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Hydrogen impacts on performance and CO2 emissions from adiesel power generator

Andre Marcelino de Morais a,1, Marco Aurelio Mendes Justino b,2,Osmano Souza Valente a,3, Sergio de Morais Hanriot a,4, Jose Ricardo Sodre a,*a Pontifical Catholic University of Minas Gerais, Department of Mechanical Engineering, Av. Dom Jose Gaspar, 500, 30535-610 Belo Horizonte,

MG, BrazilbMSX International, Electrical and Electronic Product Engineering, Av. Jose Faria da Rocha, 5911/3, 32310-210 Contagem, MG, Brazil

a r t i c l e i n f o

Article history:

Received 11 January 2013

Received in revised form

22 March 2013

Accepted 23 March 2013

Available online 22 April 2013

Keywords:

Hydrogen

Carbon dioxide

Diesel engine

Fuel consumption

* Corresponding author. Tel.: þ55 31 3319 49E-mail addresses: andre.mmor@gmail.co

com (O.S. Valente), hanriot@pucminas.br (S.1 Tel.: þ55 31 8788 5626; fax: þ55 31 3319 42 Tel.: þ55 31 2567 5993; fax: þ55 31 3319 43 Tel.: þ55 31 9951 5567; fax: þ55 31 3319 44 Tel.: þ55 31 3319 4323; fax: þ55 31 3319 4

0360-3199/$ e see front matter Copyright ªhttp://dx.doi.org/10.1016/j.ijhydene.2013.03.1

a b s t r a c t

This work investigates the performance and carbon dioxide (CO2) emissions from a sta-

tionary diesel engine fueled with diesel oil (B5) and hydrogen (H2). The performance pa-

rameters investigated were specific fuel consumption, effective engine efficiency and

volumetric efficiency. The engine was operated varying the nominal load from 0 kW to

40 kW, with diesel oil being directly injected in the combustion chamber. Hydrogen was

injected in the intake manifold, substituting diesel oil in concentrations of 5%, 10%, 15%

and 20% on energy basis, keeping the original settings of diesel oil injection. The results

show that partial substitution of diesel oil by hydrogen at the test conditions does not

affect significantly specific fuel consumption and effective engine efficiency, and decreases

the volumetric efficiency by up to 6%. On the other hand the use of hydrogen reduced CO2

emissions by up to 12%, indicating that it can be applied to engines to reduce global

warming effects.

Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction Hydrogen combustion in atmospheric air is easily ignited at

The cylinder air in diesel engines reaches temperatures lower

than the self-ignition temperature of hydrogen, of 580 �C(858 K) [1,2]. This is one of the main reasons for the recent

interest to associate hydrogen to diesel engines. This way, an

ignition source is required to use hydrogen as fuel in diesel

engines. The most common solution is the use of diesel oil as

the ignition source, thus establishing dual fuel operation.

11; fax: þ55 31 3319 4910.m (A.M. de Morais), mjusdeM. Hanriot), ricardo@p910.910.910.910.2013, Hydrogen Energy P19

concentrations from 4% to 75% v/v [3].

The ignition limit of hydrogen in air allows for its utiliza-

tion with extremely lean mixtures, thus reducing cylinder

peak temperature, while effective engine efficiency is

increased [4,5]. Results from diesel engines operating with

hydrogen fractions from 5% to 50% at different loads show

reduced combustion duration, reduced heat transfer rate to

the cylinder walls and increased effective engine efficiency,

tino@msxi.com.br (M.A. Mendes Justino), osmano.valente@gmail.ucminas.br (J.R. Sodre).

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

Table 1 e Engine and generator details.

