conversion of a gasoline engine-generator to hydrogen

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 3 7 8 1e1 3 7 9 2

Avai lab le a t www.sc iencedi rec t .com

journa l homepage : www.e lsev ier . com/ loca te /he

Conversion of a gasoline engine-generator set to a bi-fuel(hydrogen/gasoline) electronic fuel-injected power unit

D. Sainz a, P.M. Dieguez a, J.C. Urroz a, C. Sopena a,1, E. Guelbenzu b, A. Perez-Ezcurdia a,M. Benito-Amurrio a, S. Marcelino-Sadaba a, G. Arzamendi a, L.M. Gandıa a,*aEscuela Tecnica Superior de Ingenieros Industriales y de Telecomunicacion, Universidad Publica de Navarra, Campus de Arrosadıa,

E-31006 Pamplona, SpainbAcciona Energıa, Avenida Ciudad de la Innovacion no 5, E-31621 Sarriguren, Navarra, Spain

a r t i c l e i n f o

Article history:

Received 17 May 2011

Received in revised form

21 July 2011

Accepted 25 July 2011

Available online 8 September 2011

Keywords:

Bi-fuel engine-generator

Hydrogen-fueled electric generator

Hydrogen fuel

Pollutant emissions

Power unit

* Corresponding author. Tel.: þ34 948 169 60E-mail addresses: [email protected] (P.M

1 Deceased 18th December 2009.0360-3199/$ e see front matter Copyright ªdoi:10.1016/j.ijhydene.2011.07.114

a b s t r a c t

The modifications performed to convert a gasoline carbureted engine-generator set to a bi-

fuel (hydrogen/gasoline) electronic fuel-injected power unit are described. Main changes

affected the gasoline and gas injectors, the injector seats on the existing inlet manifold,

camshaft and crankshaft wheels with their corresponding Hall sensors, throttle position

and oil temperature sensors as well as the electronic management unit. When working on

gasoline, the engine-generator set was able to provide up to 8 kW of continuous electric

power (10 kW peak power), whereas working on hydrogen it provided up to 5 kW of electric

power at an engine speed of 3000 rpm. The air-to-fuel equivalence ratio (l) was adjusted to

stoichiometric (l ¼ 1) for gasoline. In contrast, when using hydrogen the engine worked

ultra-lean (l ¼ 3) in the absence of connected electric load and richer as the load increased.

Comparisons of the fuel consumptions and pollutant emissions running on gasoline and

hydrogen were performed at the same engine speed and electric loads between 1 and 5 kW.

The specific fuel consumption was much lower with the engine running on hydrogen than

on gasoline. At 5 kW of load up to 26% of thermal efficiency was reached with hydrogen

whereas only 20% was achieved with the engine running on gasoline. Regarding the NOx

emissions, they were low, of the order of 30 ppm for loads below 4 kW for the engine-

generator set working on hydrogen. The bi-fuel engine is very reliable and the required

modifications can be performed without excessive difficulties thus allowing taking

advantage of the well-established existing fabrication processes of internal combustion

engines looking to speed up the implementation of the energetic uses of hydrogen.

Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction infrastructure of the automotive industry and the great

There is a renewed and increasing interest in the hydrogen-

fueled internal combustion engines (H2ICEs). This is mainly

due to the possibility of using the current manufacture

5; fax: þ34 948 169 606.. Dieguez), lgandia@una

2011, Hydrogen Energy P

existing experience in H2ICEs design and in the adaptation of

engines developed to operate with conventional liquid

hydrocarbon fuels to run on hydrogen [1e3]. H2ICEs are

considered a technology with the potential to stimulate the

varra.es (L.M. Gandıa).

ublications, LLC. Published by Elsevier Ltd. All rights reserved.

mailto:[email protected]

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http://dx.doi.org/10.1016/j.ijhydene.2011.07.114



Fig. 1 e (A) Original commercial (MOSA GE 10000 BES/GS)

generator set; (B) Photograph of the completely modified

generator showing the gas cylinder used to store the

hydrogen fuel.

Table 2 e Specifications of the alternator.

