International Journal of Hydrogen Energy 32 (2007) 1437–1442www.elsevier.com/locate/ijhydene

Onboard fuel processor for PEM fuel cell vehicles

Brian J. Bowersa,∗, Jian L. Zhaoa, Michael Ruffoa, Rafey Khana, Druva Dattatrayaa,Nathan Dushmana, Jean-Christophe Beziatb, Fabien Boudjemaab

aNuvera Fuel Cells, Inc, 20 Acorn Park, Cambridge, MA 02140, USAbRenault, Service 64240 - FR TCR GRA 0 75, Technocentre Renault - 1 avenue du Golf, 78288 Guyancourt, France

Available online 13 December 2006

Abstract

To lower vehicle greenhouse gas emissions, many automotive companies are exploring fuel cell technologies, which combine hydrogen andoxygen to produce electricity and water. While hydrogen storage and infrastructure remain issues, Renault and Nuvera Fuel Cells are developingan onboard fuel processor, which can convert a variety of fuels into hydrogen to power these fuel cell vehicles.

The fuel processor is now small enough and powerful enough for use on a vehicle. The catalysts and heat exchangers occupy 80 l and canbe packaged with balance of plant controls components in a 150-l volume designed to fit under the vehicle. Recent systems can operate ongasoline, ethanol, and methanol with fuel inputs up to 200 kWth and hydrogen efficiencies above 77%. The startup time is now less than 4 minto lower the CO in the hydrogen stream to the target value for the fuel cell.� 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Keywords: Fuel processor; Fuel cell; Hydrogen; Onboard; Gasoline; Ethanol

1. Introduction

Society is continuing its efforts towards finding clean powersources and alternative forms of energy. In the automotive sec-tor, reduction of pollutants and greenhouse gas emissions fromthe power plant is one of the main objectives of car manufactur-ers, and innovative technologies are under active considerationto achieve this goal. One technology that has been proposedand vigorously pursued in the past decade is the proton ex-change membrane (PEM) fuel cell, an electrochemical devicethat reacts hydrogen with oxygen to produce water, electricity,and heat. The PEM fuel cell can be used in a new type of vehi-cle power plant, which produces clean electricity to move thevehicle via an electric motor.

Since today there is no existing extensive hydrogen infras-tructure and no commercially viable hydrogen storage technol-ogy for vehicles, there is a continuing debate as to how thehydrogen for these advanced vehicles will be supplied. In order

∗ Corresponding author.E-mail address: bbowers@nuvera.com (B.J. Bowers).

0360-3199/$ - see front matter � 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.ijhydene.2006.10.045

to circumvent the above issues, power systems based on PEMfuel cells can employ an onboard fuel processor that has theability to convert conventional fuels such as gasoline or ethanolinto hydrogen for the fuel cell. This option could thereby re-move the fuel infrastructure and storage issues that are a barrierto the introduction of fuel cell vehicles to the market.

Renault and Nuvera fuel cells are currently pursuing ad-vanced technologies for onboard fuel processing. This programcovers four phases over six years (2002–2008) with the goal ofproducing a fuel processing system that can be viable in com-mercial vehicles. The target fuel is gasoline, but the technologyis multi-fuel, giving the potential to convert a variety of hydro-carbon fuels such as ethanol and methanol into hydrogen foruse in a fuel cell.

This paper presents an overview of the Renault/Nuvera pro-gram and results from the current fuel processing system. Thecurrent technology employs advanced catalysts, heat exchang-ers, and controls in a system that is small enough and powerfulenough for use on a vehicle. This technology has undergonedramatic advancements in many critical areas including a 10fold decrease in volume and a 20 fold decrease in startup timein the past six years.

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2. Program overview

The Renault–Nuvera program is developing a multi-fuel fuelprocessing system (FPS) to provide hydrogen for a PEM fuelcell. The program is divided into four phases as described be-low. The main objective is to develop a fuel processor thatachieves all the technical targets needed for a successful com-mercial vehicle by 2008.

