NBSIR 74-460

Comparison of Power Output and Exhaust

Pollutants of Two Postal Service Vehicles

Operated on Three Hydrocarbon Fuels

J. E. Hill and D. A. Didion

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

September 21, 1973

Prepared for

U. S Postal Service

Bureau of Research and Engineering

Washington, 0. C. 20260

NBSIR 74-460

COMPARISON OF POWER OUTPUT AND EXHAUST

POLLUTANTS OF TWO POSTAL SERVICE VEHICLES

OPERATED ON THREE HYDROCARBON FUELS

J. E. Hill and D. A. Didion

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

September 21, 1973

Prepared for U. S. Postal Service

Bureau of Research and Engineering

Washington, D. C. 20260

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Comparison of Power Output and

Pollutants of Two Postal Service

Operated on Three Hydrocarbon

Exhaus t Vehicles

Fuels

J. E. Hill and D. A. Didion

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Wastiington, D. C. 20234

ABSTRACT

One possible solution for the reduction of pollutants

from internal combustion engines is the use of gaseous fuels

such as natural gas or propane. The best application for the

use of these fuels appears to be with fleet operators. The

federal government operates between 300,000 and 400,000

vehicles which makes it an excellent candidate for using

them. This paper describes a laboratory investigation in

wnich tne power output and pollutant levels of two Postal

Service vehicles equipped with dual-fuel systems, were determined at simulated road conditions in an environmental

chamber at temperatures from 0 °F to 110 °F.

Key Words: Air pollution; compressed natural gas

engine; dual fuel vehicles; propane

engine; vehicle emissions

1
LIST OF FIGURES

Figure 1 1/2 Ton Truck Inside the Environmental Chamber

Figure 2 Compressed Natural Gas System Schematic

Figure 3 Air-Mixer and Associated Natural Gas Fuel System

for the 1/2 Ton Truck

Figure 4 Measurement of Rate of Fuel Usage for Propane Tests

Figure 5 Carburetor Adjustment for Propane Tests

Figure 6 1 Ton Truck Inside the Environmental Chamber

Figure 7 6 Cylinder Engine Equipped with Venturi-Insert

Natural Gas Fuel System

Figure 8 Chassis Dynamometer

Figure 9 Engine Throttle Position and Dynamometer Adjustments

Being Made from the Instrumentation Room

Figure 10 Vehicle and Environmental Parameters Measured During

a Vehicle Test .

I-'igure 11 Exhaust Probe Being Placed in Position

Figure 12 Basic Adjustments Being Made for the Measurement of

NO Content of the Exhaust Gas

X

Figure 13 Schematic Representation of Gas Restrictor for the

1/2 Ton Truck Using Propane

Figure 14 1/2 Ton Truck During Cold Start Tests

Figure 15 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

Figure 16 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

Figure 17 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

Figure 18 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

Figure 19 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline
Figure 20 Hydrocarbons Versus Spark. Advance for a 1/2 Ton

Truck Using Gasoline

Figure 21 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

Figure 22 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

Figure 23 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

Figure 24 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using CNG

Figure 25 Hydrocarbons and Carbon Monoxide Versus Spark Advance

for a 1/2 Ton Truck using CNG

Figure 26 Hydrocarbons and Carbon Monoxide Versus Spark

Advance for a 1/2 Ton Truck Using CNG

Figure 27 Air-Fuel Ratio Versus Spark Advance for a 1/2 Ton

Truck Using CNG

Figure 28 Gas Pressure at Running Conditions Versus Spark

Advance for a 1/2 Ton Truck Using CNG

Figure 28 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using CNG

Figure 30 Hydrocarbons and Carbon Monoxide Versus Spark

Advance for a 1/2 Ton Truck Using CNG

Figure 31 Hydrocarbons and Carbon Monoxide Versus Spark

Advance for a 1/2 Ton Truck Using CNG

Figure 32 Air-Fuel Ratio Versus Spark Advance for a 1/2 Ton

Truck Using CNG

Figure 33 Gas Pressure at Running Conditions Versus Spark

Advance for a 1/2 Ton Truck Using CNG

Figure 34 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

Figure 35 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

Figure 36 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

Figure 37 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

ill
Figure 38 Maximum Horsepower and Nitrogen Oxides Versus AirFuel Ratio for a 1/2 Ton Truck Using CNG and

Operating at Full Throttle

Figure 39 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG and Operating

at Full Throttle

Figure AO Idle Gas Pressure Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

Figure 41 Gas Pressure at Running Conditions Versus Idle Gas

Pressure for a 1/2 Ton Truck Using CNG

Figure 42 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

Figure 43 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using CNG

Figure 44 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

Figure 45 Gas Pressure at Running Conditions Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

Figure 46 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

Figure 47 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

Figure 48 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

Figure 49 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

Figure 50 Maximum Horsepower and Pollutants Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG and Operating

at Full Throttle

Figure 51 Gas Pressure at Running Conditions Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

Figure 52 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck using CNG

Figure 53 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

Figure 54 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using LPG

IV
Figure 55 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 56 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 57 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 58 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 59 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 60 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 61 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 62 Carbon Monoxide Versus Spark Advance for a. 1/2 Ton

Truck Using LPG^

Figure 63 Air-Fuel Ratio Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 64 Air-Fuel Ratio Versus Spark Advance for a 1/2 Ton

Truck Using LPG

Figure 65 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

Figure 66 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

Figure 67 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2

Ton Truck Using LPG

Figure 68 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using LPG

Figure 69 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

Figure 70 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2

Ton Truck Using LPG

Figure 71 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using LPG

Figure 72 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

v
Figure 73 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

Figure 74 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

Figure 75 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

Figure 76 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

Figure 77 Air-Fuel Ratio Versus Power Valve Setting for a 1/2 Ton Truck Using LPG

Figure 78 Nitrogen Oxides Versus Normalized Air-Fuel Ratio

for a 1/2 Ton Truck Using CNG and LPG

Figure 79 Hydrocarbons Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

Figure 80 Carbon Monxoide Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

Figure 81 Nitrogen Oxides Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

Figure 82 Hydrocarbons Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

Figure 83 Carbon Monoxide Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

Figure 84 Nitrogen Oxides Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

Figure 85 Hydrocarbons Versus Normalized Air-Fuel Ratio for

; • a 1/2 Ton Truck Using CNG and LPG

Figure 86 Carbon Monoxide Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

Figure 87 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

Figure 88 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

Figure 89 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

Figure 90 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

vi
igure 91 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

igure 92 Carbon Monoxide Versus Spark Advance for a 1/2

Ton Truck Using Gasoline, CNG and LPG

igure 93 Nitrogen Oxides Versus Spark Advance for a 1/2

Ton Truck Using Gasoline, and LPG

igure 94 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, and LPG

igure 95 Carbon Monoxide Versus Spark Advance for a 1/2

Ton Truck Using Gasoline, and LPG

igure 96 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 97 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 98 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 99 Hydrocarbons Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure ICQ Hydrocarbons Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 101 Hydrocarbons Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 102 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 103 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 104 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 105 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using Gasoline

igure 106 Pollutants Versus Spark Advance for a 1 Ton Truck

Using CNG

igure 107 Air-Fuel Ratio Versus Spark Advance for a 1 Ton

Truck Using CNG

vi i
Figure 108 Pollutants Versus Spark Advance for a 1 Ton Truck

Using CNG

Figure 109 Pollutants Versus Spark Advance for a 1 Ton Truck

Using CNG

Figure 110 Pollutants Versus Spark Advance for a 1 Ton Truck

Using CNG

Figure 111 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using CNG

Figure 112 Hydrocarbons Versus Spark Advance for a 1 Ton Truck

Us in g CNG ^ ,, ,

.

Figure 113 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using CNG

Figure 114 Air-Fuel Ratio and Power Valve Setting Versus Spark

Advance for a 1 Ton Truck Using CNG

Figure 115 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using CNG

Figure 116 Hydrocarbons Versus Spark Advance for a 1 Ton

Truck Using CNG

Figure 117 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using CNG

Figure 118 Air-Fuel Ratio and Power Valve Setting Versus

Spark Advance for a 1 Ton Truck Using CNG

Figure 119 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using CNG v.

Figure 120 Hydrocarbons Versus Spark Advance for a 1 Ton Truck

. Using CNG -. ,, Figure 121 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using CNG

Figure 122 Air-Fuel Ratio and Power Valve Setting Versus

Spark Advance for a 1 Ton Truck Using CNG

Figure 12 3 Maximum Horsepower and Nitrogen Oxides Versus AirFuel Ratio for a 1 Ton Truck Using CNG and Operating

at Full Throttle

Figure 124 Maximum Horsepower and Hydrocarbons Versus Air-Fuel

Ratio for a 1 Ton Truck Using CNG and Operating at

Full Throttle

vi i i
Figure 125 Maximum Horsepower

Fuel Ratio for a 1 at Full Throttle

and Carbon Monoxide Versus AirTon Truck Using CNG and Operating

Figure 126 Power Valve Setting Versus Air-Fuel Ratio for a

1 Ton Truck Using CNG and Operating at Full Throttle

Figure 127 Maximum Horsepower and Nitrogen Oxides Versus

Air-Fuel Ratio for a 1 Ton Truck Using CNG and

Operating at Full Throttle

Figure 128 Maximum Horsepower and Hydrocarbons Versus AirFuel Ratio for a 1 Ton Truck Using CNG and Operating

at Full Throttle

Figure 129 Maximum Horsepower and Carbon Monoxide Versus AirFuel Ratio for a 1 Ton Truck Using CNG and Operating

at Full Throttle

Figure 130 Power Valve Setting Versus Air-Fuel Ratio for a

1 Ton Truck Using CNG and Operating at Full Throttle

IX
.

• ^ : V LIST OF TABLES

Table 1 Characteristics of the PAL CO System Operation

Table 2 General Comparison of Emissions

X
TABLE OF CONTENTS

Page

1. Introduction 1

2. Description of Vehicles and Fuel Systems ...... 8

2.1 1/2 Ton Truck 8

2.2 1 Ton Truck 15

3. Test Apparatus and Procedure 18

4. Results and Discussion - 1/2 Ton Truck . 34

4.1 Gasoline-Fueled Tests 34

4.2 Compressed Natural Gas-Fueled Tests 45

4.2.1 Spark Advance as the Independent

Variable 45

4.2.2 Air-Fuel Ratio as the Independent

Variab le 51

4.3 Propane-Fueled Tests 77

4.3.1 Spark Advance as the Independent

Variable 77

4.3.2 Air-Fuel Ratio as the Independent

Variable 95

4.4 Comparison of the Fuels HQ

4.5 Cold-Start Tests 130

4.5.1 Compressed Natural Gas and GasolineFueled Tests 130

4.5.2 Propane and Gasoline-Fueled Tests. . . . 132

5. Results and Discussion - 1 Ton Truck 133

5.1 Gasoline-Fueled Tests 133

5.2 Compressed Natural Gas-Fueled Tests 144

5.2.1 Spark Advance as the Independent

Variable 144

xi
5.2.2 Air-Fuel Ratio as the Independent

Variable 164

5.3 Cold-Start Tests 170

6. Conclusions 176

7. References 181

8. Acknowledgements 182

xii
Int roduct ion

The concern on a national scale for the quality of the

environment and in particular the nation's air, led to the

establishment of the Clean Air Act of 1970. This act and its

amendments require that strict standards of emission control

on automotive engines be met by 1976. This relatively early

date practically guarantees that the standards be met by a conventional internal combustion engine rather than by a new

approach to automotive power. Consequently, vigorous attention

is being given to possible solutions that involve modifications

to the engine as well as the fuel it burns.

The primary pollutants of internal combustion engines are

carbon monoxide (CO) and hydrocarbons (HC) and the oxides of

nitrogen (^0^^ ' They are formed during the combustion process

as follows (1)*:

" Hydrocarbons . After the spark plug ignites the fuelair mixture inside the cylinder, the flame spreads outward until it nears the cylinder wall. There the

mixture is too cool to burn and the flame is "quenched."

The partially burned gasoline vapor which remains forms

layers of hydrocarbons on the cylinder head and walls.

The deposits on the head blow out of the engine early in

the exhaust stroke. Those on the walls leave later as

as the piston scrapes them off.

*The numbers refer to references at the end of this report.
Carbon Monoxide . When fuel In the cylinder is completely

burned, it leaves the engine as harmless carbon dioxide.

But partially burned fuel finishes only part of the

chemical transformation to carbon dioxide -- the result

being carbon monoxide. Carbon monoxide forms both in the

expansion and exhaust strokes, especially when the ratio

of fuel to air is high. Because engines need fuel-rich

mixtures to run smoothly, engineers cannot easily

eliminate carbon monoxide emissions.

Nitric Oxide . Nitric oxide forms in the engine when

nitrogen and oxygen combine at high temperatures early

in the expansion stroke. The higher the temperature and

the more oxygen available, the more nitric oxide is

formed. Thus nitric oxide forms under optimal conditions

that are opposite to those under which most hydrocarbons

and carbon monoxide form: relatively more air yields

nitric oxide, more fuel yields hydrocarbons and carbon

monoxide."^

Reference (2) specifies the testing procedure and

accompanying driving cycle (CVS-3) that are to be employed in

the certification of the 1975 and 1976 vehicles* to determine

whether their mass emissions are below the following levels:

HC CO NO

1975 0.41 g/mi 3,4 g/mi 3.0 g/mi

1976 0.41 g/mi 3.4 g/mi 0.4 g/mi

*This is prior to the 1 year delay recently authorized by the

Director of the Environmental Protection Agency.
There are many engine modifications being proposed to reduce

the quantity of these pollutants to acceptable levels. These

include exhaust gas recirculation to alter the air-fuel ratio

and reduce peak, cycle temperature and the use of secondary

combustion processes (thermal reactors). The Environmental

Protection Agency recently released test results showing that

prototype vehicles equipped with the Mazda* rotary engine

produced by Toyo Kogyo of Japan have met the 1975 standards

listed above; however, the nitrogen oxide emissions were more

than double those permitted under the 1976 standard. Japan's

Honda Motor Company* recently announced that they will be

producing a four-seat passenger car that will meet the 1975

standard. It will be the first p r o du c t ion- 1 in e car with the

more drastic modification of the "s t r at i f i e d- ch a r ge " engine

(3) . A mixture of fuel that would ordinarily be too lean to

ignite in the cylinder is coaxed into burning by the ignition

of an adjoining layer of much richer fuel. To accomplish

this stratification of fuel, a small combustion chamber with

its own spark plug and valve is added at the top of each

cylinder to accomodate the richer mixture.

Modification of the basic gasoline fuel is not considered

to have major potential for reducing the pollutants. However,

the use of an entirely different fuel does' seem feasible for

some applications. One such fuel is hydrogen and recent

*Use of a trade name neither constitutes or implies endorsement

by the National Bureau of Standards.

3
experiments have been very interesting. Dr. Roger Schoeppel

of Oklahoma State University has modified a conventional

internal combustion engine for direct injection of gaseous

hydrogen into the cylinder, similar to the fuel-injection

process in a standard diesel engine. Nitrogen oxides were

found to be the only pollutant and those were at levels ten

times lower than of a gasoline engine. Similarly, Dr. Robert

Adt and a graduate student of the University of Miami modified

a standard 1971 Toyota station wagon to burn compressed

gaseous hydrogen. They found that at an average cruising

speed of 40 mph the NO^ pollutant (only one emitted) was only

18 ppm, a tiny fraction of the 984 ppm (3.1 g/mi) of the 1975

standard. However, hydrogen as a fuel has to be considered

only in terms of a long term solution due to problems yet to

be solved involving storage, safety, and production. For

example, a normal 20-gallon tankful of gasoline weighs about

120 pounds. To store the equivalent amount of energy in the

form of hydrogen gas would require a container holding 66 cubic

feet and weighing a ton. To store it as a supercold liquid

would require a tank of 353 pounds and 10.2 cubic feet, four

times the size of a normal gas tank. It therefore appears that

the future large-scale uses for hydrogen as a fuel will logically

be in airplanes, long-haul trucks, and city buses.

Other gaseous fuels that have potential for immediate

use (barring problems associated with supply) are compressed

natural gas (CNG) and liquid petroleum gas (LPG) or propane.

