Crankcase emission control system - ’K’ series

Crankcase emission control system - ’K’ series

The concentration of hydrocarbons in the crankcase of an engine is much greater than that in the vehicle’s exhaust system. In order to reduce the emission of these hydrocarbons, crankcase emission-control systems are a standard legal requirement.

The crankcase emission control system is designed to allow the engine crankcase to breathe, but prevent blow-by gas containing HC and CO pollutants from escaping to the atmosphere.

The K-series engine uses a positive crankcase ventilation system to vent the gases from the crankcase to the intake system. Gases from the crankcase are drawn into throttle housing to be burnt in the combustion chambers with the fuel mixture. The system provides effective emission control while the engine is running under all circumstances.

The camshaft cover has two apertures to faciltate engine breathing. The larger orifice is connected upstream of the throttle disc in the throttle housing via a plastic pipe with rubber hose elbows which connect to ports at the camshaft cover and throttle housing. The smaller orifice is connected to a port further downstream in the air intake line via a short rubber hose to the inlet manifold housing. A gauze oil separator is included in the camshaft cover to prevent oil mist being drawn into the engine.

When the engine is running at idle speed, the throttle disc is closed and manifold depression in the inlet manifold side of the disc causes crankcase gases to be drawn through the oil separator and small orifice in the camshaft cover. Clean air enters the crankcase through the large orifice in the camshaft cover, which then mixes with the crankcase gas before it is drawn into the engine via the inlet manifold to be burnt in the combustion chambers with the fuel mixture. This ensures unburnt and partially burnt fuel is returned for combustion and so prevents harmful crankcase gases escaping to the atmosphere.

When the engine is running with the throttle disc wide open, pressure at either side of the disc is equalized and both pipes are subjected to the same manifold depression. In this condition, most of the crankcase gases are drawn through the large orifice in the camshaft cover to be mixed with clean air at the throttle housing before being drawn into the engine for combustion.

In between the fully open and fully closed conditions of the throttle disc, the difference in manifold depression at either side of the throttle housing determines the direction of flow of ventilation through the crankcase.