Comparison of performance and combustion parameters and emissions on a variable compression ratio diesel engine fueled with CsME.

Rambabu, V. ; Prasad, V.J.J. ; Subramanyam, T. 等

Introduction

The adoptability of alternative fuels to the conventional diesel engines without rigorous modifications needs the primary analysis towards performance, combustion and emissions. In performance aspect thermal efficiency should be high and in the emissions aspect pollution should be low. Methyl or ethyl esters of vegetable oils are having nearly equal characteristics with the petroleum diesel and they can be use directly on the diesel engines [5,8]. But utilization of best compression ratio, injection pressures and with some external modification like increasing the inlet temperature of the esters [4] and by using retro fittings like exhaust gas recirculation efficiency can be improved.

In this work with out changing valve timing or valve clearance adjustments, compression ratio was changed. We know that the full cylinder volume of an IC engine is divided into two parts that is clearance volume and swept volume. When the compression ratio is increased, clearance volume gets reduced and vice-versa. There is no effect on swept volume. So when the compression ratio increased, molecules of air get more closer and pressure as well as temperature increases in the compression stroke. Into that hot compressed air, the fuel is injected. Due to this, its delay period will decrease [3].

As per the chemical structure of biodiesel, it can be seen from Table.1, their flash point and fire point temperatures are higher when compared with diesel [6,9]. These conditions will lead to increasing of delay period, which causes steep rise of pressure during combustion. High pressure and high temperature inside the cylinder will lead to formation of N[O.sub.x] [7]. On the other hand, due to the reduction of full cylinder volume, the amount of air intake, in the suction stroke will decrease and lead to incomplete combustion of fuel and as a result CO, HC emission will increase. But methyl or Ethyl esters of vegetable oils are having inbuilt oxygen and this oxygen influencing the combustion and caused for reduction of HC and CO [1,7].

Higher compression ratio caused for increasing of the pressure and temperature of intake air in the compression stroke which reduce the initial preparatory phase of combustion and hence it leads to reduction in the delay period and the operation of the engine becomes smoother. High pressure and temperatures of the compression mixture also speed up the second phase of combustion. Increased compression ratio reduces the clearance volume and therefore increases the density of the intake air in side the cylinder and the total combustion duration is reduced. The closer contact between the molecules of fuel and oxygen, caused for reducing the time of reaction [2,10]. The maximum peak pressure during the combustion process is marginally affected by the increase in compression ratio. Like wise compression ratio influences the performance as well as pollution parameters. So that, when the engine is fueled with the CsME, what will be the preferable compression ratio? is find in this experiment.

Experimentation

To conduct the experiment, cotton seed methyl ester was prepared from the raw cotton seed oil using transesterification method, in our laboratory. Transesterification is the general term used to describe the important class of organic reactions, where an ester (fatty acid ester-RCOOR') is transformed into another ester (Alkyl esterRCOOR?) through interchange of alkyl groups and is also called as alcoholysis. Transesterification is an equilibrium reaction and the transformation occurs by mixing the reactants. However, the presence of a catalyst accelerates considerably the adjustment of the equilibrium. The general equation for transesterification reaction is given below.

RCOOR' + R"OH [left and right arrow] RCOOR" + R'OH

The basic constituent of vegetable oils is triglyceride. Vegetable oils comprise of 90-98 percent triglycerides and small amounts of mono-glyceride, diglyceride and free fatty acids. In the transesterification of vegetable oils, a triglyceride reacts with an alcohol in the presence of a strong acid or base, producing a mixture of fatty acid alkyl esters and glycerol. The stoichiometric reaction requires one mole of triglyceride and three moles of alcohol. However, an excess of alcohol is used to increase the yield of alkyl esters and to allow phase separation from the glycerol formed. Several aspects including the type of catalyst (base or acid), alcohol/vegetable oil molar ratio, temperature, purity of the reactants (mainly water content in alcohol) and free fatty acid content have influence on the course of transesterification. So in this work, the reactants of high purity have been used (methyl alcohol with 99.95% purity). In the base-catalyzed process, the transesterification of vegetable oils proceeds faster than the acid-catalyzed reaction and the alkaline catalysts are less corrosive than acidic compounds. In the transesterification glycerol content from the raw oil is removed and the raw oil (cotton seed Fatty acid ester) transformed into Cotton seed methyl ester (CsME).