4
There has been considerable experience in the last several

years in converting conventional vehicles to burn these gaseous

fuels and significant reductions in hydrocarbons and carbon

monoxide have been noted along with some reduction in nitrogen

oxides. The problems of storage and carburetion have been

satisfactorily solved so that the total cost of vehicle conversion

is about $300. The pollutant reductions occur as a result of

cleaner burning in the engine.

With gasoline, the fuel must first be vaporized and then

mixed with the correct amount of air. In gaseous fuel systems,

the carburetor only needs to mix in the proper amount of air.

This makes the carburetor much simpler and more accurate.

Mixing is much more thorough and hopefully no cylinder to

cylinder variations exist. In addition, there is no liquid in

the induction system to upset the mixture or pass through the

engine unburned. It is this high degree of carburetion control

and the simple chemical composition of gaseous fuels that

makes the operation of gaseous fuel systems clean. An additional

advantage to the use of these fuels include the fact that no

tetraethyl lead or additives need to be added due to the fuels'

inherent high octane rating compared with gasoline (i.e., CNG

has a rating of 130 compared to 100 for premium gasoline) and

the associated reduced maintenance expenses.

The subject of reactivity has been mentioned frequently

by proponents of the gasified fuels. Photochemical smog is

formed by the reaction of hydrocarbons with nitric oxides in

5
the presence of sunlight (4). However, not all hydrocarbons

are really reactive. Their reactivity depends upon their

structure. They all fall into general classifications such as

saturates (paraffins and n aph th el e ne s ) , aromatics, and olefins.

The saturates have generally a low reactivity. The aromatics

occupy a middle gound and as a group, the olefin compounds have

very high reactivity (5). Consequently a comparison between

the hydrocarbon level of exhaust gases of CNG or LPG and

gasoline, as done in this study and many others, does not

necessarily give a true evaluation of the effect the fuel

usage has on the resultant smog. LPG for example is generally

composed of over 90% paraffins whereas gasoline contains

17 to 22% olefins and 20 to 25% aromatic hydrocarbons (6).

As with any new system, there are some disadvantages.

Today's vehicles must be converted in order to burn gaseous

fuels and the fuels, especially natural gas, are not readily

available in service stations. Therefore special provisions

must be made to obtain and store the fuel. These factors

restrict shops and mechanics who can be trained to convert the

vehicles and maintain them. Most mechanics are not familiar

with gaseous fuel carburetors. Also, many fleet operators

buy their fuel in bulk and have their own refueling facilities.

This practice requires special equipment to store and handle

a gaseous fuel. :

-

The Federal Government operates between 300,000 and 400,000

vehicles--an excellent candidate for using gaseous fuels.

6
Consequently, the General Services Administration launched in

October of 1969, the Federal Government's first fleet of CNG

powered test vehicles. At that time twelve vehicles in the

Los Angeles area were converted to a dual-fuel system (with

the ability to burn either gasoline or natural gas). Today

approximately 1500 GSA vehicles operate with such a system.

In addition, the Postal Service has operated a fleet of

approximately 50 vehicles in the same manner and is presently

considering expanding their operation.

The purpose of this report is to describe comprehensive

tests that were conducted on two Postal Service vehicles,

a 1/2 ton truck and a 1 ton truck, to determine performance

characteristics, especially when the trucks were operated at

ambient temperatures of approximately 0°F and 100°F. The tests

consisted of determining the emission and mechanical performance

characteristics of the vehicles when operated at various simulated

loads and speeds from idling to 50 miles per hour. Testing

conditions covered a span of environmental temperatures and

gasoline, compressed natural gas and propane were used as fuel.

A variety of different engine settings (air-fuel ratio and spark

advance) was included.

7
2. Description of Vehicles and Fuel Systems

2.1 1/2 Ton Truck

The 1/2 ton truck is shown in Figure 1 as it was tested

in an NBS environmental chamber. This truck was powered by

a 232 cubic inch, 6 cylinder engine. For the first series

of tests, the truck was equipped with a natural gas conversion

kit so that the vehicle could be run on both gasoline and compressed natural gas, A schematic diagram of the natural gas

system is shown in Figure 2. The system used two stages of

pressure regulation (Item 3 and 8 in Figure 2). A solenoid

valve prevented fuel from entering the low pressure (second

stage, Item 8) regulator when the engine was not operating.

Located on the regulator assembly (Item 5) was the connection

for the pressure gauge which served as a fuel level indicator

on the dashboard (Item 19). A one-way valve and quick disconnect fitting (Item 5) were provided for fueling. The heart

of the system was the gas-air mixer (Item 12) which replaced

the normal air cleaner on top of the carburetor and made possible use of either natural gas or gasoline interchangeably. The

air-mixer, second stage regulator, and associated equipment can

be seen in Figure 3 installed on the vehicle.

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11
This dual-fuel system was then replaced with the necessary

equipment so that a series of tests could be run using both

gasoline and propane as the fuels. LPG was run from cylinders

typically used with campers and small house trailers (see

Figure 4) through a vaporizer and regulator into an air cleaner

shown in Figure 5. The gas regulator prominently shown in

Figure 5 to the left of the air cleaner was used for the CNG

tests and was completely bypassed for the tests involving LPG.

There was one basic difference in the two systems described

above that should be noted. The r e gu 1 at o r- vap o r i z er controlled

downstream pressure at a constant preset level for both systems.

However, in addition, for the LPG dual-fuel system there was

a restrictor in the gas line between the regulator and air

cleaner (actually an integral part of the inlet port to the air

cleaner). The gas flow adjustment for the CNG system was made

by adjusting the gas pressure at the regulator. For the LPG

system, it was made by changing the position of the restrictor.

Although, it would appear to make no difference whether the

gas flov7 was adjusted by changing the driving force (pressure)

or by changing the flow resistance, there was a substantial

difference in the way in which the gas flow was controlled in

the two systems as the vehicle speed and load changed. This will

be discussed more fully in the Results and Discussion Section.

12
13
14
2.2 1 Ton Truck

The 1 ton truck is shown in Figure 6. It was equipped

with a 225 cubic inch 6 cylinder engine. The particular

dual fuel system installed on this vehicle was a different

make but worked basically the same way as the other systems.

The major differences were in the carburetion and the way in

which the flow of gas to the carburetor was controlled. Where

the other systems used an air-mixer, this system fed the gas

at a constant pressure into the throat of a venturi that was

mounted on top of the gasoline carburetor. The venturi insert

can be seen on top of the carburetor in Figure 7. The gas

flow to the insert could be adjusted by changing the position

of a power valve which is nothing more than a screw valve or

restrictor that provided additional resistance to the flow

(right before entering the carburetor) as it was turned in

and blocked off the flow path. The stem of the screw is seen

protruding out from behind the carburetor in Figure 7. Therefore one would expect the system to perform very similar to

the LPG dual-fuel system used on the 1/2 ton truck.

15
16
17
3. Test Apparatus and Procedure

In order to determine the mechanical performance and

emission characteristics of the vehicles at different temperatures, they were tested in an environmental chamber where the

temperature could be controlled over the range -50°F to 150°F.

The vehicles were mounted so that the rear wheels rested in a chassis dynamometer (Model C-200 made by the Clayton Manufacturing Company*) as shown in Figure 8. One of the rollers

is connected directly to a tachometer generator and associated

speed meter for determining the vehicle speed while the other

roller is attached directly to a power absorption unit which

provides the load for the truck. The power absorption unit

consists of a shaft, rotor, stator and heat exchanger enclosed

within a housing. The rotor is mounted on the shaft with its

vaned face directed toward the vaned face of the stator.

When a vehicle is operated on the rolls, the rotor turns at

roll speed. Fluid in the power absorption unit is picked up

by the rotor vanes and thrown into the stator vanes. The stator

vanes stop the movement of the fluid, returning the fluid

to the rotor. Constant acceleration of the fluid by the rotor

and deceleration by the stator absorbs vehicle power. The load

is varied by varying the amount of fluid allowed into the unit.

*Trade names are used in this report as a means for clear

identification to the Postal Service of their property. Use

of a trade name neither constitutes nor implies endorsement

by the National Bureau of Standards.

18
19
Measurements of rotor speed and generated torque are combined

electrically to display the power generated on an appropriate

power meter (shown in the upper part of Figure 9)

Once the vehicle was running at a specified speed and

load at a particular chamber temperature, a series of measurements

were made in order to determine the pollution and mechanical

performance characteristics of the vehicle. These measurements

are indicated in the schematic of Figure 10. As already noted,

the road speed and horsepower were determined from the meters

associated with the dynamometer. Standard 24 gauge copperconstantan thermocouples were used to determine ambient air

temperature in front of the radiator, water coolant temperature,

inlet air temperature at the carburetor, and the temperature

of exhaust pipe before the exhaust gas enters the muffler.

The temperatures were read on a potentiometer connected in

series with a multipoint thermocouple switch.

A variety of pressure measurements were made during the

tests. The fuel pump pressure (for gasoline operation) was

m.easured using a conventional bourdon-tube pressure gauge

mounted in the cab of the truck. A similar gauge indicating

in inches of Hg. vacuum was used to measure the intake manifold

pressure. The manifold was tapped and connected to the gauge

in the adjoining instrument room using 1/8 inch copper tubing.

In a similar manner, the gas pressure following the second

stage gas regulator and the exhaust pressure were measured by

taps connected to water manometers in the instrument room.

20

22
Additional pressures at several places in the gas flow system

were monitored by bourdon-tube gauges. The purpose of these

later measurements were to insure proper operation of the

systems and a sufficient gas supply in the tanks at all times.

A tach-dwell tester manufactured by the Sun Electric

Corporation* (Model TDT-11) was used to measure the degrees

of dwell and engine speed. A conventional timing light hooked

in series with the spark plug of the first engine cylinder

allowed measurement of the spark advance. A throttle position

recorder was used because the throttle position was controlled

from the adjoining instrumentation room (shown being done in

Figure 9). This recorder consisted of a small electric slavemotor and shaft attached to the throttle linkage at the engine

and a master motor was in the adjacent instrument room. The

position of the master motor indicated degree of throttle opening

between 0 and 100% (full throttle). A small servomotor system was

used to adjust the distributor for setting the spark advance

on the 1/2 ton truck. The system was calibrated with the

timing light and checked frequently. It was not mechanically

convenient to install the system in the 1 ton vehicle so the

distributor was adjusted manually.

CO, HC , and NO^ emission measurements were made. In

addition, CO2 was measured so that the air-fuel ratio could be

*Trade names are used in this report as a means for clear

identification to the Postal Service of their property. Use

of a trade name neither constitutes nor implies endorsement

by the National Bureau of Standards.

23
determined for any particular test by exhaust gas analysis.

The exhaust gas was sampled by withdrawing part of the mixture

from the exhaust pipe (see Figure 11), bubbling it through

glass traps containing water to condense out the excess water

vapor and then passing it to the various analyzers. All

analyzers were calibrated by periodically measuring the

pollutant content of containers of standard "span gas." An

0 Is on-H o r ib a * Model GSM-300 was used to measure the content of

CO and HC and a Lira* Model 300 to measure the CO^ content

(see Figure 12). Both instruments operate on the principle

of absorption of infrared energy by gas. Two identical

infrared beams are passed through two parallel stacked cells.

One cell contains a gas of known composition and the other

the sample gas. After the radiation beams pass through the

cells, they are directed -into detector units. Upon comparison

of the two beams, an electrical signal is generated proportional

to the amount of the component of interest in the sample gas.

A Dy nas ciences * Air Pollution Monitor Model NX-130 was

used to determine the amount of nitric oxides in the exhaust

gas (shown being adjusted in Figure 12). The sensor operates

on the principle similar to a fuel cell. The pollutant

diffuses through a s emi -p e rmeab le membrane and is absorbed on

a special sensing electrode capable of undergoing electrooxidation or electro-reduction. The resulting current is

*Trade names are used in this report as a means for clear

identification to the Postal Service of their property. Use

of a trade name neither constitutes nor implies endorsement by

the National Bureau of Standards.

24
25
directly proportional to the partial pressure of the pollutant

in the gas mixture. This current is amplified and the output

of the amplifier is displayed on an appropriate meter. Since

the temperature of the sample gas should be approximately room

temperature and the response time of the meter is an optimum

with a flow rate of 0.5 to 2.0 standard cubic feet per hour,

a Dynas ciences * Stack Sampling System (Model CS-1000) was

connected in series between the exhaust probe and the NO

X

analyzer (see Figure 12). The sampler houses a diaphragm pump,

heat exchanger (requiring a cold water supply), condensate trap,

and a flow meter with a built-in metering valve.

The nature of the tests conducted was such that a certain

step by step procedure was not established and then followed

throughout the entire investigation. The number of independent

variables involved coupled with the unique way in which the

vehicles and their systems performed required modifications

in the procedures as the project progressed. An attempt will

be made here to describe the testing steps common to all tests

and any deviations will be noted in discussing the tests results

In general three kinds of tests were conducted; spark

advance tests, air-fuel ratio tests, and start tests at low

*Trade names are used in this report as a means for clear

identification to the Postal Service of their property. Use

of a trade name neitner constitutes nor implies endorsement

by the National Bureau of Standards.

26
o

c

tuBu

M

CO

OJ s

0)

4-) U

o

4-1 m

tu O

a to3

m

u u

c

B o

o

o u

•H

CO >

ca o

0)3

60

•H
temperatures. In all cases, the chamber temperature was

adjusted to and controlled at a prescribed level using the

control system and sensors permanently housed in the environmental chamber facility. All chamber air temperature data used

was measured in front of the vehicle at the radiator. While

the chamber temperature was being brought to the correct

level, all instrumentation systems were powered. The time

allowed for warm-up was in all cases from a minimum of several

hours to overnight. In addition, no data were recorded on

either vehicle running at any speed or load until it was

assured that steady-state conditions had been reached. This

was determined by observing no change in vehicle coolant

temperature or pollutant readings for at least five minutes.

For the start-tests, the vehicles were allowed to soak at the

low temperature for at least 20 hours prior to attempting to

start the trucks.

Spark advance tests were conducted on the trucks running

on natural gas, propane and gasoline. Since the gasoline

carburetor jets are fixed, there were no prior adjustments to

be made in the fuel system. For the natural gas and propane

tests, specific settings were made in the gas flow system.

For the 1/2 ton truck, it was the second stage regulator pressure

when using CNG and the position of the restrictor when using

propane. For the 1 ton truck it was the position of the power

valve or restrictor. In addition, on the 1/2 ton truck using

CNG, an adjustment at the air-mixer (on a screw-valve called

28
the tweeker) had to be made. This screw-type adjustment had

an effect on the resulting air-fuel ratio (as did the secondstage regulator pressure). The procedure that was followed

in all tests (spark advance as well as air-fuel ratio tests

to be described next) was to adjust this tweeker to as lean a mixture as possible (determined by the smallest reading on the

CO meter) and still obtain a good idle (indicated by smooth

running with no missing). After these basic gas flow adjustments were made, the spark advance tests were conducted by

starting the vehicle, adjusting the idling to 550 rpm and

setting the distributor so that cylinder firing occurred at

top dead center. The throttle was moved until a specific

simulated road speed was obtained. The dynamometer was then

adjusted to a certain load, and the throttle readjusted if

necessary, to give the required road speed. After all indicators

stablized, the various readings indicated in Figure 10

were recorded. The distributor was then adjusted so that the

firing was advanced three degrees and after steady conditions

were reached, all new readings were tabulated. This procedure

was continued until the spark has been adyanced by at least

12° and in some cases even more. After the last distributor

adjustment, the dynamometer and vehicle throttle were changed

to another speed and load of interest, the distributor readjusted

to obtain idle firing at top dead center and the entire procedure

was repeated.

29
- • Air-fuel ratio tests could not be conducted on the vehicles

using gasoline as no adjustment would normally be made on

fuel flow. The procedure followed when using CNG or propane

was to adjust (while the vehicle was idling) the distributor

for a specific spark advance and the basic gas flow adjustment

to a very lean condition. The leanest setting possible on

any one vehicle sometimes depended upon the speed and load to

be used in the test. On the 1/2 ton truck using CNG, the idle

gas pressure was adjusted generally to 1.5 inches of water

gauge (and the tweeker adjusted as noted previously). On the

1/2 ton truck using propane, the restrictor was placed in the

No. 2 position (see Figure 13) . On the 1 ton truck, the power

valve was screwed out 7 or 8 turns from full in (out of a possible 22 or 23 turns). After the truck was running at the

required speed and load and all data had been recorded, the

gas flow adjustment was than changed to a slightly richer

position (1.5 inches of H^O higher in idle gas pressure for

the 1/2 ton truck using CNG, one number higher in restirctor

position for the 1/2 ton truck using propane., and 2 or 3 more

turns out on the power valve for the 1 ton truck) . This procedure was continued until the richest running possible was

obtained and then the speed and load were changed and the entire

procedure repeated.