A.C. Generation 50 Hz, synchronous,

three-phase, self-excited,

self-regulated

Three-phase generation (stand-by) 11 kVA (8.8 kW)/400 V/15.9 A

Three-phase generation (P.R.P.) 10 kVA (8 kW)/400 V/14.4 A

Single-phase generation 6 kVA (4.8 kW)/230 V/26 A

Duty cycle 100%

(Cos) 0.8

Insulation class H

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 3 7 8 1e1 3 7 9 213782

development of the hydrogen economy. Indeed, these engines

are available and very reliable, and currently much cheaper

than the options based on fuel cells with electric engines

(H2FCEs) both directly aswell as in terms of fuel cost due to the

very high purity required to the hydrogen that has to be used

to feed low-temperature fuel cells [2]. H2ICEs might be

Table 1 e Specifications of the original engine-generatorset.

Engine Air-cooled, 4-stroke, OHV, 90 l V-twin

Bore � Stroke 77 � 66 mm (3.0 � 2.6 in)

Displacement 614 cm3

Compression ratio 8.3:1

Net power output 13.5 kW at 3600 rpm

Net torque 40.6 N m at 2500 rpm

Ignition system Transistorized magneto ignition

Carburetor Horizontal type butterfly valve

Lubrication system Full pressure

Governor system Centrifugal mechanical

Air cleaner Dual element type

Dimensions (L � W � H ) 388 � 457 � 452 mm

Dry weight 42 kg

considered as a transitional technology contributing to amore

rapid introduction of hydrogen in the transport sector while

H2FCEs and hybrid configurations continue developing [1,4]. In

this regard, it is very relevant the ability of properly designed

and modified H2ICEs to operate in bi-fuel mode, that is,

running on both gasoline and hydrogen. This featuremight be

essential during the transition period for a rapid introduction

Fig. 2 e (A) Three-dimensional model of the inlet manifold

including the hydrogen injector (1), the gasoline injector (2)

and part of the intake manifold (3); (B) View of the

completely assembled intake manifold.



Fig. 3 e Detail of one of the electronic coils installed to

avoid backfire due to wasted sparks.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 3 7 8 1e1 3 7 9 2 13783

of hydrogen in the transport sector which is believed the

driving force for the use of hydrogen as a fuel [5].

With over 100 years of development maturity, the majority

of the R&D effort on H2ICEs has been directed toward their

application in the automotive sector particularly trying to

increase the power output and engine efficiency. Research

and development on this field has been led by companies as

BMW, Ford, MAN, Mazda and Quantum [6,7] as well as by

several laboratories, see e.g. [1e3,8e28]. In contrast, much less

work has been devoted to the application of H2ICEs to engine-

generator sets. However, these devices play important roles as

Fig. 4 e Electric scheme showing the wiring

auxiliary power units and energy sources for decentralized

applications as in the agricultural sector, particularly in the

developing countries, and can serve to introduce hydrogen as

a fuel in these areas [29].

There are very few examples on the manufacture or

adaptation of engine-generator sets to run on hydrogen. Jeong

et al. [30] modified a 2300 cm3 gas engine-generator originally

designed to be fueled with LPG to run on biogas (a CH4/CO2

mixture)ehydrogen blends. The generator included a vertical

water-cooled, four-cylinder, four-stroke, spark-ignition (SI)

turbocharged engine capable of yielding 22 kW of maximum

electric power at 1200 rpm. Main modifications affected the

intercooler, fueleair mixer, turbocharger and the fuel supply

line. Experiments performed at 1200 rpm and constant electric

power output of 10 kW showed that biogasehydrogen

mixtures can used to effectively feed the engine-generator set

working under lean-burn conditions. Both CO2 and NOx

emissions were reduced in comparison with the engine

operating with LPG. In a subsequent work, Lee et al. [31]

modified a 2300 cm3 gas engine-generator originally

designed to be fueled with natural gas and capable of yielding

30 kW of maximum electric power at 1800 rpm to run on

biogasehydrogen blends. In this case, the main modification

consisted in a low-pressure exhaust gas recirculation (EGR)

system. Regulations on NOx emissions were fulfilled with EGR

ratios above 15% but at the cost of reduced generating

efficiencies.

