Investigation of Effect of Intake Temperature on Low Load Limitations

Subscriber access provided by UNIV OF SOUTHERN INDIANA

Combustion

Investigation of Effect of Intake Temperature on Low Load Limitations of Methanol Partially Premixed Combustion Burak Zincir, Pravesh Shukla, Sam Shamun, Martin Tunér, Cengiz Deniz, and Bengt Johansson Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b00660 • Publication Date (Web): 24 May 2019 Downloaded from http://pubs.acs.org on May 24, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Investigation of Effect of Intake Temperature on Low Load Limitations of Methanol Partially Premixed Combustion Burak Zincira,*, Pravesh Shuklab,c, Sam Shamunb, Martin Tunerb, Cengiz Deniza, Bengt Johanssond a

b

Istanbul Technical University, Maritime Faculty, Postane Mah. Sahil Cad. Tuzla, 34940, Istanbul, Turkey, [email protected], [email protected]

Lund University, Department of Energy Sciences, Division of Combustion Engines, Lund, Scania 221 00 Sweden, [email protected], [email protected] c

Present address: Indian Institute of Technology, Department of Mechanical Engineering, Bhilai, Raipur-492015, India, [email protected] d

*

King Abdullah University of Science and Technology, Department of Mechanical Engineering, Thuwal 23955, Saudi Arabia, [email protected]

Corresponding Author

Abstract Methanol has unique properties as a fuel, and partially premixed combustion has promising results with high engine efficiency and low emissions. Low load studies with methanol partially premixed combustion are scarce, and the effect of intake temperature on low load methanol partially premixed combustion is an intriguing question. This study aims to investigate the effect of intake temperature on low load limitations of methanol partially premixed combustion by an experimental study. The engine was operated at 800 rpm under two different loads. The low load condition was done at 3 bar IMEP, and the idle condition was commenced at 1 bar IMEP. According to the results, the intake temperature affected engine stability, engine performance, and engine emissions. The combustion stability decreased by the decrease of the intake temperature. The ignition delay was longer and the peak cylinder pressure was smaller with lower intake temperature. The combustion efficiency reduced by the decrease of the intake temperature from 0.99 to 0.96 at 3 bar IMEP while it decreased from 0.99 to 0.98 at 1 bar IMEP at single injection case and split injection case. The thermodynamic efficiency remained constant at 0.43 at 3 bar IMEP, and it decreased

1 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

from 0.30 to 0.28 at 1 bar IMEP at the single injection, and it reduced from 0.26 to 0.24 at 1 bar IMEP at split injection. The gross indicated efficiency increased from 0.41 to 0.42 at 3 bar IMEP, while it reduced from 0.29 to 0.28 and 0.26 to 0.24 at 1 bar IMEP at single injection and split injection, respectively. THC emission increased, NOX emission decreased or remained constant, and CO emission remained constant by the decreasing of the intake temperature. Finally, the combustion phasing study was done at 1 bar IMEP at constant intake temperature to see the effect of the start of injection timing on the engine performance and the emissions under the idle condition. Keywords: partially premixed combustion, methanol, low load, idle condition, intake temperature

1. Introduction Global warming and more stringent legislation about emissions have driven combustion engine researches towards more efficient operation and close to zero emissions. Within this context, other combustion concepts rather than conventional diesel or spark ignition combustion are used, due to the inadequate emission reduction potential of existing combustion concepts. Homogenous charge compression ignition (HCCI) combustion is one of the concepts, which have been investigated for higher efficiency and lower emissions. High efficiency, low NOX and soot emissions can be obtained at the same time with HCCI. On the contrary, HCCI combustion concept has challenges in combustion control, low power production range, and high-pressure rise rate.1 Another combustion concept, partially premixed combustion (PPC), has been used to eliminate the drawbacks of HCCI. PPC is an intermediate process of the conventional diesel combustion and HCCI combustion. Direct injection event and auto-ignition event are separated at PPC concept.2 Fuel is injected during the compression stroke, which aims to form 2 ACS Paragon Plus Environment

Page 2 of 41

Page 3 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

a partially homogenous mixture with air, residual gases, and fuel. PPC has advantages of easy combustion control, low NOX and soot levels, and high engine efficiency. First PPC studies were done with a low compression ratio and high EGR level while combusting diesel fuel at stoichiometric operation. Later studies were performed with high octane fuels, for instance, gasoline or alcohols to separate injection of the fuel and start of the combustion.3 Various studies have been done until now at different load ranges. Belgiorno et al.,4 have done a study to evaluate the effects of the main engine calibration parameters and their combination, which influence the engine performance and emissions the most in the gasoline PPC concept by the approach of design of experiments analysis. The aim of the study was to reach high efficiency and low emission levels at three load conditions of 3, 6 and 9 bar bmep at 1500 rpm constant engine speed. They observed that the PPC concept had a 2% higher efficiency than the conventional diesel combustion. They also found that the PPC concept had lower soot and 0.5 g/kWh lower NOX emissions. Yin et al.,5 investigated the effects of the calibration parameters of PPC on the efficiency and emissions of a multicylinder engine during stable and transient operations at 5, 11 and 14 bar loads. The fuel that has been used is a mixture of 80% Swedish 95 octane pump gasoline and 20% n-Heptane. They observed that the peak gross indicated efficiency was 51.5%, and the peak net indicated efficiency was 48.7% at stable operating conditions. The transient condition had a 47.5% average net indicated efficiency. It was also indicated that NOX emission, CO emission, and THC emission comply with the Euro VI emission limits at almost all transient operating conditions. Han et al.,6 did a study to evaluate the advantages and challenges of using neat nbutanol in a diesel engine with PPC concept at around 6 bar of IMEP. They found that the indicated thermal efficiencies were 45.3% and 45.4% for n-butanol and diesel, respectively. Lower reactivity and less complete burning of n-butanol slightly reduced the combustion efficiency. It was indicated that n-butanol had lower NOX and near to zero smoke emissions. 3 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Despite all range loads of the conventional diesel engines that have been investigated in the literature, low loads have unique operating conditions, and they have taken the attention of the researchers. Low in-cylinder pressure and temperature cause poor combustion, engine stability problems, soot formation and unburned hydrocarbons in the cylinder. Low load PPC operations with higher octane fuels are more problematic. It was indicated at various studies that the combustion stability at low loads is a challenge for high octane fuel, due to high resistance to auto-ignition.7 - 9 In addition to this, overall leaner in-cylinder mixtures at low loads can result with very long ignition delay and over-retarded combustion phasing, which leads to the unstable engine operation at low loads.10,11 Optimum engine parameters are needed for stable and efficient combustion at low load conditions. Also, the researchers have been focused on low load PPC studies to achieve good combustion stability with efficient combustion and low emissions in both with low octane fuels and high octane fuels. A study about low load and the idle load was done by Wang et al.,1 They investigated low load limitations of high-octane fuels with intake temperature sweep. Primary reference fuels with octane numbers of 70, 80, and 90 were tested at 5 bar IMEP at 1200 rpm as low load and 2.5 bar IMEP at 600 rpm as idle load. Borgqvist et al.,12 investigated the low load limitations of gasoline fuels with octane numbers 69 and 87. The objective was to reach the idle operating condition, 1 bar IMEP, at the intake air temperature of 40°C. They observed that RON 69 gasoline was able to be operated at 1 bar IMEP, and RON 87 gasoline could be run at 2 bar IMEP. Another study was done with regular gasoline fuel. The aim of the study was to investigate the operating characteristics of a light-duty multi-cylinder diesel engine.13 They obtained that the combustion stability of low load gasoline PPC depends on the intake pressure, intake temperature, and fuel stratification. Solaka et al.,14 did a study about the investigation of low load limits of four fuels in the gasoline boiling range with the diesel MK1. They operated the engine under loads between 2 and 8 bar IMEP at 1500 rpm. They 4 ACS Paragon Plus Environment

