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2020-01-5061 Published 15 Jun 2020
An Investigation of the Replacement of E10, E85,
and Methane with Gasoline in Reactivity Controlled
Compression Ignition Combustion: A Comparison
of Alternative Fuels Using Reactivity Controlled
Compression Ignition Strategy
Sasan Shirvani, Saeid Shirvani, and Amir H. Shamekhi KN Toosi University of Technology
Citation: Shirvani, S., Shirvani, S., and Shamekhi, A.H., “An Investigation of the Replacement of E10, E85, and Methane with Gasoline in
Reactivity Controlled Compression Ignition Combustion: A Comparison of Alternative Fuels Using Reactivity Controlled Compression
Ignition Strategy,” SAE Technical Paper 2020-01-5061, 2020, doi:10.4271/2020-01-5061.
Abstract
of higher fuel consumption. Ethanol fraction resulted in better
T
he Reactivity Controlled Compression Ignition (RCCI) fuel oxidization, and lower unburned hydrocarbon (UHC)
strategy is a novel Low-Temperature Combustion and carbon monoxide (CO). The methane/diesel RCCI case
(LTC) strategy that is used to minimize nitrogen oxides had lower GTE compared to other RCCI cases, but it still
(NO ) and soot emissions to near zero. Methane and ethanol showed higher GTE than CDC. One of the main drawbacks
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blends are the most conventional alternatives to gasoline used of the methane/diesel RCCI case was the high levels of UHC
in the RCCI strategy. In this paper, a three-dimensional and CO, but fuel consumption was lower than gasoline/diesel
Computational Fluid Dynamics (3D-CFD) model was devel- RCCI. From the emissions standpoint, all RCCI cases managed
oped and validated against the experimental data at the load to meet EURO6 and EPA2010 emission mandates for NO ,
X
of 6.5 bar Indicated Mean Effective Pressure (IMEP) and soot, and CO. However, it is impossible for the CDC strategy
1300 rpm. E10, E85, and methane were replaced with gasoline to meet these regulations without adopting aftertreatments.
to investigate their effects on emissions and performance. In The CDC strategy had about 98% of the total produced NO
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order to make a fair comparison between cases, combustion and soot in all cases. On the other hand, 63% and 51% of the
phasing (CA50) and cylinder energy and boundary conditions total produced UHC and CO belonged to the methane/diesel
were considered constant. Conventional Diesel Combustion case. From the global warming concerns and carbon dioxide
(CDC) was also investigated with the constant cylinder energy (CO) perspective, the CDC case produced 547.1 g/kW-h CO
2 2
to make a comparison between all RCCI cases and CDC. while the methane case produced 350.9 g/kW-h CO . Other
2
Adding ethanol in gasoline showed that it can increase the cases (gasoline, E10, and E85) showed middle levels of CO
2
gross thermal efficiency (GTE) up to 1.3%, but at the expense by about 460 g/kW-h.
Keywords
Alternative fuels, E10/diesel RCCI, E85/diesel RCCI, Methane/
diesel RCCI, Conventional diesel combustion
1. Introduction
in the engines using the CDC strategy. Fuel economy, after-
T
ypical compression ignition engines usually operate treatments’ costs, and reaching higher performance incentiv-
with a high reactivity fuel like diesel, and combustion ized scholars to study advanced combustion strategies like
phasing can be controlled directly by injection timing. Low-Temperature Combustion (LTC) [1, 2].
Conventional Diesel Combustion (CDC) has high-tempera- In LTC strategies, combustion occurs with the high lean
ture regions, mixing-controlled regimes, and diffusion- mixture, and by eliminating high-temperature zones, NO
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limited nature, which cause high levels of nitrogen oxides and soot will decrease. Homogeneous Charge Compression
(NO ) and particulate matter (PM) emissions. These two Ignition (HCCI), Partially Premixed Compression Ignition
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emissions are hazardous to human life and can cause serious (PPCI), and Reactivity Controlled Compression Ignition
disease. Regarding these issues, stringent emission regulations (RCCI) are some examples of the LTC strategy. One of the
mandate automotive industries to implement aftertreatments most significant drawbacks of LTC strategies is being
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2 AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE
kinetically controlled; thus, they are subject to small changes low-reactivity fuel. It was found that GTE reduced and NO
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in the boundary conditions [3, 4]. emissions increased.