In this work the adaptation of a commercial gasoline

engine-generator set to a bi-fuel (hydrogen/gasoline) elec-

tronic fuel-injected power unit is described. In a previous

paper [27] we described the steps followed to convert the SI

of the modified engine-generator set.




gasoline-fueled engine of a Volkswagen Polo 1.4 car to run on

hydrogen. Other works by our group dealt with renewable

hydrogen production fromwater electrolysis andwind energy

[32e34]. These studies are being carried out in the framework

of an R&D contract granted by Acciona Energıa, a company

whose activities are focused in the renewables sector.

Fig. 5 e Detail of the REF sensor facing the wheel teeth.

Fig. 6 e (A) One-tooth wheel fixed to camshaft; (B) SYNC

sensor mounted on the engine block cover.

2. Engine-generator set specifications andmodifications performed

The original engine-generator set (MOSA GE 10000 BES/GS) is

shown in Fig. 1A and its main characteristics as well as that of

the alternator are compiled in Tables 1 and 2, respectively.

This device provided up to 10 kVA on three-phase or 6 kVA on

single-phase generation. The generator included a four-stroke

90� V-twin air-cooled gasoline engine (Honda GX620) of

614 cm3. Ignition was achieved by means of transistorized

magneto ignition and gasoline was supplied through

carburetor.

Several modifications have been necessary to achieve bi-

fuel operation of the engine-generator set. The completely

modified device is shown in Fig. 1B. All the engine trans-

formations and the complete test program of the bi-fuel

power unit were carried out at the Laboratory of Internal

Combustion Engines of the Public University of Navarre. The

fuel systemwas changed from carburetor to a double injection

system for both gasoline and hydrogen fuels. The ignition

system was changed to electronic spark ignition in order to

avoid wasted sparks. An electronic control unit (ECU) and

several sensors were mounted as well for proper operation of

the power unit. These modifications are described in more

detail in the following subsections.

2.1. Fuel feeding system

The inletmanifoldwasmodified to place two injectors, one for

gasoline and the other for hydrogen, resulting this way

a multi-point injection system. To this end, a three-

dimensional model of the inlet manifold was previously

obtained by means of a surface probe scanner. With the help

of this model, both injectors were placed for minimal

condensation of gasoline and best cylinder filling with

hydrogen as shown in Fig. 2A.

Aluminum blocks were added to the aluminum inlet

manifold and then both injector seats were machined. In

order to prevent hydrogen leakages due to engine vibration

the injectors were firmly fixed to the manifold by means of

a support. One accumulator or common-rail for each fuel was

fabricated to maintain the pressure constant at the injectors

inlet. The completely assembled modified intake manifold,

including the fuel injectors and accumulators, is shown in

Fig. 2B.

To complete the fuel feeding system, an electric fuel

pump with integrated pressure regulator was placed on the

gasoline tank. The fuel was pumped through a line including

a filter and connected to the gasoline common-rail. The

hydrogen was stored at 200 bar in a 18 l gas cylinder,

mounted on the engine-generator set (see Fig. 1B). Hydrogen

pressure was reduced to about 4 bar by means of a regulator.

The hydrogen line was connected to the gas accumulator

through a pipe including a pressure gauge and a manual

valve.



Fig. 9 e Photograph showing the Peak&Hold driver on the

left and the ECU (center).

Fig. 7 e Throttle position sensor attached to the carburetor

throttle shaft.


2.2. Ignition system

The original ignition system consisted of a magneto ignition

mounted over the flywheel. This produced a spark at a fixed

advance angle referred to the top dead center (TDC) but also

a wasted spark was fired at the exhaust stroke. In order to

avoid backfiring due to wasted sparks, an electronic coil for

each cylinder was installed. The electronic coils were

controlled by a digital signal from the ECU and made the

engine to work on a sequential firing mode. A detail of one of

the electronic coil is shown in Fig. 3.

2.3. Engine management system

A programmable electronic control unit (ECU) DTAfast S60 Pro

was installed. This unit was selected because of its sequential

injection and firing capability, lambda control and two

different sets of maps available. The existing electric wiring

was used and extended to reach the different sensors and

actuators used. For the proper operation of the engine the

Fig. 8 e Lambda oxygen sensor mounted in the engine

exhaust.

following electronic sensors were required to work with the

ECU: REF sensor, SYNC sensor, throttle position sensor, wide-

band lambda oxygen sensor, temperature sensor and Peak&-

Hold driver. The electric scheme developed in this work is

shown in Fig. 4.

