Chevrolet TrailBlazer, Service Manual

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movement with the inversion takes place to allow the smog layer to rise above ground
level but the pollutants still cannot dissipate. This inversion can remain for days over an
area, with the smog level only rising or lowering from ground level to a few hundred feet
high. Meanwhile, the pollutant levels increase, causing eye irritation, respiratory problems,
reduced visibility, plant damage and in some cases, even disease.
This inversion phenomenon was first noted in the Los Angeles, California area. The city
lies in terrain resembling a basin and with certain weather conditions, a cold air mass is
held in the basin while a warmer air mass covers it like a lid.
Because this type of condition was first documented as prevalent in the Los Angeles area,
this type of trapped pollution was named Los Angeles Smog, although it occurs in other
areas where a large concentration of automobiles are used and the air remains stagnant
for any length of time.
Heat Transfer
Consider the internal combustion engine as a machine in which raw materials must be
placed so a finished product comes out. As in any machine operation, a certain amount of
wasted material is formed. When we relate this to the internal combustion engine, we find
that through the input of air and fuel, we obtain power during the combustion process to
drive the vehicle. The by-product or waste of this power is, in part, heat and exhaust gases
with which we must dispose.
The heat from the combustion process can rise to over 4000°F (2204°C). The dissipation
of this heat is controlled by a ram air effect, the use of cooling fans to cause air flow and a
liquid coolant solution surrounding the combustion area to transfer the heat of combustion
through the cylinder walls and into the coolant. The coolant is then directed to a thin-
finned, multi-tube radiator, from which the excess heat is transferred to the atmosphere by
1 of the 3 heat transfer methods, conduction, convection or radiation.
The cooling of the combustion area is an important part in the control of exhaust
emissions. To understand the behavior of the combustion and transfer of its heat, consider
the air/fuel charge. It is ignited and the flame front burns progressively across the
combustion chamber until the burning charge reaches the cylinder walls. Some of the fuel
in contact with the walls is not hot enough to burn, thereby snuffing out or quenching the
combustion process. This leaves unburned fuel in the combustion chamber. This unburned
fuel is then forced out of the cylinder and into the exhaust system, along with the exhaust
gases.
Many attempts have been made to minimize the amount of unburned fuel in the
combustion chambers due to quenching, by increasing the coolant temperature and
lessening the contact area of the coolant around the combustion area. However, design
limitations within the combustion chambers prevent the complete burning of the air/fuel
charge, so a certain amount of the unburned fuel is still expelled into the exhaust system,
regardless of modifications to the engine.