not enough to estimate an actual propagation velocity because flame propagation is accelerated owing to cellular flame front caused by intrinsic instability in hydrogen-air deflagration. Therefore it is important to understand the dynamic propagation characteristics of hydrogen-air deflagration. We performed explosion tests in a closed chamber which has 300 mm diameter windows and observed flame propagation phenomena by using Schlieren photography. In the explosion experiments hydrogen-air mixtures were ignited at atmospheric pressure and room temperature and in the range of equivalence ratio from 0.2 to 1.0. Analyzing the obtained Schlieren images flame radius and flame propagation velocity were measured. As the result cellular flame fronts formed and flame propagations of hydrogen–air mixture were accelerated at the all equivalence ratios. In the case of equivalent ratio φ = 0.2 a flame floated up and could not propagate downward because the influence of buoyancy exceeded a laminar burning velocity. Based upon these propagation characteristics a favorable estimation method of flame propagation velocity including influence of flame acceleration was proposed. Moreover the influence of intrinsic instability on propagation characteristics was elucidated.

To develop ultra high-strength cold stamping steels for automobile frame parts the effects of alloying elements on hydrogen embrittlement properties of ultra high-strength low alloy transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels) were investigated using the four-point bending test and conventional strain rate tensile test (CSRT). Hydrogen embrittlement properties of the TM steels were improved by the alloying addition. Particularly 1.0 mass% chromium added TM steel indicated excellent hydrogen embrittlement resistance. This effect was attributed to (1) the decrease in the diffusible hydrogen concentration at the uniform and fine prior austenite grain and packet block and lath boundaries; (2) the suppression of hydrogen trapping at martensite matrix/cementite interfaces owing to the suppression of precipitation of cementite at the coarse martensite lath matrix; and (3) the suppression of the hydrogen diffusion to the crack initiation sites owing to the high stability of retained austenite because of the existence of retained austenite in a large amount of the martensite–austenite constituent (M–A) phase in the TM steels containing 1.0 mass% chromium

For massive utilization of hydrogen energy it is necessary to transport a large quantity of hydrogen by liquefied hydrogen carriers. However the current rule on ships carrying liquefied hydrogen in bulks do not address the maritime transport of liquefied hydrogen and the safety assessment of liquefied hydrogen carriage is thus very important. In the present study we spilled liquefied hydrogen and LNG (Liquefied Natural Gas) on the surface of various materials and compared the difference of their spread and dispersion. Liquefied hydrogen immediately dispersed upward compared to LNG. Furthermore we also measured the flammability limit of low temperature hydrogen gas. Its range at low temperature was narrower than the range at normal temperature.

Wide use of hydrogen faces significant studies to resolve hydrogen safety issues in industries worldwide. However widely acceptable safety level standards are not achieved in the present situation yet. The present paper deals with hydrogen leaks from a tube to ignite and explode in atmosphere. The experiments using a shock tube are performed to clarify the auto-ignition property of high pressure hydrogen jet spouting from a tube. In order to improve experimental repeatability and reliability the shock tube with a plunger system is applied where the PET diaphragm is ruptured by a needle in order to control a diaphragm burst pressure (hydrogen pressure). As a result it becomes possible to control the diaphragm burst pressure to obtain a local minimum value. The most important result obtained in the preset study is that the minimum diaphragm burst pressure for auto-ignition is found between 1.0 and 1.2 m of tube length using a longer tube than the one used in the previous study. This minimum tube size is not found elsewhere to suggest that the tube length has a limit size for auto-ignition. Furthermore auto-ignition and Mach disk at the tube exit are observed using a high speed camera which is set at the frame speed of 1x105 fps when the ignited hydrogen jet is spouted out the tube.

Fuel-cell vehicle run on hydrogen is known that it has better energy efficiency than existing gasoline cars. The vehicles are designed so that hydrogen leaks from the tank are stopped automatically upon detection of hydrogen leakage or detection of impact in a collision. However we investigated the characteristics of hydrogen leakage sound from a hydrogen-leaking vehicle and the threshold of discrimination of hydrogen leakage from noise at a crossing with much traffic to examine a method to rescue people safely depending on the sense of hearing in the event of a continuous hydrogen leak. Here in the discrimination threshold test we conducted the test by using helium which is alternative gas of hydrogen leakage sound. We clarified that hydrogen leakage sound from vehicles has directivity height dependence and distance dependence. Furthermore we confirmed the threshold flow rate for distinguishing hydrogen gas when hydrogen leakage is heard at a distance of 5–10 m from the center of the hydrogen leaking vehicle in a 74 dB traffic noise environment.