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SAE TECHNICALPAPER SERIES 2002-01-1011

Fast Start-Up On-Board Gasoline Reformer for

Near Zero Emissions in Spark-Ignition Engines

John E. Kirwan, Ather A. Quader and M. James GrieveDelphi Automotive Systems

Reprinted From: SI Combustion and Flow Diagnostics(SP1699)

SAE 2002 World CongressDetroit, Michigan

March 4-7, 2002


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2002-01-1011

Fast Start-Up On-Board Gasoline Reformer for Near Zero

Emissions in Spark-Ignition Engines

John E. Kirwan, Ather A. Quader and M. James GrieveDelphi Automotive Systems

Copyright 2002 Society of Automotive Engineers, Inc.

ABSTRACT

This paper describes recent progress in our program todevelop a gasoline-fueled vehicle with an on-board

reformer to provide near-zero tailpipe emissions. An on-board reformer converts gasoline (or another

hydrocarbon-containing fuel) into reformate, containinghydrogen (H2) and carbon monoxide (CO). Reformate

has very wide combustion limits to enable SI engine

operation under very dilute conditions (either ultra-lean orwith heavy exhaust gas recirculation (EGR)concentrations). In previous publications, we have

presented engine dynamometer results showing very lowemissions with bottled reformate. This paper shows

results from an engine linked to an experimental, faststart-up reformer. We present both performance data for

the reformer as well as engine emissions andperformance results. Program results continue to showan on-board reforming system to be an attractive option

for providing near-zero tailpipe emissions to meet lowemission standards.

INTRODUCTION

The Ultra Low Emission Vehicle (ULEV) II standardsproposed for 2004 introduction in California include a

Super-ULEV (SULEV) standard. Gasoline-fueledvehicles that robustly meet SULEV standards over their

useful lives offer a significant step toward eliminating theautomobile as a source of regulated pollutants.

Developing SULEVs can significantly reduce an OEMsfleet average non-methane organic gas (NMOG)

emissions. Further, the standards currently offer partialcredit toward the zero emission vehicle fleetrequirements (P-ZEV credits) for vehicles meeting

SULEV emissions standards. As the California standardsare currently written, up to 60% of the zero emissionvehicle (ZEV) requirement could be fulfilled with P-ZEV

credits from SULEV vehicles that also have zeroevaporative emissions. The maximum P-ZEV credits

possible from SULEVs would be obtained by an OEM if30% of the vehicles that it sells in California were

certified as SULEV vehicles.

Consequently, significant efforts are under way todevelop SULEV vehicle systems. Beginning with the

2000 model year, Honda [1]1and Nissan [2] each have

certified gasoline-fueled vehicles meeting the SULEV

standards. In both cases, sophisticated aftertreatmenand engine management systems have been developed

to meet the SULEV standard. More detailed descriptionsof these SULEV systems have been recently published[1-4].

Both the Honda and Nissan SULEV vehicles represent

formidable achievements. Their approaches may not bethe most appropriate solution under all conditionshowever. Aftertreatment systems such as these may

have difficulty meeting SULEV with larger, higheemitting engines. Also, poor volatility fuels can be a

problem. (This is especially significant for theNortheastern states that have adopted the Californiaemissions standards but not the California fue

requirements.) Both Honda and Nissan rely on runningrelatively lean with spark retard during warm-up for lowe

engine-out emissions and faster catalyst warm-upThese strategies can be susceptible to poor warm-up

performance with low volatility fuels.

One of Delphis SULEV strategies under developmen

uses an on-board gasoline reformer. This approach istargeted at a number of advantageous features

including:

robustness for vehicles with larger engines andheavier vehicles.

robustness to fuel variation due to low volatility (high

Driveability Index). robustness under off-cycle conditions (e.g. low

ambient temperature).

much lower loading of precious metals in the catalystsystem (especially Pd).

no compromise in exhaust system backpressure.

Synergies with automotive fuel cell systems,especially solid-oxide fuel cell (SOFC).

--------------------------------------------------------------------------1Numbers in Brackets designate references listed at the

end of the paper


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The reformer combines gasoline and air under very fuel

rich conditions. Schematically, the partial oxidation (POx)reaction within the reformer can be represented as:

Gasoline + Air !H2+ CO + N

2+ Heat (1)

+ (trace CO2, H

2O, HCs)

Reforming gasoline provides an on-board source of H2.

During the 1970s, researchers at the Jet PropulsionLaboratory (JPL) recognized that adding H

2 to gasoline

allows an engine to run very lean, due to hydrogenswide flammability limits [5]. They subsequently

developed a method for on-board H2 generation using

POx reforming of gasoline [6], and demonstrated very

low NOx on a vehicle [7]. However, a reformer could notcompete at that time with a 3-way exhaust catalyst and

closed loop fuel control for meeting the NOx standard. Arecent review paper describes a number of additionalstudies that have investigated supplementing gasoline

with H2to extend lean operation [8].

