Various efforts are in progress actively on hydrogen which has been utilized broadly for power generation, industry, and transportation, as a key technology toward the carbon neutrality. This document outlines trends in policy and technology development of hydrogen and energy carriers.

In the midst of globally accelerating moves toward a decarbonized society, Mitsubishi Heavy Industries, Ltd. (MHI) has made continuous efforts to develop hydrogen-firing Gas Turbine Combined Cycle (GTCC) power generation systems. The development of a gas turbine combustor that can operate with a mix of natural gas and 30 vol% of hydrogen has been completed for large frame gas turbines. MHI is also developing a 100% hydrogen-firing combustor. A promising Gas Turbine Combined Cycle using ammonia is also under development, facilitating energy transportation of hydrogen to further expand the lineup of carbon-free power generation systems. With these technologies, MHI is participating in hydrogen-firing GTCC projects in Europe, North America and other continents targeting commercialization in the mid-2020s. By increasing hydrogen demand, especially through large-capacity and high-efficiency GTCC systems, Mitsubishi Power is set to lead the establishment of an international hydrogen supply chain and contribute to the realization of a decarbonized society.

This paper gives an overview of recent fundamental studies on hydrogen in tribology for the future hydrogen society. Current situation in energy and environment is described first as a background, followed by some experiments on formation of hydrogen which demonstrate hydrogen is everywhere around tribo-interfaces. Processes at metal surfaces in hydrogen are described next, where trace impurities in hydrogen including water and oxygen play a significant role in tribological processes not only in metal/metal contact but also in sliding of metals with polymers, rubbers and coatings. Various chemical processes with carbon materials including DLC coatings are then described, where focuses are again on trace impurities and catalytic action of metals. Finally, diffusion of hydrogen into solid and subsequent processes are described.

At Hydrogen Refueling Station, a piston ring type high pressure hydrogen compressor that does not use lubricating oil is required for large capacity application. A tribological approach is even more important in mechanical equipment toward the establishment of a hydrogen society. We would like to propose that we will make efforts to accumulate and organize trouble information and solve problems while operating the equipment.

Industry, academia and government are making various decarbonization efforts toward the realization of carbon neutrality in 2050. Fuel cell systems that use hydrogen energy are attracting attention as one of the effective means of achieving carbon neutrality, and many countries have formulated strategies such as improving fuel cell performance, reducing costs, and installing hydrogen stations. Since hydrogen is flammable when it exceeds 4%, it is indispensable to have a seal product that can maintain stable performance for a long period of time in order to ensure the safety of hydrogen stations and FCVs. This paper describes the technical issues and research examples of rubber O-rings used in high-pressure hydrogen gas applications.

It can became possible to calculate the oil film thickness and the pressure distribution on the Hertzian contact surface of bearings,gears, traction drives, etc. by the EHL theory by Dowson et al.. For these calculations, it is important to determine the high pressure viscosity and high pressure density of lubricant. In a previous report, I constructed a theory of the relationship between viscosity, temperature and pressure. And the van der WAALS type viscosity equation was derived. Similarly, in this study, I constructed a theory of the relationship between density, temperature and pressure. As a result, it was found from the dimensional analysis that 1/3 power of density (line density) was negatively proportional to temperature. This linear equation was found to be a van der WAALS type line density equation which consists of three eigen constants: absolute zero line density ρ_t=0^1/3, line density constant 1/G and pressure constant H/G. Furthermore, the pressure constant H/G of the line density equation is equivalent to the PR of the liquid state equation and the pressure constant C/B of the van der WAALS type viscosity equation. And I report the results of estimating the high pressure density of various lubricants by the line density equation.

The objective of this study is to reveal the relationship between frictional behavior and the compatibility of rubber and lubricants in order to understand boundary lubrication mechanism of rubber. To achieve this, sliding experiments under boundary lubrication conditions were conducted using two acrylonitrile-butadiene rubbers (NBR) with the different polarity. In addition, the direct observation of sliding surface using a total reflection method was conducted in order to observe the process of generating a lubricant film. Even if the hydrodynamic lubrication was not enough to prevent a direct contact, lubricants played a role of lubricant film and the friction coefficient decreased during sliding. It was found that this was caused by swelling and deswelling of rubbers. It was concluded that, as swelling depended on the combination of rubber and lubricants, the compatibility between the rubber and the lubricant had the significant influence on the process of generating a lubricant film.