Benzin ve metanol yakıtlı bazı ateşlemeli motorlarda performans ve emisyon karakteristiklerinin incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 55981
- Danışmanlar: PROF.DR. OĞUZ BORAT
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 76
Özet
ÖZET Dünya petrol rezervlerinin gelecek yüzyılın ortalarına kadar ihtiyacı karşılayabileceği konusunda, bilim çevrelerinin derin kuşkuları bulunmaktadır. Gerek petrol rezervlerinin yakın bir gelecekte tükeneceği endişesi ve gerekse de bu ürünlerin yanması sonucunda büyük çapta bir çevre kirliliğinin yaşanması, içten yanmalı motorlarda kullanılmak üzere yeni alternatif yakıtlar aranması çalışmalarına ivme kazandırmıştır. Yapılan araştırmalar kısa vadede geleceğin yakıtının metanol olduğunu ortaya koymaktadır. Bu çalışmada Saf metanol klasik bir benzin motorunda denenmiş ve motor performansı ile egzoz emisyonlarına etki eden parametreler deneysel ve teorik olarak incelenmiştir. Çalışmanın ilk üç bölümünde dünyada ve Türkiye'de enerji problemi ele alınmış ve alternatif yakıtlar hakkında literatüre dayalı bilgiler verilmiştir. Dördüncü bölümde yapılan deneysel çalışmalar anlatılmıştır. Beşinci bölümde ise teorik çalışmalara yer verilmiş ve emme manifoldunda gelişen olaylar (benzin ve metanol için karşılaştırmalı olarak) modellenmiştir. Sonuçlar ve irdeleme bölümünde gerek deneysel ve gerekse de teorik olarak elde edilen veriler yorumlanmıştır.
Özet (Çeviri)
SUMMARY A STUDY ON THE PERFORMANCE AND EMISSION CHARACTERISTICS OF GASOLINE AND METHANOL FUELED SPARK IGNITION ENGINES. Energy is a physical necessity without which human beings can not survive. Throughout history, one of the most important factors leading to great social and political changes and causing wars has been people's desire to meet their requirements of energy. As is known, since the industrial revolution energy resources of fossil- origin have been steadily declining due to the rapid growth of the world's population, the rapid urbanisation on a global scale, and the ever-increasing use of new technologies. This fact is seen as worrisome by the experts and it motivates them to speed up the efforts to find alternatives to existing engines and engine fuels. At the present time each one of the world countries has to give serious consideration the type and source of fuel they will use in the future. One of the major effects faced with today in choosing the type of fuel to be used in the future is not only the amount of reserve but also whether it is convenient and economical both physically and chemically. Negative effects of exhausted emissions on human life and environment will also play a significant role in determining the type of alternate fuel.At the present time most of the energy requirements of the world are met from petroleum, coal and natural gas sources. Nuclear energy and hydraulic energy are also used. The World currently has 136x109 tons of fossil fuel reserves, 124x1 012 cubic meters of natural gas, and 1 041x1 09 tons of coal reserves. It has been estimated in 1991 that coal resources will last for another 239 years. Developing countries which do not have petroleum have to import energy. The oil crisis of 1973 and the Gulf war of 1991 caused world oil prices to go up and this shook the economies of the developing countries including Türkiye which imports crude oil, in large amounts. Methanol which is also known as methyl alcohol or wood alcohol, is frequently suggested as an alternative fuel for automobiles. The proponents of methanol point out that practically any kind of carbonaceous material, such as coal or renewable organic matter or municipal solid wastes, can be used to produce a gas (carbon monoxide and hydrogen) which is then readily convertible into methanol using currently available commercial processes. Methanol has also been used for many years as a fuel in race cars and boats, there fore there is little doubt about its utility as an engine fuel. It's preferred as a racing fuel chiefly for safety reasons. It is less likely to catch fire in the event of an accidental crash or collision. Also, it is said to keep the engine running cooler than with gasoline and to provide better performance, more horsepower, at high speeds. As far as toxicity and handling properties are concerned, methanol is about on a par with gasoline. Similarly with regard to air pollution; there are some differences, but these are by no means universally accepted. Methanol produces less carbon monoxide and less oxides of nitrogen than gasoline (and, of course, no hydrocarbon vapours), but it producesaldehydes and methanol vapours which gasoline does not. However, these differences are not dominant considerations. The