Impact of changing compression ratio on engine characteristics of an SI engine fueled with equi-volume blend of methanol and gasoline

Journal Pre-proof Impact of changing compression ratio on engine characteristics of an SI engine fueled with equi-volume blend of methanol and gasoline B.S. Nuthan Prasad, Jayashish Kumar Pandey, G.N. Kumar PII:

S0360-5442(19)32300-X

DOI:

https://doi.org/10.1016/j.energy.2019.116605

Reference:

EGY 116605

To appear in:

Energy

Received Date: 24 May 2019 Revised Date:

13 November 2019

Accepted Date: 22 November 2019

Please cite this article as: Nuthan Prasad BS, Pandey JK, Kumar GN, Impact of changing compression ratio on engine characteristics of an SI engine fueled with equi-volume blend of methanol and gasoline, Energy (2019), doi: https://doi.org/10.1016/j.energy.2019.116605. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Impact of changing Compression Ratio on Engine Characteristics of an SI engine fueled with equi-volume blend of Methanol and Gasoline Nuthan Prasad B. S.a*, Jayashish Kumar Pandeya, Kumar G.N.b a

Department of Mechanical Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore 575025, India *[email protected] ABSTRACT In the present investigation, experiments were conducted in wide open throttle condition (WOT) for different speed ranging from 1200 rpm to 1800 rpm at an interval of 200 on a single-cylinder four-stroke variable compression ratio (VCR) SI engine. The engine fueled with equi-volume blend of methanol/gasoline fuel, while 14° BTDC ignition timing is maintained for all three different compression ratios (8, 9 & 10). Increasing the compression ratio from CR8 to CR10 for the methanol/gasoline blend has improved combustion efficiency by increasing the peak pressure and net heat release value by 27.5 % and 30 % respectively at a speed of 1600 rpm. The performance results show a good agreement of improvisation of 25% increase in BTE, and BSFC reduction by 19% at compression ratio 10:1. At higher compression ratio 10:1, there was a significant decrease observed in CO and HC by 30-40 %, and the same trend is observed at all speeds; however, NOx emission increased with the increasing CR. Keywords: Methanol-Gasoline blend; Variable Compression Ratio; Combustion; Emission Nomenclature M50

50% methanol by volume

BTDC

before Top Dead Centre

BSFC

Brake Specific Fuel Consumption

BSEC

Brake Specific Energy Consumption

BTE

Brake Thermal Efficiency

BP

Brake Power

NOx

Oxides of Nitrogen

CO

Carbon monoxide

CO2

Carbon dioxide

HC

Hydro Carbon 1

PE

Performance Electronics

DAQ

Data Acquisition system

ECU

Electronic Control Unit

SI

Spark Ignition

CDI

Capacitor Discharge Ignition

CI

Compression Ignition

VCR

Variable Compression Ratio

EPFI

Electronic Port Fuel Injector

ADC

Analog to Digital Converter

DME

Dimethyl ether

WOT

Wide open Throttle

RGF

Residual Gas Fraction

1. INTRODUCTION Methanol as a fuel in the IC engine is strongly proposed, and its utility as a fuel has been proved by many researchers and documented in the literature. The potential alternative energy sources such as solar energy, nuclear energy, wind energy, have not shown promising capabilities against conventional fossil fuels [1]. Whereas methanol with good combustion properties, renewability, and extraction from a wide range of energy sources, has been considered as a very good alternative fuel. The favorable properties of methanol have allowed it to be directly used in unmodified IC engines. Yang and Jackson (2012) [2], estimation of China's methanol economy suggest, it is the largest producer and user of methanol according to world statistical data. In 1990, the United States amended bill called Clean Air Act Amendment; methanol came to surface because of its properties such as high octane number and oxygen presence in its chemical structure. M85 fuels became popular in the US market at 1997[3], as an alternative for leaded gasoline engines. Later critical review was done on the Methanol-fueled engine emissions and the toxicity of Methanol vapors. In the recent past, methanol has a huge demand for development of clean electrochemical energy converters (Alcohol fuel cells) to power electric vehicles; this has led way to develop new active materials for alcohol electro-oxidation process, which is low cost, durable and produce efficient electrocatalytic reaction [4,5]. Further, the favorable chemical and combustion properties of methanol and ethanol have promoted it to be commonly used as an 2

