1

Development and Field Validation Testing of an Oxidizing Catalytic

Converter and a Compatible Lube Oil for Two Stroke, Lean Burn Gas

Engines

by

Bruce Chrisman – Cameron Compression Systems

Glen Sharkowicz - ExxonMobil

Abstract

Because of the increasing emphasis on achieving low exhaust emissions for stationary

gas engines, an oxidizing converter was developed for Ajax

®

two stroke lean burn

(2SLB) engines in 2004. A few months prior to the effective compliance date for the ICE

MACT rules which require large reductions in the formaldehyde levels for engines rated

at  500 BHP, these converters were placed into service with two 700 BHP engines at a

gas transmission plant in Colorado. To assure continuous compliance with the emissions

regulations, it was guaranteed that the CO removal efficiency with the original catalyst

elements would not fall below 60% during the first six months of operation.

Oxidizing converters have been proven highly effective for many years for four stroke

stationary gas engines. However previous efforts to establish successful use of oxidizing

converters for 2SLB engines had not produced adequate long term emissions removal

efficiencies. There are several challenges associated with the use of converters on 2SLB

engines, which include: catalyst fouling from the products of combustion of the force fed

cylinder oil, relatively low exhaust temperatures, and occasional rapid pressure

fluctuations in the exhaust system.

After confirming successful emissions removal efficiencies during a 550 hour R&D Lab

test, two of these converters were placed into service in the field. This paper focuses on

the subsequent monitoring of the field performance during the first two years of operation

and on several improvements which were implemented to enhance the commercial

viability for the converters. These improvements include two major advancements to this

technology:

1. The development of a catalyst box that can be retrofitted to existing exhaust

silencers.

2. The formulation of a lube oil that avoids catalyst fouling and which can be

successfully used for cylinder and crankcase lubrication.

Gas Machinery Conference 2006

Oklahoma City, Oklahoma

October 1-4, 2006
2

Introduction

U.S. EPA HAP Regulations

Increasingly stringent air quality regulations have caused manufacturers of stationary

engines to develop a variety of innovative methods for reducing exhaust emissions from

Reciprocating Internal Combustion Engines (RICE). Until recently the methods

employed for two stroke, lean burn engines (2SLB) were focused mainly on combustion

improvements, rather than exhaust treatment. Through the use of prechambers and fuel

lean operation, NOX emissions were reduced to low levels. Through improvements in

combustion processes, the CO, volatile organic compounds (VOC) and other products of

incomplete combustion were reduced.

In February, 2004, the U.S. EPA published the requirements for reducing Hazardous Air

Pollutants (HAP) from RICE sources. These new RICE rules require the use of

Maximum Achievable Control Technology (MACT) to achieve the following

requirements for 2SLB engines:

1. A 58% reduction in CO through a catalytic converter (where CO serves as a

surrogate to indicate a satisfactory removal of formaldehyde (H2CO) from the

exhaust), or --

2. Limit the formaldehyde in the exhaust stack to 12 ppmvd @ 15% O2 in the

exhaust.

These U.S. EPA MACT rules led Ajax to develop an oxidizing converter capable of

removing more than the required amount of CO with an acceptable duration between

cleaning of the catalyst elements.

Compliance Testing

Compliance tests consist of several measurements which must be documented at

operating intervals which are specified by the air quality permit.

When using an oxidizing converter, these tests must document the engine speed and

BHP, the CO, and the exhaust oxygen levels before and after the catalyst. The precatalyst temperature and the pressure drop (P) across the catalyst must be recorded

according to 40CFR, Part 63, Subpart ZZZZ. This subpart specifies that the pre-catalyst

temperature must be  450

O

F and the P across the catalyst can not increase by more

than 2" H2O from the initial P for the catalyst.

State Regulations

Depending on the relative needs to control air quality in various engine site locations, the

states have imposed a wide variety of exhaust emissions regulations. Generally the areas

having air quality attainment problems and the areas with larger amounts of installed

RICE BHP are those which must impose the more stringent regulations for stationary

engines.
3

The Wyoming DEQ serves as a good example for states which have in recent years

required large reductions in the allowable exhaust emissions. For the last few years,

Wyoming has been requiring RICE NOX levels to be  1.0 gm/BHP-hr. In 2006, the

Wyoming DEQ issued a ruling that 2SLB engines producing more than 500 BHP must

use an oxidizing catalyst to demonstrate BACT. Operating permits for these engines will

be based on achieving CO levels less than 0.5 gm/BHP-hr and H2CO levels less than 0.08

gm/BHP-hr.