2002–2004:Phase 1: Laboratory prototype system

• Compactness, efficiency, emissionsPhase 2: Automotive prototype

• Startup time, fuel consumption, multi-fuel2004–2008:

Phase 3: Advanced automotive prototypes• Startup time and energy, transients, power plant

efficiencyPhase 4: Refined automotive prototypes

• Target: Meets all consumer specifications.

The Phase 2 system (FPS 2.5) is now developed and testingactivities for the same are nearing completion. Phase 3 of theprogram is now in progress. Pictures of FPS 2.5 and FPS 3A areshown in later sections. This paper focuses on recent Phase 2results on FPS 2.5.

3. Fuel processor design

A primary objective of the fuel processor system is to fit in acompact space on the vehicle. While fuel processing has beenused for many years to produce hydrogen at industrial scales,these facilities did not have specific size limitations. Therefore,early projects started by scaling down the known industrialtechnology to have a power appropriate for a vehicle. These firstprototypes proved that gasoline, ethanol and other automotivefuels could be processed, but they required more than 800 land a large mass to produce the required hydrogen. Since thisspace is not available on the vehicle, a major development effortfocused on reducing the volume 10 fold from the year 2000 to2003.

During Phases 1 and 2, fuel processors occupying only 80 lwere successfully designed and demonstrated. Other importantdesign criteria of the Phase 2 system are described in Table 1. Aschematic of the fuel processor system is shown in Fig. 1. Notethat the fuel processor is based on autothermal reactor (ATR)technology, followed by high-temperature and low-temperaturewater–gas–shift (HTS, LTS) reactors. The final stage beforethe fuel cells is a preferential oxidation (Prox) reactor, whichoxidizes the CO to the level needed for the fuel cell. A tail gascombustor (TGC) is used to burn the unused hydrogen exitingthe fuel cell. When under test without a fuel cell, this unusedhydrogen from the fuel cell is simulated by sending part of theProx-exit reformate (∼ 20.25%) to the TGC to give the sameheating value that would be returned from a fuel cell that uti-lizes 75.80% of the hydrogen. Since the Prox-exit reformatehas a higher concentration of hydrogen than the depleted re-formate from an actual fuel cell, extra air is added to TGC

to give the proper dilution and to maintain normal tempera-tures. The remaining 75.80% of the reformate is diverted awayfrom the test stand to simulate the hydrogen consumed by thefuel cell.

Pictures of the latest fuel processor systems are shown inFig. 2. FPS 2.5 has a maximum fuel input of 200 kWth (thermalinput based on LHV), can produce 1.3 g/s hydrogen, and occu-pies about 76 l. It is shown with the fuel and water control sys-tems surrounding the fuel processor. FPS 3A has a maximumfuel input of 215 kWth, can produce 1.4 g/s hydrogen, and oc-cupies about 80 l. It is shown packaged with its fuel and watersystems. Note that the entire package occupies about 150 l andis given a “flat” aspect ratio with a 23 cm height that allows theoption of installation under the floor of the vehicle. This givesflexibility for the layout of the vehicle with this new type ofpower plant.

4. Test results

The Phases 1 and 2 system have been tested in a variety ofconditions to confirm the performance against the target specifi-cations on gasoline [1]. This section presents additional resultson gasoline including a faster startup as well results of multi-fuel operation on ethanol, methanol, and gasoline. Some of themost important measurements are of the hydrogen productionand the reformate quality. The performance of the ATR-Proxreactor train can be checked by measuring the hydrogen effi-ciency, which is the ratio of the hydrogen flow from the Prox(kWth based on LHV) to the fuel input (also in kWth basedon LHV). Two of the major measurements for the reformatequality are the hydrogen and CO concentrations in the refor-mate. The hydrogen is of course important because it is the fuelfor the fuel cell while the CO must be limited to meet the re-quirements of the PEM fuel cell. These measurements providea consistent and convenient way of rating the performance ofmain reactor train. System level measurements would need toinclude the overall efficiency from fuel input to net electricaloutput from the fuel cell. Since the overall system efficiencywould be dependent on the fuel cell performance as well as theparasitic power (especially the onboard air compressor, whichwas not evaluated in this set of tests) the tests described belowfocus on evaluation of fuel processor only.

