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The invention of internal combustion engines is undoubtedly one of the greatest inventions of the modern era. There has been steady scientific research to look for alternative fuel which is economical, renewable and less harmful to nature and man compared to fossil fuels. The present project is one such experimental work to investigate the performance of a blend of diesel / N-pentanol in an appropriate combustion technique and to establish its suitability as a renewable fuel. The relative performance of diesel fuel and the blend of diesel / n-pentanol will also be analyzed. Diesel fuel blended with 30% n-pentanol is the fuel blend that is proposed to be used in the experiment. Researchers have established that the application of Homogeneously Charged Compression Ignition (HCCI) technique could result in in-cylinder reduction of NOx and PM. Higher thermal efficiency could also be attained. The project also covers studying the emission effect of the diesel/n-pentanol fuel blend for various fuel injection timing, various fuel injection pressure, different EGR rates and different inlet air temperature.
ABSTRACT:
The invention of internal combustion engines is undoubtedly one of the greatest inventions of the modern era. There has been steady scientific research to look for alternative fuel which is economical, renewable and less harmful to nature and man compared to fossil fuels. The present project is one such experimental work to investigate the performance of a blend of diesel / N-pentanol in an appropriate combustion technique and to establish its suitability as a renewable fuel. The relative performance of diesel fuel and the blend of diesel / n-pentanol will also be analyzed. Diesel fuel blended with 30% n-pentanol is the fuel blend that is proposed to be used in the experiment. Researchers have established that the application of Homogeneously Charged Compression Ignition (HCCI) technique could result in in-cylinder reduction of NOx and PM. Higher thermal efficiency could also be attained. The project also covers studying the emission effect of the diesel/n-pentanol fuel blend for various fuel injection timing, various fuel injection pressure, different EGR rates and different inlet air temperature.
KEYWORDS:
Bio diesel; n-pentanol; Emission characteristics; NOx; HCCI; Performance
1.Introduction
Internal combustion engines are mobile power plants which the human beings have adapted to daily life usage and have become inevitable. The growing use of IC engines in the nature of automobiles has caused congestion on the roads and degradation in air quality due to the pollutants from these power plants. Internal combustion engines oxidize hydrocarbon fuel releasing CO2 and H2O release heat energy by an exothermic reaction. Adding after treatment devises like catalytic converter, diesel oxidation catalyst, DPF, lean NOx etc., on the exhaust tail pipe will create back pressure resulting in fuel penalty. Therefore, a new combustion technique is required to reduce the pollution formation within the cylinder itself. Leading research in HCCI engine has proved that simultaneous reduction of soot and NOx is possible. It is a hybrid combustion technique combining concepts from SI engine and diesel engine.
HCCI is achieved when a completely homogeneous mixture of fuel and air is ignited by the heat generated by isentropic compression of the charge in the pistoncylinder arrangement. Combustion reaction in HCCI starts with low temperature reaction (LTR) at around 700°C for diesel fuel. The initial fuel molecules break up releasing highly reactive radicals along with some amount of heat release. The heat released stimulates further reaction resulting in increased formation of reactive radicals. After LTR the charge undergoes chemical reactions without any heat release for around 3°CA normally. This phase of no-heat lease is termed as Negative temperature coefficient (NTC). The end of NTC phase is a state where the entire charge is ready for combustion instantaneously. The entire charge undergoes complete premixed combustion and the maximum combustion temperature would be below 1800°K.
This being so, oxidation of nitrogen molecule to oxides of nitrogen (NOx) will not take place. The complete premixed combustion eliminates fuel concentration gradient. As a result, formation of PM is completely eliminated. The primary requirement for HCCI is homogeneous charge, which is achieved by volatility of the fuel. Highly volatile fuel can easily vaporize and mix efficiently with air. Alternatively, high pressure injection can also atomize the fuel to fine particle size by which it can easily mix with air. High pressure injection of fuel need viscosity close to diesel fuel so that the same fuel injection system can be used. Since the charge is compressed and ignited, higher cetane number is preferable. Higher cetane number means lower auto-ignition temperature. Therefore, combustion can be controlled by varying other parameters. Present work utilized pentanol blended biodiesel as fuel for HCCI engine which as high cetane number compared to other biodiesel and has viscosity near to the diesel. Biodiesel is an alternative to fossil fuel which provides solution to many environmental problems [1, 2]. Pentanol which is a saturated alcohol with all single bonds is a five-carbon alcohol with hydroxyl group at one end, sharing a covalent bond with carbon atom.
