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In both spark ignition engines and diesel engines, exhaust gas recirculation system (EGR) is well known as an effective technique to reduce nitrogen oxides emissions. However, wear of piston rings and cylinder liners are sharply increased by EGR. It is widely considered that sulfur oxides contained in exhaust gas strongly relate to wear. In order to clarify the pure effect of sulfur oxides on piston ring wear, we experimented by adding sulfur dioxide positively to induction air. Furthermore, we compared the measured amount of wear with the amount of sulfur dioxide absorbed into a lubricating oil film, which was estimated by a numerical model. Consequently, it is confirmed that sulfur dioxide absorbed into a lubricating oil film played an important role on piston ring wear.

The Acceptability of boiloff hydrogen to an Inert Gas Circulating Hydrogen Diesel System, providing a high thermal efficiency, zero nitrogen oxides and carbon dioxide emissions, is discussed. To simulate a reciprocating engine cycle, a rapid compression-expansion machine is used. The machine brings fundamental data, such as hydrogen jet penetration injected in high pressure chamber and combustion characteristics. The results show an acceptable amount of hydrogen premixed to intake mixture without major negative effects. They suggest that most of boiloff hydrogen, inevitable in the facility where liquid hydrogen is used, could be supplied to the intake mixture as part of the fuel of the hydrogen diesel engine, saving a pumping loss to compress it up to an injection pressure.