ON THE POSSIBILITY TO IMPROVE COMMERCIAL

VEHICLE SI ENGINE OPERATION WHEN FUELED BY

HYDROGEN DIRECT INJECTION

*Alexandru RACOVITZA a, Bogdan RADU a, Radu CHIRIAC a ,

a University POLITEHNICA Bucharest, 313 Splaiul Independentei, sect.6, Bucharest 060042, Romania

Dept. of Thermodynamics, Engines, Thermal and Refrigerant Systems

*Corresponding author: alexandru_racovitza@yahoo.com

Abstract. The use of the spark ignition engines for passenger cars under the more and more restrictive and difficult in

reaching emissions legislation standards seams to become attractive for the next period. The new technologies of fueling

and air-fuel mixtures formation as stratified charges by gasoline and hydrogen in-cylinder direct injection, associated

with methods of downsizing and downspeeding offer new perspectives to increase spark ignition engines efficiency. H2-

O2 type fuels, with low spark-energy requirement, wide flammability range and high burning velocity maintain as

important candidates for being used as fuels in spark-ignition engines, also offering CO2 and HC free combustion and

lean operation resulting in lower NOx emissions. The present work is linked to a research project dedicated to the

characteristics simulation study of a commercial Renault K7M710 engine fueled with Hydrogen using Direct Injection,

by applying AVL BOOST simulation code. Keywords: SI Engine, Gasoline and Hydrogen Direct Injection, Efficiency, Low Emissions.

1. INTRODUCTION

With the introduction of more restrictive

emissions legislation and fuel economy standards,

significant effort is being made to improve spark

ignition gasoline engines efficiency because of

their dominant use for passenger cars and better

potential for market adaptation. Modern trends

adopted by SI engines manufacturers are related to

the use of gasoline direct injection (GDI)

combined with downsizing and downspeeding

concepts in order to reduce fuel consumption

despite the obvious constrains of excessive thermal

and mechanical loads, leading to knocking

combustion and low-speed pre-ignition. To

overcome these effects, one distinctive category of

studies is related to variable valve timing (VVT)

cycle operation using variable valves overlap with

every engine speed regime [5].

A reduction of the main exhaust emissions

levels has been experimented applying exhaust gas

recirculation (EGR) when operating a

turbocharged SI engine using gasoline direct

injection (GTDI). At high load conditions similar

analysis and conclusions to the partial load ones

are obtained. The EGR also allowed the

combustion to be phased in a more efficient angle

by reducing the risk of knocking, which helped

reduce the exhaust gas temperature, despite the

elimination of the fuel enrichment strategy. A

reduction on CO and soot raw emissions was also

obtained when introducing EGR, as at partial load

conditions, but a high reduction in NOx, CO, HC

and soot emissions was observed after the catalyst

since the fuel enrichment strategy is eliminated

when cooled EGR is introduced. Results confirm

that introducing EGR is a suitable strategy to

control knocking and reduce simultaneously

exhaust gas temperature and fuel consumption [6].

With the increasing use of direct injection,

particulate emissions from gasoline engines have

also become a subject of exhaust emission

legislation. A key focus is on considering the

health effects of particles and their accumulated

components, such as polycyclic aromatic

hydrocarbons (PAH) [7]. The recent introduction

of a Particle Number (PN) limit of 6×1011 km−1 for

all Direct Injection Gasoline (GDI) vehicles

registered in Europe after September 2017, is

expected to necessitate a widespread application of

Gasoline Particulate Filters (GPF) [8].

Among other fuels alternatively used in SI

direct injection engines, hydrogen and hydro-

oxygenated compounds improve the combustion

characteristics in terms of better brake thermal

efficiency (BTE) and emissions levels. An

experimental investigation on effects of hydrogen

fractions (less equal to 11% by mass) on lean burn

combustion and emission characteristics of SI

gasoline engine was conducted on a modified

premixed gasoline engine equipped with a

hydrogen direct-injection system, under values of

relative air-fuel ratio in-between 1.0 and 1.5. With

the increasing hydrogen addition fraction, the

combustion speed increases, mean effective

pressure and thermal efficiency are improved.

Moreover, flame development and propagation

duration are shortened, the peak firing pressure

increases and its corresponding crank angle also

increases, together with the maximum rate of heat

release, the maximum mean gas temperature and

the maximum rate of pressure rise, leading to HC

and CO emissions decrease and oppositely to NOx

emission increase. As known, hydrogen direct

injection does not reduce volumetric efficiency,

therefore engine power performance improves. The

addition of hydrogen enables stable combustion at

1.5 relative air-fuel ratio and the BTE increases,

along with a significant reduction in CO and NOx

[9].