Fig. 3 shows operation of FPS 2.5 on gasoline with fuel inputpowers of 180 and 100 kWth. During this time the hydrogenefficiency is kept above the target at between 78% and 81% asmeasured by periodic gas chromatograph samples. The dry hy-drogen concentration is 40–42%. The CO is also kept below the100 ppm target. This steady-state testing is important to validatethe proper operation of the overall reactor and heat exchangersystem. Other tests of FPS 2.5 have covered 33.200 kWth ofgasoline input and thus demonstrated a 6.1 turndown ratio [1].

Fig. 4 shows operation of FPS 2.5 on ethanol at 100 kWth.Overall, the performance is similar to gasoline. The hydrogenefficiency is kept between 78% and 80%. The dry hydrogenconcentration is 41–42% while the CO is kept below the tar-get. For the ethanol testing, the computer maps are adjusted toaccount for the necessary change in the control set points of

B.J. Bowers et al. / International Journal of Hydrogen Energy 32 (2007) 1437–1442 1439

Table 1Phase 2 fuel processor design goals for 2004

Characteristic Design goal Comments

Fuel processor volume �80 l Without balance of plant components or plumbing. Includes everything between cold feedstreams and 100 ◦C fuel–cell-quality reformate outlet stream.

Fuel processor system volume 150 l Includes control valves for air, fuel, waterHeight < 229 mm “Flat” aspect ratio for vehicle installationCatalysts Non-pellet-catalyst Minimize volumePrimary fuel type Sulfur free gasoline < 2 ppm sulfur. Onboard or refinery desulfurizer assumedOther fuels Ethanol, Methanol Gasoline design allows processing of many other fuelsMaximum hydrogen in reformate 1.3 g/s ∼ 157 kWth based on LHVFull power hydrogen Efficiency �78% LHV H2/LHV ATR fuelResidual fuel (as CH4) < 1% (dry) At PrOx exitAssumed FC H2 utilization 80% At peak powerCO—steady state �100 ppmv (dry) At PrOx exit. Assumes advances in PEM technology before commercialization. Lower valuesCO—transient < 1000 ppmv (dry) are possible with a tradeoff in efficiency and/or volume.Startup time 6 min < 100 ppm CO; < 1 min needed in futureDurability 2000 h Primarily steady stateReformate pressure 3 bar At PrOx exitPressure loss �1 bar ATR air inlet—PrOx exit

Fuel

Tank

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(< 80 liters)

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simulate fuel cell when

using FC bypass

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operation

without a

fuel cell

Fig. 1. Schematic of fuel processor system.

Fig. 2. Pictures of FPS 2.5 (left) and FPS 3A (right) on laboratory test stands.

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Nuvera / Renault FPS 2.5 Fuel Processor Testing

Date: 11 March 2005 Fuel: Sulfur Free Gasoline

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Fig. 3. FPS 2.5 operation on gasoline at 180 and 100 kWth input.

Nuvera / Renault FPS 2.5 Fuel Processor Testing

Date: February 16, 2005 Fuel: Ethanol

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Fig. 4. FPS 2.5 operation on ethanol at 100 kWth input.

the fuel injectors and the operating conditions can be adjustedto optimize the hydrogen efficiency and CO. This allowsthe possibility for a fuel cell vehicle that can operate on diff-erent fuels.

Fig. 5 compares FPS 2.5 operation on four fuels: ethanol,US gasoline, Euro gasoline, and methanol at high power(> 150 kWth). Performance on the ethanol and gasolines issimilar in terms of CO (60.65 ppm) and hydrogen concentra-tion (40%). The slightly lower hydrogen efficiency obtainedon ethanol is only due to the limited test duration and non-optimized operating conditions at the high power condition.With sufficient optimization, the FPS performance on ethanol

should match or exceed that on gasoline. As expected, the testson methanol show higher hydrogen concentrations due to thefact that methanol allows for the ATR to be operated at lowertemperatures, which means less air fed into the ATR (i.e. aricher mixture). This results in higher hydrogen efficienciesthat can exceed 80%. The multi-fuel operation is facilitatedby the ATR technology, which is able to break down a varietyof fuels in the ATR reactor given sufficient temperature andproper ratios of air, fuel, and steam. After the ATR reactor,the bulk gas compositions are relatively similar for a varietyof fuels and therefore the HTS, LTS, and Prox operate in asimilar manner.

