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OCR for page 39
' ! '
Automotive Emissions
JOHN H. JOHNSON
Michigan Technological University
Pollution from Automobiles Problems and Solutions / 40
Emissions Standards and Control Approaches / 40 Fuel
Economy / 40 In-Use Passenger Car Emissions / 41
Emissions Regulations / 42
Emission Test Procedures / 43 Emission Standards / 45 U.S. Fuel
Economy Standards / 46
Vehicle and Emission Control System Technology / 46
Spark-Ignition Gasoline-Powered Vehicles / 47 Diesel-Powered
Passenger Cars: Particulate Control / 48 Diesel-Powered
Heavy-Duty Vehicles / 49
In-Use Vehicle and Engine Characteristics / 50
Gasoline-Powered Passenger Cars and Trucks / 50 Diesel-Powered
Passenger Cars / 52 Diesel-Powered Trucks / 52
Models for Predicting Future Emissions / 53
Fuels and Fuel Additives / 54
Trends in Gasoline Fuel Properties / 54 Fuel Usage
Trends / 56 Methanol-Fueled Vehicles / 56 Trends in Diesel Fuel
Properties / 59 Refueling Emissions / 59 Additives / 60
Methods for Measuring the Unregulated Pollutants / 61
Sampling / 62 Analytical Methods / 63
Current Regulated and Unregulated Emissions / 64
Regulated Emissions / 64 Unregulated Emissions / 64
Summary of Research Recommendations / 70
Air Pollution, the Automobile, and Public Health. (it) 1988 by the Health Effects
Institute. National Academy Press, Washington, I).C.
39
OCR for page 40
40
Automotive Emissions
Pollution from
Automobiles-Problems
and Solutions
Concern about the automobile as a source
of air pollution has been expressed period-
ically, but national concern was first evi-
denced in the 1960s when California estab-
lished the first new car emission standards.
The scientific basis of this effort is the
pioneering atmospheric chemistry research
of A. I. Haagen-Smit, who showed that
photochemical reactions among hydrocar-
bons (HC) and nitrogen oxides (NOX) pro-
duce the many secondary pollutants that
reduce visibility and cause eye and nose
irritation in the Los Angeles area.
This paper reviews our current knowl-
edge of automotive emi~cion~ in~l',rlin~
standards, control technology, fuel econ-
omy, fuels and additives, in-use emissions,
measurement methods for unregulated pol-
lutants, and models for predicting future
automotive emissions. Fuel economy is in-
cluded because achieving high fuel econ-
omy and low emissions together makes the
engineering effort more difficult. Emissions
and fuel economy are interrelated because
both are influenced by the engine combus-
tion system design. In practice, the strin-
gency of emission standards determines the
importance of this interrelationship. After
current knowledge in each area has been
reviewed, important gaps in our knowl-
edge are identified and research needed to
fill these gaps is described.
Emissions Standards and Control
Approaches
MA ~ _^ _% If-· ~
Evolving emission standards have resulted
in three levels of stringency, and in turn,
three types of control technology. Figure 1
describes the technologies applied in each
of the three phases and the general time
periods in which they were applied to cars,
light-duty trucks, and heavy-duty trucks
(Ford Motor Co. 1985a). The percent re-
duction in the HC, carbon monoxide
(CO), and NOX emissions are also shown.
Air/fuel (A/F) ratio, which is controlled
by the carburetor or fuel injection system,
is the most important variable in determin-
ing emissions and in applying catalyst tech-
nology. Figure 2 (Heinen 1980) is a plot of
NOX, HC, and CO concentrations in the
exhaust versus A/F ratio for a typical gas-
oline engine. It is impossible to achieve the
low emissions demanded by federal stan-
dards by A/F ratio control alone since the
concentrations of the three pollutants are
not minimums at the same A/F ratio. In
fact, when CO and HC concentrations are
a minimum, at an A/F ratio of around 16:1,
NOX production is close to a maximum.
Also shown is the A/F ratio for maximum
power (13.5:1) and maximum fuel economy
(17:1~. The region where A/F ratio exceeds
17.5:1 is the lean bum region where misfires
can occur along with slow flame speeds,
causing increased HC concentration. The
A/F ratio effects are used in all phases of
control. The stoichiometric ratio of 14.7:1 is
necessary in the Phase III control using three-
way catalysts since the A/F ratio must be in a
narrow window within + 0.05 of the stoi-
chiometric ratio to achieve high HC, CO,
and NOX control efficiencies simultaneously.
Exploring the lean burn region is an impor-
tant area of research and development be-
cause of the potential of improved fuel econ-
omy and adequate emission control with
only an oxidation catalyst.
Fuel Economy
Federal regulations also mandate automo-
tive fuel economy. The period from 1968
to 1974 resulted in primary emphasis on
emission control with loss of fuel economy
from lower compression ratios, changes in
spark timing, A/F ratio and axle ratio
changes, and exhaust gas recirculation. Fig-
ure 3 (Heavenrich et al. 1986) shows the
U. S. fleet combined, city, and highway
fuel economy data for each model year
since 1974. The figure also includes infor-
mation on average vehicle weight. The fuel
economy from 1977 to 1980 improved al-
most exactly in proportion to the decreas-
ing weight of vehicles. If the data in figure
3 were normalized to the 1978 weight mix,
it would show that fuel economy improve-
ments leveled out in 1982. With the intro
OCR for page 41
John H. Johnson
Major Emission Reduction Phases
REDUCTION (%) FROM UNCONTROLLED
TIME Light Heavy
FRAME Car Truck Truck
pre 1968
1 975
1 979
1981
1984
1 987
and
beyond
41
TECHNOLOGY APPLICATIONS
_ Phase I Uncontrolled to INITIAL CONTROL LEVELS
HCs CO NOx · Closed crankcase controls (HCs)
72% 67% 24% · Evaporative emission controls (HCs)
· Engine modifications for improved combustion
(HCs and CO)
· Air injection (thermactor) systems
_ ,. .~ ~ ^~
Ones and ~V)
· Exhaust gas recirculation (NOx)
_ Phase 11 HCs CO NOx INTERMEDIATE"TECHONOLOGY-LIMITED"
86% 82% 24% LEVELS
..................................
. · 1st-Phase controls
_.......................................
........... .. . .
· Oxidation catalysts (HO & CO control)
..........................
. .. . . . .......
...................................
_ . · Early-stage electronic engine controls
................................................ ............................. .
. (optimized fuel economy, driveability,
.... ................. .............................
_ . . emissions control performance)
...................................... .............................
~....................
.............................. ............. , .................................................
Phase 111 HCs CO NO ULTIMATE CONTROL LEVELS
...................................... ............ x
. . . ( ar) · 1 st Phase controls
............................... ............................................. .........................
. . . . . 90% 90% 50% (Truck) · Three way catalyst systems (HCs' CO1
................. ...... ,., ... . . ......... A
. Nux)
............................. , , .............. ... .................... ..