Preparation of CsME

The non-edible oil is filtered using surgical cotton to eliminate the water and particulate matter. The oil is heated to 100[degrees]C temperature and maintained at the same temperature for fifteen minutes. For a successful reaction, the oil must be free of water.

First stage (Acid catalyzed stage)

1. The filtered oil is taken in a container and heated to 35[degrees]C to melt the solid fats present in the oil.

2. Methanol of 99 % pure is added (0.1 liters/liter of oil) to the heated oil. It is stirred for five to ten minutes (Methanol is a polar compound; oil is strongly non-polar; hence a suspension will form).

3. Acid catalyzed stage caused for breaking of free fatty acid chain as shown in Fig.1

4. One milliliter of 95 % pure sulfuric acid (H2SO4) is added for each liter of oil using a graduated eye dropper.

5. The compound is stirred for one hour maintaining the temperature at 35[degrees]C.

6. Heating is stopped and the mixture is stirred for another hour.

7. The mixture is allowed to settle for eight hours in a decanter to remove glycerin and water.

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Second stage (Base catalyzed stage)

1. 6.5 grams of sodium hydroxide (NaOH) is added to 0.2 liters of methanol and stirred thoroughly to produce sodiummethoxide.

2. Half of the prepared sodiummethoxide is poured into the unheated mixture and the mixture is stirred for five minutes.

3. The mixture is heated to 55[degrees]C and for the whole reaction same temperature is maintained.

4. Remaining sodiummethoxide is added to the heated mixture and stirred at a speed between 500 and 600 rpm.

5. After one hour the mixture is poured into a decanter and allowed to settle for 8 hours. As glycerol is heavier than the bio-diesel, it will settle at the bottom. The glycerol is separated from the bio-diesel.

Water Washing

1. The separated bio-diesel is washed with water. Bubbles are generated in the water and these bubbles are passing through the raw bio-diesel. Bubbles are caused for removing of [Na.sub.2] S[O.sub.4] salt form the raw bio-diesel which formed during acid and base catalyzation processes

2. One milliliter of phosphoric acid ([H.sub.3]P[O.sub.4]) is added to the washing water.

3. One-third of this water by volume is added to the oil and bubble washed for twenty hours.

4. The mixture is allowed to settle in a decanter for one hour and the water is drained-off later.

5. The separated bio-diesel is heated to 100[degrees]C to separate traces of water. The obtained final product is the required Bio-Diesel (CsME).

Then it is characterized and compared with petroleum diesel as shown in the Table1.

Experimental procedure

For the testing of the CsME on the engine the experimental setup was prepared, which consists of Variable Compression Ratio diesel engine, Exhaust gas analyzer, Smoke meter, data acquisition system to generate P-[theta]. To inject the fuel (CsME) no modifications are done in the fuel feed system. Eddy current dynamometer was used to load the engine. Exhaust gas analyzer probe directly connected at the end of the tail pipe. So that, some portion of the exhaust gas sucked into the analyzer and it gives digital display of CO, C[O.sub.2], NO, HC, [O.sub.2]. Smoke meter attached separately to the exhaust pipe to measure the opacity of the exhaust gas in HSU. Piezoelectric pressure transducer is attached to the cylinder head and it is connected to the engine DAQ software. Crank angle encoder is attached at the crank shaft pulley through the belt. The readings obtained from the pressure transducer and crank angle encoder both are correlated in the DAQ software and P-[theta] graphs are generated. The total experimental set up shown in Fig.1. To change the Compression ratio nut and Bolt mechanism is provided at the top of the cylinder head. Bolt head is enlarged and according to the pitch of the bolt graduations are marked over it. The required compression ratio is set by rotating the lever which is connected to the bolt and it can be locked at that position. One more cam shaft is provided to operate the valves and it is driven by the engine cam shaft through belt drive. So that, due to change in compression ratio the valve operating mechanism will not be disturb. Brief description of each component used in the experiment is presented in the next subsections. After the setup was prepared different compression ratios such as 15.5:1, 16.5:1, 17.5:1, 18.5:1, 19:1 were considered and at each compression ratio, loads are varied from no load to full load. Even though, a number of readings were considered at different loads, at each compression ratio, considerable variation at 2.5 kg load increment. So the readings at No load, 1/4th load, 1/2 load, 3/4th load and full load are considered for analysis. Performance parameters, P-[theta] graphs and exhaust gas analysis data was collected at each compression ratio and at different loads. The obtained data was analyzed and necessary calculations were performed to evaluate the performance and combustion parameters of the engine. At 19:1 compression ratio engine running was erratic and the manometric fluid fluctuates a lot which indicates reveres flow air in the inlet manifold. This condition was discouraged the further increment of compression ratio.