The third series of tests involved determining the engine's

ability to start at very cold temperatures (see Figure 14)

Both CNG and gasoline fuel were used. A particular gas flow

30
4JH

O

M-I

O

J-l o

•H

}-i IJ

0}

cu Pi

to

n) O

<4-l (U O C

ca c a- o o

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4-1 n3

4-1 C c

(U •H

cn to

0)

(U a

Pi 3

(-1 a H

•H

iJ C

CO O

6 H

(U X! CM a

CO

u
Figure 14 1/2 Ton Truck During Cold Start Tests 32
adjustment and spark advance setting were made and the starter

was turned over generally for 10 to 15 seconds (or until the

vehicle started). A qualitative statement was then recorded as

to whether ttie engine started, fired, or failed to even fire.

In eacn case where it started, the engine was immediately

turned off and sufficient time was given for the coolant

temperature to return to its original value prior to changing

the spark and gas flow adjustments and attempting to start

the engine again. The battery voltage was measured periodically

and a battery charger was used whenever the voltage was below

an acceptable limit. The one additional parameter involved

in this series of tests was the use of a capacitive discharge

ignition unit (GDI) added to the vehicles. The unit consists

of an oscillator which changes the 12 volt DC battery voltage

to approximately 500 volts AC. The AC output is then rectified

to 400 volts DC and is stored on a high voltage capacitor.

Wlien the points open, a silicon controlled rectifier allows the

power to be discharged into the primary of the coil. The higher

voltage should assure more complete combustion and better

starts. The effect this CDI unit had on the starting capability

of the engines will be discussed in the Results and Discussion

Section.

33
. ,. , 4. Results and Discussion - 1/2 Ton Truck

Figures 15 through 77 show the results of tests conducted

on the 1/2 ton truck. The abscissa in most all cases is

either the spark advance measured at idling conditions or the

air-fuel ratio at the specific running condition (for the CNG

and LPG tests). The air-fuel ratio for methane and propane

were determined by exhaust gas analysis. Reference (7) outlines the procedure for determining air-fuel ratios in this

manner and additional charts not included in that report which

govern the combustion of CNG and LPG were used in this

study (Reference 8).

4.1 G as o 1 i ne - F ue le d Tests

Figures 15 through 23 show the way in which the pollutants

varied with spark advance set at idling speed for three different

running conditions and three different chamber temperatures

while the vehicle was operating on gasoline. As shown in

Figures 15, 16 and 17, when the spark was advanced, the NO

concentration increased. An explanation is that advancing the

spark firing beyond top dead center increases the peak cycle

temperature in the cylinder which controls final NO concentration

X

Spark advance simultaneously reduces the exhaust temperature which also causes an increase in the hydrocarbon concentration as shown in Figures 18, 19 and 20. It has been found

that as the flame front sweeps across the combustion chamber,

a thin layer of mixture adjacent to the cooled walls of the

34
3400

3200

3000

2800

2600

2400

^ 2200

—I

1 r

1/2 TON TRUCK

_ FUEL- GASOLINE

_ O 14 AMBIENT

72 AMBIENT

A 107 *»F

E

o.

o.

iS 2000

o

O 1800

LUO 1600

O

q:

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1200 -

1000 -

800 -

600

4001-

200

IDLE

50 MPH, 30 HP

O

^ -O^ O

ei—

1

-o

3 6 9

SPARK ADVANCE («>BTDC)

12

Figure 15 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

35
3000

2800

2600

2400

_ 1/2 TON TRUCK

_ FUEL - GASOLINE

2200 - 20 MPH, 4 HP

^

2000

E

Q.

3 1800

CO

LU

9 1600

X

o

2 1400

LU

OO 1200

cr

hz 1000

800

600

400

200

0

O 14 AMBIENT

72 ^'F AMBIENT

_ A 107 *»F AMBIENT

1

3 6 9

SPARK ADVANCE (*»BTDC)

12

Figure 16 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

36
3000

2800

2600

2400

2200

^ 2000

£

o. 3 1800

CO

9

X

o

z

111 o

o

a:

»-

_ 1/2 TON TRUCK

_ FUEL- GASOLINE

_ 72 ^'F AMBIENT

1600

1400

1200

1000 h

800

600

400 -

200 -

0

« O IDLE

20 MPH, 4 HP

A 50 MPH, 30 HP

1 i

3 6 9

SPARK ADVANCE (*»BTDC)

12

Figure 17 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline
280

240

^ 200

Ol

CO

z

O i 60

<

o

o

O I 20

80

40

_l/2 TON TRUCK, FUEL- GASOLINE _

_0 14 ^'F AMBIENT _ 72 *»F AMBIENT

IDLE

50 MPH, 30 HP

A- — TT

3 6 9

SPARK ADVANCE (*»BTDC)

12

Figure 18 Hydrocarbons Versus Spark Advance for a 1/2 1 Truck Using Gasoline

3 8
150

140

130

120

i 10

iOO

2" 90

if) 80

O

cr 70

<

o

0 60

o

1 50

40

30

20

10

0

—1 1 r

. 1/2 TON TRUCK — FUEL- GASOLINE

. 20 MPH, 4 HP

O 14 *»F AMBIENT — 72 *»F AMBIENT _ A 107 •F AMBIENT

I3 6 9

SPARK ADVANCE (*»BTDC)

12

Figure 19 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

39
280

240

—. 1/2 TON TRUCK _ FUEL- GASOLINE

72*'F AMBIENT

S 200

CO

z

o

CD

(T 160

<

O

OC

a

X 120

_ O IDLE

_ O 20 MPH, 4 HP _ A 50 MPH, 30 HP

80

40

3 6 9

SPARK ADVANCE («BTDC)

12

Figure 20 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

40
chamber fails to burn (9). Oxidation of this incompletely

consumed fuel continues outside of the cylinder in the exhaust

system provided that oxygen is present and the gas is hot

enough. Consequently, as the exhaust temperature is lowered

(as a result of advancing the spark in this case) , the hydrocarbon concentration increases.

Provided that sufficient oxygen is present for combustion,

advancing the spark should have a minimal effect on the CO

content of the exhaust gases. This is seen to have generally

been true in Figures 21, 22 and 23. The exceptions where there

was a marked increase in CO as the spark was advanced could

be explained by the fact that the mixture simultaneously became

enriched.

As was noted above, the peak cycle temperature governs the

resulting NO concentration. If chemical equilibrium were

X

achieved and maintained during the expansion stroke of the engine

cycle, the falling temperature in the expanding gases would

reduce the concentration of nitric oxide to a low level.

Unfortunately, evidence indicates that this does not occur.

Once formed, the NO stabilizes at a concentration typical of

X

equilibrium at the maximum or near maximum temperature achieved.

As the vehicle is run faster and at higher loads, this temperature increases explaining the significant jump in NO in

Figures 15 and 17 as conditions were changed from idling to

50 mph and 30 mph

41
SPARK ADVANCE (®BTDC)

Figure 21 Carbon Monoxide Versus Spark Advance for a 1/2 T

Truck Using Gasoline

4 2
5^

1.5

1.4

1.3

1.2

I.I

1.0

Id 0.9

9

XO 0.8

0.7

CQ 0.6

<

^

0.5

—r r r

1/2 TON TRUCK

_ FUEL -GASOLINE

_ 50 MPH, 30 HP

O 14 *»F AMBIENT

72 *»F AMBIENT

« A 107 «F AMBIENT

0.4

0.3 -

0.2 -

0.1 -

0.0 i 1 i

3 6 9

SPARK ADVANCE (*»BTDC)

12

Figure 22 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

43
1.5

!4

1.3

L2

1.0

lAj 0.9

9

XO 0.8

2 0.7

z

2 0.6

q:

<

1/2 TON TRUCK

FUEL- GASOLINE

72 *»F AMBIENT

-

0.5

0.4

0.3

0.2

0.1 h0.0

O IDLE

20 MPH, 4 HP

A 50 MPH, 30 HP

£1

3 6 9

SPARK ADVANCE (*»BTDC)

-

12

Figure 23 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline

44
The HC content is seen to have decreased as the vehicle was

run faster and at higher loads (see Figure 18 and 20) . The

reason for this latter trend is probably two-fold: As engine

speed increases, there is less time for quenching of the burning

charge by the cool engine walls and the higher combustion

temperatures at the higher loads promote more complete combustion

Figure 21 shows that the CO content was higher at idling

conditions than at 20 mph and 4 hp. However, there is no

explanation for the fact that the pollutant was a minimum at

20 mph and 4 hp as compared to either idling conditions or 50

inph and 30 hp (Figure 23).

There appears to have been no constant dependence of

pollutants on temperature. For example. Figures 15 and 16

show that the NO^ concentration was slightly higher at the

lower ambient temperature and Figures 18 and 19 show the

opposite trend for the hydrocarbons. The difficulty in making

any general statement concerning temperature is that the tests

were conducted in such a way that the effect that temperature

had on the carburetion could not be distinguished from the

dependence of pollutant formation on temperature.

4.2 Compressed Natural Gas-Fueled Tests

4.2.1 Spark Advance as the Independent Variable

Figures 24 through 28 are for tests at 75°F where the idle

spark advance was the independent parameter. Figure 24 shows

again (as in the case of the gasoline tests) the way in which

NO concentration increased as the spark was advanced. Data

X

^

45
E

cl

Q.

if)

UJ

o

X

o

z

Lii OO

1500

1400

1300

1200

I 100

1000

900

800

700

600

500

400

300

200

100

0

1 r

1/2 TON TRUCK

75 AMBIENT

_ 0# IDLE , 20 MPH, 4 HP

A A 50 MPH, 30 HP

4.5 IN. H2O IDLE GAS PRESSUREA

1.5 IN. H2O IDLE

GAS PRESSURE

A

- A

i

3 6 9

SPARK ADVANCE (*»BTDC)

12

Figure 24 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using CNG

46
is shown for 3 running conditions (idle, 20 mph and 4 hp, 50

mph and 30 hp) at 1.5 in. H^O and 4.5 in. H^O idle gas pressure

(igp). At the two running speeds, the NO was higher for the

X

4.5 in. H^O igp tests than for the 1.5 in. H^O igp tests.

This is to be expected since the mixtures should be richer

at the higher gas pressures (which is verified in Figure 27)

The reverse was true at idling conditions and as can be seen

from Figure 27, the mixture was richer at the lower idling

gas pressure. The very large difference in NO^ concentration

between 1.5 in. H^O igp and 4.5 in. H2O igp at the high speed

and load can again be explained by the large difference in A/F

ratio that resulted (Figure 27).*

Figures 25 and 26 show the HC and CO variation with spark

advance and running conditions at 1.5 in. H^O igp and 4.5 in.

II^O igp respectively. The data variation with speed and spark

advance is consistent with previous explanations with the

exception of the CO data at idle and 1.5 in. H^O igp. The

increase with spark advance would not have occurred had the

air-fuel ratio remained rixed at 18 or 19. However, as shown

in Figure 27, the mixture became rich as the spark was advanced,

thus causing the unusual trend.

Besides giving insight into unusual data behavior. Figure

27 illustrates that although determination of the variation

of pollutants with idle spark advance was the primary goal of

*As the mixture is enriched toward stoichiometric conditions,

NO increases as will be explained in Section 4.2.2 X

^

4 7
60

55

50

E 45

a.

CO 40

1

I 1/2 TON TRUCK

75 *»F AMBIENT

O

03

<

o

o

X,

o

>•X

35

30

25

20

15 - t 0.5^-

9 0.4

X

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CD

a:

<

o

03

02

01

0.0

O

O

O

1.5 IN. H2O IDLE GAS PRESSURE

O IDLE

20 MPH, 4 HP

A 50 MPH, 30

3 6 9

SPARK ADVANCE («BTDC)

12

Figure 25 Hydrocarbons and Carbon Monoxide Versus Spark Advance

for a 1/2 Ton Truck using CNG

48
E

a

CO

z

o

CD

<

O

o

(TO

>-

UJ

o

X

o

z

o

o

GQ

cr<

60

55

50

45

40

35

30

25

1/2 TON TRUCK _ 75 *»F AMBIENT

4.5 IN. H2O IDLE

GAS PRESSURE

20

15

t 0.5^

0.4

0.3

0-2

0.1

0.0

- O IDLE

20 MPH, 4 HP _ A 50 MPH , 30 HP

a

j_

3 6 9

SPARK ADVANCE (<»BTDC)

12

Figure 26 Hydrocarbons and Carbon Monoxide Versus Spark

Advance for a 1/2 Ton Truck Using CNG

49
1 \ —I I r

1/2 TON TRUCK , 75 *»F AMBIENT

IDLE

20 MPH, 4 HP

AA 50 MPH, 30 HP

A

24

23

22

20

9

8

£--Cr

•a.

o o.

4.5 IN. H2O IDLE GAS PRESSURE

1.5 IN. H2O IDLE GAS PRESSURE

0 3 6 9 12

SPARK ADVANCE (*»BTDC)

Figure 27 Air-Fuel Ratio Versus Spark Advance for a 1/2 Ton

Truck Using CNG

50
these tests, air-fuel ratio could not simultaneously be held

fixed during the tests because no direct measurements or control

of it was practical. Figure 28 shows that there was only slight

(if any) gas pressure variation during any one test. The change

in air-fuel ratio that resulted in some cases was then caused

by other than the fuel supply regulation system.

Figures 29 through 33 are results of CNG-fired spark

advance tests at 108°F similar to those done at 75°F. As with

the previous CNG tests and the gasoline tests, NO increased

with increasing spark advance and speed, HC increased with

increasing spark advance and decreasing speed and CO remained

practically constant with spark advance and speed. The airfuel ratio that resulted in each test is shown in Figure 32

and the very slight variation of gas pressure with spark

advance shown in Figure 33. Although there is only one data

point shown in Figure 32 for the 50 mph/30 hp test at an

idle gas pressure of 1.5 in. H^O, a line was drawn indicating

the probable dependence on spark advance (based on measurements

and calculations of air-fuel ratio completely off scale of

Figure 32).

4.2.2 Air-Fuel Ratio as the Independent Variable

Figures 34 through 41 show the results of tests conducted at

approximately 75°F with the vehicle running on compressed

natural gas. This is the first of a series of results showing

the effect air-fuel ratio has on the various pollutants.

51
12

n

10

9

O 8

CM

X

CO

CO c

QJ

<

CD

1——I——

\ r

1/2 TON TRUCK, 75 AMBIENT _ 0# IDLE

20 MPH, 4 HP

_ AA 50 MPH, 30 HP

3 -

a

LU

CO

<

UJ I

-

2

•3

4.5 IN. HgO IDLE GAS PRESSURE

1.5 IN. H2O IDLE GAS PRESSURE

—

M -

- A

^ .„„A..^ A- A -

1

3 6 9

SPARK ADVANCE («BTDC)

12

Figure 28 Gas Pressure at Running Conditions Versus Spark

Advance for a 1/2 Ton Truck Using CNG
3000

2800

2600

2400

2200 _ 2000

^ 1800

CO

g 1600

X

^

1400

z

UJ

g 1200

q:

t 1000

800

600

400 -

200 -

_ 1.5 IN. H2O IDLE GAS PRESSURE _ 0# IDLE

20 MPH, 4 HP

A A 50 MPH, 30 HP

1 f— ~T

1/2 TON TRUCK

108 AMBIENT

4.5 IN. H2O IDLE GAS PRESSURE .

3 6 9

SPARK ADVANCE (*»BTDC)

Figure 29 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using CNG

53
£

Q.

o

CD

<

o

o

o

>-X

60

55

50 -

45

35

30

25

20

-

0.5

^ 0.4

g 0.3

Z

i 0.2

S 0.1 h

<

O 0.0

T I — I I 1/2 TON TRUCK, 108 AMBIENT

O- O

O

1.5 IN. HgO IDLE GAS PRESSURE

O IDLE

20 MPH, 4 HP _ A 50 MPH , 30 HP

3 4 9

SPARK ADVANCE («*BTDC)

12

Figure 30 Hydrocarbons and Carbon Monoxide Versus Spark Advance for a 1/2 Ton Truck Usine CNG

5 4
60

55

c 50

Q.

