A Mechanism to Maintain Negative Crankcase Pressure in Turbocharged Gas Engine to Reduce Particulate Number to Meet Euro-VI Emission Regulation

Emissions regulation continually drives the automotive industry to innovate and develop. This pushes to introduce mechanism to maintain negative crankcase pressure in gas engine to meet this changing regulation. The way a turbocharger is used, to meet engine performance, can impact the pressure balance over the compressor and turbine end seals. This pressure difference can allow oil to leak through turbocharger seals. In normal engine operating condition the pressure in the turbocharger end housings is higher than the bearing housing and oil/gas flows into the bearing housing, through the oil drain to the crankcase. Under certain operating conditions, such as low idle and motoring, this pressure difference can be reversed with a higher bearing housing pressure than the pressure behind the turbine wheel. Under this condition oil will flow out of the bearing housing to the recess behind the turbine wheel, will increase the exhaust tail pipe emission, high oil consumption and damages the three-way catalyst. The bearing housing pressure will always track the crankcase pressure through oil drain pipe connected to the crankcase. With negative crankcase pressure control management, the pressure in the bearing housing can be maintain lower than pressure behind the turbine wheel throughout all engine operating conditions.