Variable compression ratio diesel engine

The VCR Engine (Modified Kirlosker AV1 engine) is a vertical single cylinder, water-cooled engine; the compression ratio is varied by raising the bore and the head of the engine. As the bore and the head of the engine is raised or lowered, the clearance volume is changed and resulting in the change of the compression ratio. The engine was coupled to an air cooled eddy current dynamometer using a tyre coupling; the output shaft of the eddy current dynamometer is fixed to a strain gauge type load cell for measuring applied load on the engine. Details of the engine are shown in Table2.

Table 2: VCR Engine Specifications.

Make                  M/S. Kirlosker Ltd modified by Legion
                      Brothers, Bangaloor, A.P

Bhp                   3.72kW
Speed                 1500 rpm (25rps)
Number Of Cylinders   1
Compression Ratio     15:1 TO 20:1
Bore                  80 mm
Stroke                110 mm
Type Of Ignition      CI
Method Of Loading     Eddy Current Dynamometer

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Exhaust gas analyzer

The Crypton 290 series 5gas analyzer is used for analyze the exhaust gas of the engine. This is a fully microprocessor controlled exhaust gas analyzer shown in Fig.2. The unit measures carbon monoxide, carbon dioxide and hydro carbons. A further channel is provided employing Electro chemical measurement of oxygen and nitric oxides.

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Smoke analyzer

The exhaust gas passes through the filter paper which is fixed inside the filter paper holder and it filters the particulate emission. Sampling pump is attached to the exhaust pipe through probe. Pulling of piston with a bulb arrangement will causes for the sucking of exhaust gas through the filter paper. After that filter paper is calibrated with a light and corresponding hatridge smoke unit was considered from the chart. Smoke analyzer shown in Fig.3.

[FIGURE 3 OMITTED]

Computer setup for evaluating P-[theta]

Computer setup with DAQ software is connected to the VCR engine for evaluating the combustion parameters such as pressure, crank angle and heat release rate. The engine is provided with a crank angle encoder to evaluate the crank angle at each instant and with respect to this angle the values of pressure and heat release rates are evaluated. The computer setup is shown in the Fig.4.

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Results and Discussions Comparative analysis of CsME with Diesel

Kirlosker AV1 engine was modified as VCR engine. The compression ratio designed by the manufacturer for this engine is 16.5:1 for diesel operation. At this compression ratio performance and emission parameters of diesel and neat CsME were compared. For petroleum diesel fuel consumption per hour decreases, break thermal efficiency increases and emissions decreases at this compression ratio. CsME calorific value is 38,100 kJ/kg , which is less than pure diesel. As a result fuel consumption per hour is more than the neat petroleum diesel (graph.1). It is also supported by brake thermal efficiency Vs load graph (graph.2), brake thermal efficiency is less than diesel.