additive with gasoline in SI engines [6,7]. When methanol used as a fuel blend with , certain chemical characteristics makes it best combination for vehicular usage [8] (A. Koenig et al. 1976), such as antiknock property and use as a fuel extender, economical when emissions are considered owing to its positive results. More importantly, it contains zero sulphur, results in reduced tailpipe acids. High load operation in an engine requires high octane number fuel; octane number can be optimized by octane enhancer and thus obtain improved engine efficiency and CO2 emissions [9]. Methanol blended gasoline provides a good advantage to fuel combustion inside a cylinder, due to the presence of extra oxygen compound, higher flame speed and high latent heat of vaporization, hence attributes to reduced CO, NOx and HC gases[10–13], while improved combustion increases CO2 emissions[14]. Sharudin et al. (2016), documented valuable information about the study of fuel properties of methanol and the nature of the combustion process when methanol/gasoline blend is used. The study on Methanol/gasoline blends has extended based on many factors such as, correlation of noise and vibrations on performance and combustion of GDI engine fueled with gasohol [16]. Recent studies are on the development of computational tools for the investigation of advanced mode of combustion, efficiency enhancement techniques, and new technology for emission control [17–19]. 1.1. Effect of Operating Parameters References states, the study of pure or blended Methanol were conducted for varying ignition time[20–23], optimal mixing ratio, and gaseous fuel as additive[24–26] and other parameter changes which affects the characteristics of the engine. The study conducted for different blend ratios of methanol with gasoline has shown a good improvement with performance and reduced emission with lower blend ratios between 5-20 percent [6,27]. Whereas, an increase of methanol blend percentage has a significant effect on power, torque, and specific fuel consumption due to its lower energy content compared to gasoline. However, SI engine operating with M85 has shown a huge drop in HC, CO, and NOx emission despite the loss of power output[28,29]. Lately, a numerical investigation conducted using computational fluid dynamics coupled to chemical kinetics, has been very handy in studying the effect of change of engine parameters on performance, combustion and emission characteristics[22,30–32]. The higher octane number of methanol attributes to improved antiknock characteristics in gasoline, which enables the gasoline-fueled engine to operate at higher compression ratios[33]. 3

Increased compression ratios could yield 5 to 20 percent more power [34]. When peak pressure and temperature decreases with lower CR, the losses inside the combustion chamber become greater, and this increases BSFC [35]. Increasing CR of SI engine while running with methanol increases brake thermal efficiency and torque substantially, also release significantly less CO, CO2, and NOx emissions [36]. The injection and ignition strategies on the SI engine fueled with methanol, and also the effect of injection nozzle parameter on regulated emissions was studied and concluded methanol engine can burn smokeless [37]. The regulated (CO, HC, and NOx) and unregulated emissions (formaldehyde and acetaldehyde) from M15 and M25 blends were tested, it is found that there was a decrease in CO and HC emissions, while NOx was higher compared to gasoline and methanol blends yield more unregulated gases [27]. An extensive study conducted with use of alcohol as a neat fuel or as a blend with gasoline has been done; however, effect of compression ratio has a huge influence on engine characteristics, Omar I. Awad et al. [38], in his review included more papers on blends of ethanol, butanol and very few on methanol; whereas, higher volumetric blend ratio of methanol review is not included in the literature. The scope of this work is to investigate the combined effect of M50 fuel and different compression ratio on performance, combustion, and emission characteristics of single-cylinder four-stroke SI Engine. No major studies were found on the effect of change of engine operating parameters for high fraction methanol blends fueled in standard SI engine model. The study here provides the convenience of use of methanol in IC engines with small operating changes. It also guides the researchers to explore the effect of change of operating parameters with a small modification to the existing engine can operate with neat methanol. Finally, spreading positive intention to use methanol in large scale and appeal for subsidizing and promote methanol as a long-term energy option for the world. 2. EXPERIMENTAL Methodology 2.1. Details of Engine setup The experimental test rig consists of 0.661-liter single cylinder water-cooled naturally aspirated Kirloskar TV1 series compression ignition engine, generally used for gen-sets and pump sets, aptly modified to operate as SI engine. The diesel fuel injector is removed and at that place 4

