Performance and Emission Characteristics of SI Engine using LPG-Ethanol Blends: A Review

Transcription

1 Performance and Emission Characteristics of SI Engine using LPG-Ethanol Blends: A Review Ashish S. Lanje 1, Prof. M. J. Deshmukh 2 1 M.Tech- Student, 2 Asst. Professor, Department of Mechanical Engineering, GCOE, Amravati (MH), India. Abstract Alternative fuels for both spark ignition and compression ignition engines have become very important owing to increased environmental protection concern, the need to reduce dependency on petroleum and even socioeconomic aspects. The investigations have been concentrated on decreasing fuel consumption by using alternative fuels and on lowering the concentration of toxic components in combustion products. As a gaseous fuel, gains from LPG have already been established in terms of low emissions of carbon monoxide, hydrocarbon. Ethanol is one of the fuel additive has some advantages such as better antiknock characteristics and the reduction of CO and HC emissions. It can be considered as renewable energy under the environmental consideration. In this study, a review of research paper on air-fuel ratio, operating cylinder pressure, ignition timing and compression ratio are some of the parameters that need to be analyzed and optimally exploited for better engine performance and reduced emissions. In the present paper a comprehensive review of various operating parameters and concerns have been prepared for better understanding of operating conditions and constraints for a LPG-Ethanol fuelled Spark Ignition engine at various compression ratios. Keywords Ethanol, LPG, Performance and emission characteristics, SI engine. I. INTRODUCTION It is the dream of engineers and scientists to develop engines and fuels such that very few quantity of harmful emissions are generated and these could be let into the surroundings without a major impact on the environment. Air pollution is predominately emitted through the exhaust of motor vehicles and the combustion of fossil fuels. Government around the world has set forth many regulatory laws to control the emissions. The growing sector of transports, rise a big alarm either for the day-byday increasing number of vehicles and for the sensible contribution to the degradation of air quality in urban areas, as well as for the global pollution. Due to high thermal efficiency and power density, IC engines are widely used for transportation and stationary power source. Kyto protocol calls for a reduction in greenhouse gas emission between 2008 to 2012 to the levels that are 5.2% below 1990 level in 38 industrialized countries. IC engines exhaust emissions, due to stringent emission norms caused engine manufacturer to examine the potential of alternative fuels. CO 2 reduction in mobility sector is a major challenge for next decade. 30 billion tons of CO 2 is added to atmosphere every year by the entire nation. One of the serious problems facing the modern technological society is the drastic increase in environmental pollution by Internal Combustion engines (IC engines). All transport vehicles with SI and CI (compression ignition) engines are equally responsible for the emitting different kinds of pollutants. Some of these are primary kinds having direct hazardous effect such as carbon monoxide, hydrocarbons, and nitrogen oxides while others are secondary pollutants such as ozone, which undergo a series of reactions in the atmosphere and become hazardous to health. The emissions exhausted into the surroundings pollute the atmosphere and cause global warming, acid rain, smog, odours and respiratory and other health hazards. The urgent need for alternative fuel is essential to replace the supplement conventional fuels. A pollutant is a component which changes the balance of environment and nature under normal condition. The major exhaust emissions HC, CO, NOx, SO 2, solid particles are and performance is increased by adding the suitable additives to the fuel reduced with the present technology. LPG is obtained from the process is the process of natural gas and crude oil extraction and as by-product of oil refining. Its primary composition is a mixture of propane and butane. It has higher octane number (105) than petrol (91-97). The use of LPG in internal combustion engines yielded higher thermal efficiency and better fuel economy compared to unleaded gasoline. This is due to mainly the higher octane rating which permits greater engine compression ratio without the occurrence of knock. LPG also has higher heating value compared to other fuels and can be liquefied in a low pressure range of 0.7 to 0.8MPa at atmospheric pressure. Gaseous fuels such as liquefied petroleum gas (LPG) and liquefied natural gas (LNG) have been widely used in commercial vehicles, and promising results were obtained in terms of fuel economy and exhaust emissions. 146