By considering environmental pollution CO and HC are slightly higher than the diesel operation at part load operation and it is nearly equal at full load operation. At full load operation increment in the NOx is higher than the diesel and it is 550PPM, where as for diesel 320PPM. Incomplete combustion is the basic reason for these pollutants and the combustion is influenced by atomization and vaporization of the fuel. At 16.5 compression ratio, CsME vaporization is poor as a result, fuel consumption per hour increases and brake thermal efficiency decreases and CO, HC slightly higher than diesel operation. However, the intake air for diesel and CsME same at this compression ratio. The inbuilt oxygen caused for emission of higher N[O.sub.x] (graph No.6). There is no appreciable variation in pressure raise for diesel and CsME at this compression ratio (graph No.7) from these observations, one can justify, increment in the Compression ratio will cause for better chemical reaction during combustion as a result fuel consumption decreases and brake thermal efficiency increases. In the view of pollutants also CO, HC decreases and C[O.sub.2] will increases at higher compression ratios. With these predictions the compression ratio for neat CsME changes from 15.5:1 to 19:1 and results were analyzed in the following sections.

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Analysis of CsME at different compression ratios

Compression ratio is one of the parameter which influences the performance of an engine. From the properties of CsME it can be observed that density, viscosity, flash and fire points are higher than petroleum diesel. On increasing of compression ratio both atomization as well as vaporization both are improved as a result fuel consumption per hour decreased (graph No.8) and thermal efficiency increased (graph No.9). CsME adopted on the diesel engine without modifications. Due to increasing of C.R the distance between the molecules of air decreases and they are very close to each other, into that fuel is injected. So the fuel will evaporates very quickly and each particle of fuel is surrounded with air, as result fuel consumption per hour will decreases. From the graph No.8, at 18.5:1 compression ratio fuel consumption per hour is minimum at full load operation. Again it has been increased on increasing of compression ratio. Due to increasing of compression ratio the swept volume will not change, but the clearance volume decreases. Inlet valve has to close after BDC where in side cylinder pressure is equal to ambient pressure. The designed inlet valve opening and closing times are not changed. Hence some portion of the air flow in reverse direction due to increasing in compression ratio, and it will causes for reduction in the intake air which is participating in the combustion. In the Volumetric efficiency Vs C.R graph (Graph.10), it can be observed that a continuous decrement in the volumetric efficiency. At higher compression ratios a rapid oscillation of fluid in the mono-metric column is observed which indicates back flow of the air, and at 19.5:1compression ratio the engine running is instable. CsME have inbuilt oxygen it caused for compensation of oxygen which is lost in intake air. As a result at 18.5:1 CR it shows low fuel consumption. But further increment caused further reduction of intake air and insufficient oxygen for combustion, so that fuel consumption again increases (graph No.8). The brake thermal efficiency is higher at 18.5:1 CR. Due to injection of fuel into the compressed air at higher compression ratio the droplet size reduces and caused for improvement in the thermal efficiency.

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Emission Analysis of CsME at different compression ratios

Due to increased closeness of molecules of air, on increasing of compression ratio and in built oxygen in the CsME caused for decreasing of HC & CO in the exhaust gas. HC& CO are minimum at 18.5:1 Compression ratio (graph No.11&12). Increment in C[O.sub.2] at 18.5:1 compression ratio supports the same. On further increment of compression ratio, leads to rich fuel combustion, it can be observed from the oxygen Vs compression ratio graph (graph 14), and causes for increasing of pollutants. There is a trade-off between complete combustion due to increase of CR and increase of pollutants due insufficient air available to participate in combustion. From the H.C Vs CR and CO Vs CR graphs, it can be observed that, a continues decrement upto 18.5:1 CR, C[O.sub.2] increases upto 18.5:1 compression ratio after that its rate of increment is less. Generally the formation of NOx is due to higher compression pressures, But from the P-? graph (graph No: 16) there is no significant increment in the peak pressure due to increase in compression ratio. At 18.5:1 Compression ratio N[O.sub.x] 280 PPM, this is less than petroleum diesel operation at 16.5:1 compression ratio. So that reduction of free oxygen from the intake air may be the reason for reduction of N[O.sub.x]. From the above discussions at 18.5:1 compression ratio thermal efficiency of CsME nearer to the petroleum diesel operation at 16.5:1 compression ratio and pollutants also less at 18.5 :1 compression ratio. Therefore 18.5:1 compression ratio is the preferable for CsME on diesel engine without modifications.

