DESIGN OF POSITIVE CRANKCASE VENTILATION VALVE FOR AUTOMOTIVE GASOLINE ENGINE - VALIDATION BY SIMULATION USING CFD AND BY EXPERIMENTS

Emission standards have been one of the driving forces behind many of the technological changes in the automotive industry. Crankcase breathing of engine is necessary in order to prevent build up of pressure and explosions due to leakage of combustion gas past the piston rings. Breathing means admitting outside air when the pistons move up creating a partial vacuum in the crankcase and releasing the gas when the pistons move down pressurising the crankcase. The gases let out will consist mostly of hydrocarbons. 20% of the total hydrocarbons emitted in a passenger car is due to crankcase gases. By introducing the Positive Crankcase Ventilation system, which is essentially sealing the crankcase and allowing the gas through the engine to be burnt off, the hydrocarbon emissions due to crankcase breathing is totally eliminated. Positive Crankcase Ventilation (PCV) system using variable flow PCV valve is used in most of the automobile gasoline engine applications. By accurately matching the ventilation flow with blowby production characteristics, the crankcase ventilation performance is optimized, while engine performance and drivability remain unaffected. The valve closes during a backfire to prevent the flame from traveling into the crankcase where it could ignite the enclosed fuel vapours. This paper focuses on the design of variable flow PCV valve, accurately matching the flow performance with engine blowby characteristics. Simulation using STAR-CD and experimental verification using the flow bench were carried out to confirm the design outputs. Very good correlation is achieved between theoretical, simulation and experimental results.