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Tech Corner-continued

Source of crankcase gases

Blow-by, as it is often called, is the result of combustion material from the combustion chamber "blowing" past the piston
rings and into the crankcase. These blow-by gases, if not ventilated, inevitably condense and combine with the oil vapor
present in the crankcase, forming sludge or causing the oil to become diluted with unburnt fuel. Excessive crankcase
pressure can furthermore lead to engine oil leaks past the crankshaft seals and other engine seals and gaskets. Therefore,
it becomes imperative that a crankcase ventilation system is used.

Atmospheric venting

Until the early 20th century, blow-by gases escaped from the crankcase by leaking through seals and gaskets. It was
considered normal for oil to leak from an engine and drip onto the ground, as this had also been the case for steam engines
in the decades before. Gaskets and shaft seals were intended to limit the leakage of oil, but they were usually not expected
to entirely prevent it. The blow-by gases would diffuse through the oil and then leak through the seals and gaskets into the
atmosphere, causing air pollution and odors. The first refinement in crankcase ventilation was the road draft tube. This is
a pipe running from the crankcase (or the valve cover on an overhead valve engine) down to an downwards-facing open
end located in the vehicle's slipstream. When the vehicle is moving, airflow across the open end of the tube creates suction
(a "draft") that pulls gases out of the crankcase. To prevent a vacuum being created, the blow-by gases are replaced by
fresh air using a device called a breather. The breather is often located in the oil cap. As per the earlier engines, the road
draft tube system also created pollution and objectionable odors. The draft tube could become clogged with snow or ice,
in which case crankcase pressure would build and cause oil leaks and gasket failure. On slow-moving delivery vehicles
and boats, there was often no suitable air slipstream for the road draft tube. In these situations, the engines used positive
pressure at the breather tube to push blow-by gases from the crankcase. Therefore, the breather air intake was often located
in the airflow behind the engine's cooling fan. The crankcase gases exited to the atmosphere via a draft tube.

Positive Crankcase Ventilation (PCV)

History

Although the modern purpose of a positive crankcase ventilation (PCV) system is to reduce air pollution, the original
purpose was to allow an engine to operate underwater without the water leaking in. The first PCV systems were built
during World War II, to allow tank engines to operate during deep fording operations, where the normal draft tube
ventilator would have allowed water to enter the crankcase and destroy the engine. In the early 1950s, Professor Arie Jan
Haagen-Smit established that pollution from automobile engines was a major cause of the smog crisis being experienced
in Los Angeles, California. The California Motor Vehicle Pollution Control Board (a precursor to the California Air
Resources Board) was established in 1960 and began researching how to prevent blow-by gases from being released
directly into the atmosphere. The PCV system was designed to re-circulate the gases into the air intake so that they could
be combined with the fresh air/fuel and more completely combusted. In 1961, California regulations required that all new
cars be sold with a PCV system, therefore representing the first implementation of vehicle emissions control device.[6]
By 1964, most new cars sold in the U.S. were so equipped by voluntary industry action so as not to have to make multiple
state-specific versions of vehicles. PCV quickly became standard equipment on all vehicles worldwide because of its
benefits not only in emissions reduction but also in engine internal cleanliness and oil lifespan In 1967, several years after
its introduction into production, the PCV system became the subject of a U.S. federal grand jury investigation, when it
was alleged by some industry critics that the Automobile Manufacturers Association (AMA) was conspiring to keep
several such smog reduction devices on the shelf to delay additional smog control. After eighteen months of investigation,
the grand jury returned a "no-bill" decision, clearing the AMA, but resulting in a consent decree that all U.S. automobile
companies agreed not to work jointly on smog control activities for a period of ten years. In the decades since, legislation