In the HCCI strategy, one of the firstly developed LTC Direct Dual-Fuel Stratification (DDFS) strategy is a
strategies, a fully premixed charge is inducted in the combus- promising pathway that benefits RCCI and PPCI simultane-
tion chamber and combustion is completely kinetically ously. This strategy can control the rate of heat release directly
controlled. Combustion in HCCI occurs at a short duration, by the near-TDC injection. To have more control over the
so the heat addition to the control volume is similar to the injection timing and reactivity stratification, two direct injec-
Otto cycle, the ideal cycle for engines. This fact will lead to tors are implemented in the combustion chamber. This
rapid combustion with high noise levels. Many researchers strategy has comparable thermal efficiency to RCCI, but it has
studied HCCI to achieve more authority over this strategy higher levels of soot emissions. Moreover, the DDFS strategy
and extend combustion duration [5, 6, 7]. In the PPCI strategy, has a higher exhaust temperature due to its near-TDC injec-
by injecting a portion of the fuel in the combustion chamber, tion that is suitable for the downstream recovery and after-
fuel stratification is created that is capable of extending the treatments [16, 17, 18, 19, 20].
combustion duration and ignition delay of the combustion Alcohol fuels are renewable sources of energy, and they
when compared with HCCI. PPCI seeks to increase the oper- are used in many countries such as Brazil, America, and China
ating range of the engine and combustion stability. PPCI in the form of blends in gasoline to increase thermal efficiency,
strategy needs an optimized fuel selection for each operating reduce emissions, and help better fuel oxidization. In addition,
condition; combustion phasing and duration cannot blending alcohol fuels with gasoline or diesel can keep the
be controlled with significant independence. Consequently, fuel cost constant during global oscillations in the fuel prices
this strategy still has a trade-off between noise and engine or global energy crisis [21]. By choosing a suitable ratio of
efficiency [8, 9, 10]. ethanol and diesel fuel, it is possible to reduce the trade-off
RCCI strategy is a promising approach to extend the between NO and soot in dual-fuel and conventional diesel
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combustion duration, which is kinetically controlled, and engines. In addition, by adopting ethanol in dual-fuel engines,
provide more control via making a reactivity gradient. In it is possible to reduce the need for EGR, especially at higher
RCCI engines, two fuels with different reactivities, such as loads [22].
isooctane (ON=100) and n-heptane (ON=0), are used to make Chuepeng et al. [23] performed an experimental investi-
a wide range of different reactivities. Fuel with low reactivity gation on the effects of ethanol in an RCCI engine at low and
(i.e., isooctane, gasoline, ethanol, or methane) is injected in mid loads. They reported that by using the ethanol compo-
the intake port, and during the compression stroke of the nent, fuel consumption increased and NO and soot decreased.
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engine, the fuel with high reactivity (i.e., n-heptane, diesel, The oxygen molecules in ethanol contribute to better fuel
biodiesel) is injected with single or double injection strategies. oxidization and a reduction in smoke. The smoke concentra-
One single strategy is used for low and mid loads of operating tion at higher loads was lower than low loads. The RCCI
conditions, while the double injection strategy is usually used aerosols with the higher ethanol/diesel ratios yielded smaller
for targeting the squish volume and piston bowl separately. sizes and greater numbers of particles.
Combustion starts in the zones with high reactivity and prop- Other scholars have studied other alcohol fuels such as
agates into the regions with low reactivity. This concept can methanol, which can be produced from different sources,
extend the combustion duration and engine operating range. including natural gas, hydrogen, biomass, coal, and coke-oven
RCCI has ultralow levels of NO and soot, with high thermal gas. Methanol has the capability to decrease NO and soot
X X
efficiency. It was reported that by using RCCI under optimized emissions, owing to this fact that methanol contains nearly
conditions, the thermal efficiency can reach 60% [11, 12, 13]. 50% of oxygen content and higher enthalpy of vaporization [24].
Gross et al. [14] performed an experimental investigation Duraisamy et al. [25] conducted an experimental inves-
on the effects of the mixture of gasoline and diesel fuel “diese- tigation on the effects of hot and cooled EGR on emissions,
line” as the high-reactivity fuel in a light-duty RCCI engine. performance, and cyclic variation of a light-duty turbocharged
The tests were performed over broad loads and speeds to diesel RCCI engine operated with methanol/diesel fuel. The
examine the effects of the mixture on emissions and perfor- tests were performed at 3.4 bar and 5.1 bar brake mean effec-
mance. It was found that brake thermal efficiency increased tive pressure (BMEP) at 1500 rpm. It was found that cooled
from 3.25% (at 2 bar) up to 18.7% (1 bar) by using dieseline EGR can decrease cyclic variation by about 26% and NO ,
X
blends. Moreover, combustion efficiency was slightly improved PM, and thermal efficiency improved with 76% and 81%
compared to conventional RCCI. CO and UHC slightly reduced. methanol mass at 3.4 and 5.1 bar, respectively. At hot EGR,
DelVescovo et al. [15] performed an experimental inves- cyclic variation, NO and PM increased compared to the
X
tigation on the effects of fuel stratification, charge prepara- cooled EGR case.