.. , ,., ..............................................
.,, .................... , . ...............
. . · Particulate traps (diesels)
............................. .
..................................................... ......................................................... .......
.................... , , : .
. . . . , .
Figure 1. Major phases in the reduction of automotive emissions. (Adapted with permission from Ford Motor
Co. 1 985a. )
auction of the oxidation catalytic converter
in 1975, improved fuel economy and re-
duced emissions occurred simultaneously.
Further emission reduction with simulta-
neous fuel economy improvement contin-
ues through application of new technology,
especially computer engine control.
In-Use Passenger Car Emissions
The in-use emissions from passenger cars
exceed the new car standards mandated by
law. Nonetheless, emissions continue to
decrease in spite of high tampering rates
and fuel switching (that is, using leaded
fuel in engines developed to run on unlead
.
Figure 5 shows EPA emission factors
data as analyzed by General Motors Corp.
(1985a). The measured emission concentra
tions for various model years are compared
to the standards that were in effect during
those years. The measured NO, concentra
tions follow the standards fairly well. Al
though the measured HC and CO concen
trations are higher than the standards, the
difference between the actual emissions and
the standards appears to be narrowing (al
though the ratio is not decreasing) as im
proved technology, more frequent inspec
tion and maintenance, and better training
of mechanics has occurred. Even though
the overall trend of emissions is down, a
ed fuel). From field surveys in 14 cities,few vehicles have high emission levels, as
Greco (1985) found the overall tamperingshown in figure 6, probably because of
rates and catalyst tampering rates shown in
figure 4.
electronic problems rather than catalyst re-
moval or misfueling problems.
OCR for page 42
42
Emissions Regulations
In the 1960s, motor vehicles were identified
as one of the primary sources of air pollu-
tants in urban areas. Emission standards for
passenger cars were first imposed in Cali-
- fornia in 1965. These were followed by
U.S. federal standards in 1968. The 1970
Clean Air Act further imposed stringent
HC, CO, and NOX reductions for 1975 and
1976. These reductions were subsequently
delayed and changed by the 1974 Energy
40r
~ 35
-
O 30
8
J 25
LL
Lu 20
LL
11
~ 15
Automotive Emissions
Maximum power
IStoichiometric mixture
Maximum fuel economy
Lean burn area
400C
300C
Q
x 200C
o
1 OOC
o
- 800 .
- 600 ~CO /
_~ 400 \ \\/
-200 _ \/\
i'" ~
O ___~' I
8 10 12
lo
'A
14 16 18 20 22
AIR/FUEL RATIO
c'
o
-
4 ~
-
-
Figure 2. Concentrations of HC, CO, and NOX emissions as a function of air/fuel
ratio in a typical gasoline engine. (Adapted with permission from Heinen 1980, and
the Society of Automotive Engineers, Inc.)
and Environmental Coordination Act and
the 1977 Clean Air Act Amendments. Rec-
ognition of the motor vehicle as a major
source of pollutants has spread to other
countries, of which many have imposed
diverse standards and test procedures re-
flecting various degrees of stringency. The
differences have come about because of dif-
ferent regulatory philosophies and air quality
goals, in combination with concerns about
the conflicting goal of improved fuel eff~-
ciency (Barnes and Donohue 1985~.
Coo
4500
10L
=
0 Highway
0< a` ~o Combined
'~ ~ City
· Weight
l
75 76 77 78 79 80 81 82 83 84 85 86
MODEL YEAR
Figure 3. U.S. fleet fuel economy and average vehicle weight by model year.
(Adapted with permission from Heavenrich et al. 1986, and the Society of
Automotive Engineers, Inc.)
4000 imp
:I1
m
3500 ~
m
I
3000
2500
J 2000
OCR for page 43
John H. Johnson
50
A
0-
30
a 20
llJ
~ 10
rig
o Overall tampering
~ Catalyst tampering
v In.
84 83 82 81 80 79 78 77 76 75
VEHICLE MODEL YEAR
Figure 4. Overall and catalyst tampering rates by
vehicle model year, based on 1984 survey. (Adapted
from Greco 1985.)
Emission Test Procedures
Passenger Cars. Emissions come princi-
pally from three automotive sources: the ex-
haust, the fuel system (evaporative), and crank-
case ventilation gases. To give the standard
(maximum allowable level of emission in
grams per mile) operational meaning, two ma-
jor aspects must be defined: the driving cycle
and the emissions sampling method. Driving
cycles are discussed below and sampling meth-
ods will be covered in a later section.
12 _ HO
10 _
8 _
6 _
4 _
~ 2 _
~ O
z 100 _
in 80 _
cn _
60 _
40 _
~20 E
u.l o
~ 5
lo:
4
3
2 _
1 _
O ~To a-" 's80 81-82 83-8s o_
control
):
VEHICLE MODEL YEAR 0
Figure 5. Average vehicle lifetime HC, CO, and NOx
emissions compared with standards (STD), by model
year for all industry passenger vehicles. (Adapted with
permission from General Motors Corp. 1985a.)
43
Regulations require exhaust emission
measurements during the operation of the
vehicle (or engine) on a dynamometer dur-
ing a driving cycle that simulates vehicle
road operation. The approach to driving
cycles by various regulatory authorities
represent two basic philosophies. Accord-
ing to the first, the driving cycle is made up
of a series of repetitions of a composite of
various vehicle operating conditions repre-
sentative of typical driving modes. The
European Economic Community and Jap-
anese cycles reflect this philosophy. Ac-
cording to the second, the composite of
driving modes is an actual simulation of a
road route. The United States, Canada,
Australia, Sweden, and Switzerland all use
a version of the federal test procedure
(FTP). The FTP cycle is divided into a
"transient" portion and a "stabilized" por-
tion with a total cycle time of 1,372 see, a
driving distance of 7.5 miles, and an aver-
age speed of 19.7 miles per hour (mph).
Two such cycles are run: one with the
vehicle at an ambient temperature of
1~30°C before start ("cold" cycle), and
one with the engine control system hot
("hot" cycle) after a 10-min shutdown after
running the cold cycle.
Trucks. Many of the light-duty trucks
intended primarily for the carrying of
goods are also capable of use as passenger
vehicles. The gross vehicle weight for
light-duty trucks in the United States is less
than 8,500 lb; trucks heavier than 8,500 lb
300-
200
:
100
.~_ ~ no. ...
I~ CAL ~
' 1 ' 1 ' -r ' 1
1 20,000 40,000 60,000 80,000
ODOMETER MILES
Figure 6. Scatter plots of CO emissions from 703
1981 model-year federal cars. (Adapted with permis-
sion from General Motors Corp. 1985a.)