Page 4 of 41

Page 5 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

found that the diesel MK1 had the lowest low load limit of 3 bar IMEP at 𝜆=1.5. All fuels were able to be operated at 2 bar IMEP if 𝜆 was increased. Also, there are low load optical engine studies in the literature. Yin et al.,15 did a study, focusing on to improve the efficiency of the combustion engine by multiple injection method under PPC. They used PRF87 as fuel and reached to the engine efficiency of 48% with the multiple injections. The study of An et al.,16 wanted to observe the influence of the intake temperature on combustion stability. They used PRF77 as fuel and found that lower intake temperature reduces the in-cylinder combustion, maximum in-cylinder pressure and indicated mean effective pressure, retards the combustion phasing, and increases the combustion stratification. Sun et al.,17 used ultra-low sulfur diesel, Fischer-Tropsch diesel and hydro-treated canola oil renewable diesel at their PPC study. They operated the engine at 1500 rpm and 3.5 bar IMEP. They observed that Fischer-Tropsch diesel has the best emission performance. The combustion event and emissions under the PPC concept can be affected by the variation of the injection parameters and intake parameters. Intake temperature, one of the intake parameters, is important for the combustion of high octane fuels. The combustion stability can be increased with a higher intake temperature.7 Coefficient of variation of IMEP (COV IMEP) is a criterion for the combustion stability, and the upper limit for the COV IMEP was 5%.18 Maurya and Agarwal had a study about the effect of the intake temperature and air-fuel ratio on cycle-to-cycle variations in an ethanol-fueled port injection HCCI engine.19 It was observed that the COV IMEP decreases by the increasing of the intake temperature. The intake temperature has also had an influence on the combustion event and engine emissions. Sarjovaara et al.,20 did a study to investigate the effect of the intake temperature on E85 ethanol/gasoline blend dual-fuel combustion. They noted that maximum in-cylinder pressure is higher at higher intake temperatures. Moreover, the rate of heat release (RoHR) peak was lower and retarded by lower intake temperatures. THC emission increased at almost all 5 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

operating loads by the decreasing of the intake temperature. NOX emission reduced with lowered intake temperature at all loads. Low intake temperature had a negative effect on combustion efficiency. There is another study, which aims to observe the effect of the intake temperature and common-rail pressure on ethanol fuelled GCI combustion.10 They found that the maximum in-cylinder pressure, apparent RoHR, and IMEP was increased by the increase of the intake temperature, due to the reduced wall wetting and increased combustible mixture. Combustion phasing (CA50) was more advanced with higher intake temperature. The reduced wall wetting and more complete combustion came with decreased THC emission and CO emission at higher intake temperatures. NOX emission should increase with higher maximum in-cylinder pressure and temperature, but it was reduced by the increase of the intake temperature in this study, due to the radiation heat transfer. Higher intake temperature increased the engine efficiency by the advanced combustion phasing. There are studies with various fuels, which investigated the effect of the intake temperature on engine emissions.21 24

Common results of these studies are, decreased THC emission and CO emission, while

increased NOX emission, except for the study22, with methanol fuel at the optimum operating parameters, by the increasing of the intake temperature. Another study of Benajes et al.,25 indicated that a high octane fuel such as gasoline can be ignited even at low load without misfires at higher intake temperatures. Based on the above literature review, various fuels have been used at PPC studies, including blending of different fuels.26 - 28 Methanol is also one of the suitable fuels with high octane rating between 107 – 109 29, which can provide separation of the fuel injection event and the combustion event. It is the simplest alcohol, which has a higher H/C ratio than the conventional fuels. In addition to this, every molecule contains one atom of oxygen. This oxygen atom assists in more efficient combustion. It also provides low CO and no soot. NOX emission is low, due to low-temperature combustion of methanol.30 It has a high heat of 6 ACS Paragon Plus Environment

Page 6 of 41

Page 7 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

vaporization, which reduces the compression work done in the cylinder when it is directly injected into the cylinder.31 The previous study,32 investigated the charge cooling effect of methanol. It was observed that the charge cooling effect slightly reduced the compression work, and in the expansion stroke, during the combustion, the charge cooling effect had existed highly. And also, methanol reduced the heat transfer loss, which has resulted in higher engine efficiency. The interest in methanol as a fuel has been increased lately, a combination of methanol and PPC concept as a low-temperature combustion process could be a possible future solution to develop clean combustion engines. Despite the many studies, have been made under PPC concept with various low octane and high octane fuels, there is still a lack of information concerning the methanol PPC concept. The combustion properties and emissions of low load operation under methanol PPC are not known adequately. In addition to this, the effect of the intake temperature on low load methanol PPC is an intriguing question. This study aims to investigate the effect of the intake temperature on the low load limitations of methanol PPC. The engine is operated under 3 bar IMEP at 800 rpm as the low load, and 1 bar IMEP at 800 rpm as the idle load. The COV IMEP and standard deviation (STD) are used as indicators of combustion stability. The lowest required intake temperatures are used to obtain acceptable COV IMEP for certain loads to observe the effects on combustion characteristics, emissions, and efficiencies. Additionally, the combustion phasing (CA50) sweep is done in the last part of the study, to observe the effect of the CA50 timing on the combustion event, emissions, and efficiencies.

2. Methodology The objective of the study is to observe the low load limitations of methanol PPC with the effect of the intake temperature. The engine stability, the combustion characteristics and the 7 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 41

emissions were investigated. Initial experiment conditions were 800 rpm, 400 bar rail pressure, and 1 bar absolute intake pressure. EGR was not used in this study. The injection timing was constant at 3 bar IMEP. Single and split injection strategies were used at 1 bar IMEP to observe the effect of various injection strategies. The injection timing was changed at 1 bar IMEP single injection strategy to provide constant CA50 around 5 °CA, and the first injection timing and the second injection timing were remained constant while using the split injection strategy. The injection event was characterized by the electrical signal to the injector. As a result, the delay of injector opening slightly affects the exact injection timing, injection duration, and ignition delay. The low load experiments were started at 3 bar IMEP with the lowest intake temperature, which maintained the lowest COV IMEPn. The upper limit for the COV IMEPn was 5%, which is an indicator of combustion stability.18 The intake temperature was reduced gradually with the aim to provide at least COV IMEPn of 5%. The same process was followed at 1 bar IMEP single injection case and split injection case for the idle condition of the engine. The intake flow was held as constant at 1 bar absolute pressure, and the fuel amount was changed to get the desired engine load. Table 1 shows the engine parameters in detail. After the main study, the combustion phasing sweep was done to see the effect of the injection timing on the combustion phasing and emissions (Table 2). Table 1. Engine test parameters. Engine parameters IMEP [bar] Injection pressure [bar] Injection strategy [-] Start of injection [°CA] Intake pressure [bar abs] Intake temperature [°C] Coolant temperature [°C] Engine Speed [rpm] EGR [%] 𝜆

Low load 3 400 Single -20 1 Variable 85 800 0 ~3.7

Idle (single inj.) 1 400 Single -25 / -19 / -13 1 Variable 85 800 0 ~7


Idle (split inj.) 1 400 Split -20 | -7 1 Variable 85 800 0 ~7.5

Page 9 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 2. Combustion phasing study parameters. Engine parameters IMEP [bar] Injection pressure [bar] Injection strategy [-] Injection Timing [°CA] CA50 [°CA] Intake pressure [bar abs] Intake temperature [°C] Coolant temperature [°C] Engine Speed [rpm] EGR [%] 𝜆