Hydrogen fuel source could be provided by

exhaust gas reforming by thermochemical energy

recovery technology with potential to improve

gasoline engine efficiency. The principle relies on

achieving energy recovery from the hot exhaust

stream by endothermic catalytic reforming of

gasoline and a fraction of the engine exhaust gas.

The reformatted hydrogen is routed back by

recirculation into the intake manifold, the method

being known as reformed exhaust gas recirculation

(REGR) [10]. An experimental research where

gasoline-air mixture was enriched with Hydrogen

Rich Gas (HRG) produced by electrical

dissociation of water has been carried out on a

passenger car SI engine at light and partial loads.

Thus, the addition of HRG has been deduced to

have a positive effect on the global combustion

process, reducing CO and HC emissions while the

maximum relative air-fuel ratio value of 1.2 was a

limit imposed by engine running stability [11].

Moreover, a following investigation was conducted

to establish the effects of adding HRG to a LPG

fuelled SI engine, pushing up to even leaner limits

the air-fuels mixtures (1.65). The new HRG gas

had been obtained by a special alkaline dynamic

electrolysis of water, under high process

efficiency. Its chemical analysis shown the

presence of 64...67% (vol.) H2, 31...33% O2 and

0...5% other H2-O2 constituents. The results

highlighted that HC, CO and CO2 emissions

decreased, while NOx generally remained high

[12].

In another study it was experimentally

investigated the effect of hydroxygen (H2+O2)

addition on performance and emissions of a

gasoline engine. Flow rate of hydroxygen gas

mixture was adjusted to 0%, 3.75% (2.5%

H2+1.25% O2) and 7.5% (5% H2+2.5% O2) by-

volume of intake charge for entire speed range of

the engine and subsequently water was injected

into the intake manifold of the SI engine to

decrease NOx emissions which were significantly

increased with hydroxygen addition. Mass flow

ratio of water with respect to gasoline was kept

constant as 0.25/1. According to the tests, carried

out at 50% load and engine speeds between 1500

and 5000 rpm, total hydrocarbons, oxides of

nitrogen and carbon monoxide were measured and

COVimep, brake power, brake thermal efficiency

and BSFC were calculated. Thus, brake power,

brake thermal efficiency and nitrogen oxides were

increased up to 11.7%, 5.9% and 141.1%, whereas

COVimep, BSFC, total hydrocarbons and carbon

monoxide were decreased down to 15.2%, 5.6%,

74.5% and 59.5%. The maximum increase of NOx

emission with hydroxygen addition was decreased

from 141.1% to 82.7% with water injection [13].

2. PROPOSED SI ENGINE MODIFICATIONS

FOR GASOLINE AND H2 INJECTION

The simulation research assisted by AVL Boost

software package [4] started from the features of a

commercial passenger car SI engine, the Renault-

Logan K7M710 1.6L type, which has been

converted to a turbocharged and direct injection

configuration in order to reveal the comparison

between both performance and efficiency

characteristics. The analysed engine, naturally

aspirated and provided with a multipoint indirect

fuel injection system initially featured: 4 cylinders

in-line, 79.5 mm bore, 80.5 mm stroke, 9.5:1

compression ratio, 1595 cm3 total displacement,

maximum power of 64 kW at 5500 rpm, maximum

torque of 128 Nm at 3000 rpm.

The modifications brought to the initial engine

consisted in installing a turbocompressor group,

switching from indirect injection to direct

injection, together with decreasing the compre-

ssion ratio and slightly increasing the maximum

engine speed. Considering these, the new obtained

turbocharged direct injected engine highlighted: 96

kW rating power at 6000 rpm, 145 Nm rating

torque at 4500 rpm, 4-in-line cylinders, 79.5 mm

bore, 82.5 mm stroke, 9:1 compression ratio, 1597

cm3 total displacement, a configuration very

similar to Ford Escort RS 1.6 l Turbo [14,15]. The

compressor delivers to the engine 1.6 bar

turbocharging pressure and the maximum pressure

for gasoline direct injection is 100 bar in

comparison with 67 bar for the original engine.

Modelling the processes from the turbo-

compressor group implies the use of the AVL

Boost v.2013.1 computer programs. The equations

refer to the conservation of the global energy

exchanged from the inside to the outside of the

cylinder and to the heat and mass flows through

the inlet and outlet systems. At this point, a Wiebe

type relation has been proposed to describe the

heat release from the cylinder and a Woschni type

formula (1990) to express the heat transfer to the

cylinder surroundings. The mass flow is given by

the equations of sonic and subsonic flow through

the valves as by the injection characteristic

imposed to the gasoline injector [14,15]. The

schematic of the entire functional engine resulted

from the analysis of all system components and

connecting elements is shown in Fig.1.