2 LPG gas as a low carbon and high octane number fuel produces lower carbon dioxide (CO 2 ) emission as compared to gasoline. The use of LPG as an alternate fuel for road vehicles has been studied extensively in recent years i.e. approximately 4 million vehicles are operating on LPG worldwide. Most of these were mainly light, medium and heavy-duty trucks originally operated on gasoline and later converted to LPG using approved and certified conversion kits. Many investigations have reported favourable results from emission perspectives when LPG is used as an alternative fuel in spark ignition engines. Emissions from LPG vehicles are significantly lower than conventionally fuelled vehicles. LPG operated vehicle reported hydrocarbon (HC) emissions as 40% lower, carbon monoxide (CO) as 60% lower and carbon dioxide (CO 2 ) as substantially reduced. In addition, since LPG has lower carbon content than gasoline, it virtually produces zero emissions of particulate matter and lower amount of NOx emission as well. Figure 1: Propane production Alcohol is one of the fuel additive (Methanol, Ethanol) has some advantage over gasoline such as better antiknock characteristics and the reduction of CO and HC emissions. Since ethanol can be fermented and distilled from biomasses, it can be considered as renewable energy under the environmental consideration, using ethanol blended with gasoline is better than methanol because of its renewability and less toxicity. Some properties of ethanol with comparison to gasoline are given in Table 1. The reduction of CO emission is apparently caused by the wide flammability and oxygenated characteristic of ethanol. Therefore, improvement in power output, efficiency and fuel economy. On the other hand, the auto-ignition temperature and flash point of ethanol are higher than those of gasoline, and the low Reid evaporation pressure which makes it safer for transportation and storage, and causing lower evaporative losses. The latent heat of evaporation of ethanol is 3 5 times higher than that of gasoline; this provides lower temperature intake manifold and increases volumetric efficiency. 147 It contains 35% oxygen that helps in complete combustion of fuel and thus reduces harmful tailpipe emissions. Although having these advantages, due to limitation in technology, economic and regional considerations ethanol as a fuel still is not used extensively. Since ethanol is a liquid fuel, the storage and dispensing of ethanol is similar to that of gasoline. In the present study, to reduce the emissions and to improve the performance of petrol engine, the modification technique is used. II. LPG AND ETHANOL AS AN ALTERNATIVE FUEL IN SI ENGINE The gaseous nature of the fuel/air mixture in an LPG vehicle s combustion chambers eliminates the cold-start problems associated with liquid fuels. LPG defuses in air fuel mixing at lower inlet temperature than is possible with either gasoline or diesel. This leads to easier starting, more reliable idling, smoother acceleration and more complete and efficient burning with less unburned hydrocarbons present in the exhaust. In contrast to gasoline engines, which produce high emission levels while running cold, LPG engine emissions remain similar whether the engine is cold or hot. Also, because LPG enters an engine s combustion chambers as a vapour, it does not strip oil from cylinder walls or dilute the oil when the engine is cold. This helps to have a longer service life and reduced maintenance costs of engine. Also helping in this regard is the fuel s high hydrogen to carbon ratio (C3H8), which enables propane powered vehicles to have less carbon build up than gasoline and diesel powered vehicles. LPG delivers roughly the same power, acceleration, and cruising speed characteristics as gasoline. Its high octane rating means engine s power output and fuel efficiency can be increased beyond what would be possible with a gasoline engine without causing Destructive Knocking. Such fine tuning can help compensate for the fuel s lower energy density. The higher ignition temperature of gas compared with petroleum based fuel leads to reduced auto ignition delay, less hazardous than any other petroleum based fuel and expected to produce less CO, NOx emissions and may cause less ozone formation than gasoline and diesel engines. Properties of any fuel depend fully on its chemical compositions which determine the performance and emission characteristics of the engine. Ethanol is an oxygen enriched chemical agent; containing 35% oxygen by weight. It therefore can be treated as partially oxidized fuel.

3 When ethanol is added to the blended fuel (gasoline) it can provide more oxygen for the combustion process and leads to the so called leaning effect. Owing to the leaning effect engine combustion is improved. Lower heating value (LHV) has an average value of 26.8 MJ/Kg and the stoichiometric air to fuel ratio has a typical value of 9.0. In comparison with commercial gasoline, ethanol has higher density and octane number. In addition the high flash point (more than 56 C) of ethanol makes the storage and transportation issues less important Ethanol has higher octane number than gasoline, thus it can lead in operation at higher compression ratios therefore, improvement in power output, efficiency and fuel consumption. Different properties of ethanol are compiled from the previous works [11, 12] and presented table 1. Table I Properties of LPG, Ethanol and Gasoline Characteristics LPG Ethanol Gasoline chemical formula C 3H 8 C 2H 5OH C 4 toc 12 Boiling point( o C) Molecular Weight (Kg/Kmol) Density at 15 o C (Kg/l) Research octane number III. ENGINE MODIFICATION REQUIRED Many propane vehicles are converted gasoline vehicles the relatively inexpensive conversion kits include a regulator/vaporizer that change liquid propane to a gaseous form and an air/fuel mixer that meters and mixes the fuel with filtered intake air before the mixture is drawn into the engine s combustion chambers. Also included in conversion kits is closed-loop feedback circuitry that continually monitors the oxygen content of the exhaust and adjusts the air/fuel ratio as necessary. LPG vehicles additionally require a special fuel tank that is strong enough to withstand the LPG storage pressure of about 130 pounds per square inch. Figure 2: The schematic view for single cylinder Spark ignition engine which is used on Ethanol- LPG blends as a fuel. Stoichiometric air fuel ratio Flame speed (m/s) Upper flammability limits in air (%vol) Lower flammability limits in air (%vol) Calorific value (KJ/Kg) IV. PRESENT STATUS OF LPG AND ETHANOL FUELLED SI ENGINE ON PERFORMANCE AND EMISSION CHARACTERISTICS Following literature survey is done to study the present status of LPG, Ethanol engine performance and emission characteristics. Thirumal Mamidi, Dr.J.G.Suryawnshi 2012, studied the effect of various compression ratios on the performance and emission characteristics of SI engine using LPG. He found that as compression ratio increases, brake thermal efficiency increases. LPG has a higher octane rating and hence the engine can run effectively at relatively high compression ratios without knock. 148