Idle condition 1 400 Single Variable 5/6/7/8/9 1 130 85 800 0 ~7

3. Experimental Setup The engine, which was used at the experimental studies, is a six-cylinder Scania D13 heavyduty engine that modified to run on one-cylinder mode. Specifications of the engine are shown in Table 3, and the experimental setup diagram is indicated in Figure 1. Table 3. Engine specifications. Engine Specifications Vd 2124 cm3 Stroke 160 mm Bore 130 mm rc 20:1 Swirl ratio 2:1 IVC -141 °CA ATDC EVO 137 °CA ATDC Umbrella Angle 148° Injector Type 10 holes MeOH Injector

The engine is coupled with an electric motor, which is controlled by a frequency converter. For this reason, the torque of the engine was not measured, but the load of the engine was calculated by the in-cylinder pressure with the assist of the pressure sensor and charge amplifier. The in-cylinder pressure was measured by a Kistler 7061B piezoelectric pressure sensor. It outputs an electric charge signal to a Kistler 5011 charge amplifier. The heat release rate was calculated based on the measured cylinder pressure. The apparent rate of heat release (aRoHR) equation is (1), while the ratio of specific heats (𝛾) is calculated with equation (2). The gross indicated mean effective pressure (IMEP) and the net indicated mean effective 9 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 41

pressure (IMEPn) are calculated with equation (3) and (4), respectively, by using measured cylinder pressures. dQhr = γ/(γ − 1) . P . dV + 1/(γ − 1) . V . dP

(1)

γ = Cp /Cv

(2)

IMEP = 1/Vd

360 0

P dV

(3)

IMEPn = 1/Vd

720 0

P dV

(4)

Where P is the in-cylinder pressure, dV is the change of cylinder volume, V is the cylinder volume, dP is the change of in-cylinder pressure, Cp is the specific heat at constant pressure, Cv is the specific heat at constant volume, and Vd is the engine displacement volume. The peak cylinder pressure, pressure rise rate, and combustion stability indicator (COV IMEPn) are derived from the cylinder pressure signal. At the same time, the start of combustion, combustion angles (CA10, CA50, CA90) and ignition delay are gathered from the calculated rate of heat release (RoHR). Pressurized air is delivered from an external compressor, and the back pressure of turbocharger can be simulated by the back pressure valve. The back pressure valve was not used in this study, since no boosting was applied. There is a 7.5 kW air heater at the intake air line for the heating purpose in this study. The intake air pressure and the intake temperature are measured from the intake manifold. The exhaust gas is sampled after the back pressure valve through a heated line, where the temperature is maintained over 190°C to avoid condensation. Emissions of CO, CO2, THC, and NOX were measured by Horiba Mexa 7500 DEGR. An IRD (infrared detector) method is used to measure the CO and CO2, whereas a CLD (Chemiluminescence detector) is used to 10 ACS Paragon Plus Environment

Page 11 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

measure the NOX and NO, while a FID (Flame ionization detector) is for THC by comparison with CH4 sample gas.

Back Pressure valve

Exhaust plenum

To ambient EGR cooler

Exhaust temperature Measuring point

EGR plenum

Emission meter

Dynamometer

Intake temperature Measuring point

EGR valve

Flow meter Pressurized air Maximum 11bar Intake plenum

Air heater

Intake pressure valve

Figure 1. Diagram of experimental setup. The fuel used in the study was chemical grade methanol which had a purity of 99.85%. Water constituted the remaining content within trace amounts of organic compounds. The properties of the methanol can be seen in Table 4. To improve the lubricity, 200 ppm of Infineum R655 was mixed to the methanol. The energy density of the additive was neglected. Table 4. Properties of methanol.33 Specifications RON MON H/C O/C LHV [MJ/kg] A/Fs Density [kg/m3] Heat of Vaporization [kJ/kg]

Methanol 107 – 109 92 4 1 19,9 6,45 792 1103

4. Results and Discussion In this section, the results of the low load condition and the idle condition are discussed separately. The discussion includes the results and comments of 3 bar IMEP in the first part


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

and 1 bar IMEP in the second part. Lastly, the combustion phasing sweep is discussed under the idle condition part. The experiments are started with a high intake temperature and reduced gradually to achieve the COV IMEPn up to 5% with the lowest required intake temperature. Figure 2 shows required intake temperatures, and Figure 3 shows in-cylinder flame temperatures at the start of combustion (CA01) for the COV IMEPn at the low load and the idle condition. The incylinder flame temperature at CA01 is calculated from the heat release curves when 1% of the total heat is released. The SI refers to the single injection case and the SPI refers to the split injection case in the figure. It can be seen that the COV IMEPn increases by the decreasing of the intake temperature. It is observed that the COV IMEPn 1% for 3 bar IMEP and the COV IMEPn 1% and COV IMEPn 2% for 1 bar IMEP are not achievable. The intake temperature requirement is narrow at the low load condition from 107°C to 102°C for COV IMEPn 2% to COV IMEPn 5%. The idle condition of the engine needs a higher intake temperature to maintain the same COV IMEPn values with the low load condition. The intake temperature requirement for the single injection case at the COV IMEPn 3% is 151°C, while it is 133°C and 122°C for the COV IMEPn 4% and 5%, respectively. It is also investigated that the idle condition with the split injection case needs a lower intake temperature than the single injection case. It is 137°C for the COV IMEPn 3%, 113°C for the COV IMEPn 4%, and 107°C for the COV IMEPn 5% at the idle condition split injection case. The reason for the lower intake temperature requirement is the split injection case reduces the cooling effect of methanol by splitting the fuel amount injected into the cylinder. The combustion chamber is cooled less with the low amount of the first injection, and the second injection is injected on to the first injection, which is warmed by the in-cylinder temperature. As a result, a lower intake temperature is required to provide the same combustion stability with the single injection. 12 ACS Paragon Plus Environment

Page 12 of 41

Page 13 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 2. Intake temperatures for COV IMEPn at the low load and idle condition.

Figure 3. In-cylinder temperatures at CA01 for low load and idle condition.

4.1 Low load condition The low load condition is commenced at 3 bar IMEP and speed at 800 rpm. The intake temperature is increased to 130°C, and reduced from this point to the lowest required temperature for each COV IMEPn value. Methanol fuel is tested at the single injection case with a constant start of injection (SOI) at -20 °CA, and without using EGR. Cylinder pressures and RoHR of the operating points are shown in Figure 4. It is seen that combustion stability reduces, and poor combustion occurs by lower intake temperature. Higher intake temperature from the COV IMEPn 5% to the COV IMEPn 2% provides advanced combustion phasing, which results with higher peak in-cylinder temperature and heat release rate. More fuel is injected at the COV IMEPn 4% and COV IMEPn 5% conditions to maintain the same IMEP. The injection duration is 1450 µs at the COV IMEPn 4% and COV IMEPn 5%, while it is 1350 µs at the COV IMEPn 2% and COV IMEPn 3%. It is also observed that RoHR curves are more widen, which indicates more heat is released to the exhaust.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 41

Figure 4. Cylinder pressure and RoHR curves at 3 bar IMEP. Combustion Stability The combustion stability means cyclic variations at the cylinder work output. The COV net IMEP (COV IMEPn) is used in this study with recorded 300 consecutive cycles and a crank angle increment of 0.2. In addition to the COV IMEPn, the standard deviation of net IMEP (STD IMEPn) is calculated in order to observe the cyclic variation from another perspective. Equation (5) and (6) are for calculation of the COV IMEPn, while equation (7) and (8) are for calculation of the mean value of IMEPn and the STD IMEPn.34 x = 1/N

N 1

xi

COV IMEPn = (

y=

σy =

N i=0 y

(5)

N i=1(xi

− x)2 / N)/ x). 100%

i /N

1/(N − 1)

(6)

(7)

N i=1[y

i − y]2

(8)

Where N is consecutive sampled cycles at the experiments, and x i is IMEPn of a specific combustion cycle, y(i) is the value of IMEPn of the i-th sample.


