This paper explains trends in carbon-neutral fuels and presents experimental verification of friction and wear issues actually occurring in pistons, piston rings, and plain bearings due to hydrogen internal combustion engines. It also shows experimental results concerning lubricant emulsification and friction/seizing phenomena associated with combustion.

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In recent years, the reduction of CO₂ emissions has become the most important issue as a countermeasure against global warming, and it is necessary to implement multi-pathway initiatives to realize a carbon-neutral society. Hydrogen engine is a technology to be studied for future hydrogen society. However, it is not easy to mount hydrogen with low energy density on a motorcycle, and hydrogen engines also have problems with abnormal combustion. Therefore, it is necessary to solve these problems cooperatively beyond the framework of the manufacturer. Accordingly, the Hydrogen Small Mobility & Engine Technology Association was established by six companies, mainly four motorcycle manufacturers. This paper introduces the research trend of motorcycle companies which is being promoted in parallel with the research trend of the Technology Research Association

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This paper focuses on the potential application of hydrogen fueled internal combustion engines (HICE) in the off-road market, examining HICE based on a diesel engine. In the transition to HICE, priority was given to compatibility with existing systems, minimizing changes from the base engine. By adopting a PFI (Port Fuel Injection) method for fuel injection, low-pressure hydrogen supply was achieved. To address the issue of backfire associated with PFI, optimization of injection pressure using a variable pressure control valve, along with adjustments to valve timing and injection timing, was implemented to suppress backflow of residual gases into the intake system and minimize hydrogen retention. Regarding pre-ignition, in addition to suppressing hotspots, the relationship between the homogenization of the air-fuel mixture and NOx emissions was examined, revealing a correlation. This engine was mounted on a generator, and efforts were made to improve the important characteristic of responsiveness in generators. As a result, it was confirmed that the responsiveness is comparable to that of existing gas engine generators.

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In order to achieve carbon neutrality worldwide, it is necessary to prepare various measures, not limited to Battery Electric Vehicles (BEVs). The use of internal combustion engines capable of utilizing high-energy-density fuels is an effective means of achieving carbon neutrality. Research on hydrogen and e-fuel as carbon-neutral fuels is actively underway among industry, academia, and government. When changing the fuel of an internal combustion engine to hydrogen or e-fuel, it is expected that there will be an impact on the piston in terms of combustion, lubrication, friction, wear, and durability. This paper introduces technical issues related to combustion and tribology in piston for internal combustion engines that have been converted to hydrogen and e-fuel.

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In order to meet EU7 regulations and CO₂ targets, it is important to treat cylinder surfaces with honing. Oil consumption and durability are issues in hydrogen engines. Precision honing reduces oil consumption by up to 32%. The surface design contributes to engine efficiency, and hydrogen engines with zero CO₂ emissions are expected in the future. Continuous research and industry collaboration are essential.

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Many countries aim for carbon neutrality by 2050, prompting research into alternative fuels like hydrogen and methanol. This study examines their impact on plain bearings in engines. Corrosion tests show hydrogen causes bismuth overlay damage, while enhanced coatings resist it. Methanol showed no corrosion, but further testing is needed.

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As the demand for higher efficiency in internal combustion engines (ICEs) continues to grow, this study proposes oil particle measurement as an effective method for monitoring component durability and sliding conditions. An application example demonstrates that key wear stages―initial wear, steady-state wear, and seizure―can be predicted through automated analysis of wear particles in lubricating oil.

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This paper aims to reduce the friction losses in vehicle engines to contribute to mitigation of global warming. We investigate the friction characteristics of fullerene-added oil by varying surface roughness under boundary lubrication conditions. The plate specimens with plateau structure surface and surface roughness Ra = 0.1-2.6 μm were prepared, and ball-on-plate tester was used to measure the friction coefficient. SUJ2 was used as both the plate and ball specimens, and PAO4 was served as base oil. The relationship between roughness parameters and both friction coefficients and wear volume was analyzed theoretically. Partial least squares (PLS) regression revealed a strong linear correlation between the friction coefficient and both profile (2-D) roughness parameters (R² = 0.932) and areal (3-D) roughness parameters (R² = 0.839) in the fullerene-added oil, suggesting that the friction coefficient can be modulated by the surface profiles in conjunction with fullerene additives. Further analysis showed that the relationships between five key profile (2-D) roughness parameters (Rsk, RΔq, Mr2, Rsm, Rku) and the friction coefficient in fullerene -added oil could be approximated by downward-convex quadratic functions (R²＞0.5). By calculating the minima of these function, the optimal surface roughness conditions were derived, demonstrating the theoretical feasibility of designing surfaces textures to predict and control friction characteristics.

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High-pressure rheology of lubricants is important for elucidating the lubrication state of metalworking, bearing and gear in the elastohydrodynamic lubrication (EHL) region. For this reason, the van der Waals liquid density equation was derived in a previous report and applied to the estimation of the high-pressure density. Furthermore, I accumulated the data on various lubricants for the three material-specific constants contained in this equation, the absolute zero density ρ_t=0, the density constant R_D, and the pressure constant P_D. In this paper, in order to enable the estimation of the high-pressure density of unknown lubricants using this equation, we performed multiple regression analysis using three constants as the objective variables, and the lubricant’s physical properties and chemical structure as explanatory variables, to create a multiple regression equation. As a result, we report that it is possible to estimate the three constants of the van der Waals liquid density equation (ρ_{t=0 mr-eq.}, R_{D mr-eq.}, and P_{D mr-eq.}) and the high-pressure density ρ_mr-eq. by simply analyzing the physical properties and chemical structure of an unknown lubricant using this multiple regression equation, without having to measure the high-pressure density experimentally using a high-pressure density measurement device.

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[in Japanese]

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