Product Description and Design Criteria

Engine Application – 2SLB

The starting point for applying an oxidizing converter to a 2SLB engine is to consider the

characteristics of the engine. An example of the type of engine used for this development

program is presented in Figure 1. These Ajax

®

engines are two stroke, spark ignition,

fuel injected, integral engine/compressor units. The engine/compressor unit shown in

Figure 1 comprises four power cylinders and three compressor cylinders. In its LE

(prechambered, or low emissions) configuration, it is rated at 800 BHP (597 KW) at 440

RPM.

Figure 1 – Typical Ajax Frame Configuration

A cross section of the two stroke power cylinder is in Figure 2, which illustrates the

method for compressing the intake air (boost pressure) on the crank end of the power

piston. This illustration shows how the pressurized intake air scavenges the cylinder,

00498
4

pushes out the residual exhaust gases from the previous firing cycle, and fills the cylinder

with fresh air.

Two-Stroke, Loop Scavenged Power Cylinder

Intake Air Valve

Gas

Injection

Valve

Prechamber

Exhaust Port

Figure 2 – Two Stroke, Loop Scavenged Power Cylinder

Experiences with Oxidizing Converters

Oxidizing converters have been used effectively for the reduction of CO and VOC

emissions for many years with four stroke engines. Previous industry experience with the

use of oxidizing converters for four stroke engines has produced satisfactory results in

terms of emissions removal efficiencies and the duration of operating time between

catalyst cleaning and/or replacement.

However prior to 2004, applications of oxidizing converters with two stroke engines had

not produced satisfactory, longer term removal of emissions. With two stroke engines,

lubricating oil must be injected into the power cylinders. Consideration of the design and

operating characteristics of the Ajax engines resulted in identifying the problems

associated with the use of oxidizing converters with 2SLB engines, which include:

1. Products from the combustion of the oil that is force fed to the power cylinders of

the 2SLB engine carry over into the exhaust and degrade the removal efficiency

of the catalyst.

2. Relatively low exhaust temperatures for these engines can reduce the oxidizing

efficiency.

3. Occasional firing into the exhaust during the starting and stopping of these

engines can damage the catalyst elements.

4. Pressure pulsations in the exhaust pipes are too high to consider placing a catalyst

close to the power cylinders, unless an exhaust manifold is used to dampen these

pulsations.

5. Care must be taken in the converter placement to avoid adversely affecting the

tuned lengths of the exhaust pipes for a 2SLB engine.
5

Objectives for the Oxidizing Converter Project

The main objective for the 2SLB converter project was to achieve better CO and H2CO

removal efficiencies than those needed for compliance with the U.S. EPA MACT

regulations. The catalyst size and composition were selected to get a CO removal of more

than 85% and a formaldehyde removal of about 75%. Another objective was to maximize

the operating time that can be accumulated between regenerations of the catalyst

elements. This duration is defined as the operating hours during which the CO removal

efficiency degrades from its initial level of 95% to the EPA MACT requirement of 58%

removal. The catalyst elements were specified so that this duration would be more than

8500 operating hours.

Other objectives included: (1) maintaining the required tuned lengths of exhaust pipes for

each cylinder to retain optimum performance for the engine, (2) keeping back pressure at

the muffler inlet below 5" H2O to avoid a power derate, and (3) ease of maintenance for

the catalyst elements, and (4) achieving a reasonable cost for the silencer/converter.

R & D Testing

Scope of Work

The lab phase of this project consisted of assuring that the design of the converter and the

specifications for the catalyst would provide the initial emissions targets. The amount of

degradation of the emissions removal over a time period also needed to be verified. A

550 hour test at the rated BHP for the lab engine was conducted to investigate this

degradation. The engine selected for these tests is a DPC-2802LE that is rated at 384

BHP (286 KW) and 440 RPM.

Emission removal efficiencies were measured frequently during the testing of the Lab

engine. Curves expressing CO and H2CO removal during the 550 hour tests are presented

in Figure 3.
6

Figure 3 – R & D Tests: CO and H2CO Removal Efficiencies

The initial removal efficiency for CO was 95%, which degraded to 93% after 425 hours.

For the last 125 hours of the lab tests, the flow area for the catalyst elements was reduced

by 40% to determine the relationship between removal efficiencies and less catalyst

material.