In order to achieve a sequential injection and ignition

system it is necessary for the control unit to know exactly the

actual angle of the engine cycle; this is done through both

crankshaft and camshaft sensors. The signal supplied by the

REF sensor is used by the ECU to determine the relative posi-

tion of the cylinders to the TDC; it also allows determining the

engine speed. A toothed wheel was designed, fabricated and

Fig. 10 e Oscilloscope screen showing the signals of the

TDC sensor (in red) and ignition (in white) after adjusting

the sensor position parameter when the ignition advance

was set to 0�. (For interpretation of the references to color

in this figure legend, the reader is referred to the web

version of this article.)




mounted on the crankshaft, fixed to the flywheel. A standard

Hall sensor was mounted as REF sensor, fixed to the engine

block and positioned facing the teeth on the wheel as shown

in Fig. 5. This sensor helped the ECU to determine the cylinder

position. In order to determine if the cylinder is on compres-

sion or exhaust stroke, intake or power stroke, an SYNC

sensorwas necessary. A one-toothwheel wasmounted on the

camshaft (Fig. 6A) and a standard Hall sensor wasmounted as

SYNC sensor on the engine block facing this wheel (Fig. 6B).

This was a very delicate modification that required opening of

the engine block. The cover of the engine block had to be

mechanized for the sensor to be installed.

The carburetor of the engine-generator set was kept up but

its fuel supply was disabled. A standard throttle position

sensor was attached to the throttle shaft of the carburetor

(Fig. 7). This potentiometer-type sensor communicated with

the ECU indicating the engine load.

Air-to-f

0

0.5

1

1.5

2

2.5

3

0 1 2

gasoline

Ignition adv

0

10

20

30

40

50

60

0 1 2 3 4

gasoline

A

B

Fig. 11 e (A) Air-to-fuel ratio and (B) ignition advance of the mo

3000 rpm as a function of the electric power output.

As it is well-known the operation of an engine running on

gasoline needs to be adjusted close to stoichiometric air-to-

fuel ratio (l), whereas using hydrogen requires leaner l

ratios to avoid risk of pre-ignition, backfire, knock and high

NOx emissions [1,2]. A wide-band lambda sensor (Bosch LSU

4.2) and lambda controller (KMS) were installed. The engine

exhaust had to be machined in such a way that the lambda

sensor could be screwed as shown in Fig. 8. The KMS

controller consists of an electronic circuit that allows con-

verting the air-to-fuel ratio (0.75 � l � 2.5) measured by the

sensor to a voltage signal which is read by the ECU. On

account of these modifications a closed-loop control of the l

value at which the engine was running could be performed.

The generator set mounted an air-cooled engine. For the

ECU to have a reference of the engine temperature, a sensor

was installed on the oil sump. The sensor tip was in contact

with the oil contained in the sump, and the sensor body was

uel ratio

3 4 5 6

Electric load (kW)hydrogen

ance (ºBTDC)

5 6 7 8 9


dified generator running on hydrogen and gasoline at




thermally insulated to minimize heat losses. This modifica-

tion was performed to help the engine with cold starts and as

a safety measure since in the event of the oil temperature

reaching a given limit value the generator set will automati-

cally stop to avoid oil overheating.

The hydrogen injectors incorporated into the engine-

generator set were Peak&Hold, that is, of the low impedance

type. The term Peak&Hold refers to the control strategy of

these injectors. Although they need a bigger power to operate

they provide a very fast response. The current intensity rises

during injector opening up to a Peak value and then falls to

Specific fuel consu

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

0 1 2

sfc on gasoline

Thermal effici

0.00

5.00

10.00

15.00

20.00

25.00

30.00

0 1 2

gasoline

A

B

Fig. 12 e (A) Specific fuel consumptions (Sfc) for gasoline and th

efficiency of the bi-fuel generator running on hydrogen and gas

a Hold value maintaining the injector opened. The hydrogen

injectors used in this work operated at 4 and 1 A during Peak

andHold, respectively. Commonhigh impedance injectors can

be driven directly by the ECU, but the low impedance ones

need a Peak&Hold driver which was not incorporated by the

ECU. The driver for both hydrogen injectors was designed,

fabricated and mounted on the generator set for a better heat

dissipation as shown in Fig. 9. Switching between gasoline

and hydrogen was driven by the ECU through a relay which

turns off the gasoline pump when hydrogen is selected. By

using a switch installed on the control panel the desired fuel is

mption (g/kWh)