Hydrogen-rich reformate has a number of attributes thatmake it an attractive fuel for very low emissions. It offersa fuel source that is very low in hydrocarbons. (Ideally

reformate converts all hydrocarbons in gasoline to COand H

2; with actual reformate roughly 10% - 15% of the

gasoline may break through the reformer ashydrocarbons during start-up). Reformate also promotes

low temperature catalyst light-off, and it has very wideflammability limits. Our H

2 enrichment strategy with an

on-board reformer implements each of the above

attributes of reformate to augment (not replace) a 3-waycatalytic aftertreatment system. The basic elements of

the system are shown schematically in Figure 1. Briefly,

the H2enrichment strategy consists of:

fueling with 100% reformate under ultra-leanconditions during cold start for near-zero engine-out

HC and NOx;

supplying reformate to the lean exhaust streamduring cold start for rapid exhaust catalyst light-off;

using gasoline supplemented with a modest fractionof reformate fueling at light and medium loads topermit high EGR dilution for ultra-low engine-out

NOx.

The present paper is focused only on the first element.The catalyst light-off and high EGR elements will be thesubject of future publications. We are currently

developing a demonstration vehicle to implement our H2

enrichment strategy. The demonstration vehicle is a

recent model production vehicle with a 2.4 L 4-cylinderengine and a manual 4-speed transmission (see [9] foradditional vehicle details). The vehicle programs

objective is to demonstrate our on-board gasolinereformer system as an enabler for meeting SULEV

emissions standards. As the program progresses, we

are periodically documenting its performance. Inprevious publications, we have outlined the H

enrichment strategy in more detail, and indicated itspotential as a SULEV enabler with data from both enginedynamometer and vehicle tests running with idea

(bottled) reformate [9 - 13]. One paper [9] also providedearly performance data from a warmed-up reforme

fueled with gasoline operating on a flow bench.

As discussed above, the H2enrichment SULEV strategy

relies on very low cold start HC emissions provided bystarting the engine with 100% reformate. Thus, fast start

up of the on-board reformer is essential to enable quickengine starting. The focus of the experiments described

in this paper were two-fold:

1. to characterize start-up performance of anexperimental reformer using gasoline combustion topreheat the reformer;

2. to evaluate the performance and emissions of asingle-cylinder engine fueled with reformate

generated by the reformer.

Described below are details of the study performed usingan experimental reformer coupled to a single-cylinder

engine. This arrangement enabled simultaneouscharacterization of reformer output and reformate-fueled

engine combustion and emissions performance duringreformer start-up. In parallel, we are currently fitting areformer system to our development vehicle and

developing the control software and calibrations to fullydemonstrate the strategies. Vehicle development work

however, is beyond the scope of this paper.

EXPERIMENTAL

SINGLE-CYLINDER ENGINE AND ACCESSORIES - A

2.4 L displacement, 4-valve per cylinder productionengine head was mounted on a single-cylinder CFR

(corporate fuel research) engine crankcase [10]. Thehead for cylinder number 3 was used. The single-

cylinder engine was coupled to an electric dynamometerOverall, the engine represents one cylinder from the

Gasoline

On-board

reformer

Exhaustcatalysts stem

Reformateto engine

Reformate for catalystheating

Fig. 1: Schematic of the On-Board Reformer System


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engine in our development vehicle. A special crankshaft

and a cylinder sleeve were fabricated and installed toduplicate the stroke and bore of the production engine.Production piston, rings, connecting rod, piston pin, and

bearings were used. The compression ratio was 9.5:1.

The engine was set up to run on gaseous as well as

liquid fuels as described in [10]. For the currentexperiment, the engine generally was run on 100%reformate fuel generated by the experimental reformerdescribed below. Baseline tests were also performed

using port fuel injected (PFI) gasoline for comparisonwith results with reformate.

EXPERIMENTAL REFORMER SETUP - Figure 2 showsa schematic layout and photo of the experimental

reformer. It is made up of components which perform thefollowing functions:

Air/Fuel metering Fuel Vaporization and Mixing

Combustion

Catalytic Reforming

Heat Exchange

Further details of the reformer components areproprietary. Two experimental reformers were fabricatedand tested. One was a full-scale reformer sized to satisfy

the flow requirements for a 2.4 liter 4-cylinder engine.The second reformer tested was a quarter-scale version

sized more appropriately for our single-cylinder test

engine.

DATA ACQUISITION EQUIPMENT - Emission analyzers

were used to measure CO, CO2, O

2, NOx and unburned

HC in the engine exhaust gas. The same emission

analyzers were used to alternatively sample from the

engine intake pipe to monitor the reformate CO, CO2and HC levels blended with the engine combustion airThe engine and reformer were instrumented usingthermocouples and pressure transducers so that virtually

any temperature or pressure of interest could bemonitored. Output from the emissions bench and various

transducers was monitored using an HP 1000 computer.

Engine performance characteristics were monitored andrecorded by a separate system. An air cooled pressuretransducer (Kistler Mod. No 6121) mounted in the

cylinder head and a shaft encoder (Hewlett Packard

HEDS6310) were used in conjunction with an ACAP(DSP Technologies) combustion analysis system. TheACAP analyzed the cylinder pressure to determine andrecord engine performance characteristics on a cycle by

cycle basis in real time.

TEST PROCEDURE - California Phase 2 (CP2)Certification fuel was used in this study, both for the

baseline PFI gasoline tests as well as for fueling thereformer. CP2 represents a low-sulfur gasolineformulated to provide relatively low exhaust emissions in

gasoline-fueled engines.

Gasoline

AirReformateFuel Vaporizer/Mixer Catalyst Heat Exchanger

Combustion

Chamber

Fig. 2: Schematic layout and photograph of experimental reformer.