tion, and premixed fuel chemistry on the performance and Natural gas is a suitable alternative to gasoline, especially
emissions of a heavy-duty single-cylinder RCCI engine. Fuel when used in dual-fuel RCCI engines. Natural gas is cheaper
stratification was varied with the change in start of injection than gasoline, and it makes a higher reactivity gradient with
(SOI) timing and injection pressure. It was found that the the high-reactivity fuel (diesel) than gasoline. In addition, it
peak gross thermal efficiency (GTE) is attainable between has a higher resistance to auto-ignition than gasoline, which
−60° ATDC and −45° ATDC regardless of intake conditions. means reaching higher compression ratios is attainable with
Furthermore, the sensitivity of combustion phasing to intake natural gas than gasoline. Natural gas is also sulfur free, and
conditions was decreased by retarding SOI. Secondly, tests in the dual-fuel engines, using natural gas/diesel can eradicate
were performed by syngas and on methane as the soot. Additionally, natural gas makes RCCI engines to reduce
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AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE 3
their need for EGR, especially at high-load operating condi- homogenous at IVC. The standard Discrete Droplet Model
tions. Making combustion duration longer in RCCI engines (DDM) was used to exchange mass, momentum, and energy
to extend their operating ranges is more possible with natural terms of parcels with fluid-phase values [31]. Primary and
gas compared to gasoline. One of the most significant draw- secondary breakup regimes were simulated by using a combi-
backs of using methane or natural gas is the higher amounts nation of the Kelvin-Helmholtz and the Rayleigh-Taylor
of methanic UHC. High UHC causes combustion loss or poor (KH-RT) breakup models [32]. Droplet collisions always occur
combustion efficiency; in the methane/diesel dual-fuel in spray modeling, especially in diesel engines. The No Time
engines, combustion loss can vary between 1% and 7% with Counter (NTC) collision approach was used, which is faster
regard to the engine load. Methane combustion has a high than O’Rourke’s model [33]. Droplet drag was employed based
exhaust gas temperature, which is suitable for the aftertreat- on the dynamic drag model to simulate variation in the shape
ment activation and downstream recovery purposes. Although of droplets [34]. To simulate the interaction of spray droplets
UHC in methane/diesel RCCI combustion is higher, under with the wall surface, three regimes due to the droplets
optimized conditions, it is possible to keep UHC and CO at Webber number will occur. These regimes are rebound, slide
acceptable levels [26, 27, 28]. and stick. It is necessary to simulate the wall film because it
Syngas is another promising alternative fuel to gasoline affects emissions, especially UHC and thermal efficiency.
in RCCI engines to reduce emissions. Syngas mainly consists O’Rourke model was utilized to simulate the splash model for
of hydrogen (H ), methane (CH), carbon monoxide (CO), the wall film [35]. In order to simulate flow turbulence,
2 4
nitrogen (N), and carbon dioxide (CO). A lean mixture of Re-Normalization Group (RNG) k-𝜀 was employed [36].
2 2
syngas in the RCCI engine can lead to reducing NO and PM. Detailed chemical kinetics was used to simulate combustion
X
Syngas is attractive because it is produced by urban and agri- modeling for the SAGE solver. SAGE model was utilized to
culture residues and for its combustion properties (high resis- calculate the concentration of each species during combus-
tance to auto-ignition and flame speed) [29, 30]. Xu et al. [29] tion. To simulate the soot formation, a model, according to
performed a numerical investigation on two types of engine Hiroyasu [37], was utilized, and for simulating the formation
fueled by syngas. Engine A is a single-cylinder engine with a of nitric oxides, the extended Zeldovich mechanism was
shallow-wide piston bowl, and engine B is a single-cylinder employed [38]. The piston surface was considered as a trans-
engine with the conventional omega-type piston. They opti- lating wall. To set a correct boundary for the walls, the law of
mized some operating parameters, including syngas composi- the wall was employed for all wall boundary conditions for
tion, fuel-supply strategies, and intake conditions using fully turbulent flow [39]. Physical models and boundary condi-
nondominated sort genetic algorithm II. The optimization tions are presented in Table 1 and Table 2, respectively. The
showed that the shape of the piston bowl determines the injec- reaction mechanism for gasoline/diesel, E10/diesel, and E85/
tion methods, while the bore of the cylinder controls injection diesel RCCI was used from [40, 41]. Moreover, the chemical
pressure. The optimal EGR rate for both engines was about species and reaction mechanism used for the simulation of
25%, and initial pressure and temperature for engine A was methane/diesel RCCI combustion was taken from [42]. To
relatively high. examine the reliability of the CFD model for different chemical
In this study, a 3D-CFD model was validated against mechanisms of all fuels, the model was validated against
experimental data of a gasoline/diesel RCCI engine operating experimental data for other loads, provided in the Appendix.
