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ABSTRACT:
Biodiesel production from non-edible oil is one of the effective ways to overcome the problems associated with energy crisis and environmental issues. Thus, cotton seed oil methyl ester (CSOME) is chosen as a potential biodiesel for the present investigations based on the availability in India. A single-cylinder, four-stroke, variable compression ratio (VCR), direct injection, diesel engine is employed to conduct experiment with three compression ratios (16:1, 17:1, 18:1). The cotton seed oil blend B20 is used as fuel. The performance test results shown that the BTE and BSFC of CSOME are slightly lower than Diesel at full load. The emission result reveals that reduced UBHC of about 16%, CO of about 11% and smoke emission of about 15% for the B20 blend of CSOME for Compression ratio 18:1 at full load conditions.
INTRODUCTION :
Rudolf diesel first enunciated the concept of diesel engine, about a century back; the experimental evaluation was demonstrated on peanut oil indicating that the vegetable oils will be the prospective future fuels in diesel engines. Recently the use of biodiesel as a substitute for crude oil based diesel fuel is triggered due to the increasing concern over the destruction of the environment caused by burning fossil fuels. Crude oil resources are finite and therefore search for alternative fuels is continuing all over the world. Bio- diesel is considered as an alternative and clean fuel because it does not contain any sulphur, aromatic hydrocarbons, metals, crude oil residues and contributes a minimal amount of net greenhouse gases to the atmosphere. Biodiesel is defined as mono-alkyl esters of long chain fatty acids derived from a renewable lipid feedstock, such as vegetable oil or animal fat and alcohols with or without a catalyst. Different vegetable oils such as soybean oil, kapok seed oil, castor oil, rapeseed oil, Jatropha curcas oil, cottonseed oil are considered as alternative fuels for diesel engines (Anbarasu, 2012). The important advantages of vegetable oils as fuel are that they are renewable, can be produced locally, cheap and less pollutant for environment compared to diesel fuel. The seed contains 17–25 wt. % oil. The fatty acid composition of cotton seed oil is mainly linoleic (55.2–55.5%), palmitic (11.67–20.1%), and oleic acids (19.2–23.26%). Transesterification is the process of converting the triglycerides of vegetable oils to their monoester by reacting them with alcohols in the presence of a catalyst. Leenus Jesu Martin et al. (Leenus, 2012) reported an increase in the BTE to 30.4% is noticed at peak output with ethyl ester of cotton seed oil (EECSO). Nurun Nabi et al. (Nurun, 2009) compared the neat diesel fuel with 30% biodiesel mixtures gives reduced CO emissions of about 24%. Jinlin Xue et al. (Jinlin, 2011) investigated cotton seed biodiesel and found that the HC emissions decreased by 14% using B5 and by 26% using B100. Huseyin Aydin et al. (Huseyin, 2010) observed that the smoke opacity is lower for B20 and B50 than D2 and B5 fuels at medium engine speeds. Jagannath Hirkude et al. (Jagannath, 2014) studies the change in CR from 16.5 to 17.5 resulted in 5.41%, 6.59% and 7.25% increases in BTE in the case of B70, B50 and B0, respectively.
EXPERIMENTAL PROCEDURE :
A direct injection (DI) Diesel engine was selected for the present investigation. Performance and emission test of Diesel and CSOME were carried out in a single cylinder, naturally aspirated, four stroke, VCR, vertical, constant speed, water-cooled, 5.2 kW Kirloskar TV1 model diesel engine coupled with eddy current dynamometer. The compression ratio can be changed without altering the combustion chamber geometry by specially designed tilting cylinder block arrangement. Engine exhaust is connected with AVL Digas analyzer is used to measure the emission parameters like CO, HC, CO2, and NOx, while AVL smoke meter is used to measure the exhaust smoke opacity. Fuel consumption was measured by the transparent glass vertical tube. Engine was started with a fuel and warmed up for ten minutes to stabilize cooling water temperature for all the tests.