Page 15 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 5 shows the cyclic variation of the engine by the intake temperature change. The COV IMEPn was discussed in the previous section. Heywood declares that the upper limit of 10% for the COV is acceptable for continuous engine stability.35 However, the COV value of 5% is taken as the upper limit for this study. The COV IMEPn decreases by the increasing of the intake temperature. It can be seen that the STD IMEPn also shows the same trend as the COV IMEPn. It decreases from 0.175 to 0.070 by the increasing of the intake temperature.

Figure 5. Cyclic variation evaluation at 3 bar IMEP. Burn Duration and Ignition Delay Change at the burn duration and ignition delay by the effect of the intake temperature is shown in Figure 6. It is observed that the burn duration is 13°CA until the point of the COV IMEPn 2% at 107°C intake temperature. It can be said that the combustion is promoted at this point by the intake temperature, and the combustion event occurred more quickly. Higher intake temperature promotes the combustion of the methanol fuel, and it increases the rate of burning of the fuel. Liao et al.36, observed at their study that the increasing temperature results in an increase in the flame speed. It is also seen in the figure that the ignition delay decreases slightly from 29°CA to 27°CA. The reason is the intake temperature and intake pressure affects charge conditions during the ignition delay period.35 Higher intake temperature


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

provides a quicker formation of an optimum environment in the cylinder for fuel autoignition.

Figure 6. Burn duration and ignition delay at 3 bar IMEP. Exhaust Temperature and Global TMAX Figure 7 shows the variation of the exhaust temperature and the global TMAX at 3 bar IMEP. The global TMAX is the maximum in-cylinder flame temperature, which is obtained from the heat release curves. It can be seen in the figure that the exhaust temperature decreases from 250°C to 235°C by the increasing of the intake temperature. On the other hand, the global TMAX increases with higher intake temperature, which indicates support of the intake temperature to the combustion event. The global TMAX rises from 1560°C to 1595°C by the increasing intake temperature. The optimum SOI for lesser heat loss to the exhaust and good combustion can be the reason for the behavior of these curves.


Page 16 of 41

Page 17 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 7. Exhaust temperature and Global TMAX at 3 bar IMEP. Maximum Pressure Rise Rate (PRRMAX) Figure 8 shows the maximum pressure rise rate (PRRMAX) with the change at the intake temperature. Scania’s recommendation for the upper limit of PRRMAX is 20 bar/°CA for the engine used in this study. PRRMAX above this value can cause damage to the engine parts, and also increase the combustion noise. It can be seen in the figure that PRRMAX values for the low load operation with methanol fuel are far below from the 20 bar/°CA. It is constant at the 3 bar/°CA until the intake temperature of 104°C, and then it increases to the 4.4 bar/°CA at 107°C.

Figure 8. Maximum pressure rise rate at 3 bar IMEP.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 41

Efficiency and Fuel Consumption Thermodynamic efficiency (ƞt) and gross indicated efficiency (ƞGIE) are calculated by the equations from (9) to (12), and combustion efficiency (ƞc) is calculated according to THC emission in the exhaust gases. FuelMEP = mf x LHV / Vd

(9)

QMEP = FuelMEP x ƞc

(10)

ƞt = IMEP/ QMEP

(11)

ƞGIE = IMEP / FuelMEP

(12)

Where FuelMEP is the fuel mean effective pressure, mf is the fuel mass, and QMEP is the heat mean effective pressure. The efficiency trends are shown in Figure 9. The results show the intake temperature did not affect ƞt too much. It is close to 0.43 at all operating points. The narrow range of the intake temperature change does not show the effect on ƞt. On the other hand, ƞGIE is in rising trend by the increasing of the intake temperature, due to higher ƞc at higher intake temperatures. ƞc is also in increasing trend with increasing intake temperature. It increases slightly from 0.96 to almost 0.99 by the increasing of the intake temperature from 102°C to 107°C. Higher intake temperature provides more complete combustion at the low load operation.


Page 19 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 9. Efficiencies at 3 bar IMEP. Figure 10 shows indicated specific fuel consumption (ISFC) at all low load operating conditions. It is almost the same with 441.2 g/kWh and 440.9 at the intake temperatures of 102°C and 103°C, respectively. And then it decreases to 434.4 g/kWh at the intake temperature of 104°C, and to 427.9 g/kWh at the intake temperature of 107°C. Improved ƞc with higher intake temperature is the reason for lower ISFC. The ISFC decreases with higher intake temperature, which has similar behavior with the study of Woo et al.37

Figure 10. Indicated specific fuel consumption at 3 bar IMEP.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Emissions Regulated emissions of the engine at low load are shown in Figure 11. Methanol has an advantage of structure with short carbon chain, whose combustion emits lesser soot and particulate matter (PM) compared to diesel fuel.38 Yao et al.39, observed at their study that by the increase of the portion of methanol in diesel – methanol mixture, there was a reduction at the engine smoke emissions. Another study indicates that the emitted PM emissions mainly from the lubrication oil rather than the combustion of methanol.40 According to this information, PM emissions are not measured in this study and assumed as almost zero. Fuel/air equivalence ratio is the main cause of carbon monoxide (CO) emissions.35 The intake temperature affects CO formation in the cylinder. It is observed that CO emissions remain constant at all operating points. It is not in the same behavior as the literature. It can be said that the narrow range of the intake temperature at the operating conditions does not affect the CO emissions. Total hydrocarbon (THC) emissions are formed by over-lean or under-mix air-fuel mixture, wall quenching of the flame, and crevice losses in diesel engines.16,35 According to Mendez et al.41, maximum in-cylinder temperature and over-leaning are the main reasons for THC emission at the low load conditions. Another study revealed that the long ignition delay time and high heat of vaporization of methanol cause to auto-ignition resistant lean mixture near the cylinder wall, which can form the larger amount of THC.42 It is observed that THC emission decreases by the increasing of the intake temperature. It reduces from 16 g/kWh to 4 g/kWh, while increasing the intake temperature from 102°C to 107°C. The NOX emission remains almost constant at all low load operating conditions. It varies between 1 g/kWh to 1.7 g/kWh. The NOX emission is highly dependent on the in-cylinder temperature. In addition to this, lesser oxygen enters into the cylinder with higher intake


Page 20 of 41

Page 21 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

temperature.1 It can be said that these two effects neutralize each other, and the NOX emission remains almost constant.

Figure 11. Emissions at 3 bar IMEP. 4.2 Idle condition The idle condition is operated at 1 bar IMEP and speed at 800 rpm. The intake temperature is increased to 170°C, and reduced from this point to the lowest required temperature for each COV IMEPn value. Methanol fuel is tested under the single injection case and the split injection case. The optimum SOIs used in the study for the single injection case are -25, -19, and -13 °CA for the COV IMEPn 5%, COV IMEPn 4%, and COV IMEPn 3%, respectively. The constant SOI at -20 °CA for the first injection and at -7 °CA for the second injection is used at the split injection case. It is aimed that the CA50 remains constant at close to 5 °CA ATDC. EGR is not used in these operating points. There are small differences between operating points at the compression side of the cylinder curves. The reason is the slight fluctuation of the intake pressure, due to the test rig compressed air piping line. The cylinder pressures and RoHR curves of the single injection case and the split injection case are shown in Figure 12 and Figure 13. It can be seen in the figures that by the decreasing of the intake temperature, the maximum cylinder pressure reduces, and it shifts towards to the expansion stroke in both under the single injection and the split injection cases. 21 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The peak value of RoHR curves decreases, and the shape of the curves is more widen with lower stability and lower intake temperature. It shows similar behavior with the low load condition. It can also be seen from RoHR curves that the split injection provides a longer combustion duration than the single injection. The split injection reduces the cooling effect of methanol in the cylinder and provides a more complete burning of the fuel with slower combustion.

Figure 12. Cylinder pressure and RoHR curves at 1 bar IMEP single injection.