at the load of 6.5 bar gross IMEP and 1300 rpm. Ethanol
blends (E10 and E85) and methane were replaced with gasoline
2.2. Model Validation
with constant cylinder energy and constant combustion
phasing in all cases. A comparative study was performed
The experiments were performed on a heavy-duty RCCI engine
between the alternative fuels to gasoline using the RCCI
at the laboratory of the University of Wisconsin-Madison. The
strategy. In addition, the CDC was also simulated and
engine is a 2.44 L Caterpillar 3401 single-cylinder oil test
compared with RCCI cases. The effects of each alternative
engine (SCOTE). Engine geometry specifications are given in
fuels on emissions, performance, thermal efficiency, and fuel
consumption were studied.
TABLE 1 Physical models were utilized in the simulation.
2. Material and Methods Breakup model Kelvin-Helmholtz and Rayleigh-Taylor
(KH-RT)
Droplet collision No Time Counter (NTC)
In this portion, a numerical 3D-CFD model was validated
Spray-wall Wall film (O’Rourke model)
against the experimental data, mesh independency was
interaction model
studied, and the appropriate mesh size was chosen for further
Drop drag model Dynamic drop drag
numerical results.
Splash model O’Rourke
Combustion SAGE chemistry detailed solver
2.1. Computational Model al.
on modeling
nati Emissions model Extended Zeldovich model for NO emissions
The simulation considers the closed cycle from the intake valve er X
closing (IVC) at −143° ATDC to the exhaust valve opening AE Int Hiroyasu soot model for soot emissions
(EVO) at 130° ATDC. Port injection was considered fully © S Turbulent modeling RNG k-𝜀
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4 AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE
TABLE 2 Boundary and initial conditions. TABLE 4 Experimental engine operating conditions
(experimental data taken from [43]).
Piston T (K) 470
Piston
Wall motion Translating IMEP (bar) 6.5
Velocity and temperature Law of the wall Engine speed (rpm) 1300
condition EGR (%) 0
Absolute roughness 0 m Intake temperature (°C) 40
Cylinders TCylinder wall (K) 425 Intake pressure (bar) 1.5
wall Wall motion Stationary Total fuel (mg/cycle) 75.0
Velocity and temperature Law of wall Premixed fuel mass of gasoline (%) 86.8
condition
Diesel injection pressure (bar) 600
Absolute roughness 0 m
Diesel SOI#1 (CAD) −58
Cylinder T (K) 425 al.
head WCyalilnl dmer ohetaidon Stationary DFriaecsetilo SnO oIf# d2i e(CseAlD fu)el in pulse#1 (%) −6737 nation
Velocity and temperature Law of wall Diesel injection duration#1 (CAD) 4.1 E Inter
Absolute roughness 0 m A
Diesel injection duration#2 (CAD) 2.0 S
©
Front face Boundary type Periodic
Periodic type Stationary
Periodic shape Sector (pie shape)
Figure 3 shows the comparison of the emissions, gross
with an angle of 60°
IMEP, and GTE for the numerical results and experimental data.
Matching boundary Back face
al.
Back face Matching boundary Front face n
o
T (K) 368 nati
PIIVVCC (bar) 1.5 E Inter 3. Results and Discussion
A
Initial gasoline mass (mg) 65.1 S
©
In this section, alternative fuels, including ethanol blends with
gasoline (E10 and E85) and methane, were replaced with
Table 3, and the tests were performed at the load of 6.5 bar gasoline as the low-reactivity fuel for the RCCI strategy. In
gross IMEP and 1300 rpm [43]. addition, all alternative cases were compared with the CDC
In order to decrease computation time, one-sixth of the strategy. In order to make a fair comparison between all cases,
chamber geometry was modeled due to the number of the cylinder energy and combustion phasing for all cases were
injector nozzles. Figure 1 shows the one-sixth of the combus- considered constant. Table 5 shows the simulation parameters
tion chamber with crevice volume and computational grid at for all cases. Initial boundary conditions were considered
TDC. Mesh independency study was performed for the CFD constant, and by changing the diesel SOI, combustion phasing
model, and an appropriate mesh size of 1.4 mm was considered was kept constant.
for further simulations, available in the Appendix. Mesh inde-
pendency was studied for three mesh sizes, including 2 mm
(coarse mesh), 1.4 mm (medium mesh), and 1 mm (fine mesh).