2.Literature review
Elina et al [3] have studied the effect of hydroxyl functional group in alcohol molecule on compression ignition and exhaust gas emissions. The results showed that addition of hydroxyl group to alkane compound increased its ignition delay. This effect is mainly attributed to the electronegativity of oxygen atom which changes the kinetic combustion mechanism. It was revealed that any LTC starts with first hydrogen abstraction followed by isomerization. Lechner et al [4] investigated the use spray cone angle injector and early injection timings are reduced nitrogen oxide (NOx) and particular matter (PM) emission in Partially Premixed Compression Ignition (PPCI) ignition strategy. It is found from investigation NOx reduced by 60% & PM reduced by 39% for 60° spray cone injection nozzle. Hisashi et al [5] analyzed PREmixed lean Diesel Combustion (PREDIC) through engine performance test and numerical modelling in a single cylinder engine through spray observation in high pressure vessel.
Tseng [6] has produced pentanol with metabolically engineered Escherichia coli. N-pentanol was produced from renewable carbon sources through microbial fermentation. About 85 mg/L of pentanol was achieved from glucose and propionate. The use of biomass has advantages in its reliability, versatility and domestic availability while it also has its limitations such as low energy density compared to coal, liquid petroleum or petroleum derived fuels. James et al [7] investigated effect of cetane number (CN) on HCCI single cylinder engine by performance and emission test. It was detected the CN less than 34 has more than 15 % total heat release in some instance time. Keiichi et al [8] experimentally investigated PREDIC with appropriate fuel spray formation. It is found that very low NOx emission (20 ppm) achieved in the PREDIC combustion zone of 1.87.
Liangjie [9] suggested that up to 30% by volume of n-pentanol could well be mixed with diesel fuel with no solvents at room temperature and could be applied on diesel engine without any modifications. Li et al [10] studied the effect of pentanol-diesel fuel mix with respect to combustion and performance. Emissions of NOx were reduced compared with using pure diesel fuel at low to middle loads. Kim et al [11] experimentally investigated the effect of multiple injection on the performance and emission analysis of Dimethyl ether (DME) fuelled engine. The results of multiple injection show nearly 75 % reduction in NOx with small reduction in indicated mean effective pressure (IMEP). Partial premixed charge compression ignition (PPCCI) reduced NOx emission nearly 97.1 % with 23 % reduction IMEP. Kim et al [12] investigated the exhaust emission of common rail diesel engine for the effect of narrow fuel spray angle injection and dual injection strategy.
HCCI and conventional diesel combustion was studied and found HCCI second injection was effective to reduce NOx emission. Rajeshkumar et al [13] has analyzed the performance and emission of two different fuel blends B40 (40% iso-butanol - 60% diesel) and P40 (40% n-pentanol - 60% diesel). P40 blend showed reduction of NOx up to 39.3% and smoke up to 15 % with fuel injection timing 230 and 21 0 CA BTDC. Smoke emissions increased drastically beyond 30% EGR. It was also observed that with increase of EGR rate a few penalties in BSFC were observed. From the above literatures it is clear that many researchers have focused on the use of bio-diesel as alternate for conventional diesel in CI engines. Although the researches done on the performance characteristics and emission test of IC engine experimentally. Some of the literatures done on the alcohol blended bio diesel with different ratios, especially on methanol, ethanol, isobutanol, n-pentanol etc. In this study n-Pentanol alcohol is blended with diesel and tested with different fuel injection angle and an emission characteristic was analyzed.
3.Experimental methodology
In this study the experimental test was conducted using HCCI. The emission characteristic of a HCCI engine using early injection strategy requires a sophisticated CRDI fuel system in order to have maximum flexibility of operating parameters like fuel injection timing and pressure. A single cylinder, air cooled, four-stroke compression ignition engine is used for the study. The fuel system was modified into a CRDI fuel injected system from conventional mechanical fuel pump. The engine is coupled to an eddy current dynamometer and the specification of engine is shown in Table 1.
In order to have independent control over fuel injection timing and injection pressure, it was necessary to upgrade the conventional fuel system to CRDI fuel system. CRDI has rail pressure sensor, inlet metering valve and fuel injector system. The rail supplied by Delphi has a pressure sensing transducer. This pressure transducer is used to measure the pressure in the rail continuously during the operation of the engine. The block diagram and engine setup are shown in Figs. 1 and 2. In order to get stable and accurate results, the engine was first brought to steady-state conditions by running HCCI engine for a particular time. The sensors in the engine are connected with data accusation system for the performance and emission test. For the exhaust gas emission AVL gas analyzer and portable smoke opacity meter was used. The engine was set to operate at constant speed of 1500 rpm with varying load condition. Initially the engine was tested with conventional diesel and result was noted and then n-pentanol blended with diesel with varying injection angle was tested and results are noted down.