45

CO

z

o

CD 40

<

o 35

o

q:

o

>- 30

X

25

20

0.5

LU

0.4

O

X

o

0.3

z

o

0.2

z

o

CD

0.1

<

o 0.0

T

1 -i 1 r

1/2 TON TRUCK, 108 AMBIENT

4.5 IN. H2O IDLE GAS PRESSURE

O IDLE

20 MPH, 4 HP

A 50 MPH , 30 HP

$ 0 0 ^ =t

12

SPARK ADVANCE (°BTDC)

Figure 31 Hydrocarbons and Carbon Monoxide Versus Spark

Advance for a 1/2 Ton Truck Using CNG

55
24

23 -

T T T

1/2 TON TRUCK, 108 ^'F AMBIENT

/

/

/

22

^ 2

ct

-J

UJ3

li. <

20

19

18

17

/

4.5 IN. H2O IDLE GAS PRESSURE

1.5 IN. H2O IDLE GAS PRESSURE

0,# IDLE

, 20 MPH, 4 HP

A,A 50 MPH, 30 HP

0 3 6 9

SPARK ADVANCE (^BTDC)

Figure 32 Air-Fuel Ratio Versus Spark Advance for a 1/2 Ton

Truck Using CNG

56
—I 1

I I

1/2 TON TRUCK

108 AMBIENT

4.5 IN. H2O IDLE GAS PRESSURE _

1.5 IN. H2O IDLE GAS PRESSURE

O IDLE

20 MPH, 4 HP _ A A 50 MPH, 30 HP

O P Q

' O

-O—

A AH

J L__

3 6 9 12

SPARK ADVANCE («»BTDC)

33 Gas Pressure at Running Conditions Versus Spark

Advance for a 1/2 Ton Truck Using CNG

57
The change in NO^ as air-fuel ratio changes (Figure 34)

results from the way in which air-fuel ratio affects the peak

temperature. As the ratio is increased from a very rich

condition towards a stoichiometric one (A/F = 17.24) , more

complete combustion results thus increasing the maximum chamber

temperature that occurs. However, once beyond a condition in

the vicinity of theoretical air, the excess air slows the speed

of the flame as it sweeps across the combustion chamber.

Consequently, the peak temperature decreases as the mixture is

mademorelean. " ~-

Figure 35 shows the way in which HC and CO varied with

the air-fuel ratio. Once beyond stoichiometric conditions

in the direction of a leaner mixture, sufficient oxygen

existed for nearly complete combustion. Therefore, the effect

of a change in the air-fuel ratio to a leaner mixture had

practically no effect on the CO or HC content. The one data

point in Figure 35 at an A/F ratio less than 17, shows how the

hydrocarbon content increases as a result of insufficient air

and incomplete combustion. Figures 36 and 37 show the same

data only at several values of idling spark setting. The

dependence on spark advance was the same as already noted.

Figures 38 and 39 give data that was obtained by running

the vehicle at 20 mph and maximum load so that the throttle was

wide open. The amount of horsepower obtained and pollutants

that resulted can be seen. This test data serves to show that

the changes that obviously give the higher peak temperatures

58
2800

2600

24001—

1

\—\—I

\—r~i—

2200 — TON TRUCK

2000

1

dd) 1800

CO

III 1600 O

O 1400

z

o 1200

o

oc 1000 Z

800

600

400

200

74 *»F AMBIENT

9*» SPARK ADVANCE

O IDLE

20 MPH, 4 HP

A 50 MPH, 30 HP

14 15 16 17 18 19 20

AIR/FUEL RATIO

21

J \ 1_J I I L_L

22 23

Figure 34 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

59
65

60

55

50

45

E 40

o.

Q.

i

'°

1 30

<

O 25

q:

^ 20

X

15

10

r- 2.8

2.6 - h 2.4

2.2

2.0

^

1.8

9 1.6 X

o

Z 14

o

• Z L2|- O

GQ

5 1.0

O

0.8

a6

0.4

0.2

„ 9* SPARK ADVANCE

0.0

1 1 1 1 1 1 r

1/2 TRUCK, 74 *»F AMBIENT

O

HC

a m—cr

O IDLE

20 MPH, 4 HP _ A 50 MPH, 30 HP

CO

J B 8

n -

14 15 16 !7 18 IS 20 21 22 23

AIR/FUEL RATIO

Figure 35 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

60
3000 T—I—I—I

1—I—I—

r

14 15 16 17 18 19 20 21 22 23

Air /FUEL RATIO

Figure 36 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

61
65

60

p 1.4 - 1.3

55 -

50

45

e 40

Qlo. 35

25

O

m 30

<

o

o

QCO

>- 20 X

15

10

1.2

I.I

1.0

20.9

UJ

I

0.8

O

z - O 0.7

Z 0.6

m

< 0.5 O

0.4 - 0.3

0.2 - 0.1

0.0

I I I—

r

HC

1/2 TON TRUCK , 74 *»F AMBIENT

IDLE - O 6 ® SPARK ADVANCE

O 12® SPARK ADVANCE

20 MPH, 4 HP

A 6 * SPARK ADVANCE

12 • SPARK ADVANCE

O

14 15 i? 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 37 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

62
95

90

85

80

^ 75

70

65

60

55

50

45

40

r- 4000

- 3600

-^3200

Q.

w2800

0)

UJ

92400

X

o

22000

UJ

o

OI600 - ZI200

I- 800

400

0

35

30

25

20

^

T

\ 1 f

1—I—

r

_ 1/2 TON TRUCK, 20 MPH

74 AMBIENT

« O 6« SPARK ADVANCE

9*^ SPARK ADVANCE

_ A I2*» SPARK ADVANCE

J L 1 1 J L

14 15 16 17 18 19 20 21

AIR /FUEL RATIO

22 23

Figure 38 Maxinum Horsepower and Nitrogen Oxides Versus AirFuel Ratio for a 1/2 Ton Truck Using CNG and

Operating at Full Throttle

63
65

60

55

50

45

£ 40

Q.

CO

35

- ^

0.9

lU

9 0,8

m 30

<

O 25 O

5 20

15

10

5

14

1.3

1.2

I.I

1.0

X

o

z

o

0.7

0.6

5 0.5

0.4

h 0.3

0.2

0.1

QO

~r-i

\—\—\—\—I—

r

— 1/2 TON TRUCK, 74 AMBIENT _ 20 MPH, MAXIMUM HP

O 6 SPARK ADVANCE

9* SPARK ADVANCE

A 12* SPARK ADVANCE

CO

I_L J \ J \ I I 14 15 1^ IT 18 19 20 21 - AIR/FUEL RATIO

22 23

Figure 39 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG and Operating

at Full Throttle

64
in the cylinders (advancing the spark from 6

° t o 12° before

t o

p - de ad -c e n t e r , and an air-fuel ratio close r t o the stoichiometric condition) also correspond to changes th at result in

more power output.

By observing the curves discussed up to th is point, it

should be clear that more significant result s i n pollutant

reduction can be obtained by emphasizing the s e tt ings to give

a proper air-fuel ratio than by emphasizing the s park setting

Figure 40 is particularly important in that i t sh ows the way

in which the air-mixer and associated contro Is in the CNG gas

system affected a change in the air-fuel rat i o as the vehicle

was run faster and loaded down. For example , i f the gas pressure

were adjusted to 2 in. H^O at idling conditions (550 rpm) and

the tweeker adjusted as lean as possible (and yet a good idling

obtained) , the A/F ratio on the vehicle tested would be

approximately 18. This is leaner than stoichiometric thus

giving complete combustion with a minimum of CO and HC . If

the truck were run faster and loaded down, it has already been

noted that with a constant air-fuel ratio, the HC would increase,

CO remain the same, and NO increase tremendously. However,

X as can be seen in the actual system, the A/F decreased

ultimately to about 22 1/2 at 50 mph and 30 hp. This caused

a certain loss in available power; however, the vehicle tested

still produced 30 hp and in addition, the NO^ was only 600 ppm.

The table below indicates the resulting pollutants for a 2 in.

65
I4p

13-

12

10

9|-

8

7

6

5

4

3

2

I -

0,

1/2 TON TRUCK, 74** F AMBI ENT, FUEL-CNG

9° SPARK ADVANCE

O IDLE

20MPH, 4HP

A 20MPH, MAXIMUM HP

O 50 MPH, 30 HP

ADO

50/30

20/MAX

14 15 16 17 18 19 20 21 22 23

AIR/FUEL RATIO

Figure 40 Idle Gas Pressure Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

65
idle gas pressure setting and three running conditions due

to the PALCO* system operation.

Table 1 Characteristics of PALCO System Operation

data - 1/2 ton idle 20 mph/4 hp 50 mph/30 hp

truck 9° BTDC SA,

2 in. H2O idle

gas pressure

Operating gas 2 in. H^O 1.5 in. H^O 0 in. H^O

pressure

approximate air- 18 21.5 22.5

fuelratio

approximate CO .07% .07% .07%

content

f approximate HC 44 ppm 30.5 ppm 23 ppm

content

approximate NO^ 270 ppm 240 ppm 600 ppm

Figure 41 shows why the A/F ratio decreased. For a given

idle gas pressure, the resulting gas pressure at running

conditions was decreased as the running speed and load were

increased. This reduced pressure no doubt forced less fuel

into the air mixer thus increasing the air-fuel ratio.

Figures 42 through 45 are for air-fuel ratio tests that

were conducted at 110°F chamber temperature. The variation

of NO , HC , and CO is as noted previously. In addition.

*Trade names are used in this report as a means for clear

identification to the Postal Service of their property. Use

of a trade name neither constitutes nor implies endorsement

by the National Bureau of Standards.

6 7
12

9mX

in

z

o

O

z

o

CJ

V>

liJ &

UJ

(T

CD

CO

UJ

CL

CO

<

O

a:

ZDCO

<

UJ5

T T T

10

8

7

6

5

4

3

2

-2

1/2 TON TRUCK, 74*' F AMBIENT, FUEL-CNG

9** SPARK ADVANCE

O IDLE

20MPH,4HP

A 20MPH, MAXIMUM HP

O50MPH,30HP

8

IDLE GAS PRESSURE ( IN. HgO)

Figure 41 Gas Pressure at Running Conditions Versus Idle Gas

Pressure tor a 1/2 Ton Truck Using CNG

68
3000

2800

2600

2400

2200

^ 2000

a,

w 1800

(/)

uiO 1600

X

o

2 1400

UI

O 1200

o:

Iz 1000

800

« 1/2 TON TRUCK _ no AMBIENT _ O 0* SPARK ADVANCE

6* SPARK ADVANCE _ A 12* SPARK ADVANCE

600

400 —

200 —

1—I

\—r~i

_ 50 MPH

J I \ \ \ I I L

14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 42 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

69
70

65

60 -

55

50

45

Q.

O.

40

CO

z

BO 35

<

OC 30

cca

>• 25

X

20

15

10

5

0

T

1 "T"

1/2 TON TRUCK

110 *»F AMBIENT

50 MPH, 30 HP

1—

r

O 0** SPARK ADVANCE

6*» SPARK ADVANCE

A 12** SPARK ADVANCE

J I I J L_ L

14 15 16 17 18 IS 20

AIR /FUEL RATIO

21 22 23

Figure 43 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using CNG

70
liJ a

o

o

1.5

1.4

1.3

1.2

i.l

1.0

0.9

0.8

0.7

1/2 TON TRUCK

110 *F AMBIENT _ 50 MPH, 30 HP _ O 0* SPARK ADVANCE _ 6* SPARK ADVANCE _ A I2*» SPARK ADVANCE

S 0.6

tr

o 0.5

0.4

0.3

0.2

0.1

0.0

T—I

\—I—I—

r

J I l_J I I L

14 15 16 17 18 19 20 21 22 23

AIR/FUEL RATIO

Figure 44 Carbon Monoxide Versus Air-Fuel Ratio for a Ton Truck Using CNG

71
12

I I

iO

9

8

liJ IT

CO

CO

111 d:

a. ^

0)0

o z

UJ 3crCO

<

us

I I I I

1/2 TON TRUCK, 110 *»F AMBIENT _ 50 MPH, 30 HP

6

5

O 0*» SPARK ADVANCE

12 • SPARK ADVANCE

A 0** SPARK ADVANCE

A I2<» SPARK ADVANCE

3

2

I

0

•I

2

3

tweeke r set

at 1.5 in.

H 2 0 idle

gas pressure

tweeker set_

at 6.5 in.

H^O idle

gas pressure

J I \ I 14 15 16 17 18 19 20

AIR/FUEL RATIO

21 22 23

Figure 45 Gas Pressure at Running Conditions Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

72
Figure 45 illustrates the magnitude of effect that the tweeker

had on the resulting air-fuel ratio. For convenience of testing,

the tweeker was adjusted at one specific idle gas pressure

(igp) and then the vehicle's simulated road speed was increased

to 50 mph . When changing the gas pressure (in order to obtain

a different A/F ratio), it was simply increased or decreased

by approximately 1.5 in. H^O (with no readjustment of the

tweeker) and data was taken. It was not important in these

laboratory tests to readjust the tweeker after each change

since different values of A/F ratio were all that were necessary.

However, at 0° and 12° spark advance the test was conducted

twice, the tweeker being adjusted at the low end of the pressure

range once and at the upper end before the second test. As

can be seen, this difference in tweeker setting for a specified

measured gas pressure caused a difference as large as 2 in the

air-f ue 1 ratio

.

Figures 46 and 47 show a comparison between the data taken

at 74°F and that at 110°F for the spark set at 6° before top

dead center at idling. It must be concluded as a result of

this comparison, that a temperature change from 70°F to 110°F

had little effect on the pollutants for the same spark advance

and A/F rat io

.

Figures 48 through 51 show the results of tests conducted

at a low temperature (17°F at the radiator). Figure 48 shows

very clearly the way in which NO^ peaked at an air-fuel ratio

just to the lean side of stoichiometric conditions. Figure

73
3000

1 1 1 1 1 1

1 1 2800 MM* 1/2 TON TRUCK

2600 MM SPARK ADVANCE

2400 50 MPH, 30 HP

2200 — O 74 *»F AMBIENT

E 2000 — 110 *F AMBIENT —

CL

Q.

1800

UJ

o 1600 —

X

o

UJ

o

1200

" \ \

O —

q:

1r~" z 1000

800

600

400

: , ,-1

, 200 ; ' •, , : r< : "

1 1 1 1 1 1 1 1 0

14 15 16 17 18 19 20 21 22 23

AIR/FUEL RATIO

Igure 46 Nitrogen Oxides Versus Air-Fuel Ratio for a 1

Ton Truck Using CNG

7 4
75

70

65

60

55

3 45

CO

40

35

30

25

20

15

1.5

1.4

h 1.3

1.2

I.I

1.0

10

5 -

0 -

55

uj 0.9

O

O 0-8

Z

o

- 2 0.7

S 0.6

<

^ 05 - 0.4

—\—I—I—I—

r

1/2 TON TRUCK

_ 6 « SPARK ADVANCE

- 50 MPH, 30 HP

« O 74 *»F AMBIENT

110 «F AMBIENT

- 0.3

0.2

0.1

0.0

1

\—

r

CO

-0)

J I I I I I I L

14 15 16 17 18 19 20 21 22

AIR/FUEL RATIO

23

Figure 47 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

75
3000

2800

2600

2400

2200

e 2000

Q.

O.

« '800

HI

o

5 1600

Z 1400 U

O

O 1200

OH

Z 1000

800

600

400

200 h0

1 \ TTTT

1/2 TON TRUCK

17 ^'F AMBIENT

9*^ SPARK ADVANCE

O 50 MPH, 30 HP

A 30 MPH, 8 HP

_L I I 14 15 16 17 SB 19 20 21 22 23

AIR/FUEL RATIO

Figure 48 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using CNG

76
49 also demonstrates what occurred with the CO content of the

exhaust gas when conditions were so rich that inefficient

combustion resulted due to a lack of sufficient air. Figure

50 shows the horsepower that was obtained from the vehicle

running at 20 mph with the throttle wide open and a 9° spark

setting. The pollutant values shown are those that resulted

from this "fully loaded" running condition. Figure 51 again

serves to show the importance of the tweeker. Comparing the

two curves for 50 mph and 30 hp, one sees that for a given

measured gas pressure at running conditions, the tweeker

setting affected a change of 2 or more in the air-fuel ratio.