OCR for page 44
44
Automotive Emissions
Table 1. Motor Vehicle Emission Standards in the United States
Emission Ratesa
Federal
California
Evap Partic- Evap Partic
Model HC CO NOX (g/ ulatesb HC+ HC CO (g/ NO.` (g/ ulatesb HC+
Year (g/mi) (g/mi) (g/mi) test) (g/mi) NOy (g/mi) mi) (g/mi) test) (g/mi) NOr
Passenger Cars
Pre
control 10.60C 84.0 4.1 47 10.60' 84.0 4.1 47
1966 6.30 51.0 (6.0)
1968 6.30 51.0 (6.0)d 6.30 51.0
1970 4.10 34.0 4.10 34.0 6
1971 4.10 34.0 4.10 34.0 4.0 6
1972 3.00 28.0 2.90 34.0 3.0 2
1973 3.00 28.0 3.0 2.90 34.0 3.0 2
1974 3.00 28.0 3.0 2.90 34.0 2.0 2
1975 1.50 15.0 3.1e 2 0.90 9.0 2.0 2
1977 1.50 15.0 2.0 2 0.41 9.0 1.5 2
1978 1.50 15.0 2.0 be 0.41 9.0 1.5 6
1980 0.41 7.0 2.0 6 0.39f 9.0 1.0 2
1981 0.41 3.4 1.0 2 0.39 7.0 0.7 2
1983 0.41 3.4 1.0 2 0.398 7.0 0.4 2
1984 0.41 3.4 1.0 2 0.39 7.0 0.4 2 0.60
1985 0.41 3.4 1.0 2 0.39 7.0 0.4 2 0.40
1986 0.41 3.4 1.0 2 0.60 0.39 7.0 0.4 2 0.20
1987 0.41 3.4 1.0 2 0.20 0.39 7.0 0.4 2 0.20
1989 0.41 3.4 1.0 2 0.20 0.39i 7.0 0.4 2 0.08
Light-Duty Trucks
1975 2.00 20.0 3.1 2 2.0
1976 2.00 20.0 3.1 2 0.90 17.0 2.0
1978 2.00 20.0 3.1 6 0.90 17.0 2.0 6
1979 1.70 18.0 2.3 6 0.50j 9.0 2.0' 6
1980 1.70 18.0 2.3 6 0.50/ 9.0 2.0' 2
1981 1.70 18.0 2.3 2 0.50 9.0 1.5 2
1983 1.70 18.0 2.3 2 0.50 ~9.0 1.0P 2
1984 0.80 10.0 2.3 2 0.50 9.0 1.0P 2
1986q 0.80 10.0 2.3 2 0.50 9.0 1.0 2
1988 0.80 10.0 1.7 2 0.50 9.0 1.0 2
(Table continued next page.)
NOTE: Evap = evaporative HC.
a Emission rates for HC, CO, NOB by (or adjusted to equivalent) 1975 Federal Test Procedure.
b Diesel passenger cars only.
c Crankcase emissions of 4.1 g/mi not included; fully controlled.
NOX emissions (no standard) increased with control of HCs and CO.
e Change in test procedure.
f NMHC standard (or 0.41 g/mi for total HC).
g 0.7 NO.~ optional standard 1983 and later, but requires limited recall authority for 7 yr/70,()00 mi.
h Optional standard, 0.3 g/mi, requires 7 yr/75,000 mi limited recall authority.
' Primary standard = 0.4 g/mi required on 90% of production after 1989.
0.41 for <4,000 lb.
k 1.5 for <4,000 lb.
0.39 for <4,000 lb (nonmethane) and in following years.
m 0.6 for >6,000 lb and in following years.
n 2.0 for >6,000 lb.
° California: 1.0 NOR optional standard for 1983 and later, but requires limited recall authority for7 yr/75,000 mi.
Primary standard = 0.4 g/mi.
OCR for page 45
John H. Johnson
45
Table 1. Continued
Emission Rates
Federal
California
Partic- Partic
HC CO NOX ulates HC ulates
(g/ (al (g/ Evap (g/ (g/ CO NO. ~Evap (g/
Model bhp- bhp- bhp- (g/ bhp- HC+ bhp- (g/bhp- (g/bhp- (g/ bhp- HC+
Year hr) hr) hr) test) hr) NOy hr) hr) hr) test) hr) NO.
Heavy-Duty Truck and Bus Engines'
1969 " ''
1972 . v
1973 40.0' 16.0
1974 40.0 16.0 40.0 16.0
1975 40.0 16.0 30.0 10.0
1977 40.0 16.0 1.0 25.0 7.5 5.0
1978 40.0 16.0 1.0 25.0 7.5 6 5.0"
1979 25.0 10.0 1.5 25.() 7.5 6 5.0
1980 1.5 25.0 10.0 1.0 25.0 7.5 2 6.0
1984 1.5 25.0 10.0 0.5 25.0 7.5 2 4.5"'
1985 1.9 37.1- 10.6Z 3cia 0 5 25.0 7.5 2 4 5i''bb
1987 1.1 14.4 10.6 3 0.5 25.0 7.5 2 4.5
1988 1.1 14.4 6.0 3 0.6 0.5 25.0 7.5 2 4.5
1991 1.1 14.4 5.0 3 0.25 0.5" 25.0" 7.5" 2 4.5
NOTE: Evap = evaporative HC.
P 1.5 for >6,000 lb.
q Full useful life requirement = 11 yr/120, 000 mi (was 5 yr/50,000 ml).
r NOX federal standard = 1.2 g/mi under 3,751-lb loaded vehicle weight (LVW), 1.7 g/mi for 23,751 lb L~W,
and 2.3 g/mi for '6,000 lb LVW.
s 1.2 for <3,751 lb.
' Various test methods, values are not strictly comparable.
U275ppmHC, 1.5% CO.
v 180 ppm HC, 1.0% CO.
w A combined standard is optional in lieu of separate HC and NO.~ standards (for example, 1 g HC + 7.5 g NO~
or 5 g tHC+NOxi).
x 1.3 for diesel.
Y 15.5 for diesel.
Z 10.7 for diesel.
aa 4.0 for >20,000 lb.
bb Gasoline only and in following years.
cc 1988 federal standards for NO y have been postponed until 1990.
Separate standard of 0.1 for all 1991 urban buses and all 1994 engines.
ee 1.3 HC, 16.5 CO, 5.1 NO~ for diesel.
SOURCE: Adapted with permission from General Motors Coro. 1986.
are classified as heavy-duty vehicles. The
driving-cycle philosophies for the light
commercial vehicles follow those for pas-
senger cars. For heavy commercial vehi-
cles, engine dynamometers are used, not
chassis dynamometers; that is, the enp;ine
rather than the vehicle is certified. The new
(effective 1985) U.S. transient test proce-
dure for heavy-duty vehicles combines the
two philosophies just described in that the
cycle is made up in a random way from
actual driving cycle data. The use of this
cycle replaces the 13-mode steady-state cy-
cle in use since 1973 in California and since
1974 nationally (U.S. Environmental Pro-
tection Agency 1972~.