Figure 13. Cylinder pressure and RoHR curves at 1 bar IMEP split injection. Combustion Stability Figure 14 shows the cyclic variation at the cylinder work at 1 bar IMEP. It is observed that below COV IMEPn 3% cannot be achieved at 1 bar IMEP. It was discussed previously that the split injection case needs a lower intake temperature than the single injection case. It is 22 ACS Paragon Plus Environment

Page 22 of 41

Page 23 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

because the split injection minimizes the cooling effect of high latent heat of vaporization of methanol by splitting the amount of fuel entered into the cylinder at once. It is also observed that the STD IMEPn values at the COV IMEPn 3% and COV IMEPn 4% are almost the same, but it is higher at the split injection case at the COV IMEPn 5%. The low intake temperature increases the STD IMEPn at the split injection case if it is compared with other operating points.

Figure 14. Cyclic variation evaluation at 1 bar IMEP. Burn Duration and Ignition Delay Figure 15 shows the burn duration and the ignition delay curves at 1 bar IMEP. The burn duration increases by the increase of the intake temperature in both cases. It rises from 13°CA to 16°CA and from 16°CA to 20°CA for the single injection case and the split injection case, respectively. Higher intake temperature warms up the combustion chamber and provides a more complete and longer combustion period. On the other hand, the ignition delay reduces with higher intake temperature, which is consistent with the study of Wang et al.43 It decreases from 26°CA to 14°CA and from 10°CA to 8°CA for the single injection case and the split injection case, respectively. The increase in the intake temperature decreases the autoignition resistance of methanol, and it burns easier. There is another outcome that the split 23 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

injection case has longer burn duration and shorter ignition delay periods. It is again the consequence of a reduction at the cooling effect of methanol in the cylinder. The fuel autoignites easier, and warmer in-cylinder environment promotes more complete combustion.

Figure 15. Burn duration and ignition delay at 1 bar IMEP. Exhaust Temperature and Global TMAX Figure 16 shows the exhaust temperature and the global TMAX at the operating conditions under 1 bar IMEP. It is observed that the exhaust temperature increases by the increase of the intake temperature. Heat loss to the exhaust is higher with higher intake temperature at this operating condition. The global TMAX reduces at almost all operating points by the increasing of the intake temperature. It can be said that the heat loss to the exhaust affects the global TMAX and reduces it when the intake temperature is higher. The SOI timing can also be another reason for the reduction of the global TMAX and increased exhaust temperature. Another observation is the split injection case has lower global TMAX values than the single injection case. This study is in parallel with a study, indicates that the single injection has higher heat rejection to the piston than the split injection.44 It can be the result of slower combustion with longer burn duration under the split injection case.


Page 24 of 41

Page 25 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 16. Exhaust temperature and Global TMAX at 1 bar IMEP. Maximum Pressure Rise Rate (PRRMAX) PRRMAX at 1 bar IMEP is shown in Figure 17. It can be seen in the figure that PRRMAX increases by the increase of the intake temperature. It increases from the 3 bar/°CA to the 7.5 bar/°CA at the single injection case and from the 4.2 bar/°CA to the 11.2 bar/°CA at the split injection case. The intake temperature supports methanol to overcome its auto-ignition resistance quicker, which results in higher PRRMAX. The split injection case has higher PRRMAX than the single injection case. Suppression of the split injection on the cooling effect of methanol provides higher PRRMAX.

Figure 17. Maximum pressure rise rate at 1 bar IMEP.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Efficiency and Fuel Consumption ƞt, ƞGIE and ƞc are shown in Figure 18. The tests revealed that ƞt reduces slightly from 0.30 to 0.28 by higher intake temperature at the single injection case, and from 0.26 to 0.24 at the split injection case. The behavior of the thermodynamic efficiency is similar to the study of Kaiadi et al.45 Higher exhaust loses with higher intake temperature can be the reason for the reduction. ƞGIE shows the same behavior as ƞt. It reduces slightly from 0.29 to 0.28 at the single injection case, and from 0.26 to 0.24 at the split injection case. ƞc is in increasing trend from 0.98 to 0.99 at the intake temperature from 122°C to 151°C for the single injection case while increasing ƞc from 0.98 to 0.99 at the intake temperature from 107°C to 137°C for the split injection case.

Figure 18. Efficiencies at 1 bar IMEP. Figure 19 shows the indicated specific fuel consumption at 1 bar IMEP. It can be seen that ISFC increases by the increase of the intake temperature at the idle load, which is consistent with the study of Wang et al.1 It is also observed that the split injection case has higher ISFC than the single injection case. This behavior shows the same trend as the study.46 The single injection case consumes between 618.9 – 642.7 g/kWh of methanol, while the split injection case consumes between 705.5 – 749.9 g/kWh of methanol.


Page 26 of 41

Page 27 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 19. Indicated specific fuel consumption at 1 bar IMEP. Emissions Figure 20 shows the emission amounts at 1 bar IMEP. The SI indicates the single injection case, and the SPI indicates the split injection case in the figures. It can be seen that CO emission is constant at 6 g/kWh at all operating points for the single injection case. It is also constant at 7 g/kWh at all operating points for the split injection case. The fuel/air equivalence ratio is not affected by the intake temperature during the operating points. As a result, CO emission remains constant. THC emission decreases by the increasing of the intake temperature in both the single injection case and the split injection case. THC emission reduces from 6 g/kWh to 2 g/kWh at the single injection case, and it reduces from 9 g/kWh to 2 g/kWh at the split injection case. Higher THC level at the split injection can be formed, because of lower in-cylinder temperature, higher crevice losses, and higher wall quenching losses, due to colder cylinder walls. NOX emissions are higher by higher intake temperatures. Another observation is the split injection case has more NOX emission than the single injection case. The single injection case has NOX emission varies from almost zero to 10 g/kWh, while the split injection case has from 9.5 g/kWh to 15 g/kWh. The split injection reduces the cooling effect of methanol at the idle condition and promotes the combustion with higher PRRMAX than the single injection case. Despite lower global TMAX than the single 27 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

injection case, the split injection case has higher NOX emissions, due to higher PRRMAX with quicker temperature rise. In addition to this, nitrogen dioxide (NO2) formation can be higher at the split injection case, because the in-cylinder temperature is lower, and the cylinder walls are colder, which promotes the NO2 formation.35

Figure 20. Emissions at 1 bar IMEP. 4.3 Combustion phasing (CA50) sweep This part of the study is done to see the effect of the combustion phasing timing on the combustion characteristics of the engine and the engine emissions. The engine speed is constant at 800 rpm, and the engine load is 1 bar IMEP. The intake pressure is 1 bar absolute with the constant intake temperature of 130°C, as the author’s selection, to avoid the combustion stability problems and higher engine emissions. The SOI is changed to do the combustion phasing sweep. It is varied between the -23 °CA BTDC to the -14 °CA BTDC to achieve exact CA50 crank angle degrees from the 5 °CA ATDC to the 9 °CA ATDC. Figure 21 shows the cylinder pressure and RoHR curves depending on the combustion phasing position at 1 bar IMEP. It is observed that the position of the peak cylinder pressure is retarded, and the maximum value of the pressure curve is decreased by the sweep of the CA50 from the 5 °CA ATDC to the 9 °CA ATDC. The maximum value of RoHR curve increases, 28 ACS Paragon Plus Environment

Page 28 of 41

Page 29 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

while shifting of the CA50 from the 5 °CA ATDC to 6 °CA ATDC, but it decreases at further sweeps. RoHR curves are more widen during the sweeps of the CA50 from the 6 °CA ATDC to the 9 °CA ATDC.