3 4 5 6

Electric load (kW)

gasoline eq. sfc for hydrogen

ency (%)

3 4 5 6

Electric load (kW)

hydrogen

e equivalent consumptions for hydrogen and (B) thermal

oline as a function of the electric power output.




selected and the ECU changes to the corresponding injection

and ignition maps. Colored LEDs installed on the front panel

showed the status of the generating set as follows: green LED

indicated that power was turned on, blue LED indicated that

hydrogen fuel was selected, red LED indicated that engine

operation was prevented due to high temperature.

2.4. ECU programming

Once the electrical wiring and all the electronics were

installed, the ECU had to be programmed for suitable engine-

generator set operation. The ECU was connected through

a long serial cable to a computer and the several engine

parameters (number of cylinders, number of injectors per

cylinder, cycle angles at which injectors or coils are activated,

etc.) were set. Moreover, every single sensor must be cali-

brated. First of all, the position of the TDC must be identified

because all the cycle angles were referred to it. This was done

through a Kistler TDC capacitive sensor installed in the spark

plug hole. An oscilloscope was used to monitor both ignition

and TDC sensor signals. Ignition advance was set to 0� and

then the position parameter was varied until the ignition

signal fired at the end of the compression strokematching the

TDC signal as illustrated in Fig. 10. The camshaft position

sensor was also calibrated by recording the REF and SYNC

signals, referring them to the TDC and adjusting the corre-

sponding ECU parameter.

3. Test facilities

A test cell adapted to work with hydrogen through suitable

hydrogen supply and safety systems and described in

a previous work was used [27]. This test bed cell consisted of

an eddy current dynamometer AVL 80 capable of absorbing up

to 80 kW of power, with a BME 300 control system allowing

performing tests using as control parameters the torque, the

accelerator position and the engine speed. The performance

of the bi-fuel generating set was investigated in the test bed

Thermal effi

26,00

26,50

27,00

27,50

28,00

28,50

29,00

29,50

30,00

0 5 10 1

Ignition adva

Fig. 13 e Thermal efficiency of the bi-fuel generator running on h

of the air-to-fuel ratio indicated.

cell. The main parameters used were the electrical output,

engine speed, injection time, ignition advance and l. A Bosch

analyzer was attached to determine CO, CO2, hydrocarbons

(HC) and O2 in the exhaust gases, and a Horiba MEXA-720NOx

analyzer was used to determine NOx. Hydrogen consumption

was measured with a Bronkhorst� EL-FLOW� F-110C mass

flow meter.

The main engine parameters were displayed and recorded

through the onboard ECU data logger, which could log main

parameters such as engine speed, injection pulse duration,

ignition advance, l and throttle position among others.

Additionally, a National Instruments NI-CompacDAQ data

acquisition system (DAS) was used. A program developed

under Labview software allowed collecting additional data

such as mean values of hydrogen consumption and NOx and

O2 at the exhaust.

4. Engine management

The engine control was done by means of the ECU after

developing the injection and ignition timing maps. To this

end, the engine speed and throttle position were given as

input signals and the width of the injection pulse and the

ignition timing were generated as output signals. Manage-

ment included also oil temperature corrections, maximum

speed engine and l control. Initially, conservative ignition

advance values were used, and injection was increased

progressively. Then ignition was slowly advanced until

adequate performance was achieved. Injection and ignition

timing maps introduced in the ECU were obtained from the

results of tests conducted in the test cell. The engine speed

was set at 3000 rpm in order to obtain a 50 Hz sine wave. The

generator set was loaded from 0 to 5 kW in steps of 500 W.