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Prior to a test, the single-cylinder engine was motored at

a steady speed with the appropriate engine air flow forthe test. Engine coolant and oil temperatures were set at

23C. The appropriate reformer air flow was established

and the vaporizer section was heated to 100C. In orderto describe the fueling strategy during testing, it isimportant to first recognize that two separate quantities

of air are required for a reformate-fueled engine. The firstquantity of air is combined with gasoline and fed to the

reformer under very fuel rich conditions (roughly 2.5 to 3times richer than stoichiometric). The reformer consumesessentially all of the oxygen provided to it to make

reformate for fueling the engine. A separate quantity ofair is provided directly to the engine. It burns with the

reformate fuel in the cylinders to power the engine.

In this paper, is used to represent fuel air equivalence

ratio according to the following equation

( )stoichF/AF/A

! = (2)

Where F/A is the mass fuel-air ratio, and (F/A)stoich

is the

stoichiometric fuel-air ratio for complete combustion. For

a stoichiometric mixture, = 1; lean fuel mixtures have

< 1, and rich mixtures have > 1. As a consequence

of the two separate air quantities, two separate fuel-air

equivalence ratios existed during engine testing. reformer

,represented the fuel-air mixture provided to the reformer.

This was determined based on the gasoline flow to thereformer plus the air flow provided only to the reformer.The second equivalence ratio represented the fuel-air

mixture provided to the engine, engine

. This parameterincluded in its calculation the additional air fed to the

engine for combustion of the reformate in the cylinders.

Tests for this study were performed with pre-vaporized

gasoline and air. (An optimized mixture preparationsystem for the reformer start-up period is under parallel

development, but not described in this paper.) Figure 3shows schematically the fueling strategy used to enablerapid gasoline-fueled preheat of the reformer-catalyst

during start-up. reformer

= 1.0 was supplied for a shortduration and burned in the combustion chamber of thereformer. The heat released by burning the

stoichiometric gasoline mixture elevated the temperature

of the catalyst. The magnitude of the temperature risedepended on the duration for which the stoichiometricmixture was supplied, called preheat-time in Figure 3.

Following the catalyst preheat, the fueling rate was

enriched to reformer

= 2.75 to begin reformate production.

The engine would begin firing when the reformer beganproducing sufficient quality reformate to support

combustion.

OPERATING CONDITIONS - A series of tests were runin which the reformer preheat-time was varied from 1

second to 10 seconds as listed in Table 1. These tests

Table 1. Engine operating conditions with full-scale

reformer

75 kPa Manifold pressure (MAP), 23C coolant and oil

engine

= 1, 100% reformate fueling

MBT spark timing (determined during steady operationwith 100% reformate)

Preheat-Timeseconds

Reformer Airflowg/s

Engine SpeedRPM

1 1.6 1300

2 1.6 1300

3 1.6 1300

4 1.6 1300

5 1.6 1300

6 1.6 1300

7 1.6 1300

8 1.6 1300

9 1.6 1300

10 1.6 1300

were done with the full-scale reformer that is sized for a4 cylinder engine. The reformer-airflow was 1.6 g/s

during these tests. This airflow was estimated tocorrespond to the reformer-airflow required to generatesufficient reformate to start and idle the 2.4 L 4-cylinde

engine in our demonstration vehicle on 100% reformate

fuel at 23C. Subsequent to these tests, preliminaryoperation of our vehicle fueled by a reformer shows tha

the reformer-airflow required during warm-up is closer to2.5 g/s. Thus these early vehicle data indicate an error in

our estimate. However, reformer bench testing hasshown that reformer start-up performance is quiteinsensitive to reformer flow rate over the range of 1.5 g/s

Fueling Strategy

Stoich heating at reformer=1

Preheat-time tstoich fuel= 1 to 10 sec

Reformate production at reformer= 2.75

0

0.5

"

" .5

2

2.5

3

- 6 - 4 - 2 0 2 4 6

t = 0

Equivalence Ratiosupplied

to reformer

Stoich fuel reformer

heating reformer= 1

tstoich fuel

Reformate productionreformer= 2.75

Fig. 3: Fueling strategy for the reformer.


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to 2.5 g/sec of reformer-airflow (see Appendix).

Therefore, we expect little difference in results with thereformer operating at 2.6 g/s airflow compared to the

results presented below at 1.6 g/s reformer airflow. Bothengine speed and load experienced by the single-cylinder engine during our experiments with the full-scale

reformer were significantly higher than typical idleconditions for the vehicle during engine warm-up. Engine

speed for the single-cylinder engine was approximately

30% higher than idle, while the load during the single-cylinder engine tests was approximately 2 times higherthan typical warm-up idle engine load. Baseline tests withPFI gasoline fueling were run on the single-cylinder

engine at identical speed and load conditions as thereformer tests. Engine results with this full-scale reformer

are not intended to be a direct measure of performanceand emissions expected from a vehicle. Rather, theengine data provide a measure of reformate

combustibility and offer an estimate of engine-out HCemissions during starting with a reformer compared to

PFI gasoline operation. In Table 1 engine

= 1 wasmaintained for tests listed with the full-scale reformer. A

stoichiometric mixture offers more rapid engine firingthan an ultra-lean mixture, especially with weakerreformate mixtures produced early during reformer start-

up.