3.1. Effects of Methane, E10,
Figure 2 illustrates a comparison between experimental data
and numerical simulation results. and E85 on Cylinder
Pressure, Heat Release,
Emissions, and
TABLE 3 HD engine geometry specification (experimental
data taken from [43]). Performance
Base engine type Caterpillar SCOTE
Figure 4 shows a comparison between simulated cylinder
Bore × stroke 13.72 × 16.51 cm pressures for all the alternative fuels and CDC with the
Connecting rod length 26.16 cm gasoline/diesel (G/D) RCCI case. In the E10 and E85 cases,
Piston pin offset None the peak cylinder pressure and AHRR increased, which
Displacement 2.44 L resulted in higher NOX, presented in Table 6. The methane/
Geometric comp. ratio 14.88:1 diesel (M/D) RCCI case has the lowest peak cylinder pressure
due to its extended AHRR. The E85/diesel (E85/D) RCCI case
Swirl ratio 0.7
has the highest peak cylinder pressure as well as AHHR, which
Bowl type Modified (bathtub)
accounts for faster ethanol combustion and flame propagation
Number of valves 4
al. compared to other cases.
IVC 143° BTDC ation Table 6 gives the results of emissions, gross IMEP, and
EVO 130° ATDC ern peak pressure rise rate (PPRR) for all cases. Figure 5 shows a
nt
Fuel injection type for direct Direct injection common rail E I comparison of the thermal efficiency, which indicated specific
A
injection (6 holes) © S fuel consumption (ISFC) and CO2 emissions between all cases.
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AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE 5
FIGURE 1 The combustion chamber and computational grid with crevice volume at TDC.
al.
n
o
ati
n
er
nt
E I
A
S
©
By adding ethanol, NO emissions increased 1.27 and 3.27 longer combustion duration. Among alternative fuels, the
X
times in the E10 and E85 cases compared to the G/D RCCI M/D case has the highest levels of UHC and CO by about
case. On the other hand, soot decreased by 15.4% and 69%, 4.72 and 2.03 orders of magnitude when compared to the
respectively, in the E10/D and E85/D cases. Alcohol fuels have G/D case. One explanation for having high amounts of UHC
oxygen content, and this feature interferes with the chemical and CO is that methane combustion has slower flame speed
production of soot emissions. Moreover, the premixing prop- and lower flame propagation than gasoline. In addition,
erties of these fuels reduce soot emissions [44]. UHC and CO methane combustion has a larger quenching distance which
decreased by adding ethanol, and IMEP increased due to high impedes better flame penetration. Thus, UHC and CO
oxidation in soot, UHC, and CO. Adding ethanol caused a concentration will increase, especially for the near-wall
sudden increase in cylinder pressure and PPRR, which zones. Most of the UHC in the M/D RCCI case consists of
accounts for the higher cylinder pressure. Figure 5 shows an methane gas, so-called methanic UHC. Fuel consumption
increase in fuel consumption in E10 and E85 cases by about in the M/D case is slightly lower than the G/D case that
3% and 40%, respectively. accounts for the high amount of lower heating value (LHV)
The M/D case has lower cylinder pressure and gross of methane compared to gasoline. GTE of the M/D case
IMEP, but NO increased, which may account for longer decreased by 4.2% due to lower gross IMEP (lower output
X
combustion duration of the methane case, indicated in work) as well as higher UHC and CO, which indicates poorer
Figure 4 and Table 6. NO increased by about 3.27 times than combustion efficiency.
X
the G/D case, while soot is near zero, indicating that methane The CDC case has diffusion-limited combustion, and by
combustion devastates carbon clusters of soot due to its single fuel injection at −7.9° ATDC, CA50 was kept constant.