Equipment Parameter Value

Engine Bore � stroke 0.102 m � 0.120 m

Total displacement 3.922 � 10�3 m3

Rated power @ 1800 rev/min 49 kW

Compression ratio 17:1

Injection timing 33�BTDCa e 5�BTDC

Valve timing IVOb 0�BTDC e IVCc

210�ATDCd EVOe

210�BTDC e EVCf

0�ATDC

Electric

generator

Number of poles 4

Voltage 220 V

Number of phases 3

Nominal power 55 kW

Frequency 60 Hz

a Before top dead center.

b Intake valve opens.

c Intake valve closes.

d After top dead center.

e Exhaust valve opens.

f Exhaust valve closes.

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 8 ( 2 0 1 3 ) 6 8 5 7e6 8 6 46858

with more convincing results obtained for hydrogen concen-

trations below 30% [6e8]. Computational studies show that

hydrogen increases effective engine efficiency of a diesel en-

gine mainly due to the differences of entropy between

hydrogen and hydrocarbon fuel combustion [9]. The addition

of hydrogen reduces the irreversibility produced by diesel oil

combustion for dual fuel operation, resulting in increased ef-

ficiency. Engine load has a major impact on effective engine

efficiency when low amounts of hydrogen are used together

with diesel oil [10].

Indirect injection of hydrogen in the intake manifold pro-

duces 22% higher effective engine efficiency at high loads and

5% higher effective engine efficiency at low loads, in com-

parison with direct injection of hydrogen in the combustion

chamber [11]. Both injection modes allow for the use of up to

38% of hydrogen as a replacement to diesel oil without loss of

effective engine efficiency.With indirect hydrogen injection, it

requires at least 30% of diesel oil to operate an engine at high

load [12].

The ignition delay strongly influences combustion stabil-

ity, effective engine efficiency and exhaust emissions. In a

diesel engine operating with diesel oil and hydrogen the

ignition delay depends on cylinder pressure, temperature and

hydrogen concentration [13]. The ignition delay of hydrogen is

higher than that of diesel oil, due to the higher octane number

and self-ignition temperature of hydrogen [1]. For direct in-

jection of hydrogen in the combustion chamber increased

injector orifice diameter reduces the ignition delay of

hydrogen-air mixtures. The mass flow rate of hydrogen de-

pends linearly on the injector orifice cross-sectional area. The

injection pressure influences jet penetration, the dispersion

angle and mixture equivalence ratio.

Other advantages associated to the use of hydrogen as a

partial replacement to diesel oil are reduced ignition failure

and faster burning speed [14]. Peak cylinder pressure is

reduced [11,15], but exhaust gas temperature is increasedwith

the use of hydrogen [16,17]. Reduced fuel consumption by the

use of hydrogen in a diesel engine has also been reported

[8,11,18]. The use of EGR combined with indirect injection of

hydrogen can reduce diesel oil consumption while increasing

combustion rate and effective engine efficiency [7,19,20].

With regard to exhaust emissions different effects of

hydrogen on diesel engines have been found. While hydrogen

is expected to reduce unburned hydrocarbons (HC) [14], car-

bon monoxide (CO) and carbon dioxide (CO2) emissions

[8,11,18] as it does not contain the carbon element in its

molecule, increased HC [18], CO and CO2 [10,14,17] emissions

have also been found by the use of hydrogen, attributed to the

reduced availability of oxygen. The lean burn of hydrogen-air

mixtures would reduce cylinder peak temperature and,

consequently, oxides of nitrogen (NOx) emissions [4e8]. In

spite of that, increased NOx emissions were also found with

the use of hydrogen as a partial replacement to diesel oil

[17,18].

Reduced sulfur dioxide (SO2) and soot emissions have been

observed by the use of hydrogen in diesel engines [8,11,18].

The use of EGR in diesel engines with direct or indirect in-

jection of hydrogen could further reduce NOx emissions,

together with CO, CO2, soot and particulate matter emissions

[7,19e21].

This work investigates the use of hydrogen as a partial

substitute to diesel oil as fuel for a diesel power generator.

Specifically, the influence of hydrogen on the overall fuel

consumption, specific fuel consumption, effective engine ef-

ficiency, volumetric efficiency, and carbon dioxide emissions

is analyzed. The investigation aims at giving further insight on

the possible benefits that can be brought by hydrogen for

stationary engine operation.