The above described engine configuration is

further modified in order to find the most effective

strategy to ensure H2 direct injection together with

the gasoline direct injection. The theoretical

schematic of the engine to be fuelled in parallel

with gasoline and hydrogen by parallel direct

injections is plotted in Fig.2 [15,16,17].

The simulation of both engines performances

using the AVL Boost software package [4] allows

the direct comparison of the rating power, rating

torque, indicated mean pressure (IMEP) and brake

specific fuel consumption (BSFC) for a range of

engine speeds within 750 rpm and 5500 rpm.

Figure 3 shows the variation of the effective

power versus the engine speed. Comparing these

values, a continuous increase could be noticed for

the turbocharged engine for all the analysed speed

range, from 30% at 1000 rpm, to 48% at 3000 rpm

and to 54% at 5500 rpm. At 5000 rpm, for the

direct injection engine, the rated power was 97

kW, compared to 64 kW, which is the top value for

the original engine.

The maximum torque highlighted value, for the

modified engine is 181 Nm at 3100 rpm, while in

the case of the original K7M710 engine the corresponding top value is 128 Nm at 3000 rpm

[14,15]. For the modified engine, at full load and

5500 rpm engine speed, the peak pressure value is

81 bar and the IMEP is 15.4 bar, while in the case

of the original engine, the maximum pressure is 67

bar and the IMEP is 10.6 bar.

Fig. 1. GDI turbocharged engine (AVL BOOST schematic)

Fig. 2. Schematic of SI Engine fueled by gasoline and

hydrogen direct injection

3. RESULTS OBTAINED BY GASOLINE

AND HYDROGEN SI ENGINE FUELING

The theoretical simulation work has been

completed in order to reveal the potential of using

small to high hydrogen fractions (2,5,10,20,50 and

100% mass.) in SI direct injection engine regarding

the increase of its performances and efficiency

together with the drop of the main emissions. The

first conclusions are encouraging the use of high

percentages of hydrogen within the full range of

engine speeds, theoretically being verified that the

higher the hydrogen fractions are used the better

the engine operational results become.

Figure 3 shows the variation of the rating power

for several used hydrogen mass fractions, at full

load, within the entire scale of engine speeds. What

is to be remarked is the significantly increase of

the power with the increase of the Hydrogen

percentage. As a result, starting with the use of

small amounts of H2 up to 100% gasoline

replacement, comparing to G100 (no Hydrogen),

the gain of power is from 1.3 % at 2% H2 until

28.3% at H100 (only Hydrogen).

This increase of the power is based both on the

increase of the BMEP values, which rise in

percents from 1.3% at 2% H2 to 28.3% at H100.

(see Fig.4) and on the increase of the maximum

firing pressure values, increasing from 0.7 % at 2%

H2 until 16.3% at H100 (see Fig.5). These

variations are subsequent to that of the maximum

rate of the firing pressure, which could be always

kept under a maximum limit of approximately 5

bar/deg.CA, being avoided a rough engine running

(see Fig.6).

The variation of the rated torque with the

engine speed at full load respecting the chosen H2

mass fractions could be also explained by the

variation of the top firing pressure, being

connected with that of BMEP and overall

influenced by the variation of the rated power. As

Figure 7 shows, for all hydrogen fractions the

calculated values for the torque maintain the

trendline of the values for G100, with the top value

corresponding to 3000 rpm. Like the rated power

values, the rated torque values increase in percents

from 1.3% at 2% H2 proportion to 28.3% at H100.

Fuel economy is well improved by the use of

greater hydrogen mass fraction because of its much

higher lower heat value (LHV) comparing to that

of gasoline. The increasing obtained rating powers

together with the higher energetic fuel fractions

lead to significant reduction of BSFC. Its minimum

value for G100 (no hydrogen) is obtained at 2000

rpm, same engine speed for all the bottom values

of BSFC, independently of the hydrogen used

fraction. In percentages, the minimum BSFC drops

continuously by hydrogen substitution as for

example with 4% when the substitution degree is

2% up to 65% when gasoline is completely

replaced by hydrogen - 100% H2 (see Fig.8). Such

important reduction in BSFC is equivalent to an

increase in the engine brake efficiency of only 20%

due to the important difference existing in the

lower heating values of the two pure fuels.