physical property which distinguishes gasoline and methanol is the heat of combustion. The heat of combustion of methanol, either on a volumetric or on a weight basis, is less than one-half that of gasoline. Consequently, transportation and distribution costs of methanol are roughly twice those of gasoline, because approximately twice the volume of material must be transported, stored and distributed to deliver equal quantities of fuel energy. Methanol can be manufactured from lignite or coal, municipal, agricultural, or forestry waste. It is estimated that the United States has 320 million tons of agricultural waste and 120 million tons of forestry waste per year. If all these waste products were converted to methanol, the US crude oil consumption would be reduced by one-third. A city with a population of 3 million would create enough waste to produce 1,000 bbl of methanol per day. The same city would require 80000 bbl of engine fuel per day. Methanol, produced from lignite or coal would cost approximately 35 cent per gal. The cost of producing methanol from a waste plant would be about 50 cent per gal. Production costs vary, depending on the feedstock and transportation costs. If alcohols were used as engine fuel by a significant percentage of the US vehicle fleet, a whole new alcohol production and distribution system would be necessary. The US methanol production is about 85,000 bbl per day while engine fuel requirements are approximately 7 million bbl per day. A plant to produce methanol from coal, with a production capacity of 120,000 bbl per day would cost $ 1.8 billion. The construction of an alcohol industry capable of supplying the engine fuel requirements of a large percentage of the US vehicle fleet would be extremely expensive. The advantages and disadvantages of alcohols can be summarised as follows;Advantages: Alcohols could replace fuels derived from crude oil and allow some nations without crude oil reserves to become self-sufficient in energy. The use of ethanol could increase and stabilise farm income. Alcohols have pump octane rating of 1 1 0 compared with gasoline, which has an octane rating of 91-100. Alcohols act as an octane booster when they are mixed with gasoline. A mix of 10% methanol and gasoline would have an octane rating of 95. Alcohols with higher octane ratings would permit the use of engines with higher compression ratios. With higher compression ratios, more power can be obtained from an engine. In other words, power output equivalent to that of a gasoline engine could be obtained from smaller engines powered with alcohols. Alcohols, with their greater latent heat of vaporisation, result in more compression work from an engine. The increased cooling of the air-fuel mixture allows more mixture to be packed into the cylinders. The use of pure methanol couJd increase the power output of engine by 10 percent compared with the same engine fueled with gasoline. Methanol has an ideal air-fuel ratio of 6.46:1, whereas the ideal gasoline air-fuel ratio is 14.9:1. Although alcohols allow greater compressive work from an engine than the gasoline, the net result has very little difference in fuel economy between alcohol, gasoline mixtures, and pure gasoline. Alcohols have greater leaning capabilities than gasoline.Disadvantages; Because alcohols act as cleaning agents, filters can become plugged gasoline fuel systems converted to alcohol. Alcohols and gasoline separate they are contaminated with small amounts of water, especially in cold weather. Phase separation of alcohol and gasoline occurs more easily with methanol. Some gasoline fuel system parts are not compatible with alcohol especially the terne plating in the fuel tank. Ethanol of small percentages mixed with gasoline will experience fewer problems, whereas pure methanol would cause serious problems including damage to the parts of the fuel system. Because alcohols do not vaporise as easily as gasoline at low temperatures, cold-starting problems can occur with the use of alcohols in cooler climates. Cold-starting problems with pure methanol could occur at temperatures below 10 °C. Some solutions for cold-starting problems caused by alcohols are: a) Blending volatile components with alcohol. b) Using an auxiliary starting fuel. c) Using electric fuel vaporisers. d) Improving fuel vaporisation with a fuel injection system rather than a carburettor. Alcohols, with their greater latent heat of vaporisation may require more intake manifold heat to prevent derivability problems.The growing enthusiasm for methanol is partly explained by historical circumstances. In the mid-1970s, just after the 1973 Arab oil embargo, nations began