B.J. Bowers et al. / International Journal of Hydrogen Energy 32 (2007) 1437–1442 1441

Multi-Fuel Operation at High Power

Nuvera-Renault Phase 2.5 Fuel Processor

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Fig. 5. FPS 2.5 operation on fuels at high power (150.180 kWth).

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Nuvera / Renault Phase 2.5 Fuel Processor Cold Startup Testing

Date: 19 May 2005 Fuel: Sulfur Free Gasoline

Elapsed Time (min)

45403530251510

Fig. 6. Startup performance of FPS 2.5 with less than 4 min to CO < 100 ppm.

In addition to multi-fuel operation, FPS 2.5 was tested for itsstartup characteristics. The startup time is of great importance tothe energy management strategy of the vehicle and the fuel usedto heat the reactors before power can be produced is importantfor the overall fuel economy. Fig. 6 shows a startup of the FPS2.5 from room temperature on gasoline. During the startup, allof the energy used to heat the system comes from the gasolineand no electrical heating is used. The ATR fuel is increasedfrom 6 to 30 kWth in 2 min. As the catalyst beds heat up, theCO drops to under 100 ppm in 3 min 43 s, following whichthe fuel cell could begin to produce power while the hydrogenefficiency and hydrogen output of the FPS continue to rampup. Note that in these conditions, the CO is kept very low and

reaches values under 10 ppm. The decrease in startup time frommore than 75 min in 1999 to less 3 min 43 s is a very importantachievement (more than 95% reduction). This reduction wasachieved through a change of catalysts from traditional pelletsto coated substrates, better integration of the various reactorsand heat exchangers, improvements in the control components,and optimization of the control strategy.

Reducing the time to low CO is important because it meansthat the fuel cell can produce power faster and it can allow moreflexibility with the sizing of a hybrid battery. It is worth notingthat while low CO is the first point of concern for startup sincethe fuel cell can begin to make power, the time to achieve fullefficiency is important to the overall fuel consumption of the

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vehicle, especially on short driving cycles. So an upcoming tar-get is to reduce the thermal mass and further improve the sys-tem layout and control system to achieve full efficiency faster.

5. Conclusions

Fuel cells are being actively pursued as a potential automo-tive power plant with the hopes of increasing efficiency andreducing overall greenhouse gas emissions. While onboardhydrogen storage and infrastructure still remain challenges,onboard fuel processors offer a promising solution to producehydrogen for the fuel cell on the vehicle using conventionalfuels such as gasoline or bio fuels such as ethanol. Thistechnology could facilitate the early introduction of fuel cellvehicles while providing the potential to power them usingvarious readily-available fuels.

Renault and Nuvera are pursuing onboard fuel processingtechnologies through a six year development program covering

four phases. The Phase 2 fuel processor (FPS 2.5) occupies lessthan 80 l and is packaged to fit into a vehicle. The results ofthe Phase 2 system include successful operation on gasoline,ethanol, and methanol. Gasoline and ethanol operation of theFPS 2.5 show similar performance. Hydrogen efficiencies meetthe targets of more than 77% while CO concentrations meetthe target of less than 100 ppm. In addition, startup tests haveshown that the fuel processor can produce hydrogen with COconcentration levels under the target in 3 min 43 s. The programis currently in Phase 3 of its development, which provides asystem rated for 7% higher power while packaged in a size andshape similar to FPS 2.5.

References

[1] Bowers BJ, Boudjemaa F, Zhao JL, Dattatraya D, Ruffo M. Performanceof an onboard fuel processor for PEM fuel cell vehicles. 2005 SAE worldcongress, 2005-01-0008.