2. Experimental section

A diesel power generator of 50 kW of nominal power was used

in the experiments. The power generator was constituted by a

four-cylinder, direct injection, naturally aspirated diesel en-

gine. Table 1 shows themain characteristics of the engine and

the electric generator. The diesel oil direct injection system

was made of a mechanical fuel pump and four injectors. The

original diesel oil injection systemwas not altered for the tests

with hydrogen.

A hydrogen injection system was adapted to the engine

intake system (Fig. 1). Four orifices were drilled in the intake

manifold to install the injection pipes, located 130 mm from

the intake valve and with inclination of 45� to the intake air

main stream. These dimensionswere similar to those adopted

by [22]. The injection system adapted to the intakemanifold is

a production unit for a flexible fuel vehicle originally devel-

oped to inject natural gas, containing a distribution rail and

four injectors. Table 2 shows the characteristics of the

hydrogen injectors. The hydrogen injection system location

does not cause any important interference on the intake

system in case of engine operation with diesel oil only.

To verify that the hydrogen injection system provides

uniform distribution to all cylinders, preliminary tests were

performed with one operating injector at a time, while the

other three injectors were disabled. The injected hydrogen

H2 injection system

130 mm

H2

H2

(a)

(b)

(c)

Fig. 1 e (a) Schematics of H2 injection system positioning,

(b) H2 injectors installed in the intake manifold and (c) H2

injection system installed in the engine.

Table 2 e Characteristics of the hydrogen injectors.

Parameter Value

Total length 47 mm

Total mass 0.035 kg

Valve body material Stainless steel

Solenoid valve material Copper

Operation temperature �40 �Ce130 �CMinimum voltage 6 V

Nominal voltage 12 V

Jet type Single stream

Number of holes 1

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 8 ( 2 0 1 3 ) 6 8 5 7e6 8 6 4 6859

mass flow rate was monitored, and it was verified to be the

same for all injectors at a common operating condition. Since

the fuel was multiport injected, that is, there was one injector

located at each engine cylinder intake port, it assured that the

fuel mass injected at a specific cylinder port would reach that

cylinder.

In order to control hydrogen injection, a dedicated elec-

tronic control unit (ECU) was developed. The hydrogen ECU

was fed by the signal from an engine speed magnetic sensor

facing a phonic wheel installed on the engine crankshaft. The

hydrogen ECU contains a microcontroller programmed in

Assembly language to control the injection timing, according

to the signal from the engine speed sensor. The hydrogen

volume injected to each cylinder is controlled by the opening

period of the injector. The data loaded in the microcontroller

memory perform the communication between the injection

system and an electrical transducer to read the engine load

power. Any change on the load demand is interpreted by the

microcontroller for instantaneous adjustment of the injector

opening period.

According to the required hydrogen flow rate through the

injector, three different injection pressures were adopted. For

flow rates between 0.035 kg/h and 0.11 kg/h, corresponding to

injector opening periods from 1.4 ms to 12.4 ms, the injector

manometric pressure was set to 2 kPa. For flow rates between

0.11 kg/h and 0.39 kg/h, corresponding to injector opening

periods from 1.4 ms to 14.4 ms, the injector manometric

pressure was adjusted to 25 kPa. Finally, for flow rates be-

tween 0.39 kg/h and 0.69 kg/h, corresponding to injector

opening periods from 5.7 ms to 13.6 ms, the injector mano-

metric pressure was set to 70 kPa. These settings allowed for

substitution from 5% to 20% of diesel oil by hydrogen on en-

ergy basis.