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Conclusions

Even though the density, viscosity of CsME is more than diesel, due to increase in compression ratio fuel droplet evaporation and atomization improved and causes for better combustion. 18.5:1 is the best compression ratio for CsME. At this compression ratio brake thermal efficiency is higher.

The closeness of molecules due to the increasing of compression ratio is caused for decreasing of unburnt HC as well as CO in the exhaust.

CsME is oxygenated fuel. Hence due to increase of compression ratio, even though the amount of air available for combustion in the suction stroke decreases, the inbuilt oxygen caused for proper combustion and caused for reduction in pollutants. In the environmental aspect also 18.5:1 is the best compression ratio for CsME.

References

[1] A.Senatore and M.Cardone "A comparative Analysis of combustion process in D.I.Diesel Engine fueled with Biodiesel and Diesel Fuel"SAE 2000 world Congress,Detroit,Michigan march 6-9,2000

[2] Kimura, S., Aoki, O., Kitahara, K., Aiyoshizawa, E. Ultra-Clean Combustion Technology Combining a Low-Temperature and Premixed Combustion Concept for Meeting Future Emission Standards. SAE Paper 2001-01-0200. 2001.

[3] Mustafa Ertunc Tat, "Investigation of oxides of Nitrogen Emissions from Biodiesel fueled Engines", Iowa state university, 2003.

[4] A.K.Babu& G. Devaradjane "Vegetable oils and their Derivatives as fuel for CI Engines" SAE 2003-01-0767

[5] Y.C Batt, N.S murthy, R.K.Datt "Use of Mahua oil (maduca indica) as a diesel fuel extender", IE(I) Journal-AG, Vol.85,June-2004.

[6] G. Amba Prasad, P.Rama Mohan, "Performance Evaluation of DI and IDI Engines with Jatropha oil based Biodiesel" IE(I) Journal-MC, Vol.86,July2005.

[7] Avinash Kumar Agarwal "Biofuels (alcohols and Bio Diesel) applications as Fuels for internal Combustion Engines", Elsevier,2006.

[8] Avinash Kumar Agarwal "Bio fuels (alcohols and biodiesel) applications as fuel for internal combustion engines" Science Direct (Elsevier) progress in energy and combustion science 33 (2007), pg.No. 233-271.

[9] SukumarPuhan, G.Nagarajan, B.V.Ramabramhmam, " Mahua (Madhuca Indica Oil) Derivatives as a renewable fuel for Diesel Engine Systems in India" A Performance and Emissions comparative study, International Journal of Green Energy, vol.4,issue-1,Jan-2007.

[10] Heywood, John B., "Internal Combustion Engine Fundamentals," Text book published by McGraw-Hill, New York, 1988.

(1) V. Rambabu, (2) V.J.J. Prasad, (3) Dr. T. Subramanyam and (4) Dr. B. Satyanarayana

(1) Assosiate Professor, (2) Sr. Assistant Professor Department of Mechanical Engineering GMR Institute of Technology, Rajam. A.P., India (3) Professor & H.O.D., Department of Mechanical Engineering (4)Vice-chancellor Andhra University,Visakhapatnam, Andhrapradesh, India

Table 1: Properties of Diesel & CsME.

S.No.   Name Of The Oil Sample/           Diesel.   Cotton seed
        Characteristics.                            Methyl Ester.

1       Density (kg/[m.sup.3]             0.833        0.866
2       Calorific value (kJ/kg)           43000        38100
3       Viscosity (cst) at 33[degrees]C     3.3         4.33
4       Cetane number                     45-55           55
5       Flash point (degrees]C)              50          160
6       Fire Point (degrees]C)               53          164