EMISSION CHARACTERISTICS OF A COMPRESSION IGNITION ENGINE USING METHYL ESTERS OF RICE BRAN OIL AND DIESEL BLENDS R. Senthilraja Department of Mechanical Engineering, Institute of Road and Transport Technology, Tamilnadu, India E-Mail: senthilrajairtt@gmail.com ABSTRACT The emission characteristics of a single cylinder four stroke compression ignition multi fuel engine when fueled with rice bran methyl ester and its 20% and 40% blends with diesel (on a volume basis) are investigated and compared with standard diesel. The suitability of rice bran oil methyl ester as a biofuel has been established in this study. Bio diesel produced from rice bran oil by transesterification process has been used in this study. Experiment has been conducted in various loads such as 0%, 25%, 50%, 75% and 100% at a fixed engine speed of 1500 rpm and at compression ratio of 17.5:1. The impact of fuel blend on exhaust gas emissions has been investigated and presented. The fuel blend which gives comparable emission with the standard diesel has been identified. The blends when used as fuel results in reduction of smoke and carbon monoxide, hydrocarbon comparable with the diesel and increase in nitrogen oxides emissions. Keyword: diesel, rice bran methyl ester, blending, emission characteristics. INTRODUCTION Increasing demand for fossil fuel has caused an intensified search for alternative sources of energy. These include availability of feedstock as related to the security of the supply and using price volatility, domestic energy sources and continuing depletion of the reserves of nonrenewable petroleum and greenhouse gas emissions. These concerns have been addressed by a variety of legislative and regulatory mandates and incentives around the world which to summarize is beyond the scope of this article. Fuels derived from biological sources such as fats and oils have received increasing attention. The esters of vegetable oils are popularly known as biodiesel. It is the process of reacting triglyceride with an alcohol in presence of a catalyst to produce glycerol and fatty acid esters. In India, attempts are being made for using non-edible and under-exploited oils for production of esters. Blending conventional diesel fuel with esters (usually methyl esters) of vegetable oils is presently the most common form of biodiesel. There have been numerous reports indicating that significant emission reductions are achieved with these blends. Several studies [Agarwal AK et al] have shown that diesel and biodiesel blends reduce smoke opacity, particulates, un-burnt hydrocarbons, carbon dioxide and carbon monoxide emissions, but nitrous monoxide emissions have slightly increased. Raheman and Phadatare tested karanja methyl ester and its blends with diesel from 20% to 80% by volume in a single cylinder direct injection diesel engine and they found that the carbon monoxide, smoke and NOX emissions were lower. Usta et al conducted an experimental study on exhaust emissions of a diesel engine fuelled with tobacco seed oil methyl ester. The results showed that the addition of tobacco seed oil methyl ester to the diesel fuel reduced CO and SO 2 emissions while causing slightly higher NO X emissions. Labeckas and Slavinskas et al analyzed the emission characteristics of four stroke, four-cylinder, direct injection, unmodified, naturally aspirated diesel engine when operating on neat rapeseed methyl ester (RPE) and its 5%, 10%, 20% and 35% blends with diesel fuel. They found that carbon monoxide, hydrocarbon and visible emissions had decreased while an oxide of nitrogen emissions increased for methyl ester compared to diesel. In this study, methyl esters of rice bran oil with diesel blends (volume basis) is chosen as a fuel for single cylinder four stroke compression ignition multi fuel engines. The methyl ester of rice bran oil and diesel fuel blends in different ratios are prepared and the emission characteristics of compression ignition engine using various blends at compression ratio 17.5:1 for 0%,25%,50%,75% and 100% load is carried out and its results is compared with standard diesel fuel. EXPERIMENTAL SETUP Figure-1. The experimental apparatus used in the tests. 1199
Figure-1 shows the schematic diagram of the experimental set up. The test engine used is a single cylinder four stroke diesel engines coupled with eddy current dynamometer. The specification of the engine is shown in Table-1. The piezoelectric pressure transducer and a crank angle encoder which measures the combustion pressure and the corresponding crank angle respectively are mounted into the engine head. The output shaft of the eddy current dynamometer is fixed to a strain gauge type load cell for measuring applied load to the engine. The temperature sensors attached to the cooling water supply system, air supply system and exhaust system is used to measure the temperature of water and air at inlet and outlet of the engine. The fuel flow is measured by the use of 20 cc burette and stopwatch. A computerized data acquisition system is used to collect, store and analyze the data during the experiment by using various sensors. Table-1. Technical specification of the engine. Engine model and type Power ( kw) Speed (rpm) Bore diameter (mm) Stroke length (mm) Cubic capacity (cm 3 ) Fuel injection pressure (bar) Compression ratio Lubrication system Cooling system Single cylinder, four stroke compression ignition, water cooled 4.4 1500 87.5 110 661 250 17.5:1 Forced feed system Water cooling EXPERIMENTAL METHODOLOGY The compression ignition engine is started by using standard diesel and when the engine reaches the operating temperature. The load such as 0%, 25%, 50%, 75% and 100% load is applied. The warm up period ends when cooling water temperature is stabilized at 60 o C. The tests are conducted at the rated speed of 1500 rpm. In every test, volumetric fuel consumption and exhaust gas emissions such as carbon monoxide (CO), hydrocarbon (HC), nitrogen oxides (NOx), carbon dioxide (CO2) and smoke are measured. At each operating conditions, the exhaust emission levels are also processed and stored in personal computer (PC) for further processing of results. The same procedure is repeated for different blends of rice bran oil methyl esters with diesel fuel at various proportions. RESULTS AND DISCUSSIONS Hydro Carbon Emission Figure-2. Hydrocarbon emission vs load for 1200