The measured data was acquired by a data and acquisition

control system built in LabVIEW software. The intake air mass

flow rate was measured through an orifice plate, built and

positioned according to ISO 5167/2003 standard, with uncer-

tainty of �2.3 kg/h. Temperature was measured through K-

type thermocouples and Pt-100 sensors positioned in several

locations: orifice plate inlet, intake pipe, exhaust pipe, cooling

water inlet, cooling water outlet, crankcase, diesel oil tank,

hydrogen supply line and ambient. The uncertainty of the

measured exhaust gas temperature was �14.9 �C; the

remaining temperatures were measured with an uncertainty

of �1.8 �C. Ambient pressure was measured through a Torri-

celli barometer with resolution of 1.3 kPa, and the ambient

humidity was measured through a thermo-hygrometer with

uncertainty of �2.5% of reading. The concentrations of CO2

and O2 were measured by a non-dispersive infrared analyzer,

with uncertainties of �0.3% and �0.1%, respectively.

The volumetric efficiency is defined by the ratio between

the actual intake air mass flow rate and the air flow rate that

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

HYDROGENCONSUMPTION(kg/h) B5H5

B5H10B5H15B5H20

Fig. 2 e Variation of hydrogen flow rate with load power

and hydrogen concentration in the fuel.

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 8 ( 2 0 1 3 ) 6 8 5 7e6 8 6 46860

would fill the engine cylinders at the reference condition of

1.013 bar, 25 �C [23]:

hV ¼ _mair

rair;refVdðu=2Þ (1)

where _mair is the actual intake air mass flow rate, rair;ref is the

air density calculated at the reference condition,Vd is the total

engine displaced volume and u is the crankshaft speed.

Diesel oil consumption was measured through a digital

platform scale placed under the fuel tank, with uncertainty of

�0.13 kg/h. The quantification of diesel oil consumption was

given by the time variation of the fuel mass in the tank:

_mB5 ¼ dmtank

dt(2)

where _mB5 is the diesel oil mass flow rate, mtank is the fuel

mass in the tank and t is the time.

The specific fuel consumption is defined as the fuel

amount required per unit power [23]:

SFC ¼ _mB5 þ _mH2

�QLHV;H2

=QLHV;B5

�

_W(3)

where SFC is the specific fuel consumption, _mB5 is the diesel oil

mass flow rate, _mH2is the hydrogen mass flow rate, QLHV;B5 is

the low heating value of diesel oil, QLHV;H2is the low heating

value of hydrogen and _W is the engine output power.

The hydrogen mass flow rate is calculated from the diesel

oil mass flow rate replaced on energy basis as follows:

_mH2¼ _mB5;repQLHV;B5

QLHV;H2

(4)

where _mB5;rep is the diesel oil mass flow rate replaced by

hydrogen.

The effective engine efficiency is given by the ratio be-

tween the load power and the energy available in the fuel

amount injected [23]:

hF ¼_W

_mB5QLHV;B5 þ _mH2QLHV;H2

(5)

where hF is the effective engine efficiency.

The air/fuel ratio (A/F) is calculated by the ratio between

the intake air mass flow rate and the diesel oil flow rate plus

the flow rate of diesel oil replaced by hydrogen:

AF¼ _mair

_mB5 þ _mH2

�QLHV;H2

=QLHV;B5

� (6)

N.2dieseloilwasused inthiswork, containing5%ofbiodiesel

(B5), predominantly methyl ester from soybean (>86%). For B5

the low heating value adopted was 43.2 MJ/kg, and, for

hydrogen, the lowheatingvalueusedwas120MJ/kg [23]. For the

tests the diesel oil was replaced by hydrogen at the concentra-

tions of 5% (B5H5), 10% (B5H10), 15% (B5H15) and 20% (B5H20).

Hydrogen flow rate was measured through a diaphragm

volumetric flow rate measuring device with reading range

from 0.060m3/h to 10m3/h andmaximumpressure of 100 kPa.

Temperature and pressure sensors were installed in the

hydrogen feeding line. Hydrogen pressure was first reduced

from the storage cylinder to the feeding line through a pri-

mary pressure regulator and, then, to the adjusted injection

pressure through a secondary pressure regulator. The injec-

tion pressure was monitored through a digital manometer

with resolution of 0.1 kPa. A plenum chamber was installed

between the secondary pressure regulator and the injectors to

attenuate pressure waves.

