High Altitude Compensation; Exhaust Emission Control - Lotus TURBO ESPRIT Service Manual

Page 16
SECTION LD
LD.
11
.
-
HIGH ALTITUDE COMPENSATION
Operating the engine at high altitude where the air density i s lower, requires that
some compensation be made by the fuel metering system to prevent the mixture
becomi ng too rich.
This
compensation
is
achieved by incorporating an aneroic capsule into the base of the
warm up regulator. The valve rod i s extended to abut against the capsule, which
i s
held i n a 'flattened' condition by atmospheric pressure and a leaf spring as shown i n
the warm up regulator diagram. A t high altitude, the reduced atmospheric pressure
results i n the aneroic capsule 'expanding' and exerting an additional closing force on
the control pressure valve, raising the control pressure and compensating the mixture
strength for altitude.
LD.
12
-
EXHAUST
EMISSION
CONTROL
The minimum production of harmful exhaust gas emissions i s achieved primarily through
the use of starter and main 'three way' catalysts combined with very accurate fuel metering.
a
The optimum air/fuel ratio for minimum emission of a l l three noxious components
-
carbon monoxide
CO,
unburnt hydrocarborn HC, and nitrogen oxide NOx, and also
for minimum f u e l consumption w i t h maximum driveabilitpis about
14
to
1
by weight.
This i s sometimes referred to as the 'stoichiometric ratio'.
The air/fuel ratio may also be represented
by
expressing the amount of air present i n
the mixture as a proportion of that amount required for a stoichiometric ratio.
This
proportion, the excess air factor, when used i n connection with Bosch fuel injection, i s
referred to by the Greek letter Lambda (L)
.
Thus, when Lambda (L) =
1
,
the correct
amount of ai; i s present, and the air/fvel ratio
=
14
to
1
.
Excess-air factor
L
When
L
I s
greater than
1,
too much air
i s
present and the mixture i s lean. When'
L
i s
less than one, too l i t t l e air i s present, and the mixture rich.