Emission Standards
United States. Emissions standards and
test procedures in the United States have
changed significantly since the first auto-
mobile emission standards were imposed in
California in 1966 (see table 1) (General
OCR for page 46
46
Automotive Emissions
Motors Corp. 1986~. Light-duty truck stan-
dards are somewhat higher than the car stan-
dards because of the differences in weight.
The U.S. passenger car regulations re-
quire that the vehicle comply with the
emission standards for five years or 50,000
miles, whichever occurs first. Certification
testing of prototype vehicles for 50,000
miles of use is based on the Automobile
Manufacturers' Association (AMA) 40.7-
mile durability cycle. The cycle consists of
numerous stops, acceleration, and high/
medium-speed driving (maximum of 55
mph) (U. S. Environmental Protection
Agency 1973~.
Europe. The European Economic Com-
munity, an inter-Europe regulatory body,
has announced future model standards for
passenger cars based on three engine size
(displacement) categories. Large-car (> 2-
liter engine displacement) standards are
roughly equivalent to current U.S. stan-
dards although there is no valid correlation
between the distinct U.S. and European
emission test cycles. Standards for medium
cars (1.~2.0 liters) are considered to fall in
the Phase I/Phase II range shown in figure
1. Requirements for small-car levels (< 1.4
liters) are comparable to Phase I require-
ments. The standards include diesels; how-
ever, large diesel cars are only required to
meet medium-car levels.
Japan. Catalyst forcing standards cur-
rently in effect for passenger cars are 0.25
HC/2.1 CO/0.25 NOX g/km for the
unique 10-mode hot start and 7.0 HC/60
CO/4.4 NOX g/test for the 11-mode cold-
start test procedures. These standards are
generally considered to be equivalent to
current U.S. California levels (Ford Motor
Co. 1985a).
U.S. Fuel Economy Standards
There have been passenger car and light-
truck fuel economy standards since 1978
and 1979, respectively. The manufacturers
are required to conduct passenger car fuel
economy tests according to the U.S. Envi-
ronmental Protection Agency (EPA) urban
or "city" driving cycle the FTP for emis
sion testing described earlier. The EPA also
has a suburban or "highway" cycle that
includes a significant amount of simulated
highway driving. A combined fuel econ-
omy number based on these two tests is
published by the EPA and the U. S. Depart-
ment of Energy and used by manufacturers
in their sales literature.
Manufacturers each have to meet the
Corporate Average Fuel Economy (CAFE)
standards for their sales-weighted fleet. Car
standards started at 18 miles per gallon
(mpg) in 1978, went to 27.5 mpg in 1985,
but were reduced to 26 mpg by the U. S. De-
partment of Transportation for 198~1988.
Vehicle and Emission
Control System Technology
The technology used for emission control
in cars changed rapidly in the 1970s as the
automotive industry spent considerable re-
search and development funds to meet the
stringent emission standards originally set
by the 1970 amend 1977 Clean Air Act
Amendments. This technology is now be-
ing optimized to reduce the product cost
associated with emission controls while im-
proving the in-use durability of the emis-
sion control systems. Heavy-duty gasoline-
powered vehicles have used this technology
as allowable emissions have progressively
decreased.
Control technology is being developed
to meet proposed standards and anticipated
changes in fuels. Proposed 1988, 1991, and
1994 particulate standards require new con-
trol systems for heavy-duty diesels. For the
United States to become less dependent on
imported petroleum fuels, there is interest
in using methanol in passenger cars and
diesel-fueled buses. There are continued
efforts to develop stratified-charge engines
for passenger cars because of their potential
for better fuel economy at equivalent emis-
sions. There is also a demand for develop-
ment of direct-injection diesels that give 15
percent better fuel economy than pre-
chamber or swirl-chamber engines with
equivalent or better emissions. An addi-
tional demand exists for an adiabatic diesel
OCR for page 47
John H. Johnson
47
engine (more precisely, a low-heat-re-
jection engine) that would have improved
fuel economy and lower emissions with a
simpler cooling system, particularly for
vehicles in the heavy-duty class.
Spark-Ignition Gasoline-Powered
Vehicles
During the past 15 years, emissions have
been significantly lowered by improved
design of the engine and fuel system while
still achieving the high fuel economy de-
manded by the federal standards and the
consumer market. These reductions have
come about by A/F ratio control, cylinder-
to-cylinder distribution of air and fuels
choke operation, combustion chamber de-
sign, fuel injection, exhaust gas recircula-
tion (EGR), ignition systems, spark tim-
ing, valve timing, and many additional
design details. The computer scheduling of
spark timing, EGR, A/F ratio, and trans
. . . . . .
mission gear ratio as a tunctlon ot engine
operating conditions are done very pre-
cisely with sensors and actuators. This
scheduling is referred to as the engine cali-
bration. With all of this technology, ve-
hicles still do not meet HC/CO/NOX
standards of 0.4/3.4/1 g/mi without after-
treatment devices. The period after 1983
has seen better optimization of systems and
removing of components to reduce costs,
but nevertheless, catalysts are still neces
sary.
Catalyst Control Systems. Meeting the
1975 MC/CO standards of 1.5/15 g/mi and
at the same time increasing the fuel econ-
omy was achieved through the broad intro-
duction of the oxidizing catalytic con-
verter. The catalyst is cold (1~30°C) at the
start of the FTP cycle and must warm up to
250-300°C before oxidation of CO and HC
occurs. The time required for this is a
function of catalyst design and position but
can be from 20 to 120 sec. The HC emitted
during this period can be one-fourth to
three-fourths of the allowable limit (Hil-
liard and Springer 1984~. The amount of
NOX emitted during the cold start is only
about 10 percent of the allowable limit.
The time period from 1975 to 1984 saw
~ 00 ~ ' NOx ,, CO
z
t) 60 _
IL
z an _
o
En
cr
o
80
40
20
_ ~
Window
O , ~ , // I I
13 14 15 16
AIR/FUEL RATIO
Figure 7. Conversion efficiency characteristics of a
three-way catalyst. (Adapted with permission from
Amann 1985.)
increased fuel economy and improved
emission control through exploitation of
the high HC and CO removal efficiency of
the oxidizing catalytic converter, so that
the engine calibration could be optimized
for efficiency. Progress was made by de-
creasing the cold-start engine-out HC and
CO emissions, by achieving faster con-
verter light-off, by reducing heat loss from
the exhaust system, and by reducing the
deterioration of catalyst performance with
cumulative driving distance (Amann 1985~.
Reducing combustion temperature by
spark retard and/or diluting the incoming
mixture with EGR provided NOX control
during the time period from 1973 to 1980.
The 1981 standards stipulate no more than
1 g/mi NOX, which could not be achieved
either by EGR or engine design and cali-
bration. Two additional catalytic ap-
proaches have gained widespread applica-
tion along with the microprocessor control
system, to provide the necessary control:
the "three-way" catalyst and the "dual"
catalyst.