Following the 550 hour test in the Lab, work began on the fabrication of two

silencer/converter units needed for the field testing phase of the oxidizing converter

project. Based on the Lab tests, the flow area and the amount of catalyst were determined

for a two cylinder, 384 BHP engine. It was decided that standardizing on one catalyst

element for the entire line of Ajax engines would be best from both cost and inventory

perspectives. The standardization was done by sizing the common catalyst element based

on one-half of the exhaust flow for the Lab two cylinder engine. The result was one

catalyst element per power cylinder for all of the engines involved. The rack for the

catalyst elements is shown in Figure 4 for a four cylinder engine. The four catalyst

elements are designed like desk drawers, which slide into the catalyst rack.
7

Figure 4 – Catalyst Element Rack

Field Validation Testing

Initial Field Application

During the Lab tests, a few engine users were contacted to inform them about our plans

for field validation testing. A gas transmission company in Colorado presented a need to

achieve large reductions in formaldehyde levels for two DPC-2804LE engines.

Most of the design work to that point of this project had focused on the installation of

catalyst racks in vertical exhaust silencers, since the vertical configuration represents

more than 95% of the applications for this kind of engine. The application in Colorado

had horizontal exhaust silencers, which the customer wanted to use for the field converter

project. Therefore a horizontal version of the silencer/converter was designed. This

configuration required the catalyst to be mounted on top of the horizontal section,

downstream from the second volume chamber of the silencer.

The resulting design for the two four cylinder field engines is described below in Figure

5.

Top View

Side View

Access Door

Access Door

Seal

Catalyst Element
8

Catalyst Box

Pressure Relief Valves

Figure 5 – Field Site: Two Converters on DPC-2804LE Engines

For these silencer/converter units, the exhaust pipes enter the first volume chamber of the

silencer between the building wall and the silencer. The rectangular box on top of the

horizontal section contains the catalyst elements and serves as the third volume chamber

of the silencer. The pipes entering the building above the silencer/converter units are for

intake air.

These two DPC-2804LE engines are design rated at 800 BHP at 440 RPM. However the

site elevation for this gas plant in Colorado is 5600 feet (1707 meters). Because these

engines are naturally aspirated, piston scavenged engines, a power derate must be applied

at higher elevations. This derate applies for site elevations higher than 1500 feet (457

meters), above which the power derate is three percent per each additional 1000 feet (305

meters). Therefore at 5600 feet, the site rating for these engines is 702 BHP at 440 RPM,

Field Monitoring Requirements

The key operating parameters which need to be monitored include the engine RPM and

BHP. The other data to be recorded include:

• Pre and post catalyst CO.

• Pre and post catalyst H2CO.

• Post catalyst NOX.

• % oxygen in the exhaust.

• Pre and post catalyst exhaust temperatures.

• P across the catalyst.

The above data were measured and recorded many times during the first two years of

operation with the two silencer/converter units. Testing was conducted by Air Pollution

Testing, Inc. These data provide the CO and H2CO removal efficiencies. They also

provide the monitoring requirements necessary to demonstrate compliance with the air

quality regulations.

Air Intake Filter
9

The EPA MACT catalyst monitoring specifications define the exhaust temperature and

catalyst P requirements as described in the Compliance Testing section of this paper.

The housing for the catalyst box was set up to meet the catalyst monitoring requirements.

Figure 6 is a close up view of the catalyst housing which shows the following features:

• Catalyst element access door.

• Bar used for clamping the catalyst elements in place to assure that no exhaust gas

will bypass the elements.

• Two ports for the temperature measurements.

• Two ports for the catalyst P measurements.

• The location of the pre-catalyst exhaust sampling.

The location of the port for post catalyst exhaust sampling is in the exhaust stack.

Figure 6 – Converter with Data Measurement Locations

Field Test Data

Tests were conducted frequently with both of the engines. Many of these tests were done

at monthly intervals, and minimal changes occurred during these short durations. During

the entire two year period, these engines have been operated at nearly the same loading

conditions, which are about 650 BHP at 435 RPM.

The changes in catalyst performance during the field tests are expressed in Figure 7.