The load applied to the engine was produced by a bank of

electric resistances located outside the test cell. The

maximum load bank capacity was 50 kW at 200 V, with

reduced inductance so that the reactance at 60 Hz could be

neglected. The bank of resistances allowed for load applica-

tion in minimum steps of 2.5 kW. The load applied to the

engine was controlled by the data acquisition and control

system developed in LabVIEW software.

The tests were carried out at steady state condition with

decreasing load, from the nominal power of 40 kWe0 kW.

Before acquiring the data at each load set the engine was kept

operating for at least 3 min, to make sure the exhaust gas

temperature and the coolant temperature were unchanged.

Three tests were performed for each fuel and operating con-

ditions in different days. The results shown in the following

section represent the average of the tests. The uncertainties of

the parameters investigated were calculated by the method-

ology presented by [24] and are shown as error bars in the

figures.

3. Results and discussion

Fig. 2 shows the variation of the hydrogen flow rate through the

injector with engine load power for the different hydrogen

concentrations in the fuel. For given hydrogen concentration in

the fuel, increasing hydrogen amount is injected to attend the

load demand. However, the hydrogen proportion injected is

not kept constant with increasing load for the different con-

centrations. With increasing hydrogen concentration in the

fuel, the hydrogen amount injected increases proportionally.

The hydrogen amount injected in the intake system affects

the intake air flow rate to the engine. It can be seen through

Fig. 3, which shows decreasing volumetric efficiency with

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

55.0

56.0

57.0

58.0

59.0

60.0

61.0

62.0

63.0

64.0VOLUMETRICEFFICIENCY(%)

B5B5H5B5H10B5H15B5H20

Fig. 3 e Variation of volumetric efficiency with load power

and hydrogen concentration in the fuel.

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

DIESELOIL(B5)CONSUMPTION(kg/h) B5

B5H5B5H10B5H15B5H20

Fig. 5 e Variation of diesel oil consumption (B5) with load

power and hydrogen concentration in the fuel.

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 8 ( 2 0 1 3 ) 6 8 5 7e6 8 6 4 6861

increased engine load and hydrogen content in the fuel. With

increasing load heat release from the engine is also increased,

thus increasing the intake system temperature. As a conse-

quence, the intake air density is decreased, thus decreasing

the volumetric efficiency. Increasing amount of hydrogen in

the intake system limits the air amount admitted into the

engine, thus reducing the volumetric efficiency. The

maximum reduction on volumetric efficiency was 6%, with

the use of 20% of hydrogen (B5H20). Reference [16] reports

reduced volumetric efficiency by 12% with the use of around

9% of hydrogen as a substitute to diesel oil. These figures are

affected by engine model and operating conditions.

Fig. 4 shows that the air/fuel ratio is decreased with

decreasing load for all fuels. This trend is influenced by both,

decreasing volumetric efficiency with increasing load (Fig. 3)

and increasing fuel flow rate with increasing load (Figs. 2 and

5). No significant changes on air/air fuel ratio are noticed

when hydrogen is added to the fuel at the concentrations

investigated.

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

10

20

30

40

50

60

70

80

90

AIR/FUELRATIO

B5B5H5B5H10B5H15B5H20

Fig. 4 e Variation of air/fuel ratio with load power and

hydrogen concentration in the fuel.

Fig. 5 shows increased diesel oil consumption with

increasing engine load power for all fuels tested. As expected,

increasing hydrogen concentration in the fuel reduces diesel

oil consumption. Higher reductions of diesel oil consumption

are observedwith the use of low amounts of hydrogen (5% and

10%) at high loads. With 35.7 kW of load power the use of 20%

of hydrogen (B5H20) reduced diesel oil consumption by 16.1%.

