Alternatif yakıtlı motorların enerji dağılımının incelenmesi /
Yazar: YUSUF ÇAY
Danışman: PROF.DR. OĞUZ BORAT
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Doktora, 1996
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Enerji dağılımı = Energy distribution ; Motorlar = Motors ; Yakıtlar = Fuels

Özet:
ALTERNATİF YAKITLI MOTORLARIN ENERJİ DA?ILIMININ İNCELENMESİ ÖZET Enerji, yaşantımızın vazgeçilmez unsurlarından biridir. Enerji tüketiminin büyük bir kısmı taşıtlarda kullanılmaktadır. Alışılagelmiş enerji kaynaklarının yanısıra, alternatif enerji kaynaklarının araştırılması büyük önem arz etmektedir. Bu çalışmada, benzinli bir motorda alternatif yakıt olarak metanol kullanılması sonucu elde edilen veriler kullanılarak benzin ve metanol yakıtları için eşit devir sayılarında motorda enerji dağılımı ve verim değerleri karşılaştırılmıştır. Metanol yakıtı kullanılması durumunda benzine göre; eşit devir sayıları için kaybolan ısı enerjisindeki düşme dolayısıyla teorik, indike ve organik verimler artarken efektif ve mekanik verimlerin düştüğü tespit edilmiştir. Konstrüktif ve işletme özellikleri bilinen bir motorun, enerji dağılımı, kütlenin korunumu, kimyasal denge ve termokimyasal veriler kullanılarak ve sayısal çözüm (Nevvton-Rapson İterasyonu) uygulanarak çevrimin simülasyonu gerçekleştirilmiştir. Simülasyon ile soğutmaya giden ısı kaybı bulunmuş, küçük krank mili açısı adımlarıyla sayısal değerler hesaplanmıştır. Ayrıca motorun emme manifoldundaki buhar yakıt oranı kontrolünün çok önemli olduğu, özellikle yüksek hız ve güçlerde bu bölgedeki ısı geçişinin iyi bir şekilde kontrol edilmesi gerektiği tespit edilmiştir. Aksi halde motor verimi, özgül yakıt sarfiyatı ve egzoz emisyonu olumsuz bir şekilde etkilenmektedir. xiii

Abstract:
SUMMARY A STUDY ON THE ENERGY DISTRIBUTION OF ALTERNATE FUELLED ENGINES A rapid increase in the world population and fast changing technological developments bring about energy problem, it is a known fact that energy is an unseparable part of the industrialisation. The development rate of the countries which could develop their own energy sources will be higher. Concentration will be focused on the solutions like the reasonable use of natural sources, nuclear power stations, hydraulic energy, the energy of wind, the temperature differences of sea-levels, tidal effects, wave effects and solar energy, ete. it is estimated that the natural energy sources will run out in a certain period of time. Hydraulic energy can not be available ali the time for the reason that the cost of production plants is high and founding period is too long. in addition to that, hydraulic energy is not available everyv/here. On the other hand the temperature differences of sea-levels require a complex range of solutions with respect to technology. As for the tide, it is applicable only in places vvhere the temperature differences of sea-levels are convenient. it is expected that the importance and the use of wind energy, nuclear energy and of solar energy will increase in the future. Nuclear energy does not only require high technology and costs too much but it is also considered to be a potential threat to the health of human beings. Natural energy sources of fossil origin steadily decrease due to factors such as industrialisation, rapid population increase and an alternative to existing motors and motor fuels, and altemate energy resources and rapid urbanisation. This fact motivates people to look for new energy resources. At the present time, a large proportion of the world's energy needs is met from petroleum, coal and natural gas sources. Besides that nuclear energy and hydraulic energy are also made use of. it is knovvn that the world today has 135,4 billion tons of the fossil fuel reserves, 124 trillion cubic meter of natural gas, and 1040.5 billion tons of coal reserves. As of the production year 1991, it is estimated that coal could be sufficient enough for 239 years, petroleum for 43,4 years and natural gas for 58,7 years. xivAlthough the use of new energy sources is negligible at present, they will be very important in the next century. The rapid growth of the vvorld's population and fast-changing technological developments increase the consumption of energy, and this causes many problems such as environmental pollution, air pollution, the corrosion of the ozone layer and various diseases. Decreasing motor emissions alone can not be a sufficient solution. The emission of carbon dioxide gas should be decreased as much as possible. The consumption of energy should also be decreased for the sake of human health. Engines which provide high performance using less energy and being economical in the use of fuel should be designed and developed. Remedial efforts should be exerted to use thermal energy given out of big motors. Methanol, vvhich is also known as methyl alcohol ör 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 ör renewable organic matter ör municipal solid wast.es, can be used to produce a gas (carbon monoxide and hydrogen) vvhich 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. Therefore 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 ör collision. Also, it is said to keep the engine running cooler than with gasoline and to provide better performance, more horsepower, at high speeds. Methanol produces less carbon monoxide and less oxides of nitrogen than gasoline (and, of course, no hydrocarbon vapours), but it produces aldehydes and methanol vapours vvhich gasoline does not. However, these differences are not dominant considerations. The physical property vvhich distinguishes gasoline and methanol is the heat of combustion. The heat of combustion of methanol, either on a volumetric ör on a vveight basis, is less than one-half that of gasoline. Consequently, transportation and distribution costs of methanol are roughly tvvice those of gasoline, because approximately tvvice the volume of material must be transported, stored and distributed to deliver equal quantities of fuel energy. in this study, gasoline is used as fuel and methanol as an alternative fuel in an automobile engine. The efficiency values of the motor for both cases are