searching for ways to gain energy independence. The major non-petroleum domestic energy resources in the US were coal, oil shale and biomass. Natural gas was virtually ignored, since it was considered to be even scarcer than petroleum. Curtailments of NG deliveries to customers in accordance with the US government's allocation scheme during the winter of 1976-1977 served to reinforce the notion that NG was a scarce resource which should have been reserved for winter heating needs. As the expensive synfuels projects floundered, attention began to shift toward methanol, at first because of the relatively advanced state of coal-to- methanol conversion technology and afterwards because of a growing realisation that much more NG existed than had been recognised. Although estimates of domestic and world-wide natural gas reserves began to be revised sharply upward in 1979, this was not widely acknowledged until several years later. The changed perception of natural gas availability is crucial because methanol can be manufactured much more cheaply and cleanly from NG than from coal. Interest in methanol began to surge around 1985 as methanol proponents shifted their arguments away from energy security, a diminishing concern, to urban air quality, a stubborn problem for which most of the easy solutions had already been exhausted. Proponents, especially in California argued that the transition to methanol transportation fuels represented the most significant opportunity for improving urban air quality. At that time, ozone air-quality standards, were being violated in virtually all major metropolitan areas, affecting over 80 million people. From this historical review of informed opinion, an important question emerges; if NG is the preferred feedstock for making methanol, thenshouldn't we consider the option of using NG directly in compressed or liquefied form? Analysts and decision makers remark that gaseous fuels are too different from liquid fuels requiring too many costly changes in motor vehicles and the fuel-distribution system to be widely used; these are exactly the same arguments that were used against methanol twenty years earlier. Experience indicates that these arguments should be carefully scrutinised, indeed, other countries, especially Canada and New Zealand, have deliberately chosen CNG over methanol. Policy inertia may be a major factor in favouring methanol. This suggests that there is a need for a careful reconsideration of methanol's perceived superiority. The salient criteria to consider an evaluation of new transportation fuels, which will be used in the following comparative analysis of methanol and CNG, are market costs, air quality impacts, national security impacts, start-up barriers, and vehicle performance attributes. In contrast to methanol, very little research has been conducted on natural gas vehicles and none on the ozone impacts of CNG emissions. Published assessments of emissions from CNG vehicles have often been overstated because they were based on retrofitted dual fuel cars and not on optimised single fuel vehicles. Such assessments offer little help in evaluating the relative attractiveness of different energy paths. What little data do exist, suggest that there is no scientific basis for claiming that either fuel is superior to the other from an air quality perspective. An assessment has been made of the relative attractiveness of vehicles optimised for a particular fuel because such an evaluation is important for selecting which fuel will ultimately be superior. But the ultimately superior option may never be reached because of start-up barriers; start-up barriers are therefore considered here as one more factor to consider in the evaluation.At this point, it is essential to focus attention on the efforts exerted to search for alternate fuels stating that they have been speeded up with the facts that the effects of exhaust gases on human life have reached a threatening extent and the people today have been consuming the existing petroleum reserves an increasing rate. As a result of that an immediate need has arisen to direct the attention to look for unconventional petroleum fuels which could be used in engines. The results of the investigations and the tests carried out show that methanol is a convenient type of fuel for a short- term solution, As for the long-term there is a wide agreement of opinion that hydrogen fueled engines will be the solution. Nevertheless, it is obviously clear that the fuels, already in use, can not be soon given up. For that reason, the main target of this study is the consideration that the changes occurring in the performance of the engine and the exhaust