Figures 52 and 53 show comparisons between the data of the

"air-fuel ratio tests" conducted at 74°F and those conducted

at ]7°F. Again it is noted that the gas system, carburetion

system, and vehicle operated in such a way that pollutants

did not change with environmental temperature provided the

air-fuel ratio and spark setting were the same.

A. 3 Propane-Fueled Tests

Figures 54 through 77 summarize the results of tests done

on the 1/2 ton truck when it was run using propane as the fuel.

4.3.1 Spark advance as the Independent Variable

Figures 54, 55, and 56 show the way in which the pollutants

varied with spark advance set at idling speed for three

different running conditions at the ambient temperature of

77
AIR/FUEL RATIO

Figure 49 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

78
300 _ 275

S 250

CO

Z 225 O

CD

< 200

O

S 175

a

^

150

I- 4400

--4000

E

Q.

33600

CO

LU

93200

X

o

^2800

UJO

O2400

q:

I72200

T—

r

125

60 -

- 1600

UJ

O

0.

UJ

CO

q:O

X

o

<

o

55

50

45

40 -

^ 301-

X

<

S 25L.

h ^

1.0

UJ 0.8

X

O 0.6

35 - ^

0.4

O

ffi 0.2

<

^0.0

1 r

CO

i

1/2 TON TRUCK

17 AMBIENT -

9* SPARK ADVANCE^

50 MPH

1 J L

14 15 16 17 18 19 20

AIR/FUEL RATIO

21 22 23

Figure 50 Maximum Horsepower and Pollutants Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG and Operating

at Full Throttle

79
12

10 -

T T

_0 50 MPH, 30 HP

30 MPH, 8 HP

T—I—I—

r

tweeker set at

7 in. H2O idle

gas pressure

_ A 50 MPH, 30 HP

__ ^50 MPH, MAXIMUM

twe eke r set at

1.5 in. id

gas pressure

7 -

6

51—

4

3

2

I -0-

-!

-2

1/2 TON TRUCK

17 *»F AMBIENT

1 1 1 1

14 15 16 17 18 19 20

AIR/FUEL RATIO

21 22 23

Figure 51 Gas Pressure at Running Conditions Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

80
3000

2800

2600

2400

2200

^ 2000

Q.

^

1800

CO

liJ 9 1600

X

o

2 1400

liJ O

O 1200

ocz 1000

800

600

400

200

1—I—n^n—I—I I [

1/2 TON TRUCK

9** SPARK ADVANCE

O 17 *»F AMBIENT

74 *»F, AMBIENT

50 MPH, 30 HP

1 I 1 1 1 J L

14 15 16 17 18 19 20 21

AIR/ FUEL RATIO

22 23

Figure 52 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck using CNG

81
E

o.

o.

in

O

a:

<

o

o

a:

o>

40

35

30

25

20

15

10

2.8

2.6

h 2.4

—\—\—n—I—I—I—I—

r

L 1/2 TON TRUCK, 9*SFV^RK ADVANCE - 50 MPH 30 HP

2.2 h

2.0

i.S

UJ

9 1.6 X

o

o

1.4 h1.2

O

CD

5 1.0 1-

O

0.8

0.6

0.4

0.2

0.0

HC

O 17 AMBIENT

74 *»F AMBIENT „

90

14 15 16 17 18 19 20 21 22 23

AIR /FUEL RATIO

Figure 53 Hydrocarbons and Carbon Monoxide Versus Air-Fuel

Ratio for a 1/2 Ton Truck Using CNG

82
E

o.

o.

in

UJ

9

X

o

UJ

o

o

a:

3000

2800

2600

2400

2200

2000

1800

1600

1400

1200

1000

800

600

400

2001-

0

T

1/2 TON TRUCK. II*»F AMBIENT,

POWER VALVE- LEAN (2-1/2), FUEL- PROPANE

O IDLE

20MPH,4HP

A 50 MPH, 30 HP

OI

•oI o

I 3 6 9

SPARK ADVANCE rBTDC)

12

Figure 54 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using LPG

83
E

o.

a.

C/3 ZO

OQ

<

O

O

q:

o

>

X

160

150

140

130

120

1 10

100

90

80

70

60

50

40

30

20

10

0

1/2 TON TRUCK, ITF AMBIENT.

POWER VALVE- LEAN (2-1/2)

FUEL- PROPANE

O IDLE

20MPH, 4HP

A 50 MPH, 30 HP

AI I 3 6 9

SPARK ADVANCE (^BTDC)

Figure 55 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using LPG

84
1/2 TON TRUCK TRUCK, I^F AMBIENT

POWER VALVE - LEAN (2- 1 /2), FUEL- PROPANE

O IDLE

20 MPH, 4HP

A 50 MPH, 30 HP

i. 0 3 6 9

SPARK ADVANCE ^BTDC)

12

56 Carbon Monoxide Versus Spark Advance for a Truck Using LPG

1/2

85
11°F. Consistent with previous findings, the pollutants increased with spark advance, the NO increased with load and

X

speed, and the HC content was the largest while the vehicle

was running at idling speed. It was expected that the CO

content would also be highest at the idling condition but this

did not occur. However, the CO content was so low for all

three running conditions that the reversal in trend is not

significant. The power valve setting at 2 1/2 gave the leanest

condition that could be used and still obtain 30 horsepower

at 50 miles per hour for this low temperature and all idling

spark settings from 0 to 12 degrees before top dead center

(BTDC) . At all other ambient temperatures it was possible to

obtain the desired load and speed with a setting of 2 on the

restrictor. It would have been possible to use a position of

2 for the low temperature if 28 or 29 horsepower had been

acceptable for the 0° BTDC setting. At no ambient temperatures

was it possible to use a position setting of 1.

Figures 57, 58, and 59 and Figures 60, 61, and 62 show

results for similar tests at 76°F ambient and 114°F ambient

respectively. All trends are consistent with the previous

results with the exception that the CO content was not the

largest at the idling conditions. As mentioned above, the

trend should not be considered significant in light of the

relative low values in all cases.

The data in Figures 63 and 64 were plotted to give insight

into the way in which this dual-fuel regulating system operated.

86
3000

2800

2600

2400

2200

1/2 TON TRUCK

_ 76 AMBIENT

POWER VALVE -LEAN (2) _ O IDLE

^

2000

E

Q. ^

I80Q

</>

liJ Q 1600

X

UJ

O

20 MPH, 4 HP

A 50 MPH, 30 HP

3 6 9

SPARK ADVANCE («>BTDC)

Figure 57 Nitrogen Oxides Versus Spark Advance for a 1/2

Truck Using LPG

87
160

150

140

130

120 -

MO

E

100

o. 90

80 -

70

60 -

50

40

30 -

20

0

1/2 TON TRUCK

76 •F AMBIENT

POWER VALVE - LEAN (2)

O IDLE

20 MPH, 4 HP

A 50 MPH, 30 HP

Ai

0 3 6 9

SPARK ADVANCE ( **BTDC)

12

Figure 58 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using LPG

88
UJ

o

X

o

0.30

0.28

0.26

0.24

0.22 — 0.20

0.18

0.16

2 0.14

Z

2 012

GQ

cr, o 0.10

0.08

0.06

0.04

0.02

0.0

\ \ \

1/2 TON TRUCK

_ 76 ''F AMBIENT

_ POWER VALVE -LEAN (2)

O IDLE

_ 20 MPH, 4 HP

A 50 MPH, 30 HP

1 1

3 6 9

SPARK ADVANCE (^'BTDC)

12

Figure 59 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using LPG

89
3000

28001-

2600

2400

2200 — 2000

E

o. 3 1800

CO

LU

9 1600

X

o

2 1400

111 O

1200

(T

t^ 1000

800

600

400

200

0

_ A 50 MPH, 30 HP

1 1 1

1/2 TON TRUCK

114 AMBIENT

POWER VALVE - LEAN (2)

O IDLE

20 MPH, 4 HP

3 6 9

SPARK ADVANCE (^BTDC)

12

Figure 60 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using LPG

90
180

170

160

150

140

130 _ 120

1

3 MO

O ioo

a:< 90

o

q:Q 80

>•X

70

60

50

40

30 h20 -

O

1/2 TON TRUCK

114 AMBIENT

POWER VALVE - LEAN (2)

O IDLE

20 MPH, 4 HP

A 50 MPH, 30 HP

9

SPARK ADVANCE (*»BTDC)

12

Figure 61 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using LPG

91
0.30

0.28

0.26

0.24

0.22

0.20

55

a

0.18

0.16

0.14

QC<

O 0.10

0.08

0.06

0.04

0.02

0.0

—r

—] ~n—

. 1/2 TON TRUCK

114 AMBIENT

POWER VALVE -LEAN (2)

O IDLE

20 MPH , 4 HP

A 50 MPH, 30 HP

3 6 9

SPARK ADVANCE (^'BTDC)

—

O

12

Figure 62 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using LPG

92
<

27

26

25

24

23

22

21

20

u 19

^ 18

<

17

16

15

14

1/2 TON TRUCK, 76*»F AMBIENT, POWER VALVE

RICH (5), FUEL-PROPANE

O IDLE

20 MPH, 4HP

A 50 MPH, 30 HP

O- O •o- •O- •- -

13

12 1

3 6 9

SPARK ADVANCE rBTDC)

12

Figure 63 Air-Fuel Ratio Versus Spark Advance for a 1/2 Ton

Truck Using LPG

93
<

-J

lU

Z)u.<

27

26

25

24

23

22

21

20

19

18

17

16

15

T 1 1 1 r

1/2 TON TRUCK, 76*»F AMBIENT, POWER VALVELEAN (2), FUEL- PROPANE

O IDLE

n 20MPH,4HP

A 50 MPH,30HP

O-

"O"

-A

-O

14

12 1

3 . 6 9

SPARK ADVANCE rBTDC)

12

Figure 6A Air-Fuel Ratio Versus Spark Advance for a 1/2 Ton

Truck Using LPG

94
With the power valve or restrictor set at the lean position and

for a given spark setting, the air-fuel ratio increased or the

mixture got leaner as the load and speed increased (see Figure

63). This is precisely the way that the PALCO* dual-fuel

system worked and seems to be best for minimizing the NO^

content of the exhaust gases. As the load and speed are

increased, the NO would increase as we have already noted.

X

However, this increase would be offset somewhat by the fuel

regulating system operation whereby the mixture would

simultaneously become leaner. Figure 64 shows that the fuel

regulating system caused just the opposite to occur when the

restrictor was positioned for a rich running condition.

4.3.2 Air-Fuel Ratio as the Independent Variable

Figures 65, 66, and 67 are for tests where the air-fuel

ratio was varied (by varying the restrictor position) while

running the vehicle at 11°F ambient temperature and a variety

of idling spark settings and running speeds and loads. As

was the case previously, the ^"^'0^ content decreased rapidly as

the air-fuel ratio was made more lean past stoichiometric

conditions. (The stoichiometric air-fuel ratio is approximately

15.7 for LPG.) In addition, the HC and CO content decreased

and leveled off at an air-fuel ratio of approximately 18.

Figures 68, 69, and 70, and Figures 71, 72, and 73 show similar

results for ambient temperatures of 72°F and 114°F respectively.

*Trade names are used in this report as a means for clear

identification to the Postal Service of their property. Use

of a trade name neither constitutes nor implies endorsement

by the National Bureau of Standards.

95
|1 LTMJ L 1 I I I I I 14 15 16 17 18 19 20 21 22 23

AIR/FUEL RATIO

Figure 65 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

9 6
150

140 —

130

1/2 TON TRUCK _ II AMBIENT

120

I 10

100

9" 90

^ 50 MPH, 30 HP _ O 0*» SPARK ADVANCE _ 6** SPARK ADVANCE

__ A 9*» SPARK ADVANCE

g 80

O

(D

OC 70

<

O

O 60

a

X 50 —

40 —

30 —

20 —

10

0

1 \ r

A la*" SPARK ADVANCE

J I \ \ \ I L

14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 66 Hydrocarbons Versus Air-Fuel Ratio for a 1/2

Truck Using LPG
0.75

0.70 -

0.65 -

0.60

0.55

"1—~i r-—I 1 r

1/2 TON TRUCK

11 *»F AMBIENT

50 MPH, 30 HP

O 0** SPARK ADVANCE — 0.50

U 0.45

Q

O 0.40

5 0.35

Z

(D 0.30

a:

<

^

0.25

0.20

0.25

0.1 0

0.05 h0.0

_ as** SPARK ADVANCE _ A 9** SPARK ADVANCE

A I2*» SPARK ADVANCE

J L I i I L

14 15 16 17 18 19 20 21 22 23

AIR/ FUEL RATIO

Figure 67 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2

Ton Truck Using LPG

98
4000

3750 -

3500 -

3250 -

3000

2750

S 2500 fco

UJ 2250 h- o

O 2000 H

liJ e> 1750

o

(T. t 1500 -

1250

1000

750 h

500

250

0

1 1 1 1

1/2 TON TRUCK

72*^ F AMBIENT _

50 MPH, 30 HP

_ O 0* SPARK ADVANCE

6* SPARK ADVANCE _ A SPARK ADVANCE

A I2*» SPARK ADVANCE

J I I L 1 1

15 16 17 18 19 20 21

AIR/ FUEL RATIO

J L

22 23 24

Figure 68 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using LPG

99
150

140

130

120

I 10

100

^ 90

E

Q.

i 80

O

OQ

OC 70

<

O

O 60

a

X 50

40

30

20

10

0

1 I \ \ \ I I r 1/2 TON TRUCK

72 AMB!ENT

50 MPH, 30 HP

O 0^ SPARK ADVANCE

O 6* SPARK ADVANCE

AS** SPARK ADVANCE

12 SPARK ADVANCE

I I \ I I I L_^ L

14 15 16 17 18 19 20

AIR/FUEL RATIO

21 22 23 24

Figure 69 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

100
3.0

2.8

2.6

2.4

2.2

^ 2.0

1.8

5^

UJ

o

g 1.6

O

2 1.4

2 1.2

S 1.0

08

0.6

0.4

0.2

0.0

14

T—I

\—I—I—I

\—\—

r

1/2 TON TRUCK

72 *F AMBIENT

50 MPH, 30 HP

O 0* SPARK ADVANCE

6** SPARK ADVANCE

A 9** SPARK ADVANCE

A la** SPARK ADVANCE

J I ] \ I I 16 17 18 19 20 21

AIR/ FUEL RATIO

22 23 24

Figure 70 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2

Ton Truck Using LPG

101 /
4250

4000

3750

3500

3250

3000

^ 2750

a

•^2500

CO

UJ

9 2250

X

o

2 2000

UJ

iD

O 1750

a:^ 1500

1250

1000

750

500

250

0

T—I—I—

r

1—I—1—I

1/2 TON TRUCK

114 *»F AMBIENT _

50 MPH, 30 HP «

O 0 SPARK ADVANCE

6 • SPARK ADVANCE

A 9* SPARK ADVANCE

la*" SPARK ADVANCE

J L 1 J L

O

J L

14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 71 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2

Ton Truck Using LPG
150

140

130

120 —

110

iOO

E

Q. 90

g 80

O

GQ

a: 70

<

g 60

>

I 50

40 —

30 —

20 —

10 —

0

1/2 TON TRUCK

114 *»F AMBIENT

50 MPH, 30 HP

O 0<» SPARK ADVANCE _ 6* SPARK ADVANCE _ A 9*» SPARK ADVANCE _ A I2*» SPARK ADVANCE

J \ L J \ \ L

14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 72 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

103
3.0

2.8

2.6

2.4

2.2

2.0 h1.8 —

O

X I 6 O

Z

i ..4

z

O 1.2

CD

<

O 1.0

0.8

0.6

0.4

0.2

0.0

1 \ I

\—\—\—\—r1/2 TON TRUCK

114 AMBIENT

50 MPH, 30 HP

O 0* SPARK ADVANCE _

6« SPARK ADVANCE

A 9« SPARK ADVANCE

12* SPARK ADVANCE _

14

J__i L_I

17 18 19 20 21

AIR/ FUEL RATIO

22 23

Figure 73 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

104
Figures 74, 75, and 76 show a comparison with ambient

temperature of the data of the air-fuel ratio tests at the

conditions of 50 mph and 30 hp and 6° BTDC idling spark advance.