Three-way catalysts are capable, within a
narrow range of exhaust stoichiometry, of
simultaneously decreasing NOX, HC, and
CO, as shown in figure 7. Within a narrow
range of values of the A/F (approximately
+ 0.05 from the optimum), all three emis-
sions are decreased with a reasonably high
efficiency. An oxygen sensor is used in the
. . . . . .
ex Bust in conjunction Wit ~ a mlcroproces
sor to make this technology feasible.
OCR for page 48
48
Automotive Emissions
CARBURETOR
Al R FU EL
DRIVER ~ AIR 1 l ETERIN l:' ELECTRONIC
SIGNAL ITHROTTLE I DEVICE I 1 CONTRA LEA
ENGINE
mu\ 1
\ - V ~
OXYG EN
SENSOR
Figure 8. System for closed-loop control of A/F
ratio. The oxygen sensor inserted in the exhaust pipe
ahead of the catalyst measures oxygen concentration
and signals the electronic controller to adjust fuel rate
continuously. (Adapted with permission from Amann
1985.)
In a dual catalyst, two catalysts are used
in series- a three-way catalyst followed by
an oxidizing catalyst. Air is injected into
the exhaust gas between the two catalysts
to provide the oxygen necessary for the
oxidizing catalyst to operate efficiently.
Once more, precise A/F ratio control is
required to make the three-way catalyst
function. During the cold-start portion of
the FTP cycle, the air supply to the oxidiz-
ing catalyst can be diverted to the exhaust
ports to add oxygen to the combustion
products of the rich start-up mixture for
faster catalyst light-off and to achieve
higher HC and CO control efficiencies in
the three-way catalyst. The dual-bed con-
verter is more complex than the single-bed
three-way catalyst, because it requires an
. .
extensive air management system.
To maintain A/F ratio control within the
narrow window, closed-loop control (feed-
back control of fuel delivery on oxygen
level in exhaust) was introduced on many
cars in 1981. The schematic of a typical
system is shown in figure 8 (Amann 1985~.
The key element in the closed-loop system
is the oxygen sensor inserted in the exhaust
pipe ahead of the catalyst. It measures
exhaust oxygen concentration and signals
an electronic controller to adjust fuel rate
continuously so that the mixture is main-
tained at the stoichiometric ratio.
Current Control Approaches. Since 1983
the number of engines with some type ot
No particular trend in emission systems is
evident except for the use of heated oxygen
sensors to initiate closed-loop operation
faster and more predictably and to maintain
it during long idling periods. The heated
sensors also deteriorate less with extended
mileage (Way 1985~. Most cars use closed
loop control with a three-way catalyst;
many also have an oxidation catalyst that is
a dual catalyst and one of three air supply
systems (pulse air, air pump, or pro
grammed pump).
Lean-Burn Combustion Systems. An im
portant engine emission control system un
der development is the lean combustion
system. This system uses a closed-loop
microprocessor in conjunction with lean
mixture sensor and an oxidation catalyst.
This alternate emission control approach
achieves good fuel economy (potential
10-15 percent improvement) and also
meets the emission standards by operating
beyond 22:1 A/F where NOX emission is
low enough to meet the 1-g/mi standard.
In this lean operating region, the engine
needs a different sensor design to provide
feedback, and also a highly turbulent fast
burn combustion system so that slow flame
speed and misfires do not cause emissions
and driveability problems. Toyota has de
veloped and marketed such a system in
Japan but not yet in the United States
(Kimbara et al. 1985~.
It may be possible to introduce this type
of system into the U. S. market, but dura
bility and driveability under hot and cold
conditions need to be examined further
(Kimbara et al. 1985~. The other important
technological limit might be that lean burn
could be restricted to cars under 2,500
3,000 lb because NOX generally increases
with vehicle weight.
Diesel-Powered Passenger Cars:
Particulate Control
There has been a major research and devel
opment effort during the past seven years
to develop aftertreatment devices for diesel
passenger cars to meet the federal 0.2 g/mi
tuel Injection has grown drastically, but standard first proposed for 1985 and later
carburetors are still used on many engines. put offuntil 1987. California has a 0.2-g/mi
OCR for page 49
John H. Johnson
r G'owp~ug
Controller ~ driver
to Battery _~
RPM ~ Power
~ control
Pressure
box
') to Glowplug driver
/ ~signal
'\bielow)
Fox. ,~ ~ Pressure
/__~/' \ transducer
Glowplug
igniter
(air
Figure 9. Diesel particulate trapping system utiliz-
ing a ceramic fiber trap, a fuel additive, glow plug
igniters, and exhaust backpressure regeneration con-
trols. (Adapted with permission from Simon and Stark
1985, and the Society of Automotive Engineers, Inc.)
standard that was initiated in 1986, and will
be lowered 0.08 g/mi in 1989. A number of
prototype systems have been built and field
tested to meet the 0.2 g/mi standard. Mer-
cedes-Benz (Abtoff et al. 1985) introduced a
catalytic trap oxidizer in 1985, in conjunc-
tion with careful modification of the engine
(in particular, the turbocharger). The sys-
tem meets and is certified to the 1986
49
California standards and has been sold in
the 11 western states. Volkswagen has de-
veloped a prototype system that uses a
Corning ceramic particulate filter in con-
junction with Lubrizol 8220 manganese
(Mn) additive. The additive consists of
nonstoichiometric Mn fatty acid salts dis-
solved in naphtha, which is metered from a
separate fuel-additive storage tank on the
vehicle (lifetime filling) and mixed with the
fuel (Wiedemann and Neumann 1985~.
Emissions of Mn oxide of all valence states,
as well as MnSO4, may occur. Data sug-
gest that most of the Mn residue is in the
form of sulfate.
General Motors has also tested a system,
shown in figure 9, with on-board tank-
blending, additive dispensing, and ceramic
fiber trap (Simon and Stark 1985~. This
system uses pressure and engine speed to
provide a measure of particulate loading for
triggering the glow plug igniters for regen-
eration. Simon and Stark (1985) investi-
gated three different additives: cerium (0.13
g Ce/liter), manganese (0.07 g Mn/liter),
and cerium plus manganese (0.07 g (Ce +
Nln)/liter). Their tests showed that vehicles
equipped with properly tuned 4.3-liter en-
gines and operated using a fuel additive
would not, on a production basis, be able
to meet the 1987 federal emissions stan-
dards at sea level or at altitude. Equipped
with particulate traps, however, the vehi-
cles would probably meet the 1987 federal
standards and might, with further engine
tailoring, be able to meet the 1989 Califor-
nia standards on a production basis.
Diesel-Powered Heavy-Duty Vehicles
Diesel-powered heavy-duty vehicles use
direct-injection turbocharged engines of
two-cycle as well as four-cycle design. Die-
sel engines are designed for a commercial
market and hence durability, reliability,
and fuel economy drive their development.
