A study on a liquid hydrogen pump with a self-clearance-adjustment structure

Abstract

Musashi's research work on hydrogen engines has demonstrated that, in respect of not only complete elimination of abnormal combustion such as knocking, pre-ignition and backfire peculiar to hydrogen engines but also high specific power brought by greater charging efficiency, hydrogen engines with high pressure hydrogen injection, spark ignition and LH 2 pump are most practical and reasonable engine system. The pressure of injection to the combustion chamber has been increased up to 10 MPa aiming at rapid injection and good mixture formation. The leakage through the clearance between the piston and the cylinder of the pump has become greater with the increase of pressure of injection. To decrease the leakage, the clearance was made smaller (up to 2.5 μm) but it was found that the clearance was so small that the piston and the cylinder of the pump were more subject to contact with each other which caused heat to be generated due to the friction. As a result, LH 2 in the pump was gasified and the piston compressed the hydrogen gas. This is called “gas pumping”, and results in disability of pumping. The authors have developed a LH 2 pump whose piston has a cup-shaped cavity; the thin wall of which expands toward the cylinder wall of the pump only when the pressure rises. From our experiments it has been found that the leakage could be reduced to about a half that of the old type pump with the clearance of 2.5 could be operated. As a result, a desirable pump performance was obtained.