At the same load, the use of 5% of hydrogen (B5H5) reduced

diesel oil consumption by 6.9%. With no load (0 kW) the use of

hydrogen at any concentration did not change significantly

the consumption of diesel oil.

The specific fuel consumption variation with engine load

power and hydrogen concentration in the fuel is shown by

Fig. 6. In general, for all hydrogen concentrations tested, the

specific fuel consumption decreases with increasing load

power until reaching a minimum value at around three

quarters of the rated power (approximately 30 kW), then it

rises again. The addition of hydrogen to the fuel did not cause

significant changes in the specific fuel consumption, with

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

0.200

0.250

0.300

0.350

0.400

0.450

0.500

0.550

0.600

0.650

SPECIFICFUELCONSUMPTION(kg/h)

B5B5H5B5H10B5H15B5H20

Fig. 6 e Variation of specific fuel consumption with load

power and hydrogen concentration in the fuel.

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

100

200

300

400

500

600

EXHAUSTGASTEMPERATURE(OC) B5

B5H5B5H10B5H15B5H20

Fig. 8 e Variation of exhaust gas temperature with load

power and hydrogen concentration in the fuel.

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 8 ( 2 0 1 3 ) 6 8 5 7e6 8 6 46862

exception to the load power of 4.8 kW and hydrogen concen-

tration of 20% (B5H20). In this case a reduction of 6.4% on the

specific fuel consumption was obtained, in comparison with

operation with diesel oil (B5).

The variation of effective engine efficiency with engine

load power and hydrogen concentration in the fuel is shown

by Fig. 7. The trends produced by the results are inversely

proportional to those observed for specific fuel consumption

(Fig. 6), as indicated by Eqs. (3) and (5). Effective engine effi-

ciency is increased with increased load power until reaching a

peak at around three quarters of the rated load power (about

30 kW), and then it decreases for higher loads. Here, the

addition of hydrogen to the fuel does not significantly change

the effective engine efficiency of B5 throughout thewhole load

range investigated.

The trends revealed for the effective engine efficiency

(Fig. 7) explain those observed for hydrogen consumption

(Fig. 2), diesel oil consumption (Fig. 5) and specific fuel con-

sumption (Fig. 6). The decrease of effective engine efficiency

noticed for loads above three quarters of the rated load (Fig. 7)

means that heat losses are increased at those conditions.

Thus, to produce the power demanded and overcome the heat

losses at those conditions fuel consumption is increased (Figs.

2 and 5). That has a direct effect on the specific fuel con-

sumption, which also increases at high loads (Fig. 6).

The results obtained for specific fuel consumption (Fig. 6)

and effective engine efficiency (Fig. 7) are, at a first view, in

disagreement with many authors who found that the use of

hydrogen in diesel engines decreases the first and increases

the latter [4e9,11,18]. However, it was observed that engine

load and speed has a significant effect on specific fuel con-

sumption with varying load and engine speed [10,25]. It has

been found that the partial substitution of diesel oil by low

amounts of hydrogen can reduce the specific fuel consump-

tions for a range of engine speeds [25]. However, at engine

speeds close to 1800 rev/min no significant changes on specific

fuel consumption were noticed, which is the case of the pre-

sent work. At this condition it seems that some positive

characteristics of hydrogen that favors specific fuel con-

sumption and effective engine efficiency, such as faster

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

0

5

10

15

20

25

30

35

40

FUELCONVERSIONEFFICIENCY(%)

B5B5H5B5H10B5H15B5H20

Fig. 7 e Variation of effective engine efficiency with load

power and hydrogen concentration in the fuel.

burning speed than diesel oil [14], are counterbalanced by

negative aspects such as higher ignition delay [1].