Figure 21. Cylinder pressure and RoHR curves at 1 bar IMEP CA50 sweep. Combustion Stability The COV IMEPn and STD IMEPn at 1 bar IMEP CA50 sweep are shown in Figure 22. The COV IMEPn is constant at 3% by the CA50 sweep from the 5 °CA ATDC to the 7 °CA ATDC. After the CA50 at the 7 °CA ATDC, it increases to 4% first, and then 6%. Also, the STD IMEPn can be assumed constant at 0.035 between 5 °CA ATDC and 7 °CA ATDC. It increases to 0.04 and 0.06 at the CA50 at 8 °CA ATDC and 9 °CA ATDC, respectively. It can be said that the combustion event is deteriorated with the shifting of the CA50 towards to the expansion side.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 22. Cyclic variation evaluation at 1 bar IMEP CA50 sweep. Burn Duration and Ignition Delay Figure 23 shows the burn duration and the ignition delay at 1 bar IMEP CA50 sweep. It is observed that the burn duration first decreases, remains constant, and then increases. RoHR is higher at 6 °CA ATDC, which is the consequence of quicker combustion (shorter burn duration). At the later points, the combustion is slower, which results in lower RoHR and longer burn duration. The plots are consistent with each other. The ignition delay is in reducing the trend. From the CA50 at the 7 °CA ATDC to the 9 °CA ATDC, the difference is too small, for this reason, it is assumed as constant. Retarding of the SOI timing results with a shorter ignition delay period.


Page 30 of 41

Page 31 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 23. Burn duration and ignition delay at 1 bar IMEP CA50 sweep. Exhaust Temperature and Global TMAX Figure 24 shows the exhaust temperature and the global TMAX variation with the CA50 sweep. The exhaust temperature increases almost at all operating points except the CA50 at the 9 °CA ATDC. But the reduction at this point is only 1°C, for this reason, this drop can be ignored. The combustion event is shifted towards the expansion stroke, which results with more heat to the exhaust. It is consistent with the study of Manente.38 It can be the reason for the rise at the exhaust temperature. It is observed that the global TMAX decreases with the CA50 sweep. It decreases from the 1260°C to the 1185°C. It can be, because of the deteriorated combustion event, and heat loss to the exhaust.

Figure 24. Exhaust temperature and Global TMAX at 1 bar IMEP CA50 sweep. Maximum Pressure Rise Rate (PRRMAX) PRRMAX variation with the CA50 sweep is shown in Figure 25. It can be seen that PRRMAX decreases with the sweep. The combustion event is shifted to the expansion stroke with the SOI timing change. The combustion event has less effect on the piston motion and the PRRMAX is decreased, due to the expanded cylinder volume. It reduces from the 5 bar/°CA to the 3.3 bar/°CA at the CA50 between 5 °CA ATDC and 9 °CA ATDC. 31 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 25. Maximum pressure rise rate at 1 bar IMEP CA50 sweep. Efficiency and Fuel Consumption Figure 26 shows the variation of ƞt, ƞGIE, and ƞc with the CA50 sweep. It is seen that ƞt shows a slight decreasing trend from 0.29 to 0.28 with the sweep of the CA50 from the 5 °CA ATDC to the 9 °CA ATDC. The reason is more heat loss to the exhaust by the changing CA50 from the 5 °CA ATDC to the 9 °CA ATDC. Similarly, ƞGIE reduces slightly from 0.29 to 0.27 by the CA50 sweep. The combustion is deteriorated, and ƞc decreases with the CA50 sweep. It reduces from 0.99 to 0.97 with the CA50 sweep. The combustion event is less complete with the shifting of the peak cylinder pressure to the expansion stroke. Figure 27 shows the indicated specific fuel consumption versus the combustion phasing crank angle. It can be seen that ISFC increases from 630.1 g/kWh to 676.1 g/kWh, due to poor combustion event. More fuel is needed to achieve the same load of the engine.


Page 32 of 41

Page 33 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 26. Efficiencies at 1 bar IMEP CA50 sweep.

Figure 27. Specific fuel consumption at 1 bar IMEP CA50 sweep. Emissions The raw emissions and the indicated specific emissions are shown in Figure 28. CO emission is almost constant at all operating conditions. CO emission is mainly controlled by the fuel/air equivalence ratio.35 The equivalence ratio does not change during the experiments, which results with the constant CO emission. THC emission increases with the CA50 sweep from 3.5 g/kWh to 12.5 g/kWh. Poor combustion with the CA50 sweep is the reason for higher THC emission. It is observed that NOX emission is slightly higher at the latter CA50 sweeps, while it is almost zero at the CA50 at the 5 °CA ATDC. It increases from 0.01g/kWh to 0.6 g/kWh from 5 °CA ATDC to 9 °CA ATDC, however, global TMAX is lower at retarded 33 ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

combustion phasing. The trend is similar as reported in previous studies.47 - 49 NOX emission increased with the sweep of SOI from -20 °CA BTDC to close to TDC in these studies. It increases rapidly, while the combustion event is between TDC and close to 20 °CA ATDC35, which can be the reason for higher NOX emissions at retarded CA50s. Another reason can be uneven in-cylinder temperature distribution during retarded CA50s. The combustion temperature of locally rich zones can exceed the high NOX formation temperature limit of 2000 K.47,50,51 Although it is higher at latter operating points, it does not exceed 1 g/kWh.

Figure 28. Emissions at 1 bar IMEP CA50 sweep.

5. Conclusions The study is about the investigation of the effect of the intake temperature on the low load limitations of the methanol PPC. The engine stability, the combustion characteristics and the engine emissions were investigated at 800 rpm, 3 bar IMEP as the low load condition and 1 bar IMEP as the idle condition. Finally, the combustion phasing sweep was done at 1 bar IMEP at the constant engine speed of 800 rpm and the constant intake temperature of 130°C to see the variation at the engine parameters, the combustion characteristics, and the engine emissions. The conclusions from the study are:


Page 34 of 41

Page 35 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels



Lower engine loads need a higher intake temperature to maintain the same COV IMEPn value. The COV IMEPn 1% for the low load condition and the COV IMEPn 1% and 2% for the idle condition are not achievable at these engine operating conditions. The split injection case requires a lower intake temperature than the single injection case. The COV IMEPn at the CA50 sweep is at required levels until 9 °CA ATDC. The STD IMEPn shows similar behavior with the COV IMEPn by the change of the intake temperature.



The burn duration and the ignition delay decrease from 13°CA to 10°CA at the low load condition by the increasing of the intake temperature. On the other hand, the burn duration rises from 13°CA to 16°CA and from 16°CA to 20°CA at the single injection case and the split injection case, respectively, by higher intake temperature. The ignition delay shows the same behavior at the idle condition with the low load condition. The split injection case has longer burn duration and shorter ignition delay duration. The ignition delay decreases from 24°CA and remains constant at 18°CA after 7 °CA ATDC at the CA50 sweep. The burn duration first decreases to 13°CA from 16°CA and then increases to 15°CA at 7 ° CA ATDC.



The combustion efficiency increases from 0.96 to almost 0.99 by the increasing of the intake temperature, on the other hand, the thermodynamic efficiency remains constant at 0.43 at 3 bar IMEP. The combustion efficiency increases slightly from 0.98 to 0.99 in both cases of 1 bar IMEP, while the thermodynamic efficiency decreases slightly from 0.30 to 0.28 and from 0.26 to 0.24 at the single injection case and the split injection case, respectively. The gross indicated efficiency increases from 0.41 to 0.42 at 3 bar IMEP, due to lower indicated specific fuel consumption at higher intake temperatures. It shows the same trend with the thermodynamic efficiency at 1 bar


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

IMEP. All efficiencies decrease with the CA50 sweep from 5 °CA ATDC to 9 °CA ATDC, due to heat loss to the exhaust and incomplete combustion event. 

The CO emission remains constant in both the low load condition and the idle condition. The split injection case has higher CO emission than the single injection case. The CA50 sweep also does not affect CO emission. THC emission decreases by the increase at the intake temperature in both the low load condition and the idle condition. The single injection case has a higher THC emission than the split injection case. THC emission increases with the CA50 sweep from 5 °CA ATDC to 9 °CA ATDC. NOX emission remains constant at the low load condition, but it increases at the idle condition and with the CA50 sweep. The split injection case has higher NOX emission than the single injection case.