The ability to run an engine very lean is a fundamentalcharacteristic of fueling with H

2-rich fuels [8]. As

described in the introduction, lean cold start fueling

comprises part of our overall H2 enrichment vehicle

strategy. Ultra-lean operation has been documented with

bottled reformate in both our engine and demonstrationvehicle [9-11]. To investigate the lean starting capabilityof the engine under conditions more representative of a

single cylinder engine, the quarter-scale reformer wastested. Table 2 shows the operating conditions for these

tests. The preheat time was 10 seconds in these tests,

while the engine

was varied from 1.0 to 0.68.

Optimizing engine

for engine performance and emissionswas beyond the scope of this paper, but will be thesubject of significant effort in our vehicle development

program.

RESULTS OF TESTS WITH PREHEAT-TIMEVARIATIONS

EFFECT OF PREHEAT-TIME ON REFORMERTEMPERATURES - The effect of preheat-time on

catalyst temperature was measured in tests withoutreformate production at a reformer air flow rate of 1.6 g/s

in the full-scale reformer. For these tests, reformer

= 1 was

maintained during the preheat-time. However, followingthe preheat, rather than enriching the mixture to begin

reformate production, the fuel to the reformer wasimmediately turned off. In these tests reformertemperature rise was due solely to reformer preheat,

without the additional temperature increase caused by

the exothermic reforming reactions.

Table 2. Engine operating conditions with quarter-scalereformer

45 kPa Manifold pressure (MAP), 23C coolant and oil

Preheat time=10 sec, 100% reformate fuelingMBT spark timing (determined during steady operationwith 100% reformate)

engine

Reformer Airflowg/s

Engine SpeedRPM

1 0.7 1330

0.93 0.7 1330

0.86 0.7 1330

0.81 0.7 1330

0.75 0.7 1330

0.68 0.7 1330

The data in Figure 4 show the measured combustion

chamber and midpoint catalyst temperatures at the endof preheat as a function of preheat-time. Two importanpoints should be noted. First, the measured combustionchamber temperature rises much more rapidly than does

the midpoint catalyst temperature. The hot combustionproducts lose significant energy as they pass through the

reformer catalyst. Therefore, temperature at the front ofthe catalyst during preheat will be greater than themidpoint catalyst temperature shown in Figure 4

Conversely, temperature at the rear of the catalyst will belower than the midpoint catalyst temperature.

Second, increase in preheat-time significantly increases

midpoint catalyst temperature. At the end of preheatmeasured midpoint catalyst temperature varies from

150C to 440C with preheat-times from 2 to 10 seconds

The higher temperatures at increased preheat-time are aconsequence of the increased amount of energyreleased from burning a larger amount of fuel.

0

200

400

600

800

1000

1200

0 2 4 6 8 10 12

Preheat Time, secs

Tempera

ture,

CCombustion Chamber

Catalyst

Fig. 4: Combustion chamber temperatureand midpoint catalyst temperature at

the end of reformer preheat.


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Reformer temperatures were measured using 1/16 inch

shielded thermocouples that showed a significant (butunquantified) lag in their time response. For example,

from reformer bench tests performed with visual accessinto the reformer, we have observed a blue flame insidethe combustion chamber immediately at the beginning of

the preheat-time. Thus, combustion gas temperatures

immediately rise to above 1000C. In contrast, thethermocouple inside the combustion chamber requires 7

seconds before its temperature exceeds 1000C.Therefore the measured combustion chambertemperature is a poor estimate of the combustion gas

temperature. Because midpoint catalyst temperatureincreases much more slowly, measured midpoint catalyst

temperature in Figure 4 is a better estimate of its actualtemperature. Still, since the thermocouple time response

is unknown for these tests, the measured midpointcatalyst temperature should be regarded as a lowerbound for the actual catalyst midpoint temperature.

EFFECT OF PREHEAT-TIME ON REFORMATE

PRODUCTION - Let us now consider results from tests

with reformate production at 1.6 g/s air flow through thefull-scale reformer. Figures 5 and 6 show CO selectivityand hydrocarbon (HC) breakthrough profiles duringreformer start-up for 2 second, 5 second and 10 second

reformer preheat-times.

These two reformer performance metrics, defined below,were determined from emissions bench measurements

of HC, CO and CO2 by sampling the reformate-air

mixture in the intake port of the engine.

( )CO2molesCOmolesCOmoles

yselectivitCO+

= (3)

=ghbreakthrouHC (4)

( )CO2molesCOmolesHCsinCmolesHCsinCmoles

++

HC breakthrough indicates the fraction of gasoline that

escapes the reforming process and remains as HCsdownstream of the reformer. CO selectivity indicates thefraction of carbon in the reformed gasoline that is

converted to CO (as desired), rather than being

completely oxidized to CO2. Perfect reformate wouldhave 0% HC breakthrough and 100% CO selectivity.High CO selectivity is important because production ofCO

2 degrades engine combustion, both due to lower

reformate fuel energy and the addition of diluent to thefuel-air mixture in the engine intake. HC breakthrough is

undesirable because it provides a source of HCs in thefuel that lead to higher engine HC emissions. We did not

have a means to measure H2production for these tests.

However, the Appendix provides mass spectrometerdata from bench tests using a similarly-configured

reformer. Mass spectrometer data from these bench

tests show that the profile of H2 production by the

reformer during start-up is similar to, but slightly lags, the

CO production profile. Thus comparing CO selectivityand HC breakthrough profiles between tests provides agood indication of overall reformate quality.