Pre-Catalyst

Measurement Port

Catalyst

Temperature Points

Access Door

Catalyst P Ports
10

Field Tests: CO and H2CO Removal Efficiencies

50

55

60

65

70

75

80

85

90

95

100

0 2000 4000 6000 8000 10000 12000 14000

Catalyst Operating Hours

E

mis

sio

n

s

R

e

m

o

v

al Efficie

n

cie

s (%) Actual Emissions Results

Expected H2CO% Based on the Relationship to CO Removal Efficiency

U.S. EPA MACT Required CO Removal%

Figure 7 – Field Tests: CO and H2CO Removal Efficiencies

As these curves describe, the CO removal efficiency degraded from 98% to 93% during

15,000 operating hours. The H2CO removal efficiency dropped from about 95% to about

87%. Because of the difficulty with field measurements of H2CO, only the first 1500

hours of the H2CO curve are supported by actual H2CO measurements. The remainder of

this curve, which is the dashed portion, is estimated based on the relationship between

H2CO and the removal efficiency for CO. Both of these curves are compared to the U.S.

EPA MACT requirement of 58% CO removal.

Pre-catalyst CO = 1.4 gm/B-h

Post-catalyst CO = 0.025 gm/B-h

Pre-catalyst H2CO = 0.24 gm/B-h

Post-catalyst H2CO = 0.010 gm/B-h

Pre-catalyst CO = 1.7 gm/B-h

Post-catalyst CO = 0.12 gm/B-h

CO

H2CO

U.S. EPA MACT

Required CO Removal %
11

The data recorded during the field tests are summarized in Table 1, which includes all of

the monitored information at a point early in the catalyst service and at a point after about

20 months of service.

Table 1: Field Tests with Two DPC-2804LE Engines

• Operating Data During the First 13,000 Hours

• Site Rated Power = 702 BHP @440 RPM

• Site Elevation = 5600 FASL (1707 Meters)

August 2004 March 2006

Catalyst Hours 1000 13,000

Engine Speed 436 430

BHP 650 630

% of Site Rated Load 93.4 91.8

Exhaust Flow (scfm) 3180 3100

% O2 in Exhaust 14.6 14.7

Pre-Catalyst Temp (°F) 620 590

Post-Catalyst Temp (°F) 585 550

P Across Catalyst (in H2O) 0.5 0.8

Pre-Catalyst – CO (

gm

/BHP-hr) 1.4 1.7

Post-Catalyst – CO (

gm

/BHP-hr) 0.025 0.12

CO Removal Efficiency 98.2 92.9

Pre-Catalyst – H2CO (

gm

/BHP-hr) 0.24 0.25

Post-Catalyst – H2CO (

gm

/BHP-hr) 0.010 0.032

(1)

H2CO Removal Efficiency 95.8 87.2

(1)

Post Catalyst NOx (

gm

/BHP-hr) 0.80 0.50

Note 1: H2CO estimated based on CO removal efficiency

In addition to the CO and H2CO emissions data in this table, there are a few other

pertinent points:

1. The pre-catalyst temperature is well above the MACT requirement of 450

O

F,

which is important because the lab testing indicates that the best removal

efficiencies are for exhaust temperatures of > 550

O

F.

2. The catalyst P increased by only a couple of tenths of an inch of water during

the first 20 months.

3. The NOX levels of 0.5 to 0.8 gm/BHP-hr are substantially less than the standard

NOX levels at the design rating for these engines. If these engines were running at

the site rating of 440 RPM and 702 BHP, then the expected NOX would be 1.8

gm/BHP-hr. However these tests were conducted at about 92% of the site rating at

which point the expected NOX would be about 0.8 gm/BHP-hr.
12

Additional Field Validation Sites

Additional silencer/converter units have recently been installed with 2SLB Ajax engines

at other gas plants in Colorado and Wyoming. Included are DPC-2803LE and DPC2804LE engine models. Results from these units will also be monitored.

Development of the Catalyst Friendly Lube Oil

Need for a Catalyst Compatible Lube Oil

A key challenge in achieving satisfactory performance of oxidizing converters with 2SLB

engines is the resolution of catalyst fouling caused by products from the combustion of

the oil that must be force fed to the power cylinders of two stroke engines.

ExxonMobil Lubricants & Specialties Company was approached by Cameron

Compression Systems to develop a lubricating oil for its Ajax 2SLB that would be

outfitted with its new catalytic converter emissions reduction system being designed to

meet increased air emissions regulations. Current gas engine oil formulations contain

materials that are known to poison various catalysts. A specially balanced formulation of

the lubricating oil was developed and a four phase evaluation was conducted to determine

the performance with respect to oxidation stability, wear protection, compatibility with

current lubricants and catalyst performance. Through these evaluations, ExxonMobil has

developed a unique lubricant formulation that provides excellent wear protection and

limited degradation and fouling of the catalytic converter system, while maintaining

premium performance in existing equipment.

