Piston rings in a piston play important roles in the performance and endurance of engine, i.e. sealing the combustion gas, controlling the lubricating engine oil as well as working as the passage of heat flow from the piston into the cylinder wall. Although the sealing of the cylinder gas is one of major objectives of compression rings, the leakage through inter-ring space, nevertheless, occurs with various adverse effects on the engine performance.
The inter-ring gas pressures were measured from a 4-strok IDI diesel engine. The tested operating conditions included motoring and firing condition with no load with engine speed ranging from 500 to 2000 rpm. A strain gege type pressure transducer was fabricated in the laboratory and it was installed in a piston for inter-ring pressure measurement.
The measured inter-ring pressure was lowered, understanderbly, as engine speed is increased. The inter-ring pressure became always higher than the cylinder pressure somewhere in the middle of expansion stroke, which is expected to cause the reversal of the inter-ring gas flow direction and 1st compression ring motion within the ring groove.