The abscissas for Figures 5 and 6 indicate time after the

beginning of reformate production. Negative values o

time represent reformer preheat with reformer= 1, and t=0represents the instant that

reformer is switched to 2.75

Before t=0, the figures provide an indication not ofreformer performance, but rather combustioncharacteristics in the reformer combustor section during

reformer preheat. Perfect stoichiometric combustionwould result in oxidation of all fuel carbon to CO

2, so tha

0

10

20

30

40

50

60

70

80

90

100

-10 0 10 20 30 40 50

Time, sec

ReformerCOselectivity,%

Reformer preheat ends, reformate

production begins at t = 0

2 second preheat

at reformer= 1

5 second preheat at

reformer= 1

10 second preheat at

reformer= 1

Reformer

pre-heat

period

Fig. 5: CO selectivity profiles during reformer start-up.

0

10

20

30

40

50

60

70

80

90

100

-10 0 10 20 30 40 50

Time, sec

Re

former

HC

brea

kthroug

h,

%

Reformer pre-heat ends, reformate

production begins at t=0

2 second preheat at

reformer= 1

5 second preheat at

reformer= 1


reformer= 1

Fig. 6. HC breakthrough profiles during reformer start-up.


9/14

both HC breakthrough and CO selectivity would be 0%. Low

CO selectivity and HC breakthrough indicate greater energyrelease for faster reformer preheat. Low HCs are also

important during this preheat phase because the enginedoes not fire during this period so that HC emissionsgenerated by the reformer during this time contribute directly

to engine exhaust emissions. (The impact of preheat HCson total engine-out HC emissions is discussed later).

Of more interest in this section are the characteristics ofFigures 5 and 6 after reformate production begins (t 0).The 10 second data shows the best reformer performanceduring reformer start-up. CO selectivity rises rapidly with a

HC breakthrough of approximately 15%. The 5 secondreformer preheat data shows performance that is only

slightly worse than the 10 second test. CO selectivity isnearly identical to the 10 second data. HC breakthrough isslightly higher, reaching a peak value of 25% approximately

6 seconds after reformate production begins. Reformerperformance is severely degraded for the 2 second preheat

data. CO selectivity rises significantly slower than for theother tests, indicating substantial quantities of CO2 diluting

the intake charge ingested by the engine. Further, HCbreakthrough peaks at nearly 50% early during reformerstart-up.

SINGLE-CYLINDER ENGINE PERFORMANCE

RESULTS - The engine performance as measured bythe net mean effective pressure (NMEP) during start-up

is shown in Figure 7 for the 2, 5, and 10 second preheat-times. For comparison the NMEP values with PFIgasoline are also plotted in Figure 7. For the PFI data, a

rich pulse of fuel (engine

= 1.8) had to be supplied initially(for 10 engine cycles) and decayed down to equivalenceratio of 1.0 to get a quick start. (This is akin to cold start

enrichment calibrations typically used in productionvehicles for rapid engine starting.) NMEP is a measure of

net engine work output and is plotted from the start ofreformate fueling. Note that several engine cycles go by

before the engine starts to fire for all three data setsplotted. The initial delay in NMEP (comprising 5 enginecycles) is due to the transport time required for the

reformate to reach the engine from the reformer. With 2second preheat-time, the engine exhibits unacceptable

start-up, with misfires and unstable combustion beforethe NMEP stabilizes above 400 kPa. With 5 second

preheat-time, initial engine combustion is much stronger,

and cycle-by-cycle variability is markedly reduced duringstart-up. With 10 second preheat, the engine starts up as

soon as reformate enters the cylinder and NMEP wasquite stable almost immediately after start-up.

The engine performance results described in this section

correlate well with reformer performance documented inFigures 5 and 6. The superiority of the engine startingperformance with the 10 second preheat is clearly evident.

PFI gasoline started the engine one cycle quicker thanreformate with 10 second preheat. But the engine stability

as indicated by the fluctuation of NMEP was much bette

with the reformate than with PFI gasoline.

SINGLE-CYLINDER ENGINE HC EMISSIONS RESULTS Hydrocarbons were observed both during reformer prehea

as well as during reformate production. The magnitude ofthe HC emitted depends on many factors and their

composition varies from pure fuel components to partiaoxidation species. The simple measurements made do no

permit us to identify the sources or the composition of theHC emissions with certainty.

The exhaust HC emissions corresponding to the startups with reformate and PFI gasoline discussed above

are shown in Figure 8. With the 2 second preheat the

misfires and poor combustion during start-up result inextremely high HC emissions. For the 5 second preheat

fairly significant HC emissions occurred during thepreheat, but decreased steadily with the onset o

reformate delivery to the engine, reaching a steady valueof about 150 ppm. With the 10 second preheat a smal

amount of HC breakthrough occurred during the preheatThis was followed by a gradual increase of HC duringstart-up until it reached a steady value of 150 ppm

Ideally with the engine running on reformate there shouldbe no HC emissions. However, recall from Figure 6 that

HC breakthrough for these tests settled at a steady value

of 10-15%. The engine combustion process appears toburn most of these hydrocarbons but a small amount(150 ppm) of unburned HC escapes combustion and isemitted in the exhaust. With PFI gasoline the exhaust HC

emissions rise quickly during start-up and reach a steadyvalue of roughly 1500 ppm.