electronically controlled CDI spark plug is installed; the intake line is converted from original air only to EPFI intake system with throttle body arrangement. The mechanical fuel pump originally installed with the engine is removed, and the cylinder block is modified as variable compression ratio (VCR) system as tilting cylinder block arrangement by the help of a push screw system designed to change the compression ratio of the engine. Compression Ratio can be varied without stopping the engine and without making any significant changes to the combustion chamber geometry. A pressure transducer (Make-PCB Piezotronics, Model SM111A22) placed in the cylinder head measures in-cylinder pressure. The DAQ (NI-USB-6210) interfaces signal to the computer for P-θ & PV diagrams. The engine is coupled with Eddy current dynamometer (Make-Technomech, Model-TMEC10) for loading purpose. Fig. 1 presents a schematic of the experimental test rig used for the study.

Fig.1. Schematic diagram of Experimental setup Crank angle encoder with trigger marked precision marker disk with 360° angle marks is mounted on the crankshaft to measure engine crank angle. The marks are scanned by a photoelectric cell, and signals are used by the engine management system.

5

The experimental lab setup view presented in Fig.2 has panel box consisting of the air box of rectangular shape at the base of the panel. The air box is fitted with a mass flow sensor and an orifice type manometer for manual reading. The fuel storage tank at the top of the set-up is also rectangular shaped with two compartments with capacity 7.5 liters each. A burette is provided with a manual three-way valve for fuel measuring, a signal interface for air and fuel flow measurements, process indicator, and engine indicator. Table 1 gives the specification of measurement devices used in the experimental trials. The engine exhaust is cooled through a water-gas heat exchanger type calorimeter. Two Rotameters, one for the calorimeter and other for engine and dynamometer water flow measurement are installed. One K type thermocouple 1.5mm diameter is installed in the exhaust manifold which can measure up to 1,260°C and six RTD temperature sensors, one for water supply to set-up, one each for water exit from engine, calorimeter and dynamometer respectively, one thermocouple for exhaust gas inlet to the calorimeter while sixth thermocouple is installed for exhaust gas out of calorimeter. A temperature sensor of the RTD type is too installed for measure ambient temperature. The whole unit enables the study of engine performance parameters. Windows-based software package supported by LAB view based ‘Engine Soft’ software, gives performance evaluation of brake power, indicated power, frictional power, BMEP, IMEP, brake thermal efficiency, indicated thermal efficiency, mechanical efficiency, volumetric efficiency, specific fuel consumption, the air-fuel ratio. Table 1. Specification of the measurement devices Equipment

Specifications

K TYPE THERMOCOUPLE

Thermocouple grade wire, (−270 to 1,260°C) Standard: ± 2.2°C or ±0.75%

RTD Temperature Sensors

PT100 Series, Sensing Element: Single 100-ohm platinum (Pt 100), 3-wire; TCR = 0.00385 ohm/ohm/°C Probe: 6mm, 316 stainless steel sheath, single RTD is embedded in alumina powder Sensitivity:Class A ±[0.15 +0.002 |t|] °C, 5 seconds response time Range: 0°C to 1150°C

6

Airflow measurement transmitter

Accuracy ≤0.25 (BFSL) % of span Response time (10-90%) ≤1 ms

Load cell

Zero balance (FSO) ±0.1 mV/V Tolerance on output (FSO) ±0.25% Non-linearity (FSO) <±0.025% Rise time- 2 ms Sensitivity - 1 mV/psi Resolution-0.1 psi Resonant frequency - 400 kHz Low frequency response (-5%)- 0.001 Hz Discharge time constant - 500 s

