71-4
Exhaust Emissions on an Uncontrolled
Passenger Car Using Variable Cam Timing
August 1970
John C. Thomson
Division of Motor Vehicle Research and Development
National Air Pollution Control Administration
Department of Health, Education and Welfare
-------
-...
I"Device Tested
The exhaust emission characteristics of an uncontrolled car.
using the Varicam camshaft timing gear were measured to
determine the effect of this device on emissions. The test
was requested by the U. S. Army Tank-Automotive Command.
To obtain emissions data, a 1962 Chevrolet Biscayne with a
283 cubic inch engine was used both with the Varicam
installed and with no device. In order to control temperatures,
which may be higher than normal due to lean carburetion and
disconnecting the vacuum advance control, a General Motors
temperature sensor was installed with the Varicam to allow
normal vacuum advance under conditions of high temperature.
For full test data the engine was operated using both the
stock carburetor and a special lean limit carburetor. This
is a carburetor with the leanest air fuel ratio allowed
during production. All tests were run using Indolene 30 fuel.
Test Used
The following tests were conducted:
1. Standard 1968 Federal test procedure for exhaust .
emissions with both cold and hot start (FTP hot or cold).
2. A closed, constant volume sampling technique using
nine (9) repeats of the Federal emissions test cycle
( 9 - cvs ) . .
Emission values were obtained both on a concentration basis
and on a mass basis.
Closed cycle data was taken using a constant volume sampling. . .
technique. The 9 CVS tecnnique""is s'imilar' fo - th'e 197~_p_~0_ce9.ur.e;-. '-n
using the 1970 driving schedule instead of the cycle prescribed
in the July 15,1970, Federal Register. The bag samples were
analyzed using non-dispersive infrared analyzers for carbon
monoxide, flame ionization detector for unburned hydrocarbons
and an electro-chemical technique for oxides of nitrogen.
Emission Results
The data shown in Table 1 compares the device using two (2)
different carburetors both with and without the Varicam
device. The GM temperature sensor was used on the Varicam
tests when the vacuum advance was disconnected. The test
run after removal of the Varicam with the same ignition and
carburetor settings showed poor driveability. The engine
performed well with the Varicam installed even with large
ignition 'changes. Thus the Varicam device~ while not showing
-------
- 2 -
any great advance by itself in emissions reduction, allows
radical change in timing without adversely affecting drive-
ability. The baseline tests described in Table 1 are tests
with the Varicam device removed and under conditions described
with each test. The primary claim for this device is for
increasing horsepower and the cam timing is set for this
effect. The effect of tailoring cam timing for emissions has
not been investigated by NAPCA, however contacts with industry
with this information are being made.
The data shown in Table 1 shows what may appear to be
inconsistent data. For the hot cycle data in the as
installed condition, both HC and CO were consistent with
prior hot start data before the carn was installed. With the
ignition optimized and a small air leak, only the first bag
sample was usable due to some unknown leakage problem. lJ~hus
the data was reported as 5 CVS, this being the first five (5)
cycles of the cold start.
After the lean carburetor was installed with the GM kit and
optimized ignition advance, both the CVS and FTP hydrocarbon
levels went up. Both CO readings went down and NOx was about
the same. When the Varicam was removed, the hydrocarbon
level on the FTP did not increase although the CVS number was
higher. This is caused by the increase in air flow due to
the inability of the engine to run smoothly on the same
settings that were possible with the Varicam.
When the engine was returned to manufacturer's specifica':;ion
for baseline measurem~nts, the CO and HC increased to the
level experienced prior to the Varicam evaluation. When the
lean carburetor was installe~both the HC and CO went down
considerably from the stock carburetor levels. The correlation
between the FTP and CVS shows changes which would indicate
that the lean carburetor air flow was similar to the air flow
found with Varicam.
Conclusions
1. The use of the Varicam allowed ignition changes without
adversely affecting driveability.
2.
The Varicam could be optimized for moderately low emissions.
3. It appears that cam timing may have some effect on
emissions and further investigations are warranted.
-------
...
TABLE
1
Varicam - Stock carb., as installed hot cycle FTP
HC = 469 ppm
co = 1. 54%
Varicam - Stock carb., ignition optimized, intake leak
FTP Cold
HC = 136 ppm
CO = 2.7%
5 CVS Cold
HC . = 4.8 gpm
CO = 76 gpm
NOx = 1.5 gpm
Varicam - Lean carb., GM kit, cold start, ignition advance
FTP
HC = 190 ppm
CO = 1. 3%
NOx = 620 ppm
9 CVS
HC = 5.5 gpm
CO = 61 gpm
NOx = 1. 7 gpm
iaseline - Lean carb., GM kit, ignition advance, poor driveability
FTP
HC =.210 ppm
CO = 2.3%
9 CVS
HC = 6. 4 gpm
CO = 61 gpm
NOx = 1.7 gpm
Baseline - Manufacturer's specification, Stock carbo
FTP
HC = 800 ppm
co = 3.6%
NOx = 408 ppm
9 CVS
HC = 12.9 gpm
CO = 123 gpm
NOx = 3.2 gpm
Baseline - Manufacturer's specification, Lean carbo
FTP
HC = 508 ppm
CO = 1. 9%
NOx = 866 ppm
9 CVS
HC = 7.3 gpm
CO = 46 gpm
NOx = 2.5 gpm
------- |