In Figure 9 we have plotted the cumulative mass of HC

emissions from the start of reformate fueling up to 20seconds of engine running. The 2 second preheat-time

-100

0

100

200

300

400

500

600

0 20 40 60 80 100

Engine Cycles

Eng

ine

Power

(NMEP

,kPa

)

2 second preheat

5 secondpreheat

10 second preheat

Gasoline baseline

Fig. 7: Effect of preheat-time on engine NMEP from thestart of reformate fueling. PFI gasoline baseline

included for comparison.


10/14

as expected resulted in extremely high cumulative mass

In Figure 9 we have plotted the cumulative mass of HCemissions from the start of reformate fueling up to 20

seconds of engine running. The 2 second preheat-timeas expected resulted in extremely high cumulative massHC at the end of 20 seconds because of the misfires and

poor combustion during start-up. The cumulative mass

HC with 5 seconds preheat-time starts with an offset a

time zero because of HC breakthrough during thepreheat-time but ends with about a 40 percent reduction

in cumulative mass HC emissions compared with PFgasoline. With the 10 second preheat-time thecumulative mass HC emissions were lowest, providing a

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16 18 20

Time, sec

CumE

ngine-OutHC,mg

2 second preheat at reformer= 1.

5 second preheat at

reformer= 1


reformer= 1

Gasoline baseline

Fig. 9: Effect of preheat-time on cumulative engine-out mass HC emissions. PFIgasoline baseline included for comparison.

0

1000

2000

3000

4000

5000

-10 0 10 20 30 40 50 60

Time, sec

Eng

ine-Ou

tHC

,ppm

C3

Reformer pre-heat ends, reformate

production begins at t=0

2 second preheat at reformer= 1.

Very high HCs due to engine misfires

and poor combustion

5 second preheat at

reformer= 1


reformer= 1

Gasoline baseline

Fig. 8: Effect of preheat-time on engine-out exhaust HC concentrations. PFIgasoline baseline included for comparison.

75 percent reduction compared with PFI gasoline afte

20 seconds of engine operation.


11/14

The HC breakthrough during the preheat-time was

subject to significant variations, and depended on theignition and early flame development in the combustion

chamber of the reformer A repeat test with 5 secondpreheat, gave much lower HC breakthrough during the

preheat-time probably because of quick ignition andfast early flame development. The low HC breakthroughduring preheat with the repeat 5 second test shows

cumulative mass HC emissions very similar to the 10

second preheat start.

RESULTS OF TESTS WITH ENGINEVARIATIONS

The purpose of these tests was to characterize the abilityof the reformate produced by the experimental reformer

to burn mixtures leaner than engine

= 1.0 during start-up.

Test with the quarter scale reformer suited for the single-

cylinder engine were run with lean engine

supplied to theengine. The reformate flow was less than half the

amount produced in the full scale reformer testsdescribed above. For comparison the engine was alsofueled with California phase 2 gasoline using port-fuel

injection (PFI) during start-up. To achieve a quick startwith PFI gasoline a rich pulse of

engine=1.8 was initially

supplied and decayed down to engine

=1.0 in 40 engine

cycles. The steady speed and load were 1330 rpm and216 kPa NMEP after the initial transient fluctuations

during start-up. Only data for engine

=1.0 and 0.75 are

shown for the tests with the scaled down reformer.

START-UP NMEP - Figure 10 shows the NMEP duringstart-up with gasoline and reformate. The NMEP withgasoline was initially higher than 216 kPa (the steady

state target value) because of the rich fueling to get a

quick start. With reformate, the NMEP rose quickly towithin 85% of the steady value and stabilized thereafterto the steady value. During stoichiometric reformate

start-up, the cyclic variations in NMEP were very low.

With lean reformate fueling engine

= 0.68, the cyclicvariations in NMEP were comparable if not slightly lower

than those for the gasoline test after the initial start-upAs explained above, the transport delay for the reformate

to reach the engine cylinder caused an initial delay of 4to 5 cycles for the rise in NMEP with reformate. Note tha

the quality of the early reformate generated by thereformer is likely to be somewhat poor with higheamounts of unburned fuel, CO2 and water vapor in the

first few fired cycles. Even so the engine appears tostart-up with negligible hesitation.

EMISSIONS - Figure 11 shows plots of NOx, HC, and

CO emissions respectively for the gasoline andreformate starts. The stoichiometric and lean reformatestarts gave substantially lower NOx and HC emissions

when compared with gasoline. In fact the NOx emissionswith the lean reformate start were at least an order of

magnitude lower than those for PFI gasoline operationClearly, the ability to run lean with reformate is a large

factor in the lower NOx emissions compared to gasolineHowever, there is also a second factor at work

Reformate contains CO2and water as described earliein Eq. (1). These constituents produced by the reformerserve the same function as EGR to dilute the fuel-ai

mixture to the engine and lower combustiontemperatures. This explains why even stoichiometric

operation with reformate provides much lower NOx thanthe gasoline baseline.

The poorer quality reformate likely to be produced duringthe early part of the reformer start-up did not appear to

adversely impact HC emissions. CO emissions werehigh during the start-up with reformate but after theengine stabilized the CO emissions with lean reformate

were also significantly lower than with gasoline. Theinitial spike in CO could be due to either incomplete

combustion during the preheat time of the reformer or theincomplete burning of the leading edge of the initially

poor quality reformate air mixture which may be beyondthe flammability limit. Further work is needed to addressthis issue.