The main types of SI engine emissions

(especially CO and NOx) are decreasing by using

higher amounts of hydrogen, this being one of the

basic goals assumed by this simulation work.

Regarding the variation of NOx concentration

from the exhaust gas, this is varying from a

reduction by 2% at 2% H2 fraction to a maximum

decrease of 46% at H100, compared to the use of

gasoline only (as revealed in Fig. 9).

Although the numbers dispersion is high, the

main effect of using higher H2 percentages also

occurs in reducing the CO concentration even at

high engine speeds, being practically eliminated

when using H100 (see Fig.10).

Pe [kW]

20

30

40

50

60

70

80

90

100

110

120

130

0 1000 2000 3000 4000 5000 6000

n [rpm]

Pe G100%

Pe G98%H2%

Pe G95%H5%

Pe G90%H10%

Pe G80%H20%

Pe G50%H50%

Pe H100%

H100%

G50% H50%

G80%H20%

G98%H2%

G90%H10%

G100%

Fig. 3. Variation of the rated power vs. engine speed at full load

BMEP [bar]

12

13

14

15

16

17

18

19

20

21

22

0 1000 2000 3000 4000 5000 6000

n [rpm]

BMEP G100%

BMEP G98%H2%

BMEP G95%H5%

BMEP G90%H10%

BMEP G80%H20%

BMEP G50%H50%

BMEP H100%

H100%

G50%H50%

G80%H20%

G95%H5%

G100

Fig. 4. Variation of BMEP vs. engine speed at full load

pmax [bar]

75

80

85

90

95

100

105

110

0 1000 2000 3000 4000 5000 6000

n [rpm]

pmax G100%

pmax G98%H2%

pmax G95%H5%

pmax G90%H10%

pmax G80%H20%

pmax G50%H50%

pmax H100%

H100%

G50%H50%

G80%H20%

G95%H5%

G98%H2%

G100%

Fig. 5. Variation of the maximum firing pressure vs. engine speed at full load

dp/da max [bar/deg]

2.8

3

3.2

3.4

3.6

3.8

4

4.2

4.4

4.6

4.8

5

5.2

0 1000 2000 3000 4000 5000 6000

n [rpm]

dp/da max G100%

dp/da max G98%H2%

dp/da max G95%H5%

dp/da max G90%H10%

dp/da maxG80%H20%

dp/da max G50%H50%

dp/da max H100%

H100%

G50%H50%

G80%H20%

G95%H5%

G100%

G90%H10%

Fig. 6. Variation of the maximum firing pressure rate vs. engine speed at full load

Me [Nm]

140

160

180

200

220

240

260

280

300

0 1000 2000 3000 4000 5000 6000

n [rpm]

Me G100%

Me G98%H2%

Me G95%H5%

Me G90%H10%

Me G80%H20%

Me G50%H50%

Me H100%

H100%

G50%H50%

G80%H20%

G90%H10%

G95%H5%

G100%

Fig. 7. Variation of rated torque vs. engine speed at full load

BSFC [g/kWh]

50

75

100

125

150

175

200

225

250

275

300

0 1000 2000 3000 4000 5000 6000

n [rpm]

BSFC G100%

BSFC G98%H2%

BSFC G95%H5%

BSFC G90%H10%

BSFCG80%H20%

BSFC G50%H50%

BSFC H100%

G100%

G98%H2%

G95%H5%

G90%H10%

G80%H20%

G50%H50%

H100%

Fig. 8. Variation of BSFC vs. engine speed at full load

NOx [g/kWh]

4

5

6

7

8

9

10

11

12

13

0 1000 2000 3000 4000 5000 6000

n [rpm]

NOx G100%

NOx G98%H2%

NOx G95%H5%

NOx G90%H10%

NOx G80%H20%

NOx G50%H50%

NOx H100%

H100%

G50%H50%

G80%H20%

G90%H10%

G95%H5%

G100%

Fig. 9. Variation of NOx vs. engine speed at full load

CO [g/kWh]

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1000 2000 3000 4000 5000 6000

n [rpm]

CO G100%

CO G98%H2%

CO G95%H5%

CO G90%H10%

CO G80%H20%

CO G50%H50%

CO H100%

G80%H20%

G98%H2%

G100%

G90%H10%

G95%H5%

Fig. 10. Variation of CO vs. engine speed at full load

4. CONCLUSIONS

The results of this study can be summarized in the following conclusions:

1. The substitution of gasoline by hydrogen in

direct injection operating mode for the spark

ignited engines could improve both maximum

power and efficiency;

2. The increase of engine output is associated

with the increase of the indicated high pressure

trace area – for similar stoichiometric mixture

operation – maintaining the maximum peak

pressure rise under a safety threshold;

3. The reduction of CO emission is encountered

for the whole engine speed range investigated, is

more pronounced with the increase of the

substitution degree and is determined by carbon

replacement with hydrogen;

4. The reduction of NOx emissions which

seems apparently surprising for higher level of

substitution degree could be explained by the

reduced oxygen mass fraction available for NO

formation resulted in the case of increased

fractions of hydrogen; this is probably determined

by the increased reactivity of hydrogen which

consumes in stoichiometric combustion a large

amount of oxygen from the same air flow rate as in

the case of pure gasoline or in the cases with reduced fractions of hydrogen.