In the CDC case, the peak cylinder pressure decreased, which
resulted in lower gross IMEP, but the combustion duration of
this case increased about three times in magnitude. NO
FIGURE 2 Comparison of numerical results with the X
increased dramatically in the CDC case due to the nature of
experimental data.
diffusion-limited combustion and longer injection duration
when compared with RCCI combustion. Soot emission also
increased in the CDC case. On the other hand, UHC and CO
had negligible amounts compared to the RCCI cases. The CDC
case has the lowest GTE compared to other cases, and it
showed a 5% lower GTE compared to the G/D case. But the
CDC case showed a comparable level of GTE to the M/D case
but at the expense of 13% higher ISFC.
EURO6 and EPA2010 emissions mandates consider
0.4 and 0.27 g/kW-h, respectively, for NO and 0.013 and
X
0.01, respectively, for soot emission. Regarding these
emission regulations, all of the RCCI cases can satisfy
EURO6 and EPA2010, while CDC is not capable of meeting
al. these standards.
n
o
ati Figure 5 illustrates the comparison of thermal efficiency,
n
er fuel consumption, and CO emissions for all cases. The E85
nt 2
E I case had the highest GTE but at the expense of higher fuel
A
© S consumption. The E85 case also produced lower CO2 per kW-h.
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6 AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE
FIGURE 3 Comparison of numerical results and experimental data.
Experimental data Numerical results
1E+03
49.1 49.3
1E+02
6.5 6.53 6.2 6.11 7.32 7.19
1E+01
1E+00
1E-01
1E-02
0.01 0.011 al.
n
1E-03 0.0014 0.0013 natio
er
1E-04 nt
E I
IMEP (bar) NOx (g/kW-h) soot (g/kW-h) UHC (g/kW-h) CO (g/kW-h) GTE (%) A
S
©
However, the variation between ethanol cases and gasoline be oxidized by using aftertreatments, this drawback can
case in CO emissions is negligible. As previously mentioned, be tackled. From that study performed by Prikhodko et al.
2
the M/D case had the lowest thermal efficiency and fuel [45], it was reported that if the exhaust gas temperature
consumption, but the CO emission of this case is at the lowest exceeds 522 K and a load of 4.2 bar brake thermal efficiency,
2
level compared to other cases. In the M/D case, CO and GTE UHC and CO can be reduced by about 88% and 100% by using
2
decreased by 23.1% and 4%, respectively. One of the big diesel oxidation catalyst (DOC). According to Table 6, the
concerns of the M/D case is the high levels of methanic HC, exhaust temperature of each case at EVO is about 800 K, which
which significantly can escalate global warming. The CDC is suitable for the activation of the DOC. Thus, by adopting
strategy had the lowest thermal efficiency and highest CO the DOC, it is possible to meet the EPA2010 standards for
2
emissions, but the CDC strategy is capable of providing great UHC for all alternative fuels.
control over combustion, unlike the RCCI strategy. Figure 7 shows the energy distribution for all cases. As
Figure 6 visualizes a comparison of emissions for all cases previously mentioned, GTE is gross thermal efficiency; HTL
in the percentage index. One hundred percent is the sum of is the heat transfer loss; EL is the exhaust loss, which is the
each emission that all cases produced, and the share of each ratio of the differences between intake and exhaust enthalpies
case of the emissions is illustrated. The CDC case produced to the cylinder energy; and CL is the combustion loss, which
NO and soot by about 97% of them, while the majority of is attributed to UHC and CO emissions. The equations for the
X
produced UHC and CO belonged to the M/D case. The shares calculation of these parameters are available in the Appendix.
of the RCCI cases of all produced NO and soot are less than The M/D RCCI case has the highest level of combustion loss
X
1.5%, indicating how the RCCI strategy produces ultralow by about 7.6% owing to high UHC and CO emissions, indi-
NO and soot emissions compared to CDC. According to cating that 7.6% of the cylinder energy cannot be oxidized
X
Figure 6, one of the most significant drawbacks of the RCCI well or participate in the combustion process. The CDC case
strategy is the high amounts of UHC and CO; however, these has the lowest amount of CL by less than 0.1%; however, in
cases can meet EPA2010 for heavy-duty engines for CO this case, 55.6% of the cylinder energy was lost by heat transfer
emission (less than 21 g/kW-h). That being said, if UHC can and exhaust losses through the combustion chamber walls
TABLE 5 Simulation parameters for all cases.
G/D RCCI E10/D RCCI E85/D RCCI M/D RCCI CDC
Engine speed (rpm) 1300 1300 1300 1300 1300
Cylinder energy (kJ) 2.97 2.97 2.97 2.97 2.97
Diesel energy fraction of total fuel (%) 16.7 16.7 16.7 16.7 100
Diesel energy fraction in the first injection (%) 67 67 67 67 100
Diesel SOI #1 (CAD) −58 −58 −58 −58 −7.9
Diesel SOI #2 (CAD) −37 −34.5 −27.1 −22
al.