DISCUSSION

The results provided above represent a significant step

in developing a fast start-up on-board reformer system

Results from our experiments show an excellencorrelation between reformate production and engine

combustion and HC emissions. Overall, with our currentgeneration of experimental hardware, the data indicate

that gasoline-fueled reformer preheat offers a means orapid reformate production that can enable cold startswith up to a 75% reduction in engine-out HCs compared

to baseline PFI gasoline operation. The ability to start theengine quickly with lean reformate mixtures and get at

least an order of magnitude reduction in NOx

-100

-50

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 90 100

Engine Cycles

NMEP,kPa

Gasoline

engine=1.0

Reformate

engine=0.68

Reformate

engine=1.0

Fig. 10: Effect of engine

on engine NMEP from the

start of reformate fueling with the quarter-scale reformer. PFI gasoline baselineincluded for comparison.


12/14

emissions compared with PFI gasoline has also beendemonstrated. Additional reductions in tailpipe emissions

should be realized when reformate heating of the

exhaust catalyst is employed for faster light-off. Overall,we find these results to be encouraging and continue toshow promise for our on-board reforming system toenable meeting SULEV.

However, significant work remains to be done on several

fronts. Currently, reformer preheat-time is 5 to 10seconds with a pre-vaporized gasoline-air mixture being

fed to the reformer. While this is relatively fast, Webelieve that this ultimately must be reduced to roughly 2seconds, and include a means for rapid fuel vaporization.

Significant efforts are under way (details are proprietary)

to enable rapid fuel vaporization and decrease reformepreheat-time. HC emissions during the reformer preheaperiod can comprise a significant fraction of total cold

start HCs with reformate. The magnitude and start-to-start variability of HC emissions due to reformer preheat

must be minimized. Ultimately, the system must exceedour current cold start HC reduction capability. Finally

significant efforts are still required to couple the reformer

system to a vehicle. One challenge here is providingappropriate transient response. A second challenge is

adapting and calibrating the reformer-vehicle system tooptimize its performance with full implementation of ou

H2enrichment strategy.

SUMMARY AND CONCLUSIONS

This paper provides an update of work-in-progress toward

our development of a H2 enrichment system for meeting

SULEV emission standards in spark-ignition engines

Results from this paper have focused on tests usinggasoline combustion to rapidly warm-up the reforme

catalyst to enable reformate-fueled engine cold starts withvery low HC emissions. Tests for this study were performedusing an experimental reformer system with pre-vaporized

gasoline and air. (An optimized mixture preparation systemfor the reformer start-up period is under paralle

development, but not described in this paper.)

The following conclusions are supported by the datapresented in this paper.

Gasoline combustion was able to rapidly preheat ourexperimental reformer. A preheat period of 5 to 10seconds (with pre-vaporized gasoline) enabled

production of good quality reformate for fast enginestarting. Shorter preheat times led to significant engine

misfires.

Reformer temperature was a strong function of preheat-time. Measured reformer midpoint catalyst temperature

varied from 150C to 440C with preheat-times from 2to 10 seconds. Due to thermocouple lag, thesemeasured temperatures are regarded as the lower

bound for the actual midpoint catalyst temperature atthese times.

HC mass emissions from reformate fueled cold starts in

a single-cylinder engine were up to 75% lower than with

gasoline fueling. The reformer preheat period showedsignificant test-to-test variability in HC emissions.Ultimately, cold start HCs must be consistently lowered

to enable a viable system for meeting SULEV.

Starting the engine with lean reformate air mixtures wasdemonstrated. An order of magnitude reduction in NOx

emissions compared with gasoline operation wasobserved.

Based on these findings, on prior published work, and onthe expected additional benefits in catalyst light-off and

Fig. 11: Effect of engine

on engine-out emissions withthe quarter-scale reformer. PFI gasoline

baseline included for comparison.

0

200

400

600

800

1000

1200

1400

1600

-10 0 10 20 30 40 50 60

Time, sec

HC,ppm

185 ppm

1480 ppm

258 ppm

Gasoline

engine=1.0

Reformate

engine=0.68

Reformate

engine=1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

-10 0 10 20 30 40 50 60

Time, sec

CO,

%Gasoline

engine=1.0

Reformate

engine=0.68

Reformate

engine=1.0

0

200

400

600

800

1000

1200

1400

-10 0 10 20 30 40 50 60

Time, sec

NOx,ppm

38 ppm

1230 ppm

220 ppm

Gasoline

engine=1.0

Reformate

engine=0.68

Reformate

engine=1.0

Reformer pre-heat ends,

reformate production begins


13/14

warmed up emissions, we remain optimistic on the

successful practical implementation of the onboard reformerstrategy to meet SULEV emissions in gasoline SI engines.

ACKNOWLEDGMENTS

Mark Smigielski is cited for fabricating the experimentalreformer for the single-cylinder engine. He also installed the

reformer, ran the experiments, maintained the single-

cylinder engine test facility, and helped with the dataprocessing. Dave Schumann and Jeff Weissman supplied

the reformer catalyst samples for this study. Rick Nashburn,Mike Salemi, Jonathon Bennett, Pete Crawford, and Brian

Allston are providing critical support in reformerdevelopment, testing and vehicle implementation.

REFERENCES

1. Kitagawa, H.; Mibe, T.; Okamatsu, K.; and Yasui, Y.Design of L4 Engine for Super Ultra Low Emission

Vehicle SAE Paper 2000-01-0887, Society ofAutomotive Engineers, March 2000.