ACKNOWLEDGMENTS

The authors of this paper acknowledge the AVL

Advanced Simulation Technologies team for its

significant support offered to them in performing the simulation part of this work.

REFERENCES

[1] Mohannadi A., Shoji M., Nakai Y., Ishikura W., Tabo, E.,

Performance and combustion characteristics of direct

injection SI hydrogen engine, International Journal of

Hydrogen Energy, 32, 296-304, 2007.

[2] Wu Z.-J., Yu X., Fu L.-Z., Deng J., Hu Z.-J., Li L.-G.,

A high efficiency oxyfuel internal combustion engine cycle

with water direct injection for waste heat recovery,

ELSEVIER Energy 70, 110-120, 2014.

[3] Klein D.J., Dica C., Georgescu C., Pamfilie C.,Chiriac R.,

Method of using lean air-fuel mixtures al all operating

regimes of a SI engine, US Patent no. US008127750B2

/March 6, 2012.

[4] AVL BOOST Theory and AVL BOOST UsersGuide,

https://www.avl.com/ro/boost

[5] Macklini D.N., Zhao H., High load performance and

combustion analysis of a four-valve direct injection

gasoline engine running in the two-stroke cycle,

ELSEVIER, Applied Energy 159,117–131, 2015.

[6] Lujan J.M., Climent H., Novella R., Rovas-Perea M.E.,

Influence of a low pressure EGR loop on a gasoline

turbocharged direct injection engine, ELSEVIER Applied

Thermal Engineering, 432-443, 2015.

[7] Überall A., Otte R., Eilts P., Krahl J., A literature research

about particle emissions from engines with direct gasoline

injection and the potential to reduce these emissions,

ELSEVIER Fuel 147, 203-207, 2015.

[8] Mamakos A., Steininger N., Martini G., Panagiota D.,

Drossionos Y., Cost effectiveness of particulate filter

installation on Direct Injection Gasoline vehicles,

ELSEVIER Atmospheric Environment 77 16-23, 2013.

[9] Du Y., Yu X., Wang J., Wu H., Dung W., Gu J.,

Research on combustion and emission characteristics of a

lean burn gasoline engine with hydrogen direct-injection,

ELSEVIER International Journal for Hydrogen Energy, 41,

3240-3248, 2016.

[10] Fennel D., Herreros J., Tsolakis A., An experimental

investigation on the performance characteristics of a

hydroxygen enriched gasoline engine with water injection,

ELSEVIER International Journal for Hydrogen Energy, 39,

5153-5162, 2014.

[11] Chiriac R., Apostolescu N., Dica C., Effects of Gasoline-

Air Enrichment with HRG Gas on Efficiency and Emissions

of a SI Engine, SAE Paper 2006-01-3431, SAE

International Congress, 2006.

[12] Birtas A., Voicu I., Niculae Gh., Racovitza A., Chiriac

R., Apostolescu N., Petcu C., Effects of LPG-Air

Enrichment with HRG Gas on Performance and Emissions

of a SI Engine, FISITA Paper no. F2010-A-064, FISITA

International Congress, 2010.

[13] Karagöz Y., Yürsuk L., Sandalci T., Dalkiliç A.S., An

experimental investigation on the performance

characteristics of a hydroxygen enriched gasoline engine

with water injection, ELSEVIER International Journal for

Hydrogen Energy, 40, 692-702, 2015.

[14] Dârţu A., A study of the performances of direct injected

turbocharged K7M710 engine, (in Romanian) Project

License, University POLITEHNICA Bucharest, July 2014.

[15] Dârţu A., Racovitza A., Chiriac R., Simulating the perfor-

mances of a DI turbocharged SI engine obtained by

converting the commercial K7M710 engine. A case study,

Automotive Engineering Revue, 8, nr.4, 2014.

[16] http://alset.at/our-solutions/

[17] http://autotehnic.files.wordpress.com/2013/08/