Diesel engine system with oil-air separator and method of operation

A diesel engine system comprising:

• an engine with combustion chambers which operate at pressures such that blowby gas escapes into a crankcase containing engine lubricating oil producing a mixture of blowby gas, including air, and oil mist;
• an oil-air separator connected by a first conduit with the crankcase to receive the mixture of blowby gas and oil, where the separator comprises an annular filter element mounted for rotation on a shaft within a chamber having an inlet for the mixture to an outer surface of the filter element and an outlet for gas passing into and through the filter element, a drain for removal from the chamber of oil separated from the gas by the oil having been centrifugally flung against a wall of the chamber;
• the outlet of the separator chamber being connected by a second conduit to supply blowby gas from which oil has been separated to an engine air inlet, and
• the drain of the separator chamber being connected to the crankcase.

A method of operating a diesel engine to avoid emissions of crankcase fumes containing blowby gas and oil mist, comprising the steps of:

• conducting crankcase fumes from the crankcase to a separator having an annular filter;
• rotating the filter and separating oil from the fumes by centrifugally flinging oil onto a surface for collection in a drain;
• conducting oil from the separator drain to the crankcase;
• conducting gas left from the fumes after separating the oil to an air inlet of the engine;
• the conducting of the crankcase fumes to the separator includes passing fumes into an outer annular space around the filter;
• and
• the conducting of the gas left from the fumes after separating the oil includes passing the gas from an inner space within the filter.