Performance Characteristics:
Brake Specific Fuel Consumption (BSFC):
The variation of BSFC with load is shown in fig. 2. It is found that the specific fuel consumption for the blend is higher than diesel at all loads. This is because of lower heating value.
Higher proportions of cotton seed oil in the blends increases the viscosity which in turn increased the specific fuel consumption due to poor atomization of the fuel. The oxygenated biodiesels may lead to the leaner combustion resulting in higher BSFC. The increase in the compression ratio leads BSFC closer to diesel due to their combustion feature. Thus BSFC of the cotton seed oil is lower for compression ratio 18 when compared to 17 and 16.
Brake Thermal Efficiency (BTE):
The fig. 1 shows the variation of brake thermal efficiency with load. In general the thermal efficiency depends on the combustion process which is a complex phenomenon that is influenced by several factors like cetane number, viscosity, calorific value. It is evident that diesel fuel has the higher brake thermal efficiency compared to cotton seed biodiesel blends. The diesel fuel has the highest thermal efficiency because of its calorific value and viscosity as compared with cotton seed oil. With the higher calorific value the amount of heat produced in the combustion chamber is more, further the combustion is complete and produced higher temperatures. The blend with compression ratio 18 has high BTE compared to compression ratio 16 and 17.
Emission Characteristics :
Carbon monoxide emission (CO):
It has been observed from fig.4 that the CO emissions are increased with increase in engine load and decrease with the increase in proportion of biodiesel in the blends. The lower CO emission of biodiesel compared to diesel fuel is due to the presence of oxygen in biodiesel which helps in complete oxidation of fuel. Thus the blend with compression ratio 18 shows less carbon monoxide emission.
Smoke emission:
The variation of smoke emission with load for neat diesel fuel and blend was shown in fig. 5. For biodiesel mixtures, smoke emission was less compared to neat diesel fuel. Due to heterogeneous nature of diesel combustion, fuel-air ratios, which affect smoke formation, tend to vary within the cylinder of a diesel engine. Smoke formation occurs primarily in the fuel-rich zone of the cylinder, at high temperatures and pressures. If the applied fuel is partially oxygenated, locally over-rich regions can be reduced and primary smoke formation can be limited. The blend with compression ratio 18 emits less smoke.
Unburnt hydrocarbon emission (UHC):
The UHC emissions depend upon mixture strength i.e. oxygen quantity and fuel viscosity in turn atomization. The UHC emissions increase with increasing load and decrease with increase in amount of biodiesel in blend. Lower heating value leads to the injection of higher quantities of fuel for the same load condition. Viscosity effect, in turn atomization, is more predominant than the oxygen availability, either inherent in fuel or present in the charge. When compared to diesel, the oxygen availability in the bio diesels is more. The blend with compression ratio 18 emits fewer hydrocarbons.
Oxides of nitrogen (NOX):
As observed from the fig. 7, the NOx emission for diesel and blend increase with the increase of compression ratio. The reason for higher NOx emission for blends is due to higher peak temperature. Hence the most significant factor that causes NOx formation is high combustion temperatures and the combustion temperature increases the compression ratio increase, so as the compression ratio increase, the amount of NOx will increase.
CONCLUSION :
In this experimental investigation the performance and emission characteristics of CSOME for various compression ratios were investigated. The result of the investigation was as follows:
1. Cotton seed oil methyl ester was prepared by transesterification process.
2. The brake thermal efficiency is slightly lower than diesel but increased with increase of compression ratio.
3. The smoke, carbon monoxide emission and hydrocarbon emission is lower than diesel and decreased with increase in compression ratio.
4. Oxides of nitrogen emission are higher for the biodiesel in all compression ratios compared to conventional diesel but decrease with increase in compression ratio.
5. Cotton seed oil biodiesel is a renewable alternate source and non-edible oil. Hence it can be substituted as a promising environmental friendly alternate source of fuel in future.