Lubricating Oil Requirements of a 2SLB Gas Engine

All lubricants perform four main functions:

1. Reduce friction.

2. Prevent wear.

3. Remove heat.

4. Prevent rust and corrosion of the lubricated components.

The lubricant must also display excellent oxidation and thermal stability, long service life

and prevention of deposits, and good film strength properties to prevent wear.

Lubricants for 2SLB gas engines are formulated with a mixture of base oils (typically

mineral) and performance enhancing additives. The base oil’s main contribution is to

provide a suitable lubricating film, thermal stability and heat removal medium. The

additives contribute additional load carrying ability (anti-wear, extreme pressure or anti

scuff additives), viscosity modifications for high and low temperatures (viscosity index

modifiers and pour point depressants), and increase the oxidation resistance of the fluid

(anti oxidants).
13

The most important property of the lubricant is viscosity, or the fluid's resistance to flow.

Viscosity is expressed in several different ways. Most commonly for engine oils the

viscosity is expressed in Centistokes (cSt) at 100°C. A typical gas engine lubricant is 13

to 14 cSt at 100°C. This equates to an SAE Engine Oil Grade of 40. Occasionally, a

multi-grade oil, like SAE 15W-40 is used where cold starts or variable ambient

conditions are expected. The viscosity of the lubricant is largely dictated by the base oil

used in the formulation. Viscosity can also be modified or enhanced with certain

additives. Viscosity index improvers and pour point depressants modify the base oil’s

viscosity characteristics at high and low temperatures to meet a wider range of operating

conditions.

The journal bearings found in an engine develop a hydrodynamic oil film that separates

the two surfaces. The thickness of this film is dictated by the viscosity of the oil at

operating temperature as well as the relative speed between the moving surfaces.

Boundary lubrication conditions can occur between piston rings and cylinder walls.

Here, anti-wear or anti-scuff agents can be useful in preventing metal to metal contact

and increased wear.

Additives also contribute to a property known as sulfated ash. The sulfated ash is the

amount of ash left when oil is burned and subsequently treated with sulfuric acid. Most

2-cycle gas engines operate with what is known as low ash or ashless engine oil. Oils

with highly sulfated ash content are not suitable for 2-cycle gas engines as a high level of

sulfated ash generally leads to undesirable deposits in the combustion chamber and intake

ports.

Typical physical and chemical properties of the intake lubricant in this study are

presented in Table 2.

Table 2: Lubricant Properties

SAE Viscosity Grade 15W-40

Viscosity, cSt @ 100C ASTM D445 13.7

Viscosity Index ASTM D2270 132

Sulfated Ash, wt% ASTM D874 0.07

Total Base Number, mg

KOH/gram

ASTM D2896 2.4

Pour Point, C ASTM D97 -33

Catalyst Friendly Challenge

The addition of an exhaust gas catalyst to an engine presents yet another challenge for the

lubricant. Some of the oil that lubricates the power cylinders is consumed during the

combustion process. Since combustion products of the lubricant will be introduced to the

exhaust stream, materials that can poison catalysts must be limited. The source of the

catalyst poison is generally introduced from additives used in the oil.
14

Zinc, phosphorous and sulfur are known catalyst poisons and their concentration and

specific chemistry need to be carefully optimized in the formulation of a catalyst

compatible lubricant. Also, attention must be paid to overall formulation balance.

Changing one parameter of a lubricant formulation to address a specific need often has

the effect of degrading performance in another area.

The most common source of zinc, phosphorous and sulfur in lubricating oils are

additives, such as zinc dialkyldithiophosphate (ZDDP). ZDDP is commonly used as an

additive to lubricating oils as an anti-wear, or load carrying enhancement.

Anti-wear capabilities are necessary in an engine oil to provide added load carrying

capability in regions where a full fluid film or hydrodynamic oil film cannot be

developed. The piston rings and walls of the power cylinder and the cross head pin

bushings are the two main areas where this can occur. Any revision to the formulation of

the lubricant must continue to address these two critical areas.