Piezo-sensor

Fig. 2. Experimental Lab Setup

1 2 3 4 5

Calorimeter Fuel burette Manometer Digital Voltmeter Load Indicator

8 9 10 11 12 7

Exhaust tailpipe Injector block Engine block Throttle body Dynamometer

6 7

Speed Indicator Rotameter

13 14

Load cell Crank Encoder

2.2. Description of Operating Conditions Fuel tested was industrial-grade methanol with a purity of 99.9%. The methanol is blended separately (splash blending followed by magnetic stirrer) and added to the fuel tank. Table 2-3 provides fuel properties for methanol and gasoline . The experiment was carried out for wideopen throttle (WOT) operating condition with engine load control strategy, based on varying ignition time at constant compression ratio. Experiments were performed under ambient temperature between 25°C to 32°C in dry conditions. During the experiment at each fixed CR engine was kept running for two minutes in the idle condition and then the operating conditions are achieved gradually by increasing the throttle opening and increasing the applied load by keeping the speed constant at 1800. After achieving WOT for 1800, the engine is kept running till stability. The experimental results are noted for 1800 WOT at maximum possible load at this speed, and then further loading is done at constant throttle opening to reduce till 1200 at intervals of 200. At each fixed speed engine is kept running till stability. The water flow to engine cooling, Dynamometer, and the calorimeter are kept at 200kg per hour. Table 2. The properties of Methanol and Gasoline [39] Fuel Property

Methanol

Gasoline

Oxygen content

50%

0

Density (kg/l)

0.79

0.735

Stoichiometric air/fuel ratio

6.45

14.6

Low calorific value (MJ/Kg)

19.66

44.5

High calorific value (MJ/Kg)

22.3

46.6

Boiling Point (°C)

64.8

30-220

Freezing Point (°C)

-98

-57

Flash Point (°C)

11

-45

Auto-ignition temperature (°C)

470

~300

8

Research Octane number

109

80-98

Motor Octane number

88.6

81-84

Flammability limit

6.7-36

1.47-7.6

Viscosity (at 20°C) (CP)

0.6

0.29

Heat of Vaporization (kJ/kg)

1100

310

Table 3. Properties of Methanol blend. Fuel

Gasoline

M50

Gasoline (volume %)

100

50

Methanol (volume %)

0

50

Density (kg/l)

0.735

0.762

Low calorific value (MJ/Kg)

46.4

33.24

Stoichiometric A/F (kg/kg)

15

6.452

Composition (C,H,O) %wt

86,14,0

62,13,25

The Engine details are given in Table 5. Operating parameters of engine are controlled by open ECU; the programmable fuel and ignition control system is developed by Performance Electronics, Ltd. PE3 series system is an engine control unit connected to windows based operating system computer through Ethernet port. PE monitor software installed on a computer, controls the fuel injector open time for every engine cycle to measure fuel consumption. It also configures Ignition timing, the type of ignition, coil charge time. An AVL DIGAS 444 exhaust gas analyzer is used to measure the exhaust gas emissions of CO (% volume), CO2 (% volume), HC (ppm), O2 (% volume), NOx (ppm) and the relative air-fuel ratio (λ). Table 4 gives the specification of the gas analyzer. The precautions are taken care of before starting the experiments like leak test, zero adjustments, and cleanliness of filters.

9

Table 4. Gas analyzer Technical specification Measured parameter

Measuring Range

Accuracy

Carbon monoxide

0-10% vol

Hydro carbon

0-20000 ppm

Carbon dioxide

0-20% vol

Nitrogen oxide Oxygen

0-5000 ppm 0-22% vol

<0.6% vol: ±0.03% vol >0.6% vol: ±5% vol <200ppm : ± 10ppm >200ppm : ± 5% of ind. value <10% vol : ±0.5% vol >10% vol : ±5% vol <500ppm : ± 50ppm <2%vol : ±0.1% vol >2% vol : ±5% vol

Table 5. Engine Specification Engine

Research Engine test setup one cylinder, four-stroke, Multifuel VCR with open ECU for petrol mode (Computerized)

CylinderBore

110 mm

CylinderStroke

87.5 mm

Compression Ratio

08-15 (Variable)