4.Results and discussion
Results were taken by experimentally testing n-pentanol diesel blend in test engine with conventional fuel system. Initially high-speed diesel was used to run the engine for the base line data. The fuel was injected at 200 bar at an injection angle of 23° BTDC. The conventional injector has 3 orifices. After the base readings were taken, the fuel system was changed to CRDI system. The experiment was repeated with 30% pentanol blended to high-speed diesel. The experimental test was performed at the rated speed of 1500 rev/min for two different fuel injection angles such as 40°BTDC, & 50°BTDC, and load was set for 20, 40, 60 and 80 % of total load. Based on the results taken from the engine test, emissions characteristics of n-pentanol biodiesel were given. Major emissions like hydro carbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), carbon dioxide (CO2) and smoke values for different injection angle and various load was found and discussed [14, 15].
The experimental results for HC emission of conventional diesel fuel and bio diesel blend (30 % of npentanol) for different injection angles are shown in Fig. 3. Initially at no load condition the HC emission was lower for conventional diesel engine test whereas bio diesel has higher emission value. With increase in load the HC emission is decreased for bio diesel blend compared to conventional fuel. At 20 % of load the HC emission is lowest on 40 BDC and 66 % more reduction compared to conventional diesel fuel. Similarly, HC emission for 50 BDC and 60 BDC is low compared to conventional diesel fuel. The reason is due to better mixing of the fuel and air with increase in combustion temperature HC emission is reduced. Similarly, the HC emission for 40, 60 and 80 % of rated load also got reduced for n-pentanol bio diesel compared to conventional diesel fuel. CO emission characteristics for various loads and injection angles are shown in Fig. 4. At no load condition, the CO emissions for early injection strategy were higher than conventional operation. At 20, 40, 60% loads the CO emissions for early injection strategy were close to conventional fuel injection. At 80% load alone the CO emissions for early injection was higher. This increase is due to richer fuel and incomplete combustion.
The characteristics of oxides of nitrogen (NOx) emission for various injection angle and load condition are shown in Fig. 5. At no load condition, the single early injection strategy showed reduced oxides of nitrogen emissions. Comparing diesel with n-pentanol NOx emission is reduced to 80% at 50 BTDC and 40 % at 40 BTDC. This is due to more time available for combustion at early injection. At 20% load, the NOx emissions were little higher than conventional operation. But the NOx emission was significantly higher at 40% and 60% loads. This was contrary to expectation. The reason for such a contrary value could be attributed to knocking at intermittent stage of operation and increase in temperature of combustion at these loads [16, 17]. Smoke is the collection of PM and soot and the emission characteristics for various load and angle are shown in Fig. 6. In a homogeneous combustion of fuel charge, the particulate matter should be minimum. In line with this logic, there was reduction in smoke emissions around 5 to 15% up to 60% load. At 80% load there was increase in soot emissions. Due to reduction in efficiency of operation there was increase in fuel demand which ended with partially burnt fuel. Also, inclined injector is prone to fuel spray hitting the cylinder head. And that has increased the smoke level at higher loads. The emission characteristics of CO2 for various load and injection angle are shown in Fig. 7. CO2 is the by-product of complete combustion. More the CO2 emissions better is the hydrocarbon molecules is easier combustion efficiency. Also due to the presence of oxygenated fuel, combustion of for all loads the CO2 emissions were observed to be more than conventional operation. As the load increased, carbon dioxide amount at the exhaust has increased.
5.Conclusion
In the present study, the effect of n-pentanol bio diesel (30% blend) with varying fuel injection angle (40 BTDC& 50 BTDC) and load (20, 40, 60 & 80%) was studied with constant speed of 1500 rpm. The following main conclusions for emission characteristics can be drawn from the study: Hydrocarbon emission was decreased with n-pentanol bio diesel compared with conventional diesel fuel with varying injection angle. It also found that the hydrocarbon emission starts to increase at high loads. Carbon monoxide emission was more in n-pentanol bio diesel compared with conventional diesel due to incomplete combustion of richness of bio diesel. At high load the emission was high due to more fuel available in the engine. A decrease in oxides of nitrogen was found at no load in n-pentanol bio diesel compared with conventional diesel. But with increase in load the oxides of nitrogen increased due to increase in temperature in combustion chamber.
Smoke emission was decreased with n-pentanol bio diesel compared to conventional diesel at no load condition. At higher load smoke emission is increased due to more fuel available and higher combustion temperature. CO2 emission was high in n-pentanol bio diesel compared with conventional diesel. Higher CO2 emission indicates higher rate of combustion which increases the efficiency of the engine. Over all the emission test of n-pentanol bio diesel with additive, indicates that it can be feasible and added advantage as an alternate fuel for diesel in CI engine.
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