4.1. Injection timing

Injection timing maps were obtained for gasoline and

hydrogen. The strategy followed for gasoline was to adjust

ciency (%)

5 20 25 30

nce (ºBTDC)

lambda 1.46lambda 1.67lambda 1.85lambda 2

ydrogen as a function of the ignition advance for the values




injection timing in order to obtain a constant air-to-fuel ratio

around the stoichiometric value, which made it possible to

reach 10 kW at peak. In the case of hydrogen, and due to the

wide flammability limits of hydrogeneair mixtures, a vari-

able l map was developed in which l ranged from about 3

without load to around 1.7 at a load of 5 kW (Fig. 11A). Above

5 kW of load the engine speed could not be maintained at

3000 rpm.

4.2. Ignition timing

Ignition is usually advanced while maintaining the air-to-fuel

ratio constant until the maximum brake torque (MBT) is

achieved. However, in the case of the engine-generator set

HC emissio

0

10

20

30

40

50

60

0 1 2 3

gasoline

A

NOx emissio

0

100

200

300

400

500

600

700

800

0 1 2 3

gasoline

B

Fig. 14 e (A) Unburned hydrocarbons (HC) and (B) NOx emissions

as a function of the electric power output.

the electric power output and engine speed depend on the

brake torque. Therefore, at a fixed electric load, the spark is

advanced in order to obtain low specific fuel consumption

values. A conservative approach was adopted in this work,

namely working with ignition advances which are far from

producing engine knock, that is, the spontaneous auto-

ignition of the end-gas [2]. As shown in Fig. 11B the ignition

advances for both fuels have to be decreased as the electric

load increases. On the other hand, the ignition advance when

the engine is running on hydrogen is lower than when

gasoline is used as fuel. The difference between these

advances increases with the electric load which can be

related to the higher combustion rate of hydrogen compared

with that of gasoline [1].

ns (ppm)

4 5 6


ns (ppm)

4 5 6


of the bi-fuel generator running on hydrogen and gasoline




5. Results and discussion

5.1. Specific fuel consumption and thermal efficiency

The tests performed at the same electric loads show overall

better specific fuel consumptions and thermal efficiencies

running on hydrogen than on gasoline. It should be noted that

using electrical power output instead of brake torque leads to

a lower final thermal efficiency because of the alternator

conversion efficiency. The tests were performed at 3000 rpm,

the nominal engine speed of the generator set. Electric loads

were varied between 0 and 5 kW in steps of 1 kW and the fuel

consumption was recorded. The specific fuel consumptions

for gasoline and the equivalent consumptions for hydrogen

are compared in Fig. 12A. As can be seen the fuel consumption

is lower running on hydrogen than on gasoline. The difference

decreases with the load from about 34% at 1 kW lower running

on hydrogen to 24% at load of 5 kW.

NOx (ppm) v

0

50

100

150

200

250

300

1,7 1,8 1,9 2

0,0

100,0

200,0

300,0

400,0

500,0

600,0

700,0

800,0

900,0

0 10 20

Adv

NO

x (p

pm

)

A

B

Fig. 15 e NOx emissions of the bi-fuel generator running on hy

ignition advance for the values of the air-to-fuel ratio indicated

The thermal efficiency is derived from the specific fuel

consumption and the results are shown in Fig. 12B. As

expected, the thermal efficiency is greater running on

hydrogen compared to gasoline. At 5 kW of load up to 26% of

thermal efficiency is reached with hydrogen whereas a value

of 20% is achieved with the engine running on gasoline. It

should be noted that the engine was not working at wide open

throttle (WOT), so its thermal efficiency could be even higher.

The better efficiency of the engine-generator set working on

hydrogen was confirmed by means of the value of the steady

oil temperature that at the same electric load was about 5 �Clower running on hydrogen than on gasoline.

When the engine is fueled with hydrogen, the ignition

timing also affects the thermal efficiency as illustrated in

Fig. 13. As can be seen, for a given air-to-fuel ratio the thermal

efficiency increases slightly with the ignition advance until

a maximum value is reached; a further increase of the

advance leads to a decrease of the efficiency. The advance

corresponding to the maximum efficiency increases with the

s lambda

2,1 2,2 2,3 2,4 2,5

30 40 50 60

ance (ºBTDC)

lambda>2.49lambda 2.38lambda 1.88lambda 1.82lambda 1.66lambda 1.48

drogen as a function of (A) the air-to-fuel ratio and (B) the

.




air-to-fuel ratio from 10� BTDC for l ¼ 1.46 to 20� BTDC for

l ¼ 2.0. Maximum thermal efficiencies under these operating

conditions were 27.5 and 29.2%, respectively.