Rated Power

4.5 KW @ 1800 rpm

Ignition Timing

24° BTDC

Dynamometer

Water-cooled Eddy current type with the loading unit

Crank angle sensor

Resolution 1 Deg, Speed 5500 RPM with TDC pulse

Data Acquisition device

NI USB-6210, 16-bit, 250kS/s

Electronic Control Unit

PE3 series ECU, full build potted enclosure

3. UNCERTAINTY ANALYSIS The necessity of evaluation of experimental uncertainties and error is to ensure that the study conducted is validated properly. The sources of uncertainties are many, such as weather condition, calibration, observation, instrument selection, and incorrect reading. The uncertainty percentages of various measuring instruments are used for the analysis of dependent variables such as BTE, brake power by partial differentiation method. The overall uncertainty of present work is found to be ±1.4%.

The uncertainties for independent parameters were found by 10

calculating the mean, standard deviation, and standard error for the repeated set of 20 readings. Finally, overall uncertainty is investigated as below: = Square root of {(CO)2 + (NOx)2 + (load)2 + (speed)2 + (time)2 + (brake power)2 + (fuel consumption)2 + (brake thermal efficiency)2 + (cylinder pressure)2 + (crank angle)2 + (manometer)2} 4. RESULTS AND DISCUSSION 4.1. Performance and Combustion Analysis Thermal efficiency value depends on the quality of the air and fuel mixture, burned in the combustion chamber.Fig.3, shows the influence of compression ratio on the thermal efficiency of the engine, the highest thermal efficiency of 29% obtained at engine speed 1600 rpm with CR10.

Fig. 3. Influence of Compression ratio on BSFC and BTE at WOT operating condition

Fig. 4. Influence of Compression ratio on volumetric efficiency at WOT operating condition

Latent heat of vaporization of methanol is higher, which allows combustion mixture to absorb more heat during vaporization, also work required to compress the mixture is less, thus improves thermal efficiency [40]. Increase of CR from 8 to 10, raises the in-cylinder temperature, thereby improving fuel vaporization, once homogeneity of the mixture is achieved the combustion efficiency of methanol blended gasoline engine shows better results. Hence results obtained while conducting experiments with CR 10 showed an increase in thermal efficiency by 25% when compared to the results of CR8. In contrast, BSFC reduces with increasing CR, and a minimum value of 0.41478 kg/kW-hr is obtained at 1600 rpm with CR10. Similar effect has 11

been observed in terms of BTE and BSFC, with other alcohol counterparts such as ethanol[41] and n-butanol [42]. It is observed for any compression ratio, thermal efficiency increases with an increase in speed and decreases the BSFC till 1600 RPM. A probable cause is that at a lower speed, WOT conditions, the available time for any stroke is more, hence heat dissipation to the components and cooling media would be more too. The heat loss inhibits cylinder temperature and pressure to increase at the end of the compression stroke; this results in less work output per unit cycle. Second, the longer stroke duration and low cylinder pressure restrict the expansion of RGF, which increases volumetric efficiency (Fig. 4). When fuel injected per cycle is fixed, the mixture inhaled by the engine becomes lean enough to cause mostly incomplete combustion. The increasing speed reduces the available time for a cycle which reduces the heat dissipation and increase the in-cylinder temperature and pressure; the volumetric efficiency decreases as well leading to attain stoichiometric air-fuel ratio, so thermal efficiency increases and followed by reduction of BSFC. However, after 1600 RPM, the time available is not enough for the combustion to complete and reduced volumetric efficiency leads to a rich mixture; hence the thermal efficiency starts decreasing. Fig. 4 presents the effect of CR change on volumetric efficiency with varying speed. The volumetric efficiency increases with increasing CR but reduces with increasing speed. Maximum volumetric efficiency is almost 75% at 1200RPM for CR10. Increasing the CR reduces the quantity of RGF, improves volumetric efficiency. However, it is observed that the volumetric efficiency compared to gasoline is better because of the high latent heat of methanol.