The curves show that the NO content of the exhaust gas increased

X

slightly with ambient temperature and there was little or no

variation with temperature in the HC and CO content. This

is consistent with previous results for the vehicle fired on

gasoline and CNG. One should be reminded that the nature of

tlie tests are such that no choking occurred or warm-up period

was allowed in the tests and comparisons were made for the same

idling spark advance, air-fuel ratio, and running speed and

load. r Figure 77 is a plot of the air-fuel ratio that resulted

from a specific restrictor position setting at 6° BTDC idling

spark advance, 50 mph and 30 hp and the three different ambient

temperatures. The setting was critical in the vicinity of the

number 2 position in that a slight variation caused a considerable cliange in the resulting air-fuel ratio. However, the

cliange in air-fuel ratio was slight once beyond the 3 position

in the direction of a rich mixture. One can see that as the

ambient temperature was lowered, the air-fuel ratio became

leaner for a given power valve setting explaining why the

valve position had to be moved to the 2 1/2 position at the

low temperature to obtain exactly 30 horsepower for all idling

spark settings. Figure 77 could be used for estimating resulting

air-fuel ratios at other idling spark settings by estimating

105
4000

3750

3500

3250

3000

2750

-g 2500

-^2250

</) UJ

9 2000

o

Z 1750

111 O

2 (500

1250

1000

750

500

250

0

1

\—I—

r ~1 \ \—

1/2 TON TRUCK _

50 MPH, 30 HP _

6* SPARK ADVANCE-

_ O M AMBIENT

72 *F AMBIENT _ A 114 AMBIENT

J I

I I

1 L

14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 74 Nitrogen Oxides Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

106
150

140

130

120

I 10

100

Q. 90

CL

80

O

CD

a 70

<

2 60

o

>

2: 50

40

30

20

10

T

1 1 \ 1 1 T"

1/2 TON TRUCK

50 MPH, 30 HP

6 SPARK ADVANCE

O II AMBIENT

14 15 16

72 ^'F AMBIENT

A 114 ^'F AMBIENT

A U -

J L I _J I I \ L

17 18 19 20 21

AIR/ FUEL RATIO

22 23

Figure 75 Hydrocarbons Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

107
3.0

2.8

2.6

2A

2.2

2.0 I—

S.8 H

UJ

o

X 1.6 -

O

z

O 1.2

GQ

< 10

0.8

0.6

0.4

0.2

0.0

14

T—I

\—I—I\—

r

1/2 TON TRUCK

50 MPH 30 HP

6** SPARK ADVANCE

O II <»F AMBIENT

O 72 *F AMBIENT

A 114 *F AMBIENT

LZJ L

17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 76 Carbon Monoxide Versus Air-Fuel Ratio for a 1/2 Ton

Truck Using LPG

108
26

24

22

a:

iij

2 18

<

16

14

12

T

1/2 TON TRUCK

50 MPH, 30 HP

6* SPARK ADVANCE

O II ^'F AMBIENT _ 72 AMBIENT

A 114 AMBIENT

i i i

2 3 4

POWER VALVE SETTING

Figure 77 Air-Fuel Ratio Versus Power Valve Setting for a 1/2 Ton Truck Using LPG

109
the change with idling spark setting from Figures 63 and 64.

4.4 Comparison of the Fuels

Figures 78 through 86 have been inserted to show a comparison between CNG and LPG as fuels for this 1/2 ton truck.

The comparison is made for 50 mph and 30 hp, and a given idling

spark setting with the independent variable being the ratio of

air-fuel ratio to stoichiometric air-fuel ratio. Data is shown

for low temperature (Figures 78, 79, and 80), moderate temperature (Figures 81, 82, and 83), and high temperature (Figures

84, 85, and 86). The NO content of the exhaust gas was a maximum closer to stoichiometric conditions for CNG than for

LPG (for all ambient temperatures 11°F - 114°F) and consequently

for a given value of A/F/(A/F stoichiometric) > 1.0, the NO^

content of the LPG exhaust gas was higher than that of the CNG

exhaust gas. As the mixture was enriched from a lean setting

towards the stoichiometric condition, the CO and HC content

of the exhaust gas did not rise significantly for CNG-fired

tests until conditions to the rich side of stoichiometric were

reached (all ambient temperatures). However, the increase

occurred to the lean side of stoichiometric for the LPG-fired

tests (all ambient temperatures).

Figures 87 through 95 show the comparison of fuels for this

1/2 ton truck on another basis. The independent variable is

the idling spark advance and data is shown for NO at 50 mph

X

110
3400

3200

3000

2800

2600

2400 _ 2200

E

S 2000

CO

LUO 1800

X

^ 1600

iiJ e>O 1400

hz 1200

1000

800

600

400

200

0

O

1/2 TON TRUCK

LOW TEMPERATURE _ 50 MPH, 30 HP-9*» SW^RK ADVANCE

O CN6, 17 «»F

LP6, II «F

1 1 1 1 1

0.90 1.0 I.I 1.2 1.3

AIR- FUEL/ STOICHIOMETRIC AIR-FUEL

Figure 78 Nitrogen Oxides Versus Normalized Air-Fuel Ratio

for a 1/2 Ton Truck Using CNG and LPG

111
150

140

130

120

I 10

100

Q. 90

Q.

^ 80

O

CD£ 70

<

O

O 60

o

X 50

40

—\ \ —

r

1/2 TON TRUCK _ LOW TEMPERATURE

50 MPH, 30 HP _ SPARK ADVANCE

O CNG, 17

LP6, mF

30 —

20

10 —

i i i

0.9 1.0 i.! 1.2 13

AIR- FUEL /STOICHIOMETRIC AIR-FUEL

Figure 79 Hydrocarbons Versus Normalized Air-Fuel Ratio fo

a 1/2 Ton Truck Using CNG and LPG

112
1 1 1 1 r

AIR -FUEL/ STOICHIOMETRIC AIR-FUEL

Figure 80 Carbon Monxoide Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

11 J
I.I 1.2 1.3 1.4

AIR-FUEL/ STOICHIOMETRIC AIR-FUEL

Figure 81 Nitrogen Oxides Versus Normalized Air-Fuel Ratio f a 1/2 Ton Truck Using CNG and LPG

114
150

140

130

120

110 _ 100

'e

a. 5 90

CO

1/2 TON TRUCK, MODERATE TEMPERATURE

50MPH, 30 HP, 9** SPARK ADVANCE

O CNG, 74°F

LPG, 72°F

O

CD

a:<

o

o

cro

>

X

80

70

60

50

40

30

20

10 -

0 1

.0 I.I 1.2 1.3

AIR-FUEL/STOICHIOMETRIC AIR-FUEL

1.4

Figure 82 Hydrocarbons Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

113
X

o

z

o

o

cr. <

3.0

2.8

2.6

2.4

2.2

2.0

UJ 1.8 o

1/2 TON TRUCK, MODERATE TEMPERATURE,

50 MPH, 30 HP, 9** SPARK ADVANCE

O CNG,74*»F

LP6, 72*F

.0 I.I 1.2 1.3

AIR-FUEL/STOICHIOMETRIC AIR-FUEL

1.4

Figure 83 Carbon Monoxide Versus Normalized Air-Fuel Ratio for

^ . a 1/2 Ton Truck Using CNG and LPG

1 1 6
3400

3200

3000

2800

2600

2400

2200

o. ^

2000

CO

tuO 1800

X

o

2 1600

UJ

KD

O 1400

CC

Z 1200

1000

800

600

400

200 I0

_ o CN6, no

LPG, 114 *F

1 1 1

1/2 TON TRUCK

HIGH TEMPERATURE _

50 MPH, 30 HP

6*» SPARK ADVANCE _

i 1 1 1 i

1.0 I.I 1.2 1.3 1.4

AIR- FUEL/ STOICHIOMETRIC AIR-FUEL

Figure 84 Nitrogen Oxides Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

i 1 7
20

1/2 TON TRUCK

HIGH TEMPERATURE

50 MPH, 30 HP

6 ** SPARK ADVANCE

O CNG, 110 ''F

LPG, 114 *»F

i i 1

n

1

1.0 i.l i.2 1.3 1.4

-FUEL/ STOICHIOMETRIC AIR-FUEL

Figure 85 Hydrocarbons Versus Normalized Air-Fuel Ratio for

a 1/2 Ton Truck Using CNG and LPG

118
3.0

2.8

2.6

2.4

2.2

~l 1

1/2 TON TRUCK

HIGH TEMPERATURE

50 MPH, 30 HP

6* SPARK ADVANCE

O CNG, 110

LPG, 114 *»F

1 1 1

1.0 1.1 1.2 1.3 1.4

AIR- FUEL/ STOICHIOMETRIC AIR-FUEL

Figure 86 Carbon Monoxide Versus Normalized Air-Fuel Ratio for

a 1/2 T«n Truck Using CNG and LPG

1 1 Q
and 30 hp and three temperature levels (Figures 87, 90, and 93)

and HC and CO at idling conditions in Figures 88, 91, and 94

and Figures 89, 92, and 95 respectively. In contrast to

Figures 78 through 86, the comparison is not made on the basis

of the same air-fuel ratio; however the data is shown for each

fuel where the leanest setting possible was used (and still

obtain 30 hp at 50 mph) . Those settings were:

gasoline

low temperature preset

moderate temperature preset

high temperature preset

CNG

1.5" idle gas

pressure

1.5" idle gas

pressure

1.5" idle gas

pressure

LFG

2 1/2 power

valve setting

2 power valve

setting

2 power valve

se tting

One can see from the curves that it was possible to maintain

the various pollutants below the following levels for an

appropriate lean setting in the fuel system (no adjustment

for gasoline) and the following idling spark settings for

ambient temperatures in the range (0 - 110°F):

6° BTDC idling spark advance

CNG

gas ol ine

NO (ppm)

300

2400

HC (ppm)

50

215

C0(%)

0.1

1 . 2

120
3400

3200

3000

2800

2600

2400

2200

2000

1800

1600

1400

1200

1000

800

600

400h

200

1 1 1 ]—

1/2 TON TRUCK, HIGH TEMPERATURE,

50MPH, 30 HP

O GASOLINE

CNG, LEAN SETTING

A LPG, LEAN SETTING (

3 6 9

SPARK ADVANCE (*>BTDC

gure 87 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

12 1
300

280 1/2 TON TRUCK, HIGH TEMPERATURE. IDLE

260

240

220

200

180

160

140

120

100

80

60

40

20

0

O GASOLINE

CNG, LEAN SETTING

A LPG,LEAN SETTING

1

A

A _

3 6 9

SPARK ADVANCE ^BTDC)

12

Figure 88 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

122
1.5

1.4

1.3

1.2

1/2 TON TRUCK, HIGH TEMPERATURE, IDLE

O GASOLINE

CNG, LEAN SETTING

A LPG, LEAN SETTING

I.I

1.0 - 0.9

UJo

X

o

z

o

2

z

o

a:<

o

0.8

0.7

0.6

0.5

0.4

0.3

0.2

O

0.1 - 6 &.

J L_

3 6 9

SPARK ADVANCE (*»BTDC)

12

Figure 89 Carbon Monoxide Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

12 3
2400

2200

g 20001

o

X

o

z

o

cr

1800

1600

1400

1200

1000

800 h

600

400

200

1/2 TON TRUCK

MODERATE TEMPERATURE

50 MPH, 30 HP

O GASOLINE

CNG, LEAN SETTING

_ A LPG, LEAN SETTING

1 i

O

1

0 3 6 9

SPARK ADVANCE (^BTDC)

12

/ Figure 90 Nitrogen Oxides Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

124
300

280

260

240

2 20

6 200

CL

o

03

cr. <

o

o

a:

o

>

X

I 80

160

140

I 20

100

80

60

40

20

0

—I r— 1

1

1/2 TON TRUCK

MODERATE TEMPERATURE

IDLE

O GASOLINE

CNG, LEAN SETTING

A LPG, LEAN SETTING

—

9

SPARK ADVANCE (**BTDC)

12

Figure 91 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, CNG and LPG

125
0 3 6 9 12

SPARK ADVANCE (*BTDC)

Figure 92 Carbon Monoxide Versus Spark Advance for a 1/2

Ton Truck Using Gasoline, CNG and LPG

126
3400

3200

3000

2800

2600

2400

E

S 2200

(fi

UJ 2000 o

XO 1800

z

UJO 1600 O

t 1400

1200

1000

800

600

400

200

1 1 n"

1/2 TON TRUCK

LOW TEMPERATURE

50 MPH, 30 HP _ O GASOLINE

A LPG, LEAN

SETTING

i 1 i

3 6 9

SPARK ADVANCE (•BTDC)

12

igure 93 Nitrogen Oxides Versus Spark Advance for a 1/2

Ton Truck Using Gasoline, and LPG
300

280

260

240

220

200

S 180

T _ 1/2 TON TRUCK - LOW TEMPERATURE

O GASOLINE

A LPG, LEAN SETTING

i

0 3 6 9

SPARK ADVANCE («BTDC)

12

Figure 94 Hydrocarbons Versus Spark Advance for a 1/2 Ton

Truck Using Gasoline, and LPG

128
u

o

X

o

z

o

z

o

CD

cr<

1.5

1.4

1.3

1.2

I.I

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

1/2 TON TRUCK

LOW TEMPERATURE

O

IDLE

O GASOLINE

» A LPG, LEAN SETTING

A -A1 1 1

3 6 9

SPARK ADVANCE («BTDC)

O

12

Figure 95 Carbon Monoxide Versus Spark Advance for a 1/2 Ton Truck Using Gasoline, and LPG

129
0° BTDC idling spark advance

NO (ppm) HC (ppm) C0(%)

LPG 500 170 0.13

gasoline 1700 190 1 .

1

4 . 5 Cold Start Tests

4.5.1 Compressed Natural Gas and Gasoline-Fueled Tests

It was decided that the most efficient procedure for

determining the starting ability of the vehicle at very cold

temperatures was to attempt to start it with gasoline and CNG

as the fuels and with a variety of settings all during the

same period of time. A series of starts were attempted at

intervals such that the engine cooling fluid had returned to

its temperature prior to starting the tests (and after overnight

soaking at chamber temperatures close to 0°F). An engine start

was defined to be self sustaining operation for approximately

five seconds. Any longer allowed running time would have

heated the engine block so as to make the subsequent soaking

period unnecessarily long. In addition to the fuels and engine

settings (gas pressure, spark advance) as independent parameters,

start tests were conducted with the standard ignition as well

as a capacitor discharge (CD) ignition system (Firewell Inc.*).

*Trade names are used in this report as a means for clear

identification to the Postal Service of their property. Use

of a trade name neither constitutes nor implies endorsement by

the National Bureau of Standards.

130
In general successful starts with the standard ignition

System were made in about 20 seconds with gasoline and about

20 seconds with CNG . No starts were ever completed with the

capacitor discharge system supplied. A detailed analysis of

the difficulty was pursued. Oscilloscope photos of the ignition

coil output and spark plug voltage patterns were made for both

standard and CD systems. These photos indicated that the

standard system was performing normally but the CD system

performance was erratic. It was conjectured that possibly

the solid state components were not performing according to

design specifications under the low temperature conditions.

A series of start tests were then conducted with the solid

state unit being maintained, first at approximately 70°F,

then 0°F, while the rest of the engine system was kept always

at 0°F. This was acomplished by alternately blowing hot air

then refrigerant on the panel-mounted solid-state unit. Each

time the unit was heated, a successful start was achieved

within 20 seconds. Each time the unit was cooled to 0°F, no

start was attained and there was a self-defeating type of starting

sound. That is, the engine would sound as though it would

fire once but then immediately the sound would die to a new

low level of cranking noise. Thus it was concluded that the

difficulty was in the solid state part of the system, most

probably in the feedback transistor. This information was

reported orally to the company representative for corrective

action. At a later date, the Firewell Company's laboratory

131
representative called confirming that tests conducted in their

laboratories indicated that the SCR transistor would not

function properly after a 24 hour soak at 0°F and that future

units would be corrected.