Diesel inj. press. (bar) 600 600 600 600 600 n
o
EGR (%) 0 0 0 0 0 nati
er
PIVC (kPa) 145 145 145 145 145 E Int
A
T (K) 370 370 370 370 370 S
IVC ©
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AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE 7
FIGURE 4 Comparison of simulated cylinder pressures for TABLE 6 Emissions and performance parameters of all cases.
all alternative fuel cases with the G/D case.
G/D E10/D E85/D M/D
RCCI RCCI RCCI RCCI CDC
Gross IMEP (bar) 6.53 6.54 6.65 6.27 5.50
NO (g/kW-h) 0.011 0.025 0.047 0.093 6.39
X
Soot (g/kW-h) 0.0013 0.0011 0.0004 0.00002 0.091
UHC (g/kW-h) 6.101 5.877 4.483 28.819 0.101
CO (g/kW-h) 7.187 4.594 1.066 14.616 0.780
PPRR (bar/deg) 5.09 5.11 8.14 2.13 5.66
al.
on CA50 (°ATDC) 5.63 5.63 5.63 5.63 5.63
ati
ern Combustion 12.17 11.91 9.12 22.18 36.27
E Int duration (deg)
A
S T (K) 795.1 799.3 804.8 832.7 814.1
© EVO
al.
n
o
ati
n
er started to burn, but the reactivity stratification is still avail-
nt
E I able, and RCCI benefits this feature to extend the
A
© S combustion duration.
and exhaust ports. As it is shown in Figure 7, by adding 10% 4. Summary/Conclusion
ethanol in gasoline, CL can be reduced by 0.6%, and GTE can
be increased to 0.4%, indicating the role of -OH radical in
In this paper, a 3D-CFD model was used to simulate dual-fuel
ethanol blends on the fuel oxidization and increasing GTE.
RCCI combustion for gasoline, ethanol, and methane fuels.
Figure 8 shows the temperature cut-planes and isothermal
The model was validated against the experimental data at the
surfaces for all cases at similar CA50 (5.63° ATDC). The CDC
load of 6.5 bar gross IMEP and 1300 rpm. The low-reactivity
case has higher local temperature zones, which result in high
fuel (gasoline) was replaced with E10, E85, and methane in
levels of NO among all cases. Adding ethanol resulted in
X the RCCI combustion to investigate their effects on the
higher reactivity stratification than the G/D case. The
combustion characteristics, performance, and emissions. In
isothermal surfaces of E10/D and E85/D show a higher strati-
order to make a fair comparison between all cases, combustion
fication compared to the G/D case. The M/D case has the
phasing and cylinder energy, as well as boundary conditions
highest reactivity gradient due to the high octane number of
for all cases, were kept constant. The main results are as follows:
methane, which is about 120. The isothermal surfaces of the
M/D case show that the higher octane number makes an • The E85/D RCCI case had the highest peak cylinder
improvement in reactivity stratification. The CDC isothermal pressure and PPRR. Thus, the gross IMEP of the E85/D
is also at constant CA50 and shows the differences in the RCCI increased, and it resulted in the highest GTE of
combustion between CDC and RCCI. All the regions in RCCI 1.3% compared to the G/D RCCI case. The results
FIGURE 5 Comparison of thermal efficiency, fuel consumption, and CO2 emissions of all cases.
GTE (%) ISFC (g/kW-h) CO (g/kW-h)
2
600
547.1
500 459 457.4 455.6
400 350.9
300
218.8
200 156 160.8 153 173.3
al.
n
o
ati 100 49.3 49.7 50.6 45.1 44.3
n
er
nt
E I 0
A
S G/D RCCI E10/D RCCI E85/D RCCI M/D RCCI CDC
©
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8 AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE
FIGURE 6 Comparison of the shares of each case in emission production.
E10/D E85/D E10/D E85/D
RCCI RCCI RCCI RCCI
0.38% 0.72% 1.19% 0.43%
M/D
G/D RCCI M/D
RCCI G/D RCCI
0.17% RCCI
1.42% 1.40%
0.02%
CDC CDC
97.32% 96.96%
NOx(g/kW-h) Soot(g/kW-h)
CDC CDC
0.22% 2.83% G/D RCCI
25.44%
G/D RCCI
13.44%
E10/D
RCCI
13.00%
E85/D
RCCI
9.91%
M/D M/D E10/D
RCCI RCCI E85/D RCCI nal.