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Fig. 5. Influence of Compression ratio on Brake Power and Torque at WOT condition

Fig.5 shows that the engine power and torque would decrease when high fraction methanol blend (M50) is fueled in SI engine under wide open throttle (WOT) condition compared to gasoline. The reason is at WOT conditions; although the engine is supplied with the same amount of fuel, the energy content of methanol blend injected into the cylinder it's much lower compared to gasoline. However, increasing the compression ratio, engine power, and torque can be improved without knock occurrence[43]. Torque is directly related to the work per unit cycle, which increases with increasing speed because of favorable condition for better combustion; however, the decreasing volumetric efficiency decreases the work per unit cycle. It can be observed from fig. 5, in all the cases from 1200 rpm to 1400 rpm, torque increases slightly but after 1400 rpm it decreases due to lower volumetric efficiency. Brake power completely depends on the amount of fuel supplied and volumetric efficiency, as speed increases the amount of fuel per unit time is more, but volumetric efficiency is less so the mixture is getting richer. As a result, more power is introduced in the engine, and hence brake power increases with speed. Increasing the compression ratio increases the cylinder pressure and temperature so more favorable condition for burning results in higher work per cycle, which increases brake power. The maximum torque of 24.1 Nm at 1400 rpm and a maximum power of 3.8 kW at 1800 rpm were obtained at 10:1 compression ratio with M50 fuel, the increment was about 5% and 8% respectively when compared with 8:1 compression ratio.

13

4.2. Effects of compression ratio on Combustion characteristics The observation from the results obtained, suggests blended methanol fuels exhibit low incylinder pressure due to its less energy content value, but still, oxygen presence provides more advanced combustion than those of conventional fuels.

(a)

(b)

(c)

(d)

Fig.6. Cylinder Pressure variation with the crank angle for different speed at WOT condition

Increasing the compression ratio improves the fuel/air proportion in the cylinder and also induces turbulence inside the cylinder; this results in increased cylinder pressure and burning speed[34]. Methanol has large heat of vaporization but higher laminar flame propagation speed compared to gasoline. High latent heat increases the ignition delay, and so the peak pressure is retarded, however higher flame speed results in faster combustion, and so the peak pressure advances. The combined effect can be observed from Fig.6a-d, as the peak pressure is insignificantly retarded. 14

The increased compression ratio decreases the ignition delay and so as the peak pressure shifts towards TDC. Increasing speed increases the in-cylinder temperature with a slightly richer mixture present, which increases the peak pressure too, as well as it shifts towards TDC. The higher heating value of gasoline contributes to its peak pressure being high. However, at in case of blends, it is observed from the figures that CR10 has peak pressure of 20.1 bar compared to 16.9 bar of CR 8 at 1200 rpm, however, at 1400rpm it increased to 21.2 bar for CR10 and 18 bar for CR 8. This increasing trend continues with 1600 rpm for CR10 reaching 24.8 bar, but for CR 8 the peak pressure falls to 17.7 bar but increases for CR 9 from 18 bar to 20.4 bar, a similar trend is observed for 1800 rpm. For CR 8 the peak pressure is almost static within a quite small range, diminishing the effect of engine speed.

(a)

(b)

(c)

(d)

Fig. 7. Net Heat Release Rate versus crank angle at a different speed at WOT condition

15

NHR mainly depends on the combination of the latent heating value of fuels and combustion efficiency [44]. Engine tests were conducted for three different compression ratios, at WOT condition for four different speeds. Cylinder volume, in-cylinder pressure, and blend ratio affect the NHR change, besides higher CR owes to increased cylinder temperature, thus results in the rise of heat release rate. The heat release rate peak is slightly close to top dead center at higher CR, which also attributes to the fact that, with higher CR air/fuel mixture density is improved, cylinder temperature rises, shortens the combustion delay and increases flame speed[34]. It is observed from Fig. 7a-d that the duration of heat release is getting short in terms of CA with increasing CR, which means the combustion duration shortens leading close to constant volume combustion. It is observed from theFig.7a-d, that maximum NHR values obtained at CR10, reaching to 24 J/deg which attributes to a 16 percent raise. The increasing speed affects shifting of the peak towards TDC for any CR value, also due to increased cylinder temperature. The effect of increasing speed on combustion duration can also be noticed as from Fig. 7a to 7d for all CR, the width of NHR curve is getting shorter from 1200rpm to 1600 rpm but slightly widens at 1800 rpm. The results point out the conditions favoring best combustion attains at 1600 rpm.