4.5.2 Propane and Gasoline-Fueled Tests

These tests were particularly significant in that the

corrected capacitor discharge ignition system (GDI) was available

for testing. After exposing the 1/2 ton truck to ambient temperatures of 0°F for 24 hours, it was found that the engine could be

started within 10 seconds using LPG or gasoline as the fuel

and with or without the GDI system. Since the vehicle could

be started so easily, it was difficult to tell whether the

GDI system made any difference. The important finding though

was that the previous malfunctioning had evidently been

corrected. : V. ;

- -

132
5. Results and Discussion - 1 Ton Truck

Figures 96 through 130 show data that was taken on the 1

ton truck. The primary independent variables during the tests

were again idling spark advance and air-fuel ratio at the

respective running conditions. The way in which the data was

taken and is shown here is similar in many ways to that which

was done on the 1/2 ton truck; however, differences did result

and will be noted.

5.1 Gasoline-Fueled Tests

Figures 96 through 105 give the results for the vehicle

run on gasoline fuel. As with the first vehicle, the independent variable was spark advance only, since air-fuel ratio

cannot be varied easily in modern carburetors.

Figures 96 and 97 show the nitrogen oxide emissions as

a function of spark advance for idle, 20 mph and 4 hp, and 50

mph and 30 hp running conditions, at three ambient temperature

levels. In general, there was a slight increase in NO^ with

spark advance, a more significant increase with ambient

temperature and, as seen more clearly in the replot on Figure

98, a very significant increase with running speed and horsepower. One data curve, namely the 50 mph - 30 hp at 17°F curve

of Figure 96, is of questionable reliability since it did not

follow the general trend with temperature noted above.

The hydrocarbon and carbon monoxide data for these same

tests are shown in Figures 99 through 101 and 102 through 105

133
1 1 r

I TON TRUCK

- FUEL- GASOLINE

50 MPH, 30 HP

IDLE

O 17 AMBIENT

O 83**F AMBIENT

A 113 «F AMBIENT

i i

-A

3 6 9

SPARK ADVANCE («»BTDC)

12

Figure 96 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using Gasoline

134
3000

2800

2600

2400

2200

2000

CL

^

1800

CO

UJ

e 1600

X

o

2 1400

UJ

O i200

(T

h5J 1000

800

600

400

200

0

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I TON TRUCK _ FUEL- GASOLINE

20 MPH, 4 HP

O 17 AMBIENT

83 *F AMBIENT

A 113 **F AMBIENT

1 1 1

3 6 9

SPARK ADVANCE C'BTDC)

Figure 97 Nitrogen Oxides Versus Spark Advance

Truck Using Gasoline
3000

2800

1 —

T" 1

i _ 1 TON TRUCK, 83 *F AMBIENT

2600 h

2400

2200 h2000 E

Q.

^

1800

CO

9 1600

X

o

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UJ

g 1200

a:

^ 1000

800 -

600

400 -

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FUEL- GASOLINE

O IDLE

20 MPH, 4 HP

A 50 MPH, 30 HP

O—

D" TT

O

1

3 6 9

SPARK ADVANCE (*»BTDC)

A -

-O

Figure 98 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using Gasoline

136
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Q.

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280

260

240

220

200

I 80

160

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o

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80

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I TON TRUCK

50 MPH, 30 HP _ O 17 *»F AMBIENT

83 «F AMBIENT

_ A 113 AMBIENT

FUEL - GASOLINE

- A

3 6 9

SPARK ADVANCE («BTDC)

12

Figure 99 Hydrocarbons Versus Spark Advance for a 1 Ton

Truck Using Gasoline

137
83 *»F AMBIENT

A 113 ^'F AMBIENT

J J I I I 0 3 6 9 12

SPARK ADVANCE (*»BTDC

)

Figure 100 Hydrocarbons Versus Spark Advance for a 1 Ton

Truck Using Gasoline

138
300

2 80

260

240

220 _ 200

E

3 180

160

CO

z

o

CD

QC

< 140

O

g 120

>-X

100

80

60

40

_ O IDLE

_ 20 MPH , 4 HP

20

0

1

\ \ 1

I TON TRUCK , 83 AMBIENT

« FUEL - GASOLINE

3 6 9

SPARK ADVANCE (*»BTDC

)

12

Figure 101 Hydrocarbons Versus Spark Advance for a 1 Ton

Truck Using Gasoline

139
7.5

70 h6.5

6.0 -

5.5 -

T

1— \ 1 r

I TON TRUCK, 50 MPH, 30 HP

FUEL - GASOLINE

O 17 ^'F AMBIENT

83 •F AMBIENT

A 1 1 3 *»F AMBIENT

3 6 9

SPARK ADVANCE («BTDC)

12

Figure 102 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using Gasoline

140
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70

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6.0

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XO 4.0

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FUEL- GASOLINE _ O 17 *»F AMBIENT

83 *»F AMBIENT

» A 113 *»F AMBIENT

0.5 h0.0

9 ^

2!

3 6 9

SPARK ADVANCE (*»BTDC)

12

gure 103 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using Gasoline

14 1
75

70

6.5

6.0 h5.5-

5.0

UJ 4.5 o

X

o 4.0 z

o

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<

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T— 1 rI TON TRUCK, IDLE

O 17 *F AMBIENT

83 *»F AMBIENT

A 113 AMBIENT

FUEL- GASOLINE

0 12

SPARK ADVANCE (^BTDC)

Figure 104 Carbon Monoxide Versus Spark Advance for a 1 To

Truck Using Gasoline

142
7.5

70

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6.0

5.5

5.0

U 4.5 O

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q:

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- I TON TRUCK

« 83 ^'F AMBIENT

O IDLE

20 MPH, 4 HP - A 50 MPH, 30 HP - FUEL - GASOLINE

12

SPARK ADVANCE (*»BTDC)

Figure 105 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using Gasoline

143
respectively. For both these pollutants at either 20 mph or

50 mph, the higher the ambient temperature, the larger were

the emissions. This occurred since the throttle was opened

wider to maintain the same horsepower (as the temperature was

increased) and thus the air-fuel ratio was slightly decreased.

(The HC and CO emissions are extremely sensitive to A/F ratio

on the rich side of the stoichiometric condition where normal

gasoline carburetors operate.) The idle data (Figure 100 and

Figure 104) show little dependence on ambient temperature since

the prime influence is the independent fuel adjustment screw

for smooth running. As with the first vehicle, the spark

advance had only a modest effect on hydrocarbons and in most

cases an even less effect on the carbon monoxide. As can be

seen in Figures 101 and 105, these two pollutants went down

as the running speed was increased.

5.2 Compressed Natural Gas-Fueled Tests

5.2.1 Spark Advance as the Independent Variable

Figures 106 and 108 show the results of two sets of tests

run at 5°F and 109°F ambient conditions for 20 mph-4 hp and

idle conditions respectively. The usual 50 mph-30 hp test was

not performed because the engine exhaust manifold began to

"glow" from the heat under that load. The glowing manifold

was measured to be in excess of 1350°F and it was considered

too dangerous to the exhaust valve stems to continue testing

at that condition. The comparison of the data at different

144
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^ 600

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o. 50

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O 5 **F AMBIENT, RV.= 12 1/4 TURNS

109 «F AMBIENT, RV. =12 1/4 TURNS

/

3 6 9

SPARK ADVANCE (*'BTDC)

12

106 Pollutants Versus Spark Advance for a 1 Ton Truck

Using CNG

145
21.8

2i.4

21.0

< 20.6

-8

^ 2Q2

<

19.8

19.4

19.0

0

I TON DODGE, 20 MPH, 4 HP _ POWER VALVE AT 12 1/4 TURNS FROM FULL IN

O 5 ®F AMBIENT _ 109 **F AMBIENT

6

SPARK ADVANCE

(«BTDC)

12

Figure 107 Air-Fuel Ratio Versus Spark Advance for a 1 Ton

Truck Using CNG

146
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1.0

^

0.8

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350

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POWER VALVE AT 12 1/4 TURNS FROM

FULL IN

- 6^

CO

^ ^

NOx

If

1 1

3 6 9

SPARK ADVANCE (°BTDC)

12

Figure 108 Pollutants Versus Spark Advance for a 1 Ton Truck

Using CNG

147
ambient temperatures indicates that there was no change in

carbon monoxide emissions and little change in hydrocarbons

as the temperature was increased. The hydrocarbon curves do

diverge but the data scatter and fluctuations of either test

prevent making any conclusive deductions about temperature.

Such scatter is often encountered because of the HC sensitivity

to engine maintenance. The NO did not change under idle

conditions but did decrease somewhat with increasing temperature

at 20 mph and 4 hp. The tests at 109°F were repeated several

times for the same power valve setting and the NO levels varied

X

greatly. However, the air-fuel ratio was determined for each

test and it was found to change each time in spite of the same

power valve setting and the same gas regulator pressure.

Figure 107 shows the air-fuel ratio that occurred in the one

109°F test that was chosen for plotting. It was chosen

because the air-fuel ratio was similar to the one 5°F test (as

seen in Figure 107) . Since the comparison was made with the

same spark advance and air-fuel ratio, the difference in NO ^ X

may be due to the increased mixture density at lower temperatures. The more significant result, however, was the variation

in air-fuel ratio that occurred with the same power valve setting.

Figures 109 and 110 show a comparison of the emissions

when operating with the capacitor discharge ignition system

and the standard ignition system under 5°F ambient conditions.

As can be seen, no significant differences were noted. Start

tests with the GDI system on this vehicle are discussed later

in this report

.

148
650

UJ

o

X

o

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0.6

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I TON DODGE, 5 *»F, 20 MPH , 4 HP

POWER VALVE AT 12 1/4 TURNS

O STANDARD IGNITION

GDI

O

0 3 6 9

SPARK ADVANCE (^'BTDC)

Figure 109 Pollutants Versus Spark Advance for a 1 Ton Truck

Using CNG

149
300

— 1.0

>5

yj 0.8 Q

X

o 0.6

z

o

:s 0.4

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CD 0.2

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Q.

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GL

T

DODGE, 5*»F, SDLE

POWER VALVE AT 12 1/4 TURNS

it—

HC

O STANDARD IGNITION

A GDI

CO

NOx

3 6 9

SPARK ADVANCE (°BTDC)

A)

12

Figure 110 Pollutants Versus Spark Advance for a 1 Ton Truck

Using CNG

150
Figures 111 through 122 are the results of a unique series

of tests performed in an attempt to find the optimum settings

for spark advance and air-fuel ratio. The criteria imposed

was that at each speed (50 mph, 20 mph) the mixture would be

leaned so that the respective power (30 hp, 4 hp) designated as necessary by the Postal Service requirements would be the

maximum power available. This presumably would yield the

minimum pollution while still offering a marginal vehicle

performance. The tests were begun at 0° spark advance with

the throttle wide open. At 50 mph the power valve was turned

until the fuel rate was sufficient to produce only 30 horsepower at the wheels. Then, as the spark was advanced, and more

power became available the power valve was turned in to limit

the vehicle to 30 hp. These same settings were noted and then

duplicated for the 20 mph and idle tests at each spark setting.

On each of the graphs, the data for the respective gasoline

test was replotted from previous graphs for comparison.

Figures 111, 112, and 113 are the results for 8°F ambient.

Figures 115, 116, and 117 are for 82°F ambient, and Figures

119, 120, and 121 are for 110°F ambient. In general, the

tendency for the NO to increase with increasing spark advance

was offset by the leaning of the mixture. On the other hand,

hydrocarbons tended to increase probably due to the slowing

down of the flame speed by the leaning out procedure. As

expected the carbon monoxide was so minimal that no change was

detected. One additional limitation was that by the time 12°

151
3000

2800

2600

-

1

2000

Q.

Q.

1800

</>

iLi a 1600

X

o

1400

yjOO 1200

cr

Iz 1000

T T

TRUCK, 8 **F AMBIENT

O IDLE

O 20 MPH, 4 HP

A 50 MPH, 30 HP

FUEL - GASOLINE — FUEL- COMPRESSED NATURAL GAS

o

£3_

O ^

y =^^^^

0 3 6 9

SPARK ADVANCE (^'BTDO

12

Figure 111 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using CNG

152
375

350

325

300

275

250

I 225

Q.

if) 200

z

o

£ 175

<OO 150

tr. o

X 125

100

75

50

25

0

I TON TRUCK, 8 «F AMBIENT

O IDLE

20 MPH, 4 HP

A 50 MPH, 30 HP

FUEL, GASOLINE

FUEL, CNG

O

1

3 6 9

SPARK ADVANCE (*»BTDC)

Figure 112 Hydrocarbons Versus Spark Advance for a 1 Ton Truck

Using CNG

153
hiO

X

o

z

o

7.5

70

6.5

6.0

5.5 h5.0

$5

4.5

4.0

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Z 3.0 o

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sr. < 2.5

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T T T

I TON TRUCK, 8 *F AMBIENT

O IDLE

A 20 MPH, 4 HP

X 50 MPH , 30 HP

FUEL - COMPRESSED NATURAL GAS

FUEL - GASOLINE

^TZTTT^^^mrz^ A—-^A A

0 3 6 9

SPARK ADVANCE (*>BTDC)

12

Figure 113 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using CNG

154
12

- O

LU tr

^

CO 3 _

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> U- -I

-J O -I

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7

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I TON TRUCK, 8 *»F AMBIENT

A 50 MPH, 30 HP

20 MPH, 4 HP

9

SPARK ADVANCE («BTDC)

12

Figure 114 Air-Fuel Ratio and Power Valve Setting Versus Spark

Advance for a 1 Ton Truck Using CNG

155
3000

2800

2600

2400

2200

- c 2000

Q.

Q.

\ 800

a S DUU X

o

1400

jjj

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t

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f 1 TRUCK, 82 ^'F AMB8ENT

O IDLE

O 20 MPH, 4 HP

A 50 MPH, 30 HP

Ar

FUEL - GASOLINE

FUEL- COiViPRESSED NATURAL GAS

•a 13"

400

200

0

O oO _

9 —9

Q

-B-—^8

3 6 9

SPARK ADVANCE («BTDC)

12

Figure 115 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using CNG

156
300

280

260

240

220

200

^ 180

o.o. ^

160

CO

g 140

<

O 120

O

a:

? 100

X

80

60

40

20

0

I TON TRUCK, 82 *F AMBIENT

FUEL- GASOLINE

|_ FUEL- CNG

O IDLE _ 20 MPH, 4 HP

T T T T

r o

A- —

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A ^

1 i 1 i

3 6 9

SPARK ADVANCE (*»BTDC)

12

Figure 116 Hydrocarbons Versus Spark Advance for a 1 Ton

Truck Using CNG

15 7
i.5 -

0.5

TON TRUCK, 82 *»F AMBIENT

O IDLE

A 20

X 50 MPH, 30 HP

FUEL- GASOLINE

FUEL- COMPRESSED NATURAL GAS «

12

SPARK ADVANCE («»BTDC)

Figure 117 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using CNG

158
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IUJ

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23

22

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20

19

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I TON TRUCK, 82 AMBIENT

A 50 MPH, 30 HP

12

SPARK ADVANCE (^'BTDC)

Figure 118 Air-Fuel Ratio and Power Valve Setting Versus

Spark Advance for a 1 Ton Truck Using CNG

159
3000

2800 —

2600

2400

2200

Q. 2000

Q

X

O

O IDLE

A O 20 MPH , 4 HP

A 50 MPH, 30 HP

2

1600

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o

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600

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FUEL- COMPRESSED NATURAL GAS

ED—

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OA

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3 6 9

SPARK ADVANCE («BTDC)

12

Figure 119 Nitrogen Oxides Versus Spark Advance for a 1 Ton

Truck Using CNG

160
300

280

260

240

220

^ 200

E

o. ^ 180

CO

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q:

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80

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- I TON TRUCK, 110 *»F AMBIENT

T T T T

FUEL- GASOLINE

FUEL- CN6

O

O

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20 MPH, 4 HP

A 50 MPH, 30 HP

O

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Tl'

A-

"A"

I 1

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3 6 9 12

SPARK ADVANCE (*BTDC)

Figure 120 Hydrocarbons Versus Spark Advance for a 1 Ton Truck

Using CNG

161
7.5

70

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6.0

5.5

5.0

- I TON TRUCK,

O IDLE

A 20

—11 no *F AMBIENT

X 50 , 30 HP

o

4.5

XFUEL - GASOLiNE

—

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FUEL - COMPRESSED NATURAL GAS-

(fi rih—

0 3 6 9

SPARK ADVANCE

rk

12

Figure 121 Carbon Monoxide Versus Spark Advance for a 1 Ton

Truck Using CNG

162
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19

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I TON TRUCK

no *»F AMBIENT

A 50 MPH, 30 HP

1 1 1

3 6 9

SPARK ADVANCE (*BTDC)

12

Figure 12 2 Air-Fuel Ratio and Power Valve Setting Versus

Spark. Advance for a 1 Ton Truck Using CNG

163
BTDC was reached the mixture was so lean that low speed running

conditions were not always acceptable.