The increased exhaust gas temperature with increasing

load shown by Fig. 8 is a consequence of higher fuel amount

injected to be burned (Figs. 2 and 5), thus taking combustion

longer to be completed [23]. No significant change on the

exhaust gas temperature with the use of hydrogen was

noticed in the load range investigated (Fig. 8). That is an

indication that combustion durationwas not strongly affected

by hydrogen. At the conditions of the tests, the effects of the

faster burning speed of hydrogen [14] seems to have been

canceled by its longer ignition delay [1], in comparison with

diesel oil. Similarly to the exhaust gas temperature (Fig. 8),

Fig. 9 shows no significant change on exhaust oxygen con-

centration when hydrogen is used as a complementary fuel to

diesel oil. Oxygen concentration in the exhaust gas is

decreased with increasing load, as its consumption is

increased to burn the increased fuel amount injected (Figs. 2

and 5).

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

5.0

7.5

10.0

12.5

15.0

17.5

20.0

O2(%)

B5B5H5B5H10B5H15B5H20

Fig. 9 e Variation of exhaust oxygen emissions with load

power and hydrogen concentration in the fuel.

0 5 10 15 20 25 30 35 40LOAD POWER (kW)

0.0

2.0

4.0

6.0

8.0

10.0

12.0CO2(%)

B5B5H5B5H10B5H15B5H20

Fig. 10 e Variation of exhaust carbon dioxide emissions

with load power and hydrogen concentration in the fuel.

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 8 ( 2 0 1 3 ) 6 8 5 7e6 8 6 4 6863

In Fig. 10, carbon dioxide production is increased with

increasing load because of mixture enrichment, making it

closer to the stoichiometric condition, where CO2 concentra-

tion would reach its maximum value. As the diesel engine

operates with approximately the same intake air flow rate for

a fixed crankshaft speed at the different loads, the increased

fuel flow rate to supply increasing power demand (Figs. 2 and

5) makes the engine operate with less air excess (Fig. 9). The

use of hydrogen reduces CO2 emission because it does not

contain the carbon element in its molecule, in opposition to

diesel oil, that is composed by different hydrocarbons. At any

engine load, carbon dioxide emission is reduced as hydrogen

concentration in the fuel is increased. This result had also

been observed by [8,11,18], and it indicates that the use of

hydrogen as diesel engine fuel can be an attractive strategy to

reduce global warming effects.

Overall, the results suggest that the use of hydrogen does

not bring benefits on fuel consumption for stationary appli-

cation of diesel engines with mechanical control of diesel oil

injection. As the engine was operated with no modification in

its original setting, the mixture ignition was dictated by the

diesel oil mechanical injection system. Maybe improvements

can be obtained with the use of electronic diesel oil injection

systemwhen operating with hydrogen. Alteration of diesel oil

injection timing for dual fuel operation with hydrogen can be

a way to further increase effective engine efficiency and

reduce exhaust pollutant emissions [6,7]. Retarded injection

timing of diesel oil has previously shown advantages for dual

fuel operation of diesel oil and hydrogen, in comparison with

operation with diesel oil only [26]. A positive consideration is

that application of hydrogen in stationary diesel engines can

be a useful technique to reduce CO2 emissions and, conse-

quently, global warming effects.

4. Conclusions

The use of up to 20% of hydrogen as a replacement fuel to

diesel oil has provided safe operation and did not require

modifications of the engine original settings. Fuel consump-

tion and effective engine efficiency were not affected when

hydrogen was used as a complementary fuel to diesel oil

stationary engine operation with unmodified diesel oil injec-

tion settings. Optimized injection settings could have led to

different results, as it has previously been shown by other

authors [6,7,26]. Maximum fuel consumption reduction and

effective engine efficiency were observed at about three

quarters of the rated engine power for all hydrogen concen-

trations used. The application of hydrogen as fuel reduced

carbon dioxide emissions by up to 12%. This indicates the

employment of hydrogen as a useful strategy to reduce the

global warming impacts of engine exhaust gas. That will

depend on the hydrogen source and the amount of upstream

CO2 associated with hydrogen production.

Acknowledgments

The authors thank CEMIG GT-292 Research Project for the

financial support to this work.

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