emissions, by using methanol fuel without making a considerable alteration in the constructions of these engines, will be scientifically studied. For long years methanol-gasoline blends or neat methanol have been used in some vehicles particularly in race cars and planes but these vehicles were mainly designed for methanol. At present, there are millions of engines in the world and the manufacturing of these engines will be continuing for some while. This work, therefore, is carried out to show what the performance of the existing engines will be like after some necessary alterations on them. In this study, engine performance and exhaust emission characteristics have been investigated on currently gasoline powered spark ignition engine converted to neat methanol. A four cycle, four cylinder, 1.3 liter displacement engine for a conventional passenger car has been tested under variable loading conditions. With the purpose of achieving a success gasoline is used as fuel and methanol as an alternative fuel in an automobile motor. In both cases the performance and emission values of the motor are recorded and acomparison is made between them. The results of the experimental and theoretical studies using pure methanol in the spark ignition gasoline engine are as follows. The latent heat of vaporisation of pure methanol fuel is 3.28 times grater than gasoline fuel. Similarly, the lower heat value of gasoline fuel is 2.43 times grater than pure methanol fuel. So the fuel consumption of the methanol fueled engine is about 2.43 times grater than that of gasoline fueled engine. Because of these specifications, the intake manifold of the methanol fueled engine needs more heating energy than that of gasoline fueled engine. In this study, we also theoretically compared the need of heat energy for intake manifolds of both methanol and gasoline fueled engines. It is possible to evaluate the amount of required energy for gasoline mod and methanol mod of the engine with energy equations and experimental measurements. In this study the ratio of vapour to liquid fuel in the intake manifold has been taken as parameter and the need of heat for both gasoline and methanol mod has been shown quantitatively. From here we conclude that QMIQB=4,8 while V IF-\ and the heat value required for increasing the temperature of gasoline 0fl=1OOOJ/s and if 0B=6OOJ/s; Qm l Qb=72- For the first start operations when the engine is cold, that is to say for the conditions like the ratio of V IF is at low value, for example; Qm!Qb~^^ wnen V/F-0,4 and Öfi=600 J/s. On the other hand when QB=2Q0 J/s, QMIQB=8,5. In other words, the rate of heat increases as the engine gets colder. In case of insufficient intake manifold heating the fuel enters the cylinders as liquid. The negative aspects appearing can easily be seen when looking at the performance characteristic curves. For gasoline mode,engine specific fuel consumption is approximately 400 g/kWh when the engine speed is 1400 rpm and mean effective pressure is 531 kPa. These values are regarded as economical operating point for gasoline mode. For the same point, the specific fuel consumption for methanol mode is higher than 1000 g/kWh. Economical range limits are between 1200 rpm and 1400 rpm for methanol and 1400 rpm to 1800 rpm for gasoline. Also similar situation can be seen in emission values. For gasoline mode, the values of CO increases from 2% to 7% as the engine speed and load increase. But for methanol mode the CO values are likely to increase finally up to 5%. For the conditions that X =1, V IF =0.6 and mair =0.07 kg/s, when we study the evaporation in the intake manifold, we see that if the amount of heat given from the intake manifold is not sufficient enough, evaporation does not realise as desired. This increases the volumetric efficiency, but the fuel enters the cylinders as liquid. For the high speeds of engine, this effects the ratio of V/F'm the engine and it does not remain the same in each cycle. For that reason it gives way to a change in characteristic values such as ignition, flame increasing and maximum pressure point from cycle to cycle. Finally when the heat value in the intake manifold is not sufficient enough, It causes a vibration in the operation of the engine. For both engine performance and exhaust emission, in the methanol mode, it is essential that the engine intake manifold heating should be improved according to the experimental and theoretical studies that we have done. Especially were the motor vehicles are running with high power, the engine intake manifold needs heating at the rate which is determined in this study.
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