63.44% 51.59% RCCI 16.25% atio
n
3.89% er
nt
UHC(g/kW-h) CO(g/kW-h) AE I
S
©
FIGURE 7 The comparison of the energy distribution of all cases.
GTE EL+HTL CL
100% 4.2 3.6 1.3 7.6 0.1
90%
80%
70% 46.5 46.7 48.1 47.3 55.6
60%
50%
40%
30%
49.3 49.7 50.6
20% 45.1 44.3 al.
n
o
10% ati
n
er
0% nt
E I
G/D RCCI E10/D RCCI E85/D RCCI M/D RCCI CDC SA
©
Downloaded from SAE International by Saeid Shirvani, Thursday, September 02, 2021
AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE 9
FIGURE 8 Temperature cut-planes and isothermal surfaces showed high levels of methanic UHC and CO than
for all cases at similar CA50. other cases.
• The CDC case resulted in the lowest gross IMEP and
GTE. Fuel consumption of this case was at the highest
level compared to RCCI cases. The CDC case had higher
levels of CO emissions by about 19.2%, and the M/D
2
case had lower CO by about 23.6% compared to the G/D
2
RCCI case.
• All of the RCCI cases can meet EURO6 and EPA2010
emission mandates for NO , soot, and CO emissions.
G/D RCCI X
However, the CDC case cannot meet these regulations
for NO and soot without using aftertreatments.
X
Definitions/Abbreviations
AHRR - Apparent Heat Release Rate
E10/D RCCI
BMEP - Brake Mean Effective Pressure
BTDC - Before Top Dead Center
CA50 - The Crank Angle where 50% of fuel burn
CAD - Crank Angle Degree
CDC - Conventional Diesel Combustion
CFD - Computational Fluid Dynamics
E85/D RCCI
CL - Combustion Loss
CO - Carbon monoxide
CO2 - Carbon dioxide
DDM - Discrete Droplet Model
DOC - Diesel Oxidation Catalysts
E10 - Ethanol-gasoline blend with 10% ethanol by volume
M/D RCCI
E10/D RCCI - E10/Diesel RCCI
E85 - Ethanol-gasoline blend with 85% ethanol by volume
E85/D RCCI - E20/Diesel RCCI
EL - Exhaust Loss
EVC - Exhaust Valve Closing
EVO - Exhaust Valve Opening
nal. CDC
natio Temperature (K) G/D RCCI - Gasoline/Diesel RCCI
nter GHG - Greenhouse Gas
E I
A GTE - Gross Thermal Efficiency
S
©
HCCI - Homogeneous Charge Compression Ignition
HTHR - High-Temperature Heat Release
indicated that adding ethanol (-OH radical) yielded
HTL - Heat Transfer Loss
higher oxidization in soot, UHC, and CO; consequently,
combustion loss can be decreased by adding a percentage IARC - International Agency for Research on Cancer
of ethanol in gasoline. However, fuel consumption in the
IMEP - Indicated Mean Effective Pressure
E10 and E85 cases increased by 3% and 40%,
ISFC - Indicated Specific Fuel Consumption
respectively, compared to the G/D case.
IVC - Intake Valve Closing
• Substituting gasoline with methane resulted in the lower
cylinder pressure and gross IMEP, and it affected GTE IVO - Intake Valve Opening
negatively by 4.2%. But the fuel consumption of the KH-RT - Kelvin-Helmholtz-Rayleigh-Taylor
methane case was at the lowest level when compared to
LHV - Lower Heating Value
other cases, owing to higher LHV of methane. NO of
X
LTHR - Low-Temperature Heat Release
the methane case increased by a factor of 4.3 compared
to the G/D case, and soot was eradicated. The M/D case M/D RCCI - Methane/Diesel RCCI
Downloaded from SAE International by Saeid Shirvani, Thursday, September 02, 2021
10 AN INVESTIGATION OF THE REPLACEMENT OF E10, E85, AND METHANE
NO - Nitrogen Oxides 10. Sellnau, M., Moore, W., Sinnamon, J., Hoyer, K. et al., “GDCI
X
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NTC - No Time Counter
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PCCI - Premixed Charge Compression Ignition
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PCI - Premixed Compression Ignition
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PM - Particulate Matter
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PPRR - Peak Pressure Rise Rate
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RI - Ringing Intensity SAE Technical Paper 2013-01-0279, 2013, https://doi.
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RNG k-𝜀 - Re-Normalization Group k-𝜀
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