MACHINERY LUBRICATION- INDIA SEPTEMBER-OCTOBER 2019 | Page 8

AS I SEE IT
the liner usually occurs during the
compression stroke. The oil control ring
scrapes the oil from the cylinder wall.
The scraped oil flows to the ring drain
holes/cavities. Oil left behind on the
cylinder wall is needed to lubricate the
compression rings. Once oil moves past
the compression rings, it is difficult for
the oil to return to the sump. However,
blow-by gases can provide a transport
medium to help recycle the oil back to
the sump (see Figure 1).
5,000
4,500
Engine C
4,000
Long-haul
Class 8 Truck
3,500
3,000
Engine B
2,500
2,000
1,500
1,000
Engine A
500
0
1
5
9
13
17
21
25
29
33
37
41
45
49
THOUSANDS OF MILES SINCE OIL CHANGE
Figure 3. Effects of the oil change interval on miles per quart of oil (Ref. Carver, Exxon)
chamber during normal operation. Hot
exhaust gases burn oil on stems of the
exhaust valves. If there’s too much
clearance between the valve stems and
guides, the engine will suck more oil
down the guides and into the cylinders.
This could be caused by valve guide
wear and seals that are worn, cracked,
missing, broken or improperly installed.
The engine may still have good
compression but will burn a lot of oil.
Oil Flow Through the Piston Ring-pack
Engine oil is designed to produce an oil
film on the cylinder walls. While the oil
control ring on the piston squeegees
much of it off, a thin film will still
remain. When the engine decelerates,
high negative pressures suck oil in the
combustion chamber and out the
exhaust manifold.
The problem is more pronounced when
rings or cylinders are badly worn or
damaged, but it can also occur if the
cylinders were not honed properly
(out-of-round or surface finish defects)
when the engine was built (or rebuilt) or
if the rings were installed improperly.
6 | September - October 2019 |
Much of the oil that is transported
through the piston ring-pack and along
Piston Ring-pack Deposits and
Movement
Piston ring-pack deposits can sharply
reduce ring movement and flexing.
Likewise, ring movement can greatly
influence where deposits form and the
How Oil Consumption Influences
Tailpipe Emissions and Health
As engines age and wear, they become greater consumers of crankcase oil. Solid
contaminants combined with soot and other oil suspensions influence engine wear,
deposits and oil economy (oil consumption rate). When oil is consumed, it enters the
combustion chamber, burns with the fuel and is pushed out with exhaust gases as
particles and volatile hydrocarbons.
Fresh new lubricants have more volatile light-end molecules and are more prone to
hydrocarbon emissions. As the oil ages, the hydrocarbon emission levels off but can
pick up again if the oil becomes contaminated with fuel (fuel dilution), such as from
short run times or long idles. However, in general, the service life of the oil has no
significant influence on carbon monoxide and nitric-oxide emissions.
The level of exhaust emissions can increase considerably over time, corresponding
to engine wear and deposit formation. This leads not only to greater exhaust
particulates but also to a higher percentage that are hydrocarbon, which is a
byproduct of oil consumption. It has been observed that lubricating oil is a significant
contributor to the particulate emissions signature as the engine ages, especially with
diesel engines. The obvious strategy to control/reduce hydrocarbon emissions is to
decrease oil consumption. This, in large part, is accomplished only by controlling
combustion efficiency, wear and deposits (especially through good lubrication and
filtration practices).
Nitrogen oxides (NOx) consist of nitric oxide (NO) and nitrogen dioxide (NO2).
These ozone precursors also lead to smog when exposed to hydrocarbon gases
and sunlight. As a health hazard, NOx can potentially cause irritation and
damage to lung tissue as well as paralysis. Because of regulatory requirements
and environmental protection pressures to lower both particulates and NO2,
increased pressure has been placed on lubricant formulation, engine design and filter
performance.
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