4.3. Exhaust Emissions

(a) CO emissions with different speed

(b) CO2 emissions with different speed

16

(c) NOx emissions with different speed

(d) HC emissions with different speed

Fig.8. Exhaust gases emitted for different Compression ratios at WOT

Fig.8a shows the variation of CO emission with different speed. It is observed that CO emissions decrease with the increase of CR; CO emissions are majorly related to the completion of combustion[36]. For lower CR, as was discussed above, heat is dissipated to the cylinder wall, and cooling media, along with this large amount of heat is consumed for atomization of fuel, hence results in lower cylinder temperature as well as higher volumetric efficiency which leads to the much leaner burning mixture. Due to the non-homogeneity of combustion mixture, the conversion of CO into CO2 is restricted. Increasing CR increases the cylinder temperature and pressure, which is much favorable condition for combustion results in decreased CO. However, increasing speed in WOT increases load as well as fuel requirement; hence, the mixture gets richer. The cylinder temperature is also increased with speed; however, an increased amount of fuel requires more heat for atomization and higher cylinder temperature to be maintained for complete combustion. Due to which the CO conversion to CO2 gets restricted and so the CO emissions are more. The CO2 emissions are opposite to the CO emissions for any speed concerning CR variation, as shown in Fig.8b. Higher CR results in better combustion and so as the CO2 emission, however, comparing a particular CR for different speeds, the story is entirely different, the increasing speed increases with the amount of fuel inlet, resulting in a relatively rich mixture and so the

17

formation of CO2[45]. Hence, because of the large amount of fuel inducted in the stream of charge, CO2 and CO both increases. NOx emission can be observed from Fig.8c as increasing with CR and speed; the formation of NOx depends solely on the cylinder temperature and availability of oxygen. Increasing CR increases the cylinder pressure and temperature, which is a favorable condition of combustion and so increasing the peak temperature[46]. However, the increase in speed also has a similar impact. Higher speed provides less chance for the cylinder to get cool and so the cylinder temperature increases. Though for the top speed of 1800 rpm, CO emission is more, which is the result of excess fuel provided, the amount of fuel burnt per unit time is more and so as the temperature, resulting in higher NOx emission. Oxygen-enriched fuels account for reduced HC. It is observed from Fig.8d, that HC emission decreases as the CR are increased; a possible cause is just the higher cylinder pressure and temperature being favorable for combustion. However, the HC emission decreases as engine speed increases; the probable cause is though the combustion is not complete at higher speed, the condition for combustion is good, and so most of the fuel is getting burnt partially to produce CO but not getting converted to CO2. The mixture is rich, and so there is an insufficient amount of oxygen to convert CO into CO2. 5. Conclusions Experimental investigation (performance, combustion, and emission analysis) of methanolblended gasoline-fueled in single-cylinder, four-stroke, VCR Engine, was conducted and best results for optimized compression ratio is shown. Tests were conducted for different compression ratio (8, 9 & 10), and the following results concluded. •

M50 fueled SI engine exhibits excellent results at CR10, compared to compression ratios.

•

The outcome of results suggests higher compression ratio provides better combustion with high fraction methanol blend, chemical properties of methanol attribute to good agreement of improvisation in BTE and BSEC.

18

•

NOx, CO and HC emissions reduction observed between 30-40 % with CR10 when compared to gasoline fuel.

•

Higher CR improves the fuel/air proportion in the cylinder and also induces turbulence, which in turn improves quality of fuel atomizing, thus CO2 increases with methanol addition credited for improved combustion

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HIGHLIGHTS •

High octane number and oxygen content are two key factors associated with methanol

•

Methanol is a good fuel when operated at higher compression

•

CR change has a significant effect on performance characteristics of M50 fuel

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M50 fuel with CR10 exhibits excellent combustion efficiency

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Burning low carbon-hydrogen ratio M50 fuel reduce CO and HC emission

Declaration of interests ■The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: