ORIGINAL ARTICLE
Influence of injection timing and compression ratio
on performance, emission and combustion
characteristics of Annona methyl ester operated
diesel engine
Senthil Ramalingam
*, Silambarasan Rajendran, Ravichandiran Nattan
Department of Mechanical Engineering, University College of Engineering Villupuram, Tamil Nadu, India Received 28 January 2015; revised 29 April 2015; accepted 12 May 2015
Available online 6 July 2015
KEYWORDS Annona methyl esters; Injection timing; Compression ratio; Performance; Emission; Combustion
Abstract This study targets at finding the effects of the engine design parameters viz. compression ratio (CR) and fuel injection timing (IT) jointly on the performance with regard to specific fuel con-sumption (SFC), brake thermal efficiency (BTHE) and emissions of CO, HC, Smoke and NOxwith
Annona methyl ester (A20) as fuel. Thus A20 can be effectively used in a diesel engine without any modification. Compression ratio of 19.5 along with injection timing of 30bTDC (before top dead centre) will give better performance and lower emission which is very close to diesel. Comparison of performance and emission was done for different values of compression ratio along with injection timing to find best possible combination for operating engine with A20. It is found that the com-bined increase of compression ratio and injection timing increases the BTE and reduces SFC while having lower emissions. Diesel (20%) saved, will greatly meet the demand of fuel in railways. ª 2015 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an
open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Annona squamosais a member of the family of Custard apple trees called Annonaceae and a species of the genus Annona known mostly for its edible fruits Annona. It is commonly found in India and Cultivated in Thailand and it originates from the West Indies and South America. A. squamosa pro-duces fruits that are usually called sugar apple or custard apple in English, sitafal in Marathi, sharifa in Hindi, sitaphalam in Tamil and Telugu in India and corossolier and cailleux, pom-miercannelle in French. It is mainly grown in gardens for its fruits and ornamental value. It is considered as beneficial for Abbreviations: BP, brake power; SFC, specific fuel consumption;
BSFC, brake specific fuel consumption; BTE, brake thermal efficiency; CI, compression ignition; CR, compression ratio; IT, injection timing; CA, crank angle; CO, carbon monoxide; HC, hydrocarbon; NOx, oxides of nitrogen; HRR, heat release rate; CHRR, cumulative heat release rate; CV, calorific value; DI, direct injection; NDIR, non-dispersive infrared; ppm, parts per million; AME, Annona methyl ester * Corresponding author.
E-mail address:drrs1970@gmail.com(R. Senthil).
Peer review under responsibility of Faculty of Engineering, Alexandria University.
H O S T E D BY
Alexandria University
Alexandria Engineering Journal
www.elsevier.com/locate/aej www.sciencedirect.com
http://dx.doi.org/10.1016/j.aej.2015.05.008
1110-0168ª 2015 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
cardiac disease, diabetes, hyperthyroidism and cancer. The root is considered as a drastic purgative.
In this paper we reported that A20 gives better performance and reduction emissions are achieved. These studies were car-ried out in different types of engines (stationary/mobile; single cylinder/multi cylinder; constant speed/variable speed) with bio-diesel prepared from different oil origins. To sum up the results of these studies, a cumulative study taking some or all the parameters at a time in one type of engine is still miss-ing. To fill this gap, the study was done with an objective of finding the optimum engine design parameters viz. compres-sion ratio and injection timing, for better performance of diesel blended with bio-diesel (A20) obtained from Annona oil. The aim was to establish the modifications required in small, con-stant speed, direct injection diesel engines used extensively for agricultural applications so that these can be made to run on diesel and bio-diesel blend with better performance and at the same time improve the emissions.
As per the US department of Energy[1], the world’s oil sup-ply will reach its maximum production and midpoint of deple-tion sometime around the year 2020. Future projecdeple-tions indicate that the only feasible option is the production of syn-thetic fuels derived from non-petroleum sources[2]. For substi-tuting the petroleum fuels used in internal combustion engines, fuels of bio-origin provide a feasible solution to the twin crises of ‘fossil fuel depletion’ and ‘environmental degradation’. For diesel engines, a significant research effort has been directed towards using vegetable oils and their derivatives as fuels. Non-edible vegetable oils in their natural form called as straight vegetable oils (SVO), methyl or ethyl esters known as treated vegetable oils, and esterified vegetable oils referred to as bio-diesel fall in the category of biofuels. Bio-diesel is considered a promising alternative fuel for use in diesel engi-nes, boilers and other combustion equipments. These are bio-degradable, can be mixed with diesel in any ratio and are free from sulphur. Although bio-diesel has many advantages over diesel fuel, there are several problems that need to be addressed such as its lower calorific value, higher flash point, higher viscosity, poor cold flow properties, poor oxidative sta-bility and sometimes its comparatively higher emission of nitrogen oxides[3]. Bio-diesel obtained from some feedstocks might produce slightly more oxides of nitrogen (1–6%), which is an ozone depressor, than those of fossil origin fuels but can be managed with the utilization of blended fuel of bio-diesel and high speed diesel fuel[4]. It is found that the lower concen-trations of bio-diesel blends improve the thermal efficiency. Reduction in emission and brake specific fuel consumption is also observed while using B10[5]. The operating parameters must be optimized in light of the specific fuel properties. Effect of injection parameters[6–12]such as spray[13], injec-tion timing and compression ratio[14–18] has been studied in detail at many places. Most of the research studies con-cluded that in the existing design of engine and parameters at which engines are operating, a 20% blend of bio-diesel with diesel works well[4]. Many researchers indicated the need of research in the areas of engine modifications so as to suit to higher blends without severe drop in performance so that the renewability advantages along with emission reduction can be harnessed to a greater extent. Effect of variations in these parameters has been studied taking one or more parameters at a time[19].
2. Transesterification of vegetable oils
Transesterification is the process of using an alcohol (e.g. methanol or ethanol) in the presence of catalyst such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), which chemically breaks the molecule of the raw oil into methyl or ethyl esters with glycerol as a by-product, which reduces the high viscosity of oils. This method also reduces the molecular weight of the oil to 1/3 of its original value, reduces the viscosity, and increases the volatility and cetane number to levels comparable to diesel fuel. Conversion not greatly affects the gross heat of combustion. Transesterification is the change of the trivalent glycerin molecules against 3 mole-cules of monovalent alcohol methanol. Each is a monoester. In the most vegetable oils, fatty acids with 16 and 18 carbon atoms predominate.
3. Experimental setup
The schematic diagram of the engine test rig used is shown in
Fig. 1. The engine is fully equipped with measurements of all operating parameters. In the study, compression ignition engine was run with AME (A20) at different compression ratios (16.5, 17.5, 18.5, 19.5 and 20.5) and injection timings (24, 27, 30 and 33 bTDC) to evaluate the performance, emis-sions and combustion characteristics at 50% load. The results were compared against the diesel fuel results as well as for dif-ferent combinations of compression ratio and injection timing. The properties of Annona methyl ester and diesel are shown in
Table 1.
3.1. Specifications of the apparatus
In the test rig there are several instruments/equipments that have been used for the purpose of the experiment. Brief spec-ifications of the instruments are given below.
3.1.1. Diesel engine
Manufacturer Kirloskar oil engines limited Type of engine Vertical, 4-Stroke Single cylinder
Maximum power 8 HP
Max brake power 6.02 kW
Speed 1800 rpm
Compression ratio 17.5:1
Bore and stroke 87.5· 110 (mm)
Injection pressure 200 bar
3.1.2. Smoke meter
Smoke meter is used to determine the smoke density of the engine exhaust. The AVL 437 smoke meter has been designed for simple one man operation from alongside a vehicle for either free acceleration or steady state test procedures. Control is via a compact and rugged handset with a digital L.C.D. Any out of range parameters are automatically flagged to the operator. The brief specifications of the smoke meter are given below:
Type AVL 437 smoke meter
Make AVL India Pvt. Ltd
Measuring range 0 to 100HSU
3.1.3. Exhaust gas analyzer
Manufacturer SMS Autoline Equipments private limited
Type Crypton 290 five gas analyzer
3.2. Testing procedure
Engine was started, warmed up at low idle, long enough to establish the recommended oil pressure, and was checked for
any fuel, oil leaks. The engine was run on no-load condition and speed was adjusted to 1800 rpm by adjusting fuel injection pump. Engine was run to gain uniform speed, after which it was gradually loaded. Experiments were conducted at different torque levels (0, 8, 16, 24 and 32 Nm). The engine was run for 10 min and data were collected during last 3 min. For 20% biodiesel, performance tests were carried out at five different compression ratios and four different injection timings.
The exhaust gas is the sample from exhaust pipeline and passed through a four gas analyzer for measurement of carbon monoxide, carbon dioxide, unburnt hydrocarbon, and oxides of nitrogen present in exhaust gases. A smoke meter is used for measurement of smoke capacity. The measurement range and accuracy of the exhaust gas analyzer and smoke meter is shown inTable 2.
4. Results and discussion
Test engine was run with different fuels and time for 10 cc fuel consumption was calculated.
4.1. Effect of injection timing on performance, emission and combustion characteristics
4.1.1. Specific fuel consumption (SFC)
Fig. 2shows the variations of specific fuel consumption for injection timing and for A20 blend when compared to the neat diesel fuel. 30bTDC of injection timing gives lowest SFC as compared to all other Injection Timings and neat diesel fuel. The specific fuel consumption of the A20 blend at the injection timing of 30bTDC is 0.346 kg/kW h whereas for diesel it is 0.385 kg/kW h. This may be due to higher viscosity and low volatility which causes better utilization of oxygen leading to better combustion.
4.1.2. Brake thermal efficiency (BTE)
Fig. 3 shows the variations of brake thermal efficiency for injection timing and for A20 blend when compared to the neat diesel fuel. 30bTDC gives highest BTE than all other injection timings when compared to that of neat diesel fuel. The brake thermal efficiency of the A20 blend at the injection timing of 30bTDC is 21.95% and almost equal to that of neat diesel fuel (23.35%). This may be due to combination of low volatil-ity and mass flow rate which indicates inputs to the engine, which in case of A20, are more compared to neat diesel.
Table 1 Fuel properties of AME and diesel.
Properties Diesel AME
Cetane no 48 52 Specific gravity 0.83 0.8802 Viscosity @ 40C 3.9 5.18 Calorific value (MJ/kg) 43 36.4 Density (g/cm3) 0.830 0.880 Flash point (C) 56 76 Fire point (C) 64 92 Oxygen content (%) – 11
Table 2 Experiment uncertainties.
Parameters Systematic errors (±)
Speed 1 ± rpm Load ±0.1 N Time ±0.1 s Brake power ±0.15 kW Temperature ±1 Pressure ±1 bar NOX ±10 ppm CO ±0.03% CO2 ±0.03% HC ±12 ppm Smoke ±1HSU
4.1.3. Carbon monoxide (CO)
Fig. 4shows the variations of Carbon monoxide for injection timing and for A20 blend when compared to the neat diesel fuel. 30bTDC gives low CO emission than all other injection timings when compared to that of neat diesel fuel. The brake thermal efficiency of the A20 blend at the injection timing of 30bTDC is 0.08 ppm whereas for diesel it is 0.095 ppm. This may be due to oxygen concentration and cetane number. Since AME fuel contains oxygen it acts as a lesser combustion promoter inside the cylinder.
4.1.4. Oxides of nitrogen (NOx)
Fig. 5 shows oxides of nitrogen for different compression ratios and for A20 blend when compared to the neat diesel fuel. 30bTDC gives low NOxemission than all other injection timings and compared to that of neat diesel fuel there is a slight increase in NOxemissions. The NOxemission of the A20 blend at the injection timing of 30bTDC is 340 ppm whereas for die-sel it is 320 ppm. This may be due to the presence in biodiedie-sel of oxygen, which leads to complete combustion of biodiesel than diesel. As a result, maximum temperature inside cylinder is more in case of biodiesel than diesel.
4.1.5. Hydrocarbon (HC)
Fig. 6shows the variations of hydrocarbon emission for injec-tion timing and for A20 blend when compared to that of neat diesel fuel. 30bTDC gives low HC emission than all other injection timings when compared to that of neat diesel fuel.
The HC emission of the A20 blend at the injection timing of 30bTDC is 460 ppm whereas for diesel it is 470 ppm. This may be due to viscosity and surface tension that affect penetra-tion rate and droplet size of fuel, which in turn affect mixing of fuel and air. Cetane number of fuel also plays a vital role in ignition process.
4.2. Smoke
Fig. 7 shows the variations of smoke emission for injection timing and for A20 blend when compared to that of neat diesel fuel. 30bTDC gives low smoke emission than all other 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 24 27 30 33 SFC (kg/kW-h) Injecon TIming ( 0bTDC) Diesel A20
Figure 2 Injection timing vs. Specific fuel consumption.
0 5 10 15 20 25 24 27 30 33 BTE (%) Injecon Timing ( 0 bTDC) Diesel A20
Figure 3 Injection timing vs. Brake thermal efficiency.
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 24 27 30 33 CO (%) Injecon Timing ( 0bTDC) Diesel A20
Figure 4 Injection timing vs. Carbon monoxide.
0 100 200 300 400 500 600 24 27 30 33 NO X (PPM) Injecon Timing ( 0bTDC) Diesel A20
Figure 5 Injection timing vs. Oxide of nitrogen.
420 440 460 480 500 520 540 24 27 30 33 HC (PPM) Injecon Timing (0 bTDC) Diesel A20
injection timings when compared to that of neat diesel fuel. The smoke emission of the A20 blend at the injection timing of 30bTDC is 73HSU whereas for diesel it is 77HSU. This is due to that biodiesel contains excess oxygen, locally over the rich region which decreases the formation of crucial smoke restricted by the favourable effect of the oxygen content bio-diesel. This is due to greater accumulation of the fuel during ignition delay period and leads to the fuel injected earlier into the combustion chamber.
4.2.1. Cylinder pressure
Fig. 8 shows variations of cylinder pressure with respect to crank angle for different injection timings and for A20 when compared to that of neat diesel fuel. The peak pressure decreases by 4.5% for A20 blend at 24bTDC, increases by 5.7% for A20 blend at 30bTDC and increases by 1.4% for A20 blend at 33bTDC when compared to A20 blend at 27bTDC.
4.2.2. Heat release rate (HRR)
Fig. 9 shows variations of heat release rate with respect to crank angle for different compression ratios and for A20 when compared to that of neat diesel fuel. The maximum HRR increases by 6.8% for A20 blend at 24bTDC, decreases by 2.03% for A20 blend at 30bTDC and decreases by 0.66% for A20 blend at 33bTDC when compared to A20 blend at 27bTDC. At normal engine conditions the minimum delay
occurs with start of injection 10–15bTDC. The increase in the delay time with earlier or later injection timing occurs because of the air temperature and pressure during delay period.
4.2.3. Cumulative heat release rate
Fig. 10shows variations of cumulative heat release rate with respect to crank angle for different compression ratios and for A20 when compared to that of neat diesel fuel. The maxi-mum Cumulative HRR decreases by 13.8% for A20 blend at 24bTDC, decreases by 20.23% for A20 blend at 30bTDC and decreases by 19.04% for A20 blend at 33bTDC when compared to A20 blend at 27bTDC.
4.3. Effect of compression ratio on performance, emission and combustion characteristics
4.3.1. Specific fuel consumption (SFC)
Fig. 11shows variations of specific fuel consumption for dif-ferent compression ratios and for A20 blend when compared to that of neat diesel fuel. 19.5:1 of compression ratio gives lowest SFC as compared to all other compression ratios and neat diesel fuel. The specific fuel consumption of the A20 blend at the compression ratio of 19.5:1 is 0.30 kg/kW h whereas for diesel it is 0.32 kg/kW h. This is due to the fact that increase in compression ratio reduces BSFC due to reduction in dilution of charge by residual gases, which results in better BTE and lower BSFC. However increase in BSFC is observed with lower compression ratio due to slow combustion pressure because of more charge diameter and lower compression pres-sure and temperature.
0 10 20 30 40 50 60 70 80 90 100 24 27 30 33 Smoke (HSU) Injecon Timing ( 0 bTDC) Diesel A20
Figure 7 Injection timing vs. Smoke.
-10 0 10 20 30 40 50 60 70 80 90 180 280 380 480 580 PRESSURE (bar)
CRANK ANGLE (deg)
DIESEL A20
Figure 8 Crank angle vs. Pressure.
-60 -40 -20 0 20 40 60 80 100 180 280 380 480 580 HRR (J/deg CA)
CRANK ANGLE (deg)
DIESEL A20
Figure 9 Crank angle vs. Heat release rate.
0 50 100 150 200 250 300 350 400 180 280 380 480 580 CUMM. HRR (J/deg CA)
CRANK ANGLE (deg)
DIESEL
A20
4.3.2. Brake thermal efficiency (BTE)
Fig. 12shows variations of brake thermal efficiency for differ-ent compression ratios and for A20 blend when compared to that of neat diesel fuel. 19.5:1 of compression ratio gives high-est BTE as compared to all other compression ratios and neat diesel fuel. The BTE of the A20 blend at the compression ratio of 19.5:1 is 30.67% and it is almost to that of neat diesel fuel (31.41%). This is due to the fact that increase in compression ratio ensures more complete combustion due to injection of fuel in higher temperature and pressure compressed air, better air–fuel mixing and faster evaporation, whereas, reduction in compression ratio resulted in lower BTE due to lower com-pression pressure and temperature, slow combustion process, and more dilution by residual gas.
4.3.3. Carbon monoxide (CO)
Fig. 13 shows variations of carbon monoxide for different compression ratios and for A20 blend when compared to that of neat diesel fuel. 19.5:1 of compression ratio gives lowest CO emission as compared to all other compression ratios and the neat diesel fuel. The CO emission of the A20 blend at the com-pression ratio of 19.5:1 is 0.05 ppm whereas for diesel it is 0.06 ppm. This may be due to better combustion, and less dilu-tion of charge by residual gases accelerates the carbon oxida-tion to form carbon dioxide. At lower compression ratio, the carbon monoxide emissions are increased due to more dilution of fresh air with residual gases, lower compression temperature and poor mixing of fuel and air.
4.3.4. Oxides of nitrogen (NOx)
Fig. 14 shows variations of oxides of nitrogen for different compression ratios and for A20 blend when compared to that of neat diesel fuel. 19.5:1 of compression ratio gives lowest NOxas compared to all other compression ratio and the slight increase in NOx emission as compared to that of neat diesel fuel. The NOxemission of the A20 blend at the compression ratio of 19.5:1 is 515 ppm whereas for diesel it is 510 ppm. This may be due to the fact that increase in compression ratio increases the combustion pressure and temperature which accelerates the oxidation of nitrogen to form oxides of nitro-gen. At lower compression ratio, the combustion takes place during expansion stroke which results in lower combustion temperature and pressure which leads to lower NOxemission. 4.3.5. Hydrocarbon (HC)
Fig. 15shows variations of hydrocarbon emission for different compression ratios and for A20 blend when compared to that of neat diesel fuel. 19.5:1 of compression ratio gives lowest HC emission as compared to all other compression ratios and the neat diesel fuel. The HC emission of the A20 blend at the com-pression ratio of 19.5:1 is 26 ppm whereas for diesel it is 29 ppm. This may be due to the increase in the air temperature at the end of compression stroke, enhancement in combustion temperature and reduction in charge dilution which leads to better combustion and reduction in hydrocarbon emissions. Increase in hydrocarbon emission is observed with reduction in compression ratio which is due to slow combustion process. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 16.5 17.5 18.5 19.5 20.5 SFC (kg/kW-h) Compression Ratio Compression Ratio Diesel A20
Figure 11 Compression Ratio vs. Specific fuel consumption.
0 5 10 15 20 25 30 35 16.5 17.5 18.5 19.5 20.5 BTE (%) Compression Ratio Compression Ratio Diesel A20
Figure 12 Compression Ratio vs. Brake thermal efficiency.
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 16.5 17.5 18.5 19.5 20.5 CO (%) Compression Ratio Compression Ratio Diesel A20
Figure 13 Compression Ratio vs. Carbon monoxide.
0 100 200 300 400 500 600 700 800 16.5 17.5 18.5 19.5 20.5 NO X (PPM) Compression Ratio Compression Ratio Diesel A20
4.4. Smoke
Fig. 16shows variations of smoke emission for different com-pression ratios and for A20 blend when compared to that of neat diesel fuel. 19.5:1 of compression ratio gives lowest smoke emission as compared to all other compression ratios and the neat diesel fuel. The smoke emission of the A20 blend at the compression ratio of 19.5:1 is 15.7HSU whereas for diesel it is 16.5HSU. This is due to biodiesel that consists of two oxy-gen atoms which leads to the oxidation of soot and thereby reducing the soot emissions.
4.4.1. Cylinder pressure
Fig. 17shows variations of cylinder pressure with respect to crank angle for different compression ratios and for A20 when
compared to that of neat diesel fuel. The cylinder pressure for A20 blend is almost equal to that of neat diesel fuel. This is due to longer ignition delay and lower cetane number of the blend. The cylinder pressure of the neat diesel fuel is higher than that of A20 blend at lower compression ratio. This is due to faster and complete combustion inside the combustion chamber. The maximum rate of increase in pressure is increasing with com-pression ratio for different blends.
4.4.2. Heat release rate
Fig. 18shows the variations of heat release rate with respect to crank angle for different compression ratios and for A20 blend when compared to that of neat diesel fuel. The HRR is ana-lyzed based on the changes in crank angle variation of the cylinder. The HRR is increased with lower compression ratio and slightly decreased at higher compression ratio. The HRR of neat diesel is higher than that of A20 blend due to its reduced viscosity and better spray formation.
4.4.3. Cumulative heat release rate
Fig. 19shows the variations of heat release rate with respect to crank angle for different compression ratios and for A20 blend 0 5 10 15 20 25 30 16.5 17.5 18.5 19.5 20.5 HC (PPM) C Compression n Ratio Diesel A20
Figure 15 Compression Ratio vs. Hydrocarbon emission.
0 2 4 6 8 10 12 14 16 18 20 16.5 17.5 18.5 19.5 20.5 Smoke C Compression n Ratio Diesel A20
Figure 16 Compression Ratio vs. Smoke.
0 10 20 30 40 50 60 70 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 diesel A20
Crank angle (deg)
Cylinder Pressure (bar)
Figure 17 Crank angle vs. Pressure.
0 10 20 30 40 50 60 70 80 90 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 Diesel A20
Crank angle (deg)
HRR (J/deg
CA)
Figure 18 Crank angle vs. Heat release rate.
0 50 100 150 200 250 300 350 400 450 500 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 A20 Diesel
Crank angle (deg)
CHRR (J/deg
CA)
when compared to that of neat diesel fuel. The maximum Cumulative HRR decreases by 12.20% for A20 blend at 16.5:1, decreases by 6.84% for A20 blend at 18.5:1, decreases by 15.50% for A20 blend at 19.5:1 and decreases by 11.39% for A20 blend at 20.5:1 when compared to A20 blend at 17.5:1. This may be due to injection of more quantity of fuel during larger delay period and slow combustion.
5. Conclusion
Injection timing of 30bTDC, along with compression ratio of 19.5 gives better performance, combustion and lower emis-sions when compared with standard Injection timing of 27bTDC and compression ratio of 17.5. For all tested values, A20 provides best results in terms of BTE, higher heat release rate, and lower emissions of HC, CO and NOx. Hence A20 can be effectively used as an alternative biodiesel with Injection timing of 30bTDC along with compression ratio of 19.5 in tested engine. Even though only 20% of Annona methyl ester is added with 80% pure diesel, will meet to a certain extent the shortage of availability of pure diesel. Annona is available with lower cost when compared to diesel in present scenario. Hence AME will be economical also for diesel trains.
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