Figures 114, 118, and 122 are respective test correlations

between the A/F ratio setting for each spark advance and the

power valve setting.

5.2.2 Air-Fuel Ratio as the Independent Variable

, Figures 123 through 126 show the results of tests conducted

to determine the maximum power capability of the vehicle (and

amount of associated pollutants) operating on CNG at a moderate

temperature. The way in which NO , HC , and CO varied with

air-fuel ratio was exactly the same as was noted and discussed

on the first vehicle. The change in spark advance from 0°

before top-dead-center to 12° before top-dead-center produced

a significant increase in road horsepower with a corresponding

increase in emissions, particularly NO^. If the criteria for

performance were 30 horsepower at 50 miles per hour, the curves

show that it would be possible to maintain NO below some

X

arbitrary level, say 1000 ppm, in various ways. For example,

with a spark advance of 12° and an A/F ratio > 21.5 (see

Figure 123) or with an advance of 0° and a leaner A/F ratio

than 19, the NO^ would be below 1000 ppm. Checking the other

emissions would suggest that of the two alternatives less spark

advance and richer mixture would be more advantageous in that

there would be less hydrocarbons.

164
AIR/FUEL RATIO

Figure 123 Maximum Horsepower and Nitrogen Oxides Versus AirFuel Ratio for a 1 Ton Truck Using CNG and Operating

at Full Throttle

16 5
40

38

S: 36

X

34-

o

Q.

y 32

^ 30

Q

<

S 281-

26

24

22-

20-

18

90

85

80 -

£ 60

o.

(/) 55

2:O

ffi § 50

u

o

Q 45

>

X

40

35-

30-

25

20

15

14

I I I f ^ j I

! TON DODGE, 86" F, 50 MPH, FUEL-CNG

O 0** SPARK ADVANCE

12** SPARK ADVANCE

1

15. 16 17 18 19 20

AIR/FUEL RATIO

21 22 23

Figure 124 Maximum Horseposer and Hydrocarbons Versus Air-Fue

Ratio for a 1 Ton Truck Using CNG and Operating at

. - " Full Throt tie

166
46

44

42

40

38

CL 3.6 I

34

32

30

28

26

24

22

20

18

16-

3.0

2.8

2.6

2.4

22

2.0

1.8

LlI i 1-6

o

1 1.4

z

o

S

1-2

<

0.8

0.6

0.4-

0.2

0.0

I I —1 ~i 1——I

1

I TON DODGE. 86** F. 50 MPH, FUEL- CNG

O O** SPARK ADVANCE

12** SPARK ADVANCE

O]

J L O-D1

14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 12 5 Maximum Horsepower and Carbon Monoxide Versus AirFuel Ratio for a 1 Ton Truck Using CNG and Operating

at Full Throttle

167
2 o

CO O

W CO

si

2^

28

26

24 h"

22

18 -

16

14

I TON DODGE, 86

50 MPH, MAXIMUM HORSEPOWER

0"* SPARK ADVANCE

12® SPARK ADVANCE

!6 17 18 19 20

AIR/FUEL RATIO

22 23

Figure 126 Power Valve Setting Versus Air-Fuel Ratio for a

1 Ton Truck Using CNG and Operating at Full Throttle

168
For this natural gas system, it has already been mentioned

that a power valve in the form of a simple screw line obstruction,

was used to vary the gas flow rate after the last stage pressure

regulator. The results of a correlation between the valve

settings and the A/F ratio are presented in Figure 126. An

inspection of the mechanism, however, indicated that it was

not designed for precise repeatability in setting and it is

questionable whether other similar valves using the same settings

would yield these same results.

It was pointed out that the operation of the CNG fuel

system for the 1/2 ton truck was such that for a given second

stage regulator pressure and tweeker setting the air-fuel

ratio became leaner as the vehicle was run at higher speeds

and loads. The same behavior was noted for the LPG fuel

system when a lean setting (2) was chosen. This is advantageous

since the NO concentration would decrease significantly with

the simultaneous leaning process. There appear to be indications

that the fuel system for this second truck operates in the

opposite way. From Figure 107, it can be seen that for a running

condition of 20 mph/4 hp, a power valve setting of 12 1/4 turns

resulted in an air-fuel ratio of approximately 21. From Figure

126, the same power valve setting for a larger load and speed

(50 mph/maximum horsepower) gave an air-fuel ratio of approximately 18. Such a response is compatible with the way in which

ordinary gasoline carburetors behave; however, it is not the

most desirable operation from the standpoint of minimum NO^

emiss ions

169
' Figures 127, 128, and 129 are emission plots for tests

run at ambient conditions of 14°F and 112"?. A constant speed

of 20 mph was maintained and the dynamometer horsepower recorded

was a maximum since the throttle was full open. Under these

conditions the emissions were greater for the low temperature

condition but the available horsepower was also greater. This

is logical since a constant volume engine would receive a greater mass flow of mixture under the more dense air conditions

of the cooler environment. The spark advance of 9° BTDC was

somewhat arbitrarily selected because it was felt that it is

near the optimum setting. There is no technical reason to

indicate that the ambient temperature effect would have been

significantly different at another advance setting.

Figure 130 is again a correlation between the power valve

setting and the air-fuel ratio. The results indicate that this

fuel system responded to give a leaner mixture for the same

power valve setting as the ambient temperature was decreased.

5.3 Cold-Start Tests

The start tests for this vehicle were conducted along the

same general lines as for the 1/2 ton truck. After allowing

the truck to soak at a 0°F chamber for only 3 hours, the tests

were started using CNG as the fuel and employing the standard

ignition. Regardless of the spark setting and whether the

throttle was used or not, no start could be obtained. When the

GDI system was used, starting was successful in 12 seconds at

170
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32

30

28

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- 3600

- 3400

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1600

1400

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1200

1000

T T T T T T T

I TON DODGE, 20 MPH, 9*» SPARK

ADVANCE

O 14 *F AMBIENT

Q 112 AMBIENT

NO —

1 1 1 1 1

14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 127 Maximum Horsepower and Nitrogen Oxides Versus

Air-Fuel Ratio for a 1 Ton Truck Using CNG and

Operating at Full Throttle

171
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32

30

28

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10

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100

95

90

85

80 -

75

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O 84 AMBIENT

D IS2 AMBIENT

,9** SPARK

ADVANCE

1 J L

14 15 16 17 18 19 20

AIR/FUEL RATIO

21 22 23

Figure 128 Maximum Horsepower and Hydrocarbons Versus AirFuel Ratio for a 1 Ton Truck Using CNG and Operating

. at Full Throt tie

172
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I TON DODGE, 20 MPH, 9*^ SPARK

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O 14 AMBIENT

112 AMBIENT

1

14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 129 Maximum Horsepower and Carbon Monoxide Versus AirFuel Ratio for a 1 Ton Truck Using CNG and Operating

at Full Throttle

173
26

26

24

-22

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1—

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ar- 16

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1 TON DODGE, 9* SPARK ADVANCE

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A 112 AMBIENT

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14 15 16 17 18 19 20 21

AIR/FUEL RATIO

22 23

Figure 130 Power Valve Setting Versus Air-Fuel Ratio for a

1 Ton Truck Using CNG and Operating at Full Throttle

174
0° spark advance when the throttle was used. However, when

the standard ignition was tried again, starting was also

successful. Gasoline start tests were then begun. After

trying both ignition systems and with and without use of the

throttle, starting could only be obtained by entering the

chamber, removing the air cleaner, and choking the carburetor

by hand

Because the soaking time was so short in the tests

discussed above, it was decided to allow the vehicle to remain

at 0°F overnight and repeat the tests. After 21 hours at this

low temperature, the vehicle could not be started under any

circumstances (regardless of fuel, ignition system, spark

advance and use of choke and throttle) . It was felt that

the starting difficulties lie with the engine rather than the

ignition systems.

175
6 . Cone lus ions

The following specific conclusions are made concerning

running the 1/2 ton vehicle on compressed natural gas:

,1. Idling was never a problem since the tweeker could

. ; „ ,. always be adjusted to give a good idle regardless

of temperature or idle gas pressure (0 - 110°F).

, 2. An idle gas pressure setting of 3 in. H2O or less

was necessary to keep the NO^ below 1000 ppm while

: .? the vehicle was running at 50 mph/30 hp (0 - 110°F).

3. The idle gas pressure had to be kept above 1.5 in.

H^O to insure 30 hp at 50 mph (0 - 110°F).

4. The optimum spark advance for good performance and

low emission was 6*' BTDC (0 - 110°F) .

The following specific conclusions can be made concerning

running the 1/2 ton vehicle on propane:

1. Idling was never a problem with the vehicle regardless

of temperature (0 - 110°F)

.

2. The optimum power valve setting for minimum pollutants

and acceptable power was position 2.

3. The optimum idling spark setting for minimum pollutants

and acceptable power was 0° BTDC.

The following conclusions can be made concerning running

the 1 ton vehicle on compressed natural gas:

; 1. Idling was generally poor regardless of power valve

setting and resulting air-fuel ratio in the region of

a lean mixture (0 - 110°F) .

2.' To insure acceptable running the power valve had to be

adjusted so that the air-fuel ratio was no leaner than

21 while producing 30 horsepower at 50 mph (0 - 110°F).

3. The optimum spark advance for good performance and

low emissions was 6° BTDC (0 - 110°F)

.

176
The various tables contained in this report reflect the

considerable reduction achieved in emissions throughout the

load, speed, ambient conditions and spark timing range, of

engines operated on natural gas or propane as opposed to

gasoline. In most cases, the inherent difference in fuel composition results in considerably cleaner combustion when

operating under load and speed conditions required by typical

Postal Service delivery vehicles.

As a "bench-mark", comparing test results to present

data and future Federal emission limits. Table 2 indicates

the requirements and results of the 1/2 ton vehicle (3940

pounds) and the 1 ton vehicle (4700 pounds) . The range of

test result data shown in the table are for carburetor and

spark settings that would be chosen when using the respective

systems. It must be emphasized that the test data reflects

performance curves and portable gas analysis instrumentation

and has minimal relationship to the Federal test requirements

which are based upon a critically controlled operating cycle

with constant volume sampling of emissions by selected laborato

instrumentation. Further, the vehicles under test were both

1969 models, with minimal emission control equipment designed

to satisfy requirements only for that year.

177
TABLE 5

GENERAL COMPARISON OF EMISSIONS

Vehi cles

1 Q 7 _ S (3.1 gm/mi)

NO

X

1 Q 7

( . 40 gm/mi

)

(Range)

1/? Tnn Vphlrle

(3940 lbs)

Gasoline 7 71 ppm 102 ppm 300-2400 ppm

1/2 Ton Vehicle

(3940 lbs) CNG 7 71 ppm 102 ppm 100-300 ppm

1/2 Ton Vehicle

(3940 lbs) LPG 771 ppm 102 ppm 100-500 ppm

1 Ton Vehicle

(4700 lbs)

Gasoline 718 ppm 95 ppm 700-2300 ppm

1 Ton Vehicle

(4700 lbs) CNG 718 ppm 95 ppm 75-1000 ppm

178
TABLE 5 (cont'd)

Vehicles

1972-4

(3.4 gm/mi

)

Hn r\j 1975-6

(.41 gm/mi

)

Test Results

(Range )

1/2 Ton Vehicle

(3940 lbs)

(jasoime 2 6 8 p p ni 31 pp ni xj — zij Ol^; 1-.T-.Tn Ppni

1/2 Ton Vehicle

(3940 lbs) CNG 268 ppm 31 p pm 23-48 ppm

1/2 Ton Vehicle

(3940 lbs) LPG 2 6 8 ppm 31 ppm 15-170 ppm

1 Ton Vehicle

(4700 lbs)

Gas oline 250 ppm 30 ppm 60-240 ppm

1 Ton Vehicle

(4700 lbs) CNG 250 ppm 30 ppm 15-225 ppm

179
TABLE 5 (cont'd)

CO

Vehl c les

1972-4

(34 gm/mi)

1975-6

(3.4 gm/ mi

)

Test Results

(Range)

1/2 Ton Vehicle

(3940 lbs)

Gas ol ine 1.7% 0.14% 0 . 12-1 . 2%

1/2 Ton Vehicle

(3940 lbs) CNG 1.7% ' 0.14% 0 .05-0 .12%

1/2 Ton Vehicle

(3940 lbs) LPG 1.7% ;

,

: 0-1^^ 0 .06-0 . 13%

1 Ton Vehicle

(4700 lbs)

Gasoline 1.5% ,, 0.13% 0 .2-4.5%

1 Ton Vehicle

(4700 lbs) CNG 1.5% 0 .13% 0 .02-0 . 1%

180
7. References

1. Heywood, John B., James C. Keck, et. al . , "Quantify Auto

Pollution Processes", Mechanical Engineering , pg. 38,

Feb ruary 19 73.

2. Federal Register, Vol. 36, No. 128, Part II, July 2, 1971.

3. Conta, L. D., "I-C Engine and the Environment", Mechanical

Engineering , pg. 29, July 1972.

4. Caplan, J. D. "Smog Chemistry Points the Way to Rational

Vehicle Emission Control", SAE Paper 650641, August 16-19,

1965 .

5. "Search", by^. Te chn i c al Information Center, General Motors

Research Laboratory, May/June, 1966.

6. "Motor Vehicles, Air Pollution, and Health", Surgeon

General's Report to the U. S. Congress, June 1962.

7. Eltigne, Lamont, "Fuel-Air Ratios and Distribution from

Exhaust Gas Composition", SAE Paper 680114, 1968.

8. Personal communication with Sue A. Gendernalik, Automotive

Research, Ethyl Corporation, Ferndale, Michigan.

9. Amann , C. A., "Thermodynamics and Smog", presented at the

American Society for Engineering Education Annual Meeting,

Annapolis, Maryland, June 21-24, 1971.

10. Bolt, J. A., and D. E. Cole, Low Emission Power Plant

Systems: A Technical Evaluation , University of Michigan

Short Course, Ann Arbor, Michigan, August 7-11, 1972.

11. Bulpitt, W. S., A Comparative Study of the Exhaust Emissions

of a Wankel Engine Using Gasoline and Natural Gas as Fuels , M. S. Thesis, Georgia Institute of Technology, Atlanta,

Georgia, April, 1972.

181
8. Acknowledgements

The authors would like to acknowledge the very capable

assistance given in the laboratory throughout the duration of

this study by Mr. John Grimes, Mr. David Ward, and Mr. Boyd

Shomaker of NBS and Mr. Bud Windell of the U. S. Postal Service.

Their comments and suggestions were invaluable in determining

appropriate testing procedures and diagnosing experimental

problems as they occurred.

182
NBS-IMA (REV. 7-73)

U.S. DEPT. OF COMM. BIBUIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 74-460

2. Gov't Accession

No.

3. Recipient's Acces.sion No.

4. TlTLt: AND SUBTl l'Lt Comparison of power Output and Exhaust Pollutants of Two

Postal Service Vehicles Operated on Three Hydrocarbon Fuels

5. Publication Date

6. Performing Organization Code

J.E. Hill and D.A. Didion

8. Performing Organ. Report No. NBSIR 74-460

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4624141

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U. S. Postal Service

Bureau of Research and Engineering

Washington, D. C. 20260

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

One possible solution for the reduction of pollutants from internal combustion

engines is the use of gaseous fuels such as natural gas or propane. The best

application for the use of these fuels appears to be with fleet operators. The

federal government operates between 300,000 and 400,000 vehicles which makes it an excellent candidate for using them. This paper describes a laboratory investtigation in which the power output and pollutant levels of two Postal Service

vehicles equipped with dual -fuel systems, were determined at simulated road

conditions in an environmental chamber at temperatures from 0 °F to 100 °F.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Air pollution; compressed natural gas engine; dual fuel vehicles; propane engine;

vehicle emissions

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