The approaches enforced to date to meet
the standards for particulates, HCs, and
NOX have involved improved turbocharg-
ers, intercooling, improved fuel systems
and nozzles, and electronic fuel injection
control. To reduce NOX emissions and
improve fuel economy, some manufactur
OCR for page 66
66
Automotive Emissions
Table 10. Qualitative Analysis of Nonpolar and Moderately Polar Fractions of Diesel Particulate
Extract
Compound
Approximate Concentration
in Oldsmobile Extract (ppm)
Nonpolar fractions
Phenanthrenes and anthracene
Methylphenanthrenes and methylanthracenes
Dimethylphenanthrenes and dimethylanthracenes
Pyrene
Fluoranthene
Methylpyrenes and methylfluoranthenes
Chrysene
Cyclopenta|cdlpyrene
Benzotghi]fluoranthene
Benz~ajanthracene
Benzota~pyrene
Other PAHs, heterocyclics
HCs and alkylbenzenes
Total nonpolar fractions
Moderately polar fractions
PAH ketones
Fluorenones
Methylfluorenones
Dimethylfluorenones
Anthrones and phenanthrones
Methylanthrones and methylphenanthrones
D imeth ylan thrones and dim eth ylp hen anthro nes
Fluoranthones and pyrones
Benzanthrones
Xanthones
Methylxanthones
Thioxanthones
Methylthioxanthones
Total
PAH carboxaldehydes
Fluorene carboxaldehydes
Methyl fluorene carboxaldehydes
Phenanthrene and anthracene carboxaldehydes
Methylanthracene and methylphenanthrene carboxaldehydes
Dimethylanthracene and dimethylphenanthrene carboxaldehydes
Benz~ajanthracene, chrysene, and triphenylene carboxaldehydes
Naphthalene dicarboxaldehydes
Dimethylnaphthalene carboxaldehydes
Trimethyluaphthalene carboxaldehydes
Pyrene and fluoranthene carboxaldehydes
Xanthene carboxaldehydes
Dibenzofuran carboxaldehydes
Total
PAH acid anhydrides
Naphthalene dicarboxylic acid anhydrides
Methylnaphthalene dicarboxylic acid anhydrides
Dimethylnaphthalene dicarboxylic acid anhydrides
Anthracene and phenanthrene dicarboxylic acid anhydrides
Total
(Table continued next page.)
600
1,400
3,000
1,700
1,400
800
100
20
100
500
40
30,000
500,000
539,700
4,000
400
200
1,600
1,600
1,300
1,200
200
300
200
1,600
900
13,500
1,600
400
2,600
1,600
400
400
300
300
1,000
1,600
600
400
1 1,200
3,000
1,000
500
600
5,100
OCR for page 67
John H. Johnson
67
Table 10. Continued
Compound
Approximate Concentration
in Oldsmobile Extract (ppm)
Hydroxy PAHs
Hydroxyfluorene
Methylhydroxyfluorene
Dimethylhydroxyfluorene
Hydroxyanthracenes and hydroxyphenanthrenes
Hydroxymethylanthracenes and hydroxymethylphenanthrenes
Hydroxydimethylanthracenes and hydroxydimethylphenanthrenes
Hydroxyfluorenone
Hydroxyxanthone
Hydroxyxanthene
Total
PAH quinones
Fluorene quinones
Methylfluorene quinones
Dimethylfluorene quinones
Anthracene and phenanthrene quinones
Methylanthracene and methylphenanthrene quinones
Fluoranthene and pyrene quinones
Naphthot1,8-cdlpyrene 1,3-dione
Total
Nitro-PAHs
Nitrofluorenes
Nitroanthracenes and nitrophenanthrenes
Nitrofluoranthenes
Nitropyrenes
Methylnitropyrenes and methylnitrofluoranthenes
Total
Other oxygenated PAHs
PAH carryover from nonpolar fraction
Phthalates, HC contaminants
Total, moderately polar fractions
1,400
400
1,500
600
900
1,300
2,000
1,300
1,000
10,400
700
600
500
1,900
2,000
200
600
6,500
30
70
10
150
20
280
8,000
6,000
30,000
91,000
SOURCE: Adapted with permission from the National Research Council 1983b.
The particulate-extract in the high-per-
formance liquid chromatograph (HPLC)
eluent can be separated into nonpolar,
moderately polar, and highly polar frac-
tions. The fractions can then be further
analyzed by gas chromatography/mass
spectrometry (GC/MS). Table 10 lists the
results of such an analysis of the nonpolar
and moderately polar fractions of a partic-
ulate extract from an Oldsmobile diesel
vehicle, including the approximate extract
concentrations for this particular vehicle.
The highly polar fraction has not been fully
characterized. It contains the PAH carbox-
ylic acids, acid anhydrides, and probably
sulfonates and other highly polar species
(National Research Council 1983b).
Most (75 percent) of the direct bacterial
mutagenicity resides in the moderately po-
lar fraction. The remaining direct mutage-
nicity is in the highly polar fraction. These
aspects are discussed further in the National
Research Council's report (1983b).
Over 50 chromatographic peaks of nitro-
PAH compounds have been identified in
diesel particulate extracts, as listed in table
11. The most abundant of the nitro-PAHs
is 1-nitropyrene, ranging from 25 to 2,000
ppm in the vehicle extracts studies. The
other nitro-PAHs are present at concentra-
tions from below the ppm range to a few
ppm. The nitropyrenes have been studied
in greater detail than other PAH com-
pounds. They are released in diesel and
OCR for page 68
68
Table 11. Nitroarenes in Diesel Exhaust Particulate Extracts
Mononitroarenes
N i tro in den e
Nitroacenaphthylene
Nitroacenaphthene
Nitrobiphenyl
Nitrofluorene
Nitromethylacenaphthylene
Nitromethylacenaphthene
Nitromethylbiphenyl
Nitroanthracene
Nitrophenanthrene
Nitromethylfluorene
Nitromethylanthracene
Nitromethylphenanthrene
Nitrotrimethylnaphthalene
Nitrofluoranthene
Nitropyrene
Nitro (C2-alkyl) anthracene
Nitro (C2-alkyl) phenanthrene
Nitrobenzofluorene
Nitromethylfluoranthene
Nitromethylpyrene
Nitro (C3-alkyl) anthracene
Nitro (C3-alkyl) phenanthrene
Nitrochrysene
Nitrobenzoanthracene
Nitronaphthacene
Nitrotriphenylene
Nitromethylnaphthacene or
nitromethylchrysene
Nitromethylbenzanthracene
Nitromethyltriphenylene
Nitrobenzopyrene
Nitroperylene
Nitrobenzofluoranthene
Automotive Emissions
Polynitroarenes
Dinitromethylnaphthalene
Dinitrofluorene
Dinitromethylbiphenyl
Dinitrophenanthrene
Dinitropyrene
Trinitropyrene
Trinitro (C5-alkyl) fluorene
Dinitro (C6-alkyl) fluorene
Dinitro(C4-alkyl)pyrene
Nitro-oxyarenes
Nitronaphthaquinone
Nitrodihydroxynaphthalene
Nitronaphthalic acid
Nitrofluorenone
Nitroanthrone
Nitrophenanthrone
Nitroanthraquinone
Nitrohydroxymethylfluorene
Nitrofluoranthone
Nitropyrone
N itro fl u o ran theneq uin one
Nitropyrenequinone
Nitrodimethylanthracene carboxaldehyde
N it rodi m eth yl p henan t hrene ca rb o x aldeh y de
Other nitrogen compounds
Benzocinnoline
Methylbenzocinnoline
Phenylnaphthylamine
(C2-alkyl) phenyloaphthylamine
SOURCE: Adapted with permission from the National Research Council 1983b.
gasoline exhaust (according to particulate
extracts) at rates of approximately 8.0
(diesel fuel), 0.30 (leaded gasoline), and
0.20 mg/mi (unleaded gasoline) (National
Research Council 1983b).
1-Nitropyrene has been the only ni-
tro-PAH detected in spark-ignition par-
ticulate extracts. Very low 1-nitropyrene
particulate extract concentrations have
been found recently in on-road heavy-
duty diesel and light-duty spark-ignition
vehicles (National Research Council
1 983b).
Gasoline-Powered Vehicle Refueling Hydro-
carbons. Williams (1985) has reported the
concentration of HCs in the breathing zone
of individuals during vehicle refueling. Gas
chromatographic data for gasoline and the
refueling vapor indicate that only the lower
molecular weight, more volatile com-
pounds are emitted. Williams concluded
that:
1. Vapor composition does not equal
1- . .
gaso~ne compos~t~on;
2. Range of total HC concentrations
varied widely with the environmental con-
ditions, resulting in exposures from 8 to
3,000 ppmC; and
3. Propane, butane, and pentane provide
more than 80 percent of total exposure.
OCR for page 69
John H..Iohnson
69
Areas in Need of Additional Research. To
do efficient particulate control develop-
ment work and to better understand emis-
sion characteristics, there is a need for a
fast-response real-time particulate mass
measurement instrument. The tapered ele-
ment oscillating microbalance (TEOM)
holds the most promise, but there is
a gap between what is known about its
principle of operation and the reality of
making its use practical for measuring par-
ticulates.
The other instrument gap involves ~ea-
suring methanol accurately. Formaldehyde
has also been identified as a potentially
important unregulated pollutant that needs
careful real-time measurement and control
because it is generally considered to be a
carcinogen.
Measurement of particulate emissions
from heavy-duty diesel engines using the
EPA test procedures with dilution tunnels
is inadequate. The current reneatabilitv of
measurements is poor.
Barsic (1984)
showed trom a round-robin test that the
root mean square of the 2-~ standard devi-
ations were 76 percent of a 0.25 g/bhp-hr
standard for six heavy-duty diesel engines
tested in seven laboratories. For measure-
ments intended to implement the 0.25
g/bhp-hr or the 0.1 g/bhp-hr standard, this
variation is unacceptable.
It is uncertain whether particulate emis-
sion standards should be based on amount
of total particulate matter, on which cur-
rent standards are based, or amount of
soluble organic component extracted from
the particulates. The soluble organic com-
ponent is the portion of the particulate that
has been shown to be mutagenic and pos-
sibly carcinogenic (Claxton 1983), suggest-
ing that future health-related regulations
should be based on this fraction. Basing
standards on the soluble organic compo-
nent poses the problem of separating and
quantifying the specific toxic components
by one of the present methods solvent
extraction, vacuum sublimation, or ther-
mogravimetric analysis. Variability associ-
ated with the separation methods and sam-
pling condition affects the mass of the
soluble fraction collected, compounding
the previously stated measurement vari
ability problem for the total particulate
matter.
Present measurement methods for the
collection of vapor-phase HCs from diesel
engines do not collect all the compounds.
Characterization of potentially toxic HCs
is not possible if they cannot all be col-
lected.
There is need to continue the develop-
ment and use of advanced HPLC and
GC/MS techniques In conjunction warn
separation methods to more accurately
measure the amounts of key biologically
active HCs in the particulate as well as the
vapor phases. The nitroaromatics are im-
portant compounds whose concentrations
in diesel exhaust with and without partic-
ulate traps should be measured more accu-
rately.
There is a need to investigate and de-
velop measurement methods that quantify
diesel odor. Pioneering work was carried
out in the late 1960s and early 1970s, but
was dropped around 1978 because of the
potential health effects of diesel particulate
emissions. Diesel odor, along with partic-
ulates, is still the typical person's percep-
tion of the diesel pollutants that are of
concern. There is a need to apply odor
measurement methods to new engines used
in light-duty and heavy-duty vehicles and
advanced engines that use particulate traps
or incorporate advanced high-temperature
materials.
Refined organic compound measure-
ment is particularly important to advance
the development of low-heat-rejection (or
commonly called adiabatic, as an ideal goal)
diesel engines because their combustion
chamber wall and gas temperatures will be
higher. This elevated temperature will in-
crease the amount of lubricating oil appear-
ing as particulate emissions and has the
potential of producing reactions between
the HCs and oxygen/HNO3/NOx and
other such gaseous mixtures to form toxic
and biologically active species.
A particular need in unregulated pollu-
tant characterization data for gasoline en-
gines is additional nitrous acid (HNO2)
data as an extension to Pitts et al. (1984~.
That paper showed higher levels of HNO2
from older (1974 and earlier) light-duty
OCR for page 70
70
Automotive Emissions
vehicles than from 1982 and newer cars that
use three-way catalyst systems. The data
show that even though the number of older
cars is small, their HNO2 emission levels
are so high that they may be the major
source of all gaseous HNO2 from automo-
tive emissions. HNO2 is a key precursor to
photochemical air pollution and is also an
inhalable nitrite.
There is little known about how and
when the nitro-PAHs are formed in the
exhaust system (or the dilution tunnel) of
diesel engines. Flow reactor studies with
the basic species NO, NO2, CO, CON,
N2, 02, S02, HCs present in the ex-
haust, along with detailed engine studies
that include the effects of the particles
in the reactions, could help resolve this
issue.
Recommendation 9. PAH Measure-
ments. There is a need for a program of
comparative measurements of PAHs in
partial-exhaust sampling systems and in
full-flow dilution tunnel systems, with
measurements made in the atmosphere
downwind from the plume, for the pur-
pose of determining how well laboratory
data reflect the true composition of emis-
sions into the atmosphere.
Recommendation 10. Kinetics of Ni-
tro-PAH Formation. Research is recom-
mended to discover how and when nitro-
PAHs are formed in the diesel engine
exhaust system and dilution tunnel. This
work can best be done by flow reactor
studies of the basic gases in conjunction
with detailed engine studies that include the
actual HCs and particles.