Evaluation of candidate formulations required a four phase approach. First, the engine

oil formulation team at the ExxonMobil Research and Engineering Technical Center

developed a unique additive system for use with catalyst equipped engines that also

meets the needs of existing engines. A series of laboratory bench tests were conducted

on several candidate formulations. Based on the results of these screening tests, a revised

and enhanced formulation was presented to Cameron for the second phase of the

evaluation in the power and compressor cylinders of an exhaust catalyst equipped engine.

Engine Evaluations of the New Formulation

For the second phase of the evaluation, a candidate formulation of the lubricant was

applied to a test engine at Cameron’s facility in Oklahoma City. An Ajax 2802LE engine,

equipped with an exhaust catalyst system, was run under simulated service conditions.

The oil was applied to the power cylinders to determine if there was any performance

loss in regards to wear and deposits, and to evaluate if there were any negative effects on

the catalyst system.

A total of 550 hours was accumulated with the candidate formulation, engine and

catalyst. There were no indications of unusual distress or deposits in the power or

compressor cylinders. The piston rings were subsequently inspected with no obvious

signs of wear. The catalyst maintained a CO removal efficiency of more than 90%

throughout the evaluation. Given the excellent results of the lab engine tests, production

engines equipped with the catalyst system were identified for the third phase of the

evaluation.

Field Tests with the New Formulation

Two Ajax 2804LE engines equipped with the new catalyst system in western Colorado

were identified by Cameron and ExxonMobil as suitable field test sites for the lubricant.

The lubricant was applied to the power and compressor cylinders of these engines in July

of 2004. After accumulating approximately 5,500 hours of operation, ExxonMobil

Equipment Builder and Field Engineering Services personnel conducted a boroscopic
15

Piston Crown

inspection of both engines in conjunction with the engine operator and Cameron

personnel.

The results of the inspection showed excellent performance of the lubricant in the power

and compressor cylinders.

Figure 8: Boroscopic View of Power Cylinder Ports

As is represented by Figure 8, there were no significant port deposits in either engine and

only minimal surface scratching on two of the power cylinders of one engine. Catalyst

conversion efficiency had been maintained well within desired limits. This indicated that

the enhanced formulation had maintained its load carrying and thermal stability

properties, as well as doing no harm to the exhaust catalyst system.

Since most engine operators prefer to use the same lubricant in the cylinders as well as

the crankcase, the fourth phase was to evaluate performance in the engine frame. One of

the two 2804LE engines used for the power cylinder evaluation was selected for the

fourth critical stage of the test. The bearings in the engine were replaced to provide a

consistent base line and restarted in August of 2005.

In early 2006, after accumulating 4,000 hours of operation, an inspection of the engine

frame was again conducted by ExxonMobil and Cameron personnel. The main,

crosshead and connecting rod bearings were inspected for any signs of abnormal wear.

The inspection revealed that the bearings in the engine frame showed no signs of

abnormal wear after the 4,000 hours of operation with the enhanced formulation. The

conditions for the crossheads and the power rod bearings are presented in Figures 9 and

10, respectively. As is represented in these photos, the wear was minimal for all of the

crossheads and bearings.

Exhaust Port

Intake Ports
17

As depicted in Figure 11, oil analysis data also indicate that there are no issues with oil

life or wear in this test engine. The amount of iron and lead wear metal present in the oil

is well below typical alert limits for the used oil and is within normal operating

parameters for these engines. Also, the oxidation level measured is below condemning

limits for the amount of operating hours on the oil.

Figure 11 – Oil Analysis Results

Further to the excellent performance of the lubricant in the power cylinders and frame,

the performance of the catalyst was also evaluated. After more than 13,000 hours of

operation, the catalyst was performing with > 93% CO removal efficiency. These results

completed and successfully validated the final phase of evaluation proving the new

exhaust catalysts system and lubricant were working together in several test conditions

and regimes.

Summary of the Lube Oil Validation

Field evaluations by the cross functional team also demonstrate that the specially

balanced formulation meets or exceeds wear protection requirements while mitigating

any negative effects the lubricant could have on the exhaust gas catalyst system.

Production Versions of the Oxidizing Converter

Enhanced Design Configurations

Following the demonstrations of successful performance of the two oxidizing converters

at the Colorado gas plant, a design review was conducted to optimize the configuration

Iron and Lead Wear History

0

5

10

15

20

25

30

35

40

0 823 1646 2226 2949 3565 4116 4616 4933 5433 6000

Oil Hours

Pb (Lead)

Fe (Iron)

Wear Metal

Limit

Oxidation

(Ab/cm)

Oxidation Limit

(Ab/cm)

Pb (Lead)

Fe (Iron)

Oxidation (Ab/cm)

(Ab/cm)

Oxidation Limit

Wear Metal Limit

P

P

M

or A

b/c

m
18

for the silencer/converter units. In addition to improving the design for the converter, this

review also included the aspects of making it easier to produce the converter and of

extending the application range of the converter to a wide variety of Ajax engines.

Most Ajax engines use vertical exhaust silencers. To increase the application range for

the converter, 3-D models were produced for arrangements of one, two, three, and four

catalyst elements of the appropriate size to accommodate all current production engine

models. As an example of these converter configurations, Figure 12 is a model for a

vertical silencer/converter for a two cylinder engine. This model shows two exhaust pipes

entering the first volume chamber of the silencer and the location of the two element

catalyst rack.

Figure 12 – Typical Silencer/Converter for a Two Cylinder Engine

Improving the Commercial Viability for the Converter

The first two silencer/converter units were fabricated in the Ajax facility. During and

after the fabrication of these converters, suggestions were received from the welders and

engineering personnel who were involved with the production of the converters. Several

of these suggestions led to simpler methods for producing the catalyst boxes and the

converters.

Access Door

Exhaust Inlets

Catalyst Box

Pressure Relief Valve
19

Performance Guarantees for Engines with Converters

Based on the Lab and field validation testing conducted to date, the expected exhaust

emissions with the oxidizing converter can be determined for various engine models. The

engine users need guaranteed emissions information defined over a specific time period.

Table 3 contains the expected data for 2803LE and 2804LE engines when the converter

first goes into service and after one year of operation. The guaranteed emissions data

after six months of service are also reported in this table.

Table 3: Expected & Guaranteed Emissions Results with Converter

• Site rated BHP = 200 BHP per cylinder at 440 RPM

• Site elevation < 1500 FASL

Standard

2803LE

or 2804LE

Initial

Expected

Performance

with

Converter

Performance

Guarantee with

Converter

(After

6 Months)

Expected

Peformance

(After One

Year)

Rated BHP per

cylinder

200 200 200 200

NOX (gm/BHP-hr) 1.9 1.8 2.0 1.8

CO (gm/BHP-hr) 1.2 0.05 0.40 0.15

NMHC (gm/BHP-hr) 1.2 0.40 0.60 0.55

NMNEHC (gm/BHPhr)0.5 0.20 0.30 0.25

H2CO (gm/BHP-hr) 0.30 0.02 0.15 0.05

Exhaust Flow Per

Cylinder (ACFM)

1530 1555 1555 1555

Exhaust Stack Temp.

(

O

F)

515 530 530 530

Retrofitting Converters to Existing Engines

Air quality regulations are affecting increasing numbers of the older engines which have

been in service for many years. In most of these cases, the engines become subject to the

latest emissions regulations because they have been moved to a new site or because the

addition of engines to an older site exceeds the total allowable emissions for that site.

To minimize the costs involved with retrofitting converters, a method was developed that

allows the installation of a catalyst box into an existing exhaust silencer.
20

To increase the range of applications for the retrofit of a catalyst box, the performance for

those engine models more likely to be affected by air quality regulations was considered.

In addition, the various existing configurations for exhaust silencers were considered.

The main goal for this part of the project was to define the least number of catalyst box

configurations needed to satisfy the maximum number of retrofit applications.

For most engine models and most muffler configurations, an existing silencer can be

changed into a combination silencer/converter unit by cutting the silencer through the

second volume chamber and installing the catalyst box at that point.

The retrofit of a catalyst box to the silencer of a four cylinder engine/compressor package

is shown in Figure 13. For this engine model the exhaust for adjacent cylinders is

manifolded into one exhaust pipe, so there are two exhaust pipes from this engine to the

vertical silencer. Both of these exhaust pipes are aimed toward a pressure relief cover in

the first volume chamber of the muffler. The catalyst box is installed in the second

volume chamber.

Figure 13 – Silencer/Converter on a Four Cylinder Engine Package
21

Combining Oxidizing Converters with Exhaust Expansion Chambers

The oxidizing converter for 2SLB engines removes much of the partially burned

combustion products from the exhaust stream. It has been proven highly effective in

removing CO, VOC’s, and formaldehyde. However most air quality regulations for

stationary engines also include the need for low NOX levels.