2. Nishizawa, K.; Momoshima, S.; Koga, M.; Tsuchida,H.; and Yamamoto, S. Development of New

Technologies Targeting Zero Emissions for GasolineEngines SAE Paper 2000-01-0890 Society ofAutomotive Engineers, March 2000.

3. Masaki, U.; Akazaki, S.; Yasui, Y.; and Iwaki, Y. AQuick Warm-up System during Engine Start-up

Period Using Adaptive Control of Intake Air andIgnition TimingSAE Paper 2000-01-0551, Society ofAutomotive Engineers, March 2000.

4. Nishizawa, K.; Mitsuishi, S.; Mori, K.; andYamamoto, S. Development of Second Generation

Gasoline P-ZEV Technology SAE Paper 2001-01-1310, Society of Automotive Engineers, March 2001.

5. Breshears, R.; Cotrill, H.; and Rupe, J. PartialHydrogen Injection into Internal CombustionEngines Effect on Emissions and Fuel Economy

First Symposium on Low Pollution Power SystemsDevelopment, Ann Arbor, MI, 1973.

6. Houseman, J.; and Cerini, D. J. On-Board HydrogenGenerator for a Partial Hydrogen Injection Internal

Combustion EngineSAE paper 740600, Society ofAutomotive Engineers, 1974.

7. Houseman, J.; and Hoehn, F. W. A Two-Charge

Engine Concept: Hydrogen EnrichmentSAE paper

741169, Society of Automotive Engineers, 1974.8. Jamal, Y.; and Wyszynski, M. L. On-Board

Generation of Hydrogen-Rich Gaseous Fuels A

Review, International Journal of Hydrogen Energy,Vol. 19, No. 7, pp. 557-572, Elsevier Science, 1994.

9. Kirwan, J. E.; Quader, A. A.; and Grieve, M. J. An

On-Board Gasoline Reforming System for MeetingSULEV Emissions Requirements in a Spark-Ignition

Engine Proceedings of the Global PowertrainCongress, Detroit, Michigan, June, 2000.

10. Kirwan, J. E.; Quader, A. A.; and Grieve, M. J

Advanced Engine Management Using On-BoardGasoline Partial Oxidation Reforming for Meeting

Super-ULEV (SULEV) Emissions Standards SAETrans. Paper 1999-01-2927, Society of Automotive

Engineers, August 1999.11. Grieve, M. J.; Kirwan, J. E.; and Quader, A. A

Integration of a Small On-board Reformer to a

Conventional Gasoline Internal Combustion Engine

System to Enable a Practical and Robust Nearly-zero Emission Vehicle Proceedings of the GlobaPowertrain Congress, Stuttgart, Germany, Octobe1999.

12. Grieve, M. J. Hydrogen Leveraging for Near ZeroEmission Vehicles with Conventional or Mild Hybrid

Powertrains and Gasoline Fuel, Proceedings of theGlobal Powertrain Congress, Detroit, Michigan

October 1998.13. Kirwan, J. E.; Quader, A. A.; and Grieve, M. J

Development of a Fast Start-up On-Board Gasoline

Reformer for Near Zero Emissions in Spark-IgnitionEngines, Proceedings of the 10

th Aachen

Colloquium on Automobile and Engine Technology(Aachener Kolloquium Fahrzeung- und

Motorentechnik), 8-10 October, 2001.

APPENDIX BENCH TESTS WITHEXPERIMENTAL REFORMER

In addition to engine testing with the reformer, bench testsare also ongoing to characterize reformer performanceduring start-up. The reformer used for bench tests is

different hardware from that used on the engine, but isessentially the same size as the full-scale reformer and has

the same components as described above in the text(vaporizer, combuster and reformer-catalyst).

In these bench tests, a mass spectrometer provides time-resolved measurements of reformate composition. Figure A-

1 shows typical reformate composition from a start-up testwith 9 second reformer preheat and two different reforme

airflow rates. The graph on the left is with 1.5 g/s reformeair flow the graph on the right is with 2.5 g/s reformer airflow. Notice that there is very little difference in the start-up

behavior between the two reformer air flow rates for the first15 seconds. During the preheat phase, stoichiometric

gasoline combustion produces mostly CO2. After 9

seconds, the fueling mixture is enriched and reformateproduction begins rapidly. CO and H2 concentration profilesare well-correlated, indicating that our measurement of COin engine testing is a good indicator of H2 production as

well. Note that within 3 seconds after reformate productionbegins, CO and H2 yields are both greater than 60% of thei

final value. The reformate yield is somewhat higher for thelower flow rate after 30 seconds. At 1.5 g/s air flow, CO and

H2 are about 21% each compared to about 17% each fo2.5 g/s airflow.


14/14

0

5

10

15

20

25

0 5 10 15 20 25 30

Time from Fueling Start (seconds)

ReformerO

utput,mole%

0

3.5

CO2 from

gasoline

preheatH2

CO

reformer= 1.0reformer= 2.8

0

5

10

15

20

25

30

0 5 10 15 20 25 30

Time from Fueling Start (seconds)

ReformerO

utput,mole%

0.00

3.50

CO2 from

gasoline

preheat

H2

CO

reformer= 1.0

reformer= 2.8

Figure A-1. Reformer output during start-up from bench tests at reformer airflowrates of 1.5 g/s (left figure) and 2.5 g/s (right figure).

fast start-up on-board gasoline reformer 2002

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