4 The CO and HC emissions increase as the compression ratio, speed, and load increase. In the case of using LPG in SI engines, the burning rate of fuel is increased, and thus, the combustion duration is decreased. Therefore, the cylinder pressures and temperatures Predicted for LPG is higher compared to gasoline. Combustion of gaseous fuels like LPG occurs in a nearly uniform fuel air mixture leading to a reduction in incomplete combustion deposits such as soot on the walls of combustion chamber. When using Gasoline fuel the BSEC consumption values slightly lower than the using LPG fuel. Because the Calorific value of Gasoline is (43MJ/Kg) less compared to the LPG (46.1MJ/Kg).When load increase on the engine the CO, HC and CO2 emissions increases. Figure 3: Engine performance at various compression ratios on different load. [1] 149 Figure 4: Emission characteristics at various compression ratios on different load. [1] M.A. Ceviz, F. Yuksel 2006, investigated the effect on the cyclic variation and exhaust emission using LPG as a fuel for SI engine in terms of lean operation. He found that the increase in the relative air fuel ratio increases the coefficient of variations in imep; however, LPG decreases the cyclic variations and emissions, and it is a more suitable fuel for lean combustion engine when compared with gasoline. It can be concluded that the higher laminar flame speed of LPG and good mixing of gaseous fuels with air causes a decrease in cyclic variations, and higher H/C ratio of LPG decreases the engine emissions. N.K. Miller Jothi, G. Nagarajan and S. Renganarayanan 2008, Studied the effect of exhaust gas recirculation on diesel engine using LPG with diethyl ether. His results showed that by EGR technique, at part loads the brake thermal efficiency increases by about 2.5% and at full load, NO concentration could be considerably reduced to about 68% as compared to LPG operation without EGR.