The most effective method for achieving low NOX levels is the use of a prechamber.

Depending on the properties of the engine involved, a prechamber configuration can

generally produce a 60 – 90% reduction in the NOX, as compared to the baseline open

chamber design. Prechambers provide a consistent, reliable means for igniting the air fuel

mixture and for projecting this burning charge throughout the combustion chamber. This

principle allows very lean air fuel mixtures in the main chamber, which reduces

combustion temperatures, which therefore forms less NOX during combustion.

For the prechambered, two stroke engines tested, there is generally a small increase in

NOX across the catalyst. This increase is typically one to four percent of the pre-catalyst

NOX level. With these prechambered engines, there are two effective methods for NOX

reduction. One method requires a deration of the site rated BHP. Typically a five percent

reduction from the normal site rated load will reduce the NOX level by as much as 50%.

The other method for reducing the NOX for the prechambered, 2SLB engine is the

addition of exhaust expansion chambers. The results of combining the oxidizing

converter with expansion chambers include a substantial reduction for all of the pertinent

emissions. The effects on the exhaust emissions levels are:

• A NOX reduction of 60% because of more trapped air in the power cylinders.

• A CO reduction of 58 – 94% depending upon the age and condition of the catalyst

elements.

• A VOC reduction of 40 – 70%.

• A H2CO reduction of 50 – 90%.

Other Emissions Control Methods

In addition to the successful application of oxidizing converters to these 2SLB engines,

other methods for the reduction of emissions are being investigated. A preliminary

feasibility study indicates that the unburned fuel constituents in the exhaust can also be

reduced through improving the processes of air fuel mixing and combustion. Included in

this project are changes to the combustion chamber, gas injection valves, prechamber,

and the ignition system. These changes are expected to reduce VOC’s and H2CO, and

should also provide improved fuel economy.

Summary and Conclusions

Based on the analyses of data from the Lab and the field test sites, it is concluded that

oxidizing converters can be applied effectively to 2SLB engines. The amount of

emissions reduction is acceptable for nearly all gas plant sites and the duration between
22

cleaning and/or replacement of catalyst elements should be acceptable to nearly all

engine users.

It is evident that the five main challenges associated with the application of converters to

2SLB engines have been successfully resolved. The catalyst friendly gas engine oil

formulation meets or exceeds the performance requirements for current and future 2SLB

gas engines. This oil provides satisfactory lubricating and wear protection properties in

the power cylinders and in the crankcase.

Sufficient data have been collected during two years of field testing to support the

definition of guaranteed CO and H2CO emissions removal efficiencies over an extended

time period.

Acknowledgements

The authors express their appreciation to the personnel involved with the operation of the

Williams Field Services gas transmission plant where the field validation testing was

conducted.

We also want to thank Tom Hurley, who conducted the research testing, assisted with the

first field tests, and provided design input for the converter project.

References

1. Chrisman, B., 1983, “Regulations and Control Technology for Stationary Engine Exhaust

Emissions,” Casper Oil Show and Conference, Casper, WY.

2. Chrisman, B., Bartos, J., 2004, “Development and Testing of a Catalytic Converter for the

Reduction of CO and H2CO Emissions from a Two-Stroke Lean Burn Gas Engine,” Gas

Machinery Conference, Albuquerque, NM.

3. Defoort, D., Olsen, D., and Willson, B, 2002, “Performance Evaluation of Oxidation Catalysts for

Natural Gas Reciprocating Engines,” Gas Machinery Conference, Nashville, TN.

4. Environmental Protection Agency, “National Emission Standards for Hazardous Air Pollutants for

Stationary Reciprocating Internal Combustion Engines”, June, 2004; 40 CFR Part 63 [OAR –

2002-0059; FRL-7630-8; RIN 2060-AG-63].

5. Environmental Protection Agency, “Fact Sheet – Final Rule to Reduce Hazardous Air Emissions

from Reciprocating Internal Combustion Engines”, March, 9

th

, 2004.

6. Heywood, J.B., 1988, Internal Combustion Engine Fundamentals, McGraw-Hill, New York, NY.

7. Willson, B., Olsen, D., 1998, “Formaldehyde Formation Mechanisms in Large-Bore Natural Gas

Engines,” Gas Machinery Conference, Denver, CO.