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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: [email protected]
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.
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