5 However, higher EGR percentage affects the combustion rate and significant reduction in peak pressure at maximum load. O.Badr, N.Alsayed and M. Manaf 1997, Presents the experimental results of a parametric study on lean operational limits of Ricardo E6 Engine using propane and LPG as a fuel, the three different criterion, (1) detectable misfire on leaning the mixture, (2) first detectable firing under motoring condition when the mixture is been enriched slowly & (3) when the torque riches zero on leaning the mixture, for defining the engine lean limits are used. From the above experiments they had showed that as the spark timing was advanced both lean knocking and misfiring limits were reduced, As the compression ratio was increased, misfiring limit shows some decrease with LPG air mixture while with propane air mixture change only a little. Lean knocking limit decreases sharply with increase in compression ratio. Dhanapal Balaji, Periyasamy Govindrajan, Jayaraj Venkatesan 2010, Investigated the effect of using unleaded gasoline and additives blend on SI engine combustion and exhaust emission. He found that, using ethanol-unleaded gasoline blend leads to a significant reduction in exhaust emissions. On the other hand blending of all ethanol fuels the CO2 concentration increases. The addition of ethanol to unleaded gasoline the maximum pressure will be reduced for ethanol blends, the flame speed will increase, so that the spark timing of ethanol blends has to be optimized. By adding the ethanol with pure gasoline with various percentages the octane numbers of ethanol blends are increased. This leads to increase the compression ratio and power output. So, brake thermal efficiency of ethanol blends increased. Huseyin Serdar Yucesu, Tolga Topgul, Can Cinar, Melih Okur 2006, Studied the effect of ethanol-gasoline blends on engine performance and exhaust emission in different compression ratio in SI engine. He found that, with increasing compression ratio up to 11:1, engine torque increased with E0 fuel, at 2000 rpm engine speed. At the higher compression ratios the torque output did not change noticeably. At 13:1 compression ratio compared with 8:1 compression ratio, the highest increment was obtained for both fuels E40 and E60. At 11:1 compression ratio compared with 8:1, the BSFC of E0 fuel reached minimum value and decreased about 10%, after this compression ratio the BSFC increased. The fuels containing high ratios of ethanol; E40 and E60 have important effects on the reduction exhaust emissions. The maximum decrease in HC emission was obtained using E60. Ibrahim Thamer Nazzal 2011, Studied the effect of gasoline-alcohol blend on the performance of SI engine. The results are presented in terms of speed and their effects are indicated that when ethanol gasoline and methanol gasoline blended fuel is used, the brake power of the engine slightly increase. While the brake thermal efficiency increases compared with gasoline fuel. At the same time, it can be found that B.S.F.C. Also enhance compared with gasoline fuel. The exhaust gas temperature decrease compared with gasoline fuel. The addition of methanol to gasoline increases the octane number. Hence, it enables the gasoline engine to operate at higher compression ratios. C. Ananda Srinivasan and C.G. Saravanan 2010, Studied the effects of ethanol-blended gasoline with oxygenated additives on multi-cylinder SI engine. He found that the blend increased brake thermal efficiency more than gasoline. The emission tests found that the CO slightly decreased, while HC and O2 increased moderately and CO2 and NOx appreciably decreased. In addition, combustion analyses were made with the help of combustion analyzer, in which cylinder pressure and heat release rate were analysed. Rong Horng Chen, Li-Bin Chiang, Chung-Nan Chen 2011, Investigated the effect of ethanol-gasoline blended fuel on cold-start emission of an SI engine. More ethanol content in the blended fuel makes the air-fuel mixture leaner and also affects the RVP value. The engine could be started stably with E5, E10, E20, and E30. The HC and CO emissions decreased significantly with more ethanol than 20% added. However, for E40 the engine idling became unstable because the air-fuel mixture was too lean. Therefore, the ethanol content in gasoline for best cold-start emissions was determined to be at least 20 per cent but no greater than 30 percent. Longfei Chen, Richard Stone, Dave Richardson 2012, Studied the effect of gasoline/ethanol blends on the characteristics of size-resolved particulate number and mass concentration in a single-cylinder optical access engine using a differential mobility spectrometer under cold and warm conditions at a stoichiometric condition. He found that, as the ethanol volumetric percentage increases, both the total Particulate number and Particulate mass increase by a maximum of 16 and 11 for cold conditions and 7 and 8 for warm conditions. The mixture inhomogeneity increases as the ethanol content increases for E50, E70, and E85 and this would explain the increased level of particulate emissions. 150

6 Mustafa Koc,Yakup Sekmen,Tolga Topgil 2009, Studied the effect of ethanol-unleaded gasoline blends on engine performance and exhaust emission in SI engine. He found that, the effects of unleaded gasoline (E0) and unleaded gasoline ethanol blends (E50 and E85) on engine performance and pollutant emissions were investigated experimentally in a single cylinder four-stroke sparkignition engine at two compression ratios (10:1 and 11:1). The engine speed was changed from 1500 to 5000 rpm at wide open throttle. The results of the engine test showed that ethanol addition to unleaded gasoline increase the engine torque, power and fuel consumption and reduce carbon monoxide, nitrogen oxides and hydrocarbon emissions. It was also found that ethanol gasoline blends allow increasing compression ratio without knock occurrence. Figure 6: Variation of NOX emission with engine speed for different ethanol-gasoline blends. [12] The above literature review shows the improved combustion characteristics, performance and emissions characteristics with LPG and Ethanol blends as an alternative fuel to gasoline at various condition such as changing the piston cavities, air fuel ratio, speed etc. Further research has to be carried out by changing compression ratio and ignition timing to compare the performance and emissions characteristics. Figure 5: Variation of HC emission with engine speed for different ethanol-gasoline blends [12] V. CONCLUSION Based on the reviewed paper for the emissions and performance, its concluded that the LPG represents a good fuel alternative for gasoline and therefore must be taken into consideration in the future for transport purpose. And different properties of ethanol which are crucial for the assessment of performance and emission characteristics of an engine have been discussed and compared to those of conventional gasoline. 151

7 Apart from the fuel storage and delivery mechanism, LPG-Ethanol engines similar to petrol engines, and deliver nearly similar performance and good in emission characteristics than Gasoline. The power, torque increases at a certain percentages of ethanol in the blends and BSFC increases with the increment of the percentage of ethanol in the blend. Also octane number and volumetric efficiency increases with the increase in percentage of ethanol in the blend In the short term, LPG and Ethanol as an alternative fuels reviewed could displace 10 percent of current usage of oil, or bring significant reductions in CO, CO2 emissions and help to reduce harmful greenhouse gas emissions. In the next five to ten years, LPG will be more widely available and gaining market share across vehicle ranges. 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