Recommendation 11. Particulate Mea-
surement Variability. Research is required
to reduce the variability in heavy-duty die-
sel particulate measurements. Work needs
to be undertaken to determine how to
better control the parameters that influence
this variability.
a Recommendation 12. HC Character-
ization. There is a need for research on the
complete characterization of particulate-
phase and gas-phase HCs in diesel exhaust.
a Recommendation 13. Diesel Odor.
There is a need to investigate and develop
analytical methods that quantify diesel
odor. This research should take advantage
of the knowledge gained in the past eight
years about measuring particulate-bound
and vapor-phase HCs.
Recommendation 14. Nitrous Acid.
Additional data should be obtained about
HNO2 emissions from older gasoline-
powered vehicles. The literature shows
high levels of HNO2 from older cars that
may be contributing significantly to in-
creased photochemical smog and direct ef-
fects.
. .
Summary of Research Recommendations
HIGH PRIORITY
Based upon current information, the following research studies
are most likely to yield useful data.
Recommendation 1 Tampering and misfueling statistics are fairly well developed but
Tampering and their effect on emissions is not as well known. Therefore, work
Misfiteling should be done to better characterize the effect of tampering and
misfueling on emissions from vehicles and to better assess their
effect on ambient pollutant concentrations.
OCR for page 71
John H..Iohnson
71
Recommendation2 There is a need for continued research on particulate control
Diesel Particulate technology, including the regeneration systems, to reduce the cost
Emissions and and complexity of these systems and the associated fuel economy
Control penalties. Work needs to continue with various additives, substrate
materials, regeneration systems, and controls to develop optimum
systems that are able to decrease the diesel particulate emissions
to the levels of 0.1 ~/bho-hr for heavy-duty diesels and 0.08 Mimi
- ~ ---r ~~~ ~~ '
for light-duty vehicles required in California. In conjunction with
this research there is a need to measure the metal species and the
size distribution of the particles coming from diesel particulate
traps.
Recommendation 4 Real-time measurements of formaldehyde concentration should
Formaldehyde be performed under transient and extreme conditions such as
Measurements acceleration and deceleration, low temperature, light load, and
extended idling with restricted ventilation. This research work
should be done with and without catalysts since worst-case condi
tions in the field will occur with catalysts removed. Similar
measurements should be made on bus engines.
Recommendation 7 Data should be obtained about the size distribution of particles in
Diesel Fuel diesel exhaust and about the metal species they contain with and
Additives without a particulate trap, with a diesel fuel containing a typical
additive under consideration for production use. Data on the HCs
bound to the particles and the vapor-phase HCs should also be
obtained.
Recommendation 10 Research is recommended to discover how and when nitro
Kinetics of Nitro- PAHs are formed in the diesel engine exhaust system and dilution
PAH Formation tunnel. This work can best be done by flow reactor studies of the
basic gases in conjunction with detailed engine studies that include
the actual HCs and particulates.
Recommendation 11
Particulate
Measurement
Variability
Research is required to reduce the variability in heavy-duty diesel
particulate measurements. Work needs to be undertaken to deter-
mine how to better control the parameters that influence this
variability.
Recommendation 12 There is a need for research on the complete characterization of
HC Characterization particulate-phase and gas-phase HCs in diesel exhaust.
MEDIUM PRIORITY
Recommendations An improved vehicle evaporative emissions model should be
Evaporative developed that is valid over various types of operating conditions
Emission Model for a variety of ambient temperatures. At the same time, changes
should be made in the EPA test procedure to obtain the data
necessary to properly design and size the evaporative system for the
high-temperature soak situation, and data should be sought that
can be used in EPA's MOBILES computer model for other use
patterns of cars.
OCR for page 72
72
Automotive Emissions
Recommendation 5 An automotive quality No. 2 diesel fuel with low sulfur and low
Automotive Quality aromatics is necessary if low particulate emissions are to be
No. 2 Diesel Fuel achieved. Research should be undertaken in cooperation with the
automotive and petroleum industries to decide on effective and
economical cetane number, sulfur and aromatic content, and 90
percent boiling point temperature specification limits for automo
tive quality No. 2 diesel fuel, and to formulate fuels that meet the
specifications. The need for this research becomes more urgent as
diesel fuel usage continues to increase. Improved emissions and
more control options require low-sulfur diesel fuel.
Recommendation 6 Some combination of field RVP control along with a test fuel
Evaporative with typical RVP (or calculation corrections for RVP differences)
Emissions Control should be developed. Controlling RVP in motor gasoline, an
approach successfully applied in California, is needed generally for
controlling field evaporative.emissions. The question of whether
car manufacturers should be testing with a worst-case RVP test fuel
or a typical fuel needs further study.
Recommendations Studies should begin immediately with an evaluation of the
Emissions best available emissions data on engines operating with and with
Measurement out emission control devices, to determine which of the unregu
Methods lated pollutants really pose a potential threat to human health.
Other unregulated pollutants might be added to this list if their
concentrations reflect engine or emission control device perform
ance.
Next, every effort should be made to improve the analytical
procedures presently used to measure the concentrations of those
pollutants, to the point where they can be readily carried out by
technicians. This may require that packaged sets of reagents and
equipment be marketed for a specific analysis. For example, pre
packed traps might be available for collecting gaseous HCs prior to
thermal desorption onto a gas chromatograph with a specified capil
lary column for the analysis of specific HCs at predetermined condi
tions.
Recommendation 9 There is a need for a program of comparative measurements of
PAH measurements PAHs in partial-exhaust sampling systems and in full-flow dilution
tunnel systems, with measurements made in the atmosphere down
wind from the plume, for the purpose of determining how well
laboratory data reflect the true composition of emissions into the
atmosphere.
Recommendation 13 There is a need to investigate and develop analytical methods that
Diesel Odor quantify diesel odor. This research should take advantage of the
knowledge gained in the past eight years about measuring partic
ulate-bound and vapor-phase HCs.
Recommendation 14 Additional data should be obtained about HNO2 emissions from
Nitrous Acid older gasoline-powered vehicles. The literature shows high levels
of HNO2 from older cars that may be contributing significantly to
increased photochemical smog and direct effects.
OCR for page 73
lohn H..Iohnson
Acknowledgment
I would like to thank Peter V. Woon for all
of his assistance in the preparation of this
paper.
References
Abtoff, J., Schuster H. C., and Langer, J. 1985. The
trap oxidizers an emission control technology for
diesel engines, Society of Automotive Engineers
Paper 850015, Warrendale, Pa.
Alson, J. 1985. EPA methanol vehicle emissions test
programs, talk at EPA Region VI Methanol Work-
shop, May 1985, Dallas, Tex.
Amann, C. A. 1985. The powertrain, fuel economy
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Representative terms from entire chapter:
fuel economy
