EMISSIONS
AND EXHAUST
BASICS
Every kitchen has leftovers and garbage, and this engine
kitchen is no exception.Today’s cars reduce these leftovers
with a precise, calculated combustion recipe; they then recycle
any remaining leftovers via the emission system; and they
dump the garbage with a few escaping leftovers out the
tailpipe (Figure 7–1).
127
Chapter 7
Figure 7–1
New cars reduce and recycle recipe left-
overs with minimal garbage dumping into
the world’s atmospheric garbage can.
128 ■ Recipes for Car Care: The Consumer’s Guide to Auto Health
Unfortunately, the world’s atmosphere is the garbage can. Ideally, there
are no leftovers and a little, harmless garbage consisting of water and
carbon dioxide.
The combustion recipe is:
Air + Fuel + Spark = Power + Garbage (water and carbon dioxide)
O2 + HC + Match = Hp + H2O + CO2
The air’s oxygen (O2) combines with fuel (HC for hydrocarbons) to pro-
duce power (Hp for horsepower) and garbage (water, H2O; and carbon
dioxide, CO2; note that carbon dioxide has two oxygens, di[two]oxides
O2). (Figure 7–2). Remember that water at the tailpipe is a sign of a suc-
cessful combustion recipe. (It reminds me of planes flying overhead,
with their vapor trails tagging behind.Their vapor—water steaming—
indicates a fine recipe. )
Unfortunately, reality sets in and instigates a little trouble: too often
there are extra HCs (fuel) in the recipe. Some escape out the tailpipe
as HC which pollutes; others combine with the limited O2 (oxygen) to
form CO (carbon monoxide; note that carbon monoxide has only one
oxygen—a small point but it creates a very poisonous gas).The
Figure 7–2
Fuel (hydrocarbons) and oxygen (O2) react chemi-
cally to produce water (H2O) and carbon dioxide
(CO2.) Problems arise with too many hydrocarbons.
Chapter 7: Emissions and Exhaust ■ 129
tailpipe then emits HC and CO (and NOX for nitrous oxides), all big air
polluters.
With hydrocarbons, carbon monoxide, and nitrous oxides billowing out
tailpipes (very bad news for the ozone layer, air quality,