This paper confirms that the engine can be operated at the low load conditions with the methanol PPC at good stability, even at idle load (1 bar IMEP), with appropriate intake temperature. Future work can be cold operating of the engine at the low load operation to see cold start behavior of the methanol PPC, and close to stoichiometric operation at the low load operation, which has the benefit using a three-way catalyst to achieve lower engine emissions. Nomenclatures and Abbreviations A/Fs

Stoichiometric air to fuel ratio

ATDC

After top dead center

BTDC

Before top dead center

BTE

Brake thermal efficiency

CA01

Start of combustion

COV IMEPn

Coefficient of variation of net indicated mean effective pressure

CP

Specific heat at constant pressure

CV

Specific heat at constant volume

DISI

Direct injection spark ignition

EGR

Exhaust gas recirculation

EVO

Exhaust valve opening

FuelMEP

Fuel mean effective pressure

GCI

Gasoline compression ignition

Global Tmax

Maximum in-cylinder flame temperature


Page 36 of 41

Page 37 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

G.ON

Gasoline octane number

HCCI

Homogeneous charge compression ignition

IMEP

Indicated mean effective pressure

IMEPn

Net indicated mean effective pressure

ISFC

Indicated specific fuel consumption

IVC

Intake valve closing

LHV

Lower heating value

MON

Motor octane number

PPC

Partially premixed combustion

PRF

Primary reference fuel

PRRMAX

Maximum pressure rise rate

QMEP

Heat mean effective pressure

rc

Compression ratio

RoHR

Rate of heat release

RON

Research octane number

SI

Single injection

SPI

Split injection

SOI

Start of injection

SoMI

Start of main injection

STD

Standard deviation

Vd

Engine displacement volume

°CA

Crank angle degree

σIMEP

Standard deviation of IMEP

ƞC

Combustion efficiency

ƞGIE

Gross indicated efficiency

ƞt

Thermodynamic efficiency

𝜆

Air-fuel equivalence ratio

γ

The ratio of specific heats

Acknowledgment This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR2017-CPF-3319. References (1) Wang, S.; van der Waart, K.; Somers, B.; and de Goey, P. Experimental study on the potential of higher octane number fuels for low load partially premixed combustion. SAE Technical Paper, 2017, 2017-01-0750, doi:10.4271/2017-01-0750.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(2) Tuner, M. Review and benchmarking of alternative fuels in conventional and advanced engine concepts with emphasis on efficiency, CO2, and regulated emissions. SAE Technical Paper, 2016, 2016-01-0882, doi:10.4271/2016-01-0882. (3) Kaiadi, M.; Johansson, B.; Lundgren, M; Gaynor, J. A. Sensitivity analysis study on ethanol partially premixed combustion. SAE Int. J. Engines 6(1): 2013, doi:10.4271/2013-01-0269. (4) Belgiorno, G.; Dimitrakopoulos, N.; Di Blasio, G.; Beatrice, C.; Tunestal, P.; Tuner, M. Effect of the engine calibration parameters on gasoline partially premixed combustion performance and emissions compared to conventional diesel combustion in a light-duty Euro 6 engine. Applied Energy, 2018, 228, 2221 – 2234. (5) Yin, L.; Turesson, G.; Tunestal, P.; Johansson, R. Evaluation and transient control of an advanced multicylinder engine based on partially premixed combustion. Applied Energy, 2019, 233-234, 1015 – 1026. (6) Han, X.; Yang, Z.; Wang, M.; Tjong, J.; Zheng, M. Clean combustion of n-butanol as a next generation biofuel for diesel engines. Applied Energy, 2017, 198, 347 – 359. (7) Tang, Q.; Liu, H.; Li, M.; Yao, M. Optical study of spray-wall impingement impact on early, injection gasoline partially premixed combustion at low engine load. Applied Energy, 2017, 185, 708 – 719. (8) Benajes, J.; Molina, S.; Garcia, A.; Monsalve-Serrano, J.; Durrett, R. Performance and engine-out emissions evaluation of the double injection strategy applied to the gasoline partially premixed compression ignition spark assisted combustion concept. Applied Energy, 2014, 134, 90 – 101. (9) Benajes, J.; Molina, S.; Garcia, A.; Monsalve-Serrano, J.; Durrett, R. Conceptual model description of the double injection strategy applied to the gasoline partially premixed compression ignition combustion concept with spark assistance. Applied Energy, 2014, 129, 1 – 9. (10) Woo, C.; Kook, S.; Hawkes, E. R. Effect of intake air temperature and common-rail pressure on ethanol combustion in a single-cylinder light-duty diesel engine. Fuel, 2016, 180, 9 – 19. (11) An, Y.; Jaasim, M.; Raman, V.; Perez, F. E. H.; Sim, J.; Chang, J.; Im, H. G.; Johansson, B. Homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) in compression ignition engine with low octane gasoline. Energy, 2018, 158, 181 – 191. (12) Borgqvist, P.; Tunestal, P.; Johansson, B. Gasoline partially premixed combustion in a light duty engine at low load and idle operating conditions. SAE Technical Paper, 2012, 2012-01-0687, doi:10.4271/2012-010687. (13) Weall, A.; Collings, N. Gasoline fuelled partially premixed compression ignition in a light duty multi cylinder engine: a study of low load and low speed operation. SAE Int. J. Engines 2(1): 2009, doi:10.4271/200901-1791. (14) Solaka, H.; Aronsson, U.; Tuner, M.; Johansson, B. Investigation of partially premixed combustion characteristics in low load range with regards to fuel octane number in a light-duty diesel engine. SAE Technical Paper, 2012, 2012-01-0684, doi:10.4271/2012-01-0684. (15) Yin, L.; Lundgren, M.; Wang, Z.; Stamatoglou, P.; Richter, M.; Andersson, Ö.; Tunestal, P. High efficient internal combustion engine using partially premixed combustion with multiple injections. Applied Energy, 2019, 233-234, 516 – 523. (16) An, Y.; Raman, V.; Tang, Q.; Shi, H.; Sim, J.; Chang, J.; Magnotti, G.; Johansson, B. Combustion stability study of partially premixed combustion with low-octane fuel at low engine load conditions. Applied Energy, 2019, 235, 56 – 67.