5.2. Pollutant emissions

When working on hydrogen, CO and unburned hydrocarbons

(HC) emissions due to lubricating oil burning were very low. In

this case, the most important pollutants in the exhaust gases

were nitrogen oxides (NOx). Unburned hydrogen emissions

were negligible for l values lower than 3. HC, CO and CO2

emissions when running on gasoline were the typical ones for

this type of engines that do not incorporate a catalytic

converter. As shown in Fig. 14A HC emissions when using

gasoline were relatively constant and around 48 ppm for loads

below 4 kW but decreased to 35 ppm at 5 kW of load. When

using hydrogen, the HC concentration in the exhaust was

about 8e9 ppm irrespective of the load.

As concerns the NOx emissions, the results can be seen in

Fig. 14B. When running on gasoline the NOx emissions rise as

the load increases from about 160 ppm at 1 kW up to 750 ppm

at 5 kW. On the other hand, running on hydrogen the NOx

emissions were much lower, of the order of 30 ppm for loads

below 4 kW and up to 125 ppm at 5 kW.

It has been found that NOx emissions of the hydrogen-

fueled engine depended mainly on the air-to-fuel ratio as

shown in Fig. 15A. As far as l is above 2 the NOx could be

maintained at the 60e40 ppm level; however, for values of l

below 2, the NOx emissions increased rapidly. Indeed, it can

be seen in Fig. 15B that the NOx emissions are in the

120e430 ppm range at l ¼ 1.66 and that they increase up to

310e770 ppm at l ¼ 1.48. This is a well-known behavior

related to the combustion temperature, that increases as the

mixture becomes richer (lower l) thus favoring the thermal

NOx formation. Interestingly, for l below 2 the ignition

advance has a marked influence on the NOx emissions since

the concentration of these pollutants in the exhaust gases

increases as the ignition advance increases as well. It seems

likely that this result is due to an increased residence time

in the cylinder of the reacting mixture formed after ignition

as the advance increases. A similar effect on the NOx

emissions was found in our previous study with the SI

engine of a Volkswagen Polo 1.4 car modified to run on

hydrogen [27].

6. Conclusions

The conversion of a commercial gasoline-fueled engine-

generator set to an electronic fuel-injected generator running

on both hydrogen and gasoline has been carried out. Main

modifications included the inlet manifold, low-pressure

hydrogen accumulator, gasoline and hydrogen injectors, the

installation of a programmable electronic control unit as well

as a gas cylinder of 18 l to store hydrogen at 200 bar.

The modified bi-fuel generator set running on hydrogen

supplied up to 5e6 kW at the nominal engine speed of

3000 rpm and l of 1.5. The specific fuel consumption was

much more favorable with hydrogen resulting in consump-

tions between 34 and 24% lower than running on gasoline for

loads in the 1e5 kW range. The operation on hydrogen

produced nitrogen oxides emissions that were 5e7 times

lower than when using gasoline provided that l for hydrogen

is maintained above 2.

The adaptation of internal combustion engines, particu-

larly the spark ignition ones to work bi-fuel (hydrogen/gaso-

line) is relatively easy and it is not expensive. These modified

engines have great potential for speeding up the implantation

of the energetic uses of hydrogen, not only for the trans-

portation sector, but also for the distributed production of

electricity. The creation and development of a hydrogen

infrastructure would also be benefited. These advantages

mainly arise from the fact that the well-established fabrica-

tion processes of internal combustion engines could be

maintained almost unchanged. Moreover, gasoline use in bi-

fuel engines could be restricted to peak power demand

periods.

Acknowledgments

We would like to express our gratitude to our friend Carlos

Sopena, tragically deceased on December 18, 2009. Dear Car-

los, we will follow your teachings to finish your work.

We gratefully acknowledge Acciona Biocombustibles S.A.

for its financial support under R&D contract to the Public

University of Navarra OTRI 2006 13 118 (CENIT project:

SPHERA). LMG, GA and PMD also acknowledge financial

support by Ministry of Science and Innovation of the Spanish

Government (ENE2009-14522-C05-03 and TRA2009-0265-02).

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