HC is mainly caused by misfire in a locally rich region or locally lean region. From the Figure-2, it is observed that HC emission increases with the increasing load of the engine. The blends of rice bran methyl ester with diesel increases HC emission than of that neat diesel fuel and also the blend of 40% rice bran methyl ester with the diesel fuel shows slightly increased value. The effects of fuel viscosity, on the fuel spray quality, are expected to produce some HC increase with vegetable oil fuels [Devan PK et al]. Due to the longer ignition delay, the accumulation of fuel in the combustion chamber may cause the higher hydro carbon emission (Muralidharan K et al). Nitrogen Oxides (NOx) Emission Figure-3. NOx emissions vs load for From the Figure-3, it is observed that NO X increases with the increasing load of the engine. This is probably due to higher combustion temperature in the engine cylinder with increasing load. The increasing concentration of biodiesel in the blend increases the NO X emission. The blends show increased NO X than diesel fuel. At full load of the engine, the maximum NO X is observed. This may be due to higher combustion chamber temperature, which in turn is indicated by the prevailing exhaust gas temperature. With increase in the exhaust gas temperature, NOx emission also increased. That s why; biodiesel fuel has the potential to emit more NOx as compared to that of diesel fueled engines [Puhan S, Chhina R, Lapuerta M, Deshmukh SJ et al]. Carbon Monoxide Emission Figure-4. Carbon monoxide emission vs load for From the Figure-4, it is observed that CO emission decreases with the increasing load of the engine. At lower load, the blend shows higher CO emission and at higher load is comparable with the base diesel. The effects of fuel viscosity on fuel spray quality would be expected to make some CO increase with vegetable oil fuels. [Devan PK et al]. The percentage of CO increases due to rising temperature in the combustion chamber, physical and chemical properties of the fuel, air fuel ratio, shortage of oxygen at high speed, and lesser amount of time available for complete combustion [Arpa Orhan et al]. Carbon Dioxide Emission Figure-5. Carbon dioxide emission vs load for 1201
From the Figure-5, it shows that CO 2 increases with the increasing load of the engine. The increasing concentration of rice bran methyl ester in the blend increases CO 2 emission than that of the neat diesel fuel. The accumulation of CO 2 in the atmosphere leads to many environmental problems like ozone depletion and global warming. The CO 2 emission from the combustion of bio fuels can be absorbed by the plants and the carbon dioxide level and is kept constant in the atmosphere. (K. Muralidharan et al). Smoke investigated and compared with neat diesel fuel. Based on the experimental study, the following conclusions are summarized as follows: HC emission of the 40% concentration of rice bran methyl ester in the blend was comparable with base diesel fuel. The fuel blends increased NO X emission at all load of the engine. CO emission increased at lower, medium load and at higher load comparable with the diesel fuel. CO 2 for the blend slightly increased at all load of the engine. Smoke reduced at all load of the engine for all the fuel blends. REFERENCES [1] Agarwal AK, Das LM, 2000. Biodiesel development and characterization for use as a fuel in compression ignition engines. Am Soc Mech Engrs J Eng, Gas Turb Power. 123: 440-7. Figure-6. Smoke at different loads. From the Figure-6, it is observed that smoke slightly increases with increasing load upto 75% and at full load increases drastically. The blends reduce the smoke than the neat diesel fuel. It is observed that smoke decreases for blends compared to diesel fuel, especially at high loads. The presence of atomic bound oxygen in biodiesl satisfies positive chemical control over soot formation. The tendency to generate soot by the fuel dense region inside a blend diffusion flame sheath is reduced, due improved mixing owing to better atomization and vaporization of blends. This is also attributed to the engine running overall leaner, with the combustion being now assisted by the presence of the fuel-bound oxygen of the ethanol and biodiesel even in locally rich zones which seems to have the dominating influence [Xiao Z, Boruff PA et al]. In-cylinder combustion photography showed lower luminosity flames for the blends, revealing the lower net soot produced percentages in its blends with diesel fuel [Xingcai L, Chen H et al]. This also proves the superior mixing of blends with air prior to premixed combustion phase and inbuilt oxygen in fuel results in more oxidation of soot particles to decreases the smoke level in the exhaust. CONCLUSIONS In this study, the exhaust emission of direct injection diesel engine fuelled with methyl esters of rice bran oil as neat biodiesel and its blend with diesel are [2] Raheman H, Phadatare AG. 2004. Diesel engine emissions and performance from blends of karanja methyl ester and diesel. Biomass and Bioenergy. 27:393 7. [3] Usta N. 2005. An experimental study on performance and exhaust emissions of a diesel engine fuelled with tobacco seed oil methyl ester. Energy Conversion and Management. 2005; 46: 2373 86. [4] Labeckas G, Slavinskas S, 2006. The effect of rapeseed oil methyl ester on direct injection diesel engine performance and exhaust emissions. Energy Conversion and Management. 47: 1954-67. [5] Muralidharan K, Vasudevan D, 2011. Performance, emission and combustion characteristics of a variable compression ratio engine using methyl esters of waste cooking oil and diesel blends, Applied Energy 88, 3959-3968. [6] Devan PK, Mahalakshmi NV, 2009. A study of Performance, emission and combustion characteristics of a compression ignition engine using methyl ester of paradise oil eucalyptus oil blends. Appl Energy. 86, 675-80. [7] Puhan S, Vedaraman N, Sankaranarayan G, Boppana, V, 2005. Ram, Performance and emission study of mahua oil (madhuca India oil) ethyl ester in a 4-1202
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