Page 38 of 41

Page 39 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(17) Sun, C.; Kang, D.; Bohac, S. N.; Boehman, A. L. Impact of fuel and injection timing on partially premixed charge compression ignition combustion. Energy Fuels, 2016, 30, 4331 – 4345. (18) Przybyla, G.; Postrzednik, S.; Zmudka, Z. The impact of air-fuel mixture composition on SI engine performance during natural gas and producer gas combustion. IOP Conference Series: Materials Science and Engineering, Vol. 148, No. 1, p. 12082, September 2016. (19) Maurya, R. K.; Agarwal, A. K. Experimental investigation on the effect of intake air temperature and airfuel ratio on cycle-to-cycle variations of HCCI combustion and performance parameters. Applied Energy, 2011, 88, 1153 – 1163. (20) Sarjovaara, T.; Larmi, M.; Vuorinen, V. Effect of charge air temperature on E85 dual-fuel diesel combustion. Fuel, 2015, 153, 6 – 12. (21) Kumar, K. S.; Raj, R. Effect of fuel injection timing and elevated intake air temperature on the combustion and emission characteristics of dual fuel operated diesel engine. Procedia Engineering, 2013, 64, 1191 – 1198. (22) Wu, H.; Fan, C.; He, J.; Hsu, T. Optimal factors estimation for diesel/methanol engines changing methanol injection timing and inlet air pressure. Energy, 2017, 141, 1819 – 1828. (23) Papagiannakis, R. G. Study of air inlet preheating and EGR impacts for improving the operation of compression ignition engine running under dual fuel mode. Energy Conversion Management, 2013, 68, 40 – 53. (24) Pan, W.; Yao, C.; Han, G.; Wei, H.; Wang, Q. The impact of intake air temperature on performance and exhaust emissions of a diesel methanol dual fuel engine. Fuel, 2015, 162, 101 – 110. (25) Benajes, J.; Martin, J.; Novella, R.; Thein, K. Understanding the performance of the multiple injection gasoline partially premixed combustion concept implemented in a 2-stroke high speed direct injection compression ignition engine. Applied Energy, 2016, 161, 465 – 475. (26) Leermakers, C. A. J.; Bakker, P. C.; Nijssen, B. C. W.; Somers, L. M. T.; Johansson, B. H. Low octane fuel composition effects on the load range capability of partially premixed combustion. Fuel, 2014, 135, 210 – 222. (27) Naser, N.; Jaasim, M.; Atef, N.; Chung, S. H.; Im, H. G.; Sarathy, S. M. On the effects of fuel properties and injection timing in partially premixed compression ignition of low octane fuels. Fuel, 2017, 207, 373 – 388. (28) Mao, B.; Liu, H.; Zheng, Z.; Yao, M. Influence of fuel properties on multi-cylinder PPC operation over a wide range of EGR and operating conditions. Fuel, 2018, 215, 352 – 362. (29) International Energy Agency. Implementing agreement for advanced motor fuels, methanol, http://www.iea-amf.org/content/fuel_information/methanol; [accessed 7 September 2018]. (30) Gong, C.; Peng, L.; Chen, Y.; Liu, J.; Liu, F.; Han, Y. Computational study of intake temperature effects on mixture formation, combustion and unregulated emissions of a DISI methanol engine during cold start. Fuel, 2018, 234, 1269 – 1277. (31) Kristersson, G. Partially premixed combustion with methanol in a heavy duty engine. Thesis for the Degree of Master of Science, Lund University, Department of Energy Science, Division of Combustion Engines, Sweden; 2015. (32) Shamun, S.; Zincir, B.; Shukla, P.; Valladolid, P. G.; Verhelst, S.; Tuner, M. Quantification and analysis of the charge cooling effect of methanol in a compression ignition engine utilizing PPC strategy. Proceedings of the ASME 2018, Internal Combustion Engine Division Fall Technical Conference, ICEF2018, 4-7 November 2018, San Diego, CA, USA.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(33) Shamun, S.; Shen, M.; Johansson, B.; Tuner, M. et al. Exhaust PM analysis of alcohol fueled heavy-duty engine utilizing PPC. SAE Int. J. Engines 9(4): 2016, doi: 10.4271/2016-01-2288. (34) Czarnigowski, J. Analysis of cycle-to-cycle variation and non-uniformity of energy production: tests on individual cylinders of a radial piston engine. Applied Thermal Engineering, 2011, 31, 1816 – 1824. (35) Heywood, J. B. Internal combustion engine fundamentals. McGraw-Hill Education, 1988. (36) Liao, S. Y.; Jiang, D. M.; Huang, Z. H.; Shen, W. D.; Yuan, C.; Cheng, Q. Laminar burning velocities for mixtures of methanol and air at elevated temperatures. Energy Conversion and Management, 2007, 48, 857 – 863. (37) Woo, C.; Kook, S.; Hawkes, E. R. Effect of intake air temperature and common-rail pressure on ethanol combustion in a single-cylinder light-duty diesel engine. Fuel, 2016, 180, 9 – 19. (38) Manente, V. Gasoline partially premixed combustion - an advanced internal combustion engine concept aimed to high efficiency, low emissions and low acoustic noise in the whole range. Thesis for the PhD., Lund University, Department of Energy Science, Division of Combustion Engines, Sweden; 2010. (39) Yao, C.; Cheung, C. S.; Cheng, C.; Wang, Y.; Chan, T. L.; Lee, S. C. Effect of diesel/methanol compound combustion on diesel engine combustion and emissions. Energy Conversion and Management, 2008, 49, 1696 – 1704. (40) Shamun, S.; Novakovic, M.; Malmborg, V. B.; Preger, C.; Shen, M.; Messing, M. E.; Pagels, J.; Tuner, M.; Tunestål, P. Detailed characterization of particulate matter in alcohol exhaust emissions. 9 th International Conference on Modeling and Diagnostics for Advanced Engine Systems, COMODIA 2017, 25 – 28 July 2017, Okayama, Japan. doi: 10.1299/jmsesdm.2017.9.B304. (41) Mendez, S.; Kashdan, J. T.; Bruneaux, G.; Thirouard, B.; Vangraefschepe, F. Formation of unburned hydrocarbons in low temperature diesel combustion. SAE Int. J. Engines, 2(2):205-225, 2010, doi:4271/200901-2729. (42) Pucilowski, M.; Jangi, M.; Shamun, S.; Li, C.; Tuner, M.; Xue-Song, B. Effect of start of injection on the combustion characteristics in a heavy-duty DICI engine running on methanol. SAE Technical Paper, 2017, 201701-0560, doi:10.4271/2017-01-0560. (43) Wang, Q.; Yao, C.; Dou, Z.; Wang, B.; Wu, T. Effect of intake pre-heating and injection timing on combustion and emission characteristics of a methanol fumigated diesel engine at part load. Fuel, 2015, 159, 796 – 802. (44) Tanov, S.; Salvador-Iborra, J.; Andersson, Ö.; Olmeda, P.; Garcia, A. Influence of the number of injections on piston heat rejection under low temperature combustion conditions in an optical compressionignition engine. Energy Conversion and Management, 2017, 153, 335 – 345. (45) Kaiadi, M.; Johansson, B.; Lundgren, M.; Gaynor, J. A. Experimental investigation on different injection strategies for ethanol partially premixed combustion. SAE Technical Paper, 2013, 2013-01-0281, doi:10.4271/2013-01-0281. (46) Kim, D.; Bae, C. Application of double-injection strategy on gasoline compression ignition engine under low load condition. Fuel, 2017, 203, 792 – 801. (47) Li, C.; Yin, L.; Shamun, S.; Tuner, M.; Johansson, B.; Solsjo, R.; Bai, X. Transition from HCCI to PPC: The sensitivity of combustion phasing to the intake temperature and the injection timing with and without EGR. SAE Technical Paper, 2016, 2016-01-0767, doi: 10.4271/2016-01-0767.


Page 40 of 41

Page 41 of 41 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(48) Li, C.; Xu, L.; Bai, X.; Tunestal, P.; Tuner, M. Effect of piston geometry on stratification formation in the transition from HCCI to PPC. SAE Technical Paper, 2018, 2018-01-1800, doi: 10.4271/2018-01-1800. (49) An, Y.; Jaasim, M.; Raman, V.; Im, H. G.; Johansson, B. In-cylinder combustion and soot evolution in the transition from conventional compression ignition (CI) mode to partially premixed combustion (PPC) mode. Energy Fuels, 2018, 32, 2306 – 2320. (50) Kim, D.; Ekoto, I.; Colban, W.; Miles, P. C. In-cylinder CO and UHC imaging in a light-duty diesel engine during PPCI low-temperature combustion. SAE Int. J. Fuels Lubr. 1(1): 933-956, 2009, doi: 10.4271/2008-01-1602. (51) Miles, P. C.; Choi, D.; Pickett, L. M.; Singh, I. P.; Henein, N.; Rempel Ewert, B. A.; Yun, H.; Reltz, R. D. Rate-limiting processes in late-injection, low temperature diesel combustion regimes. Thiesel 2004, Conference on Thermo-and Fluid Dynamic Processes in Diesel Engines: September 7-10, 2004, Valencia, Spain.


Investigation of Effect of Intake Temperature on Low Load Limitations

Recommend Documents