recorded and a comparison is made betvveen them. The data obtained during the use of methanol as an altemate fuel in a gasoline engine and the distribution of energy have been used, and efficiency values have been compared for the same rotation in both gasoline and methanol fuels and also the characteristic values of the engine have been computed in the modes of gasoline and methanol. XVAt the beginning of the compression in the engine pressure and temperature values are at a low point. As the speed rate rises the time required for the evaporation of the liquid fuel, diffusion, air circulation and mixture shortens. Towards the end of the compression, the pressure and the temperature rise and the fuel entirely evaporates. However if the speed rate is high, the time required for the combustion of the fuel shortens, and it gives rise to the possibility of fuel-steam. Therefore at high speed rates, CO and HC emission values increase. it has been discovered that it is very significant to check the ratio of steam to fuel in the air-intake manifold, and that the heat transfer in this area should be well controlled. Otherwise, the engine efficiency affects the exhaust emission negatively. in gasoline mode, the speed rate is between 1800 [rpm] and 2500 [rpm], the consumption of specific fuel is at a minimum rate and it is 3500 g/kWh. Hovvever this rate of specific fuel consumption raises above 1000 [g/kWh] in methanol mode under the same operating conditions. in methanol mode, the speed rate is between 1400 [rpm] and 1800 [rpm], the consumption of specific fuel is at a minimum rate and it is 900 [g/kWh]. Betvveen the same speed rates, the consumption of specific fuel is 400 [g/kWh] for gasoline. it is seen from the figures that the engine performance values in gasoline mode are greater than those of methanol under the same operating conditions, and the consumption of specific fuel in methanol mode is two-fold when compared to gasoline mode. Since the rate of compression has not been changed, the performance values of methanol are negatively affected in methanol mode. According to these values the distribution of energy and efficiency values are determined. Then in both of these fuel types, the calculations of effective, theoretical, indicative, mechanical and organic efficiencies are performed and a comparison is made. in the engine, mechanical efficiency increases, in methanol mode in comparison to gasoline mode because of a decline in the amount of vvasting heat for equal speed rates. The effective efficiency is 30% in gasoline mode. For an engine having the values of 1800 [rpm] and 4.7 [kW] but this efficiency is 26% in gasoline mode. Where as it goes up to 82% in methanol mode. in addition, indicative efficiency is 33% in gasoline mode and it is 61% in that of methanol. Besides that, mechanical efficiency is 80% in gasoline mode and it is 42% in the case of methanol. in methanol mode, it is found that the thermic, the indicative and the organic efficiencies of the engine are high because the temperature vvasting to the sides is less and the temperature left out through the exhaust pipe is less. The effective and mechanical efficiency values however decline since the lovver thermal value of the heat is too low for methanol fuel. xviThe distribution of energy, the protection of mass and the simulation of cycle for an engine, whose constructive characteristics are given, have been examined by using termo-chemical balance and termo-chemical data and by applying a numerical solution method (Nevvton-Rapson Iteration). The amount of energy to the cooling system has been calculated with simulation, and the calculations of numerical values have been performed by using small crank-shaft angle steps. The amount of heat vvasting to the cooling system has been computed with simulation for methanol and gasoline fuels, and it is -24 [kW] for n=1200 [rpm] rotation speed in gasoline mode. in the calculations equivalence ratio c|)=1, the exponent of the law of combustion u=5, crank-shaft angle CCAA =25° (before the top dead point), ctYs =25° (after the top dead point). When the rotation speed rate is increased, it is -50 [kW] for n=5400 [rpm]. Under the same operational conditions, it is -23 [kW] in methanol mode and when the rotation speed rate is increased it is -58 [kW] for n=5400 [rpm]. Exhaust emission figures are computed by taking into account the ignition equation and the balance of water gas, and these figures are compared with the emission values measured in the experiment. Now, let us look at the situation of exhaust emissions. Under normal conditions CO emission is at a minimum rate of 3% but it goes up to 7% as the engine speed rate and the load increase in gasoline mode. Hovvever it shows an increase from 1 % to 5% in methanol mode. On the other hand the value of HC emissions is 1200 [ppm] at low speed rates and low load in gasoline mode. This value decreases to 300 [ppm] as the load and the speed rate increase. Hovvever in methanol mode the HC emission values vary between 1100 [ppm] and 250 [ppm]. The main reason as to why these emission values increase with high speed rates and loads is due to the insufficient time of combustion and unbalance between air and fuel mixture. And the reason as to why methanol emission values are greater than normal is that the fuel enters the combustion room as liquid because it cannot be heated sufficiently enough within the air-intaking manifold. The fact that the evaporation temperature of alcohol is higher than that of gasoline and that the ratio of air to fuel is low causes the density of filling to rise taking the temperature of filling into account, and this gives a rise to volumetric efficiency. Since the evaporation temperature of methanol is high, when the air-intake manifold is heated with the exhaust manifold, the temperature of intake filling falls. Cooling in the intaking manifold increases depending on the fuel increasing in the alcohol fuelled motors especially in high speed operations. As a result of this compression, temperature, at the start, falls in comparison to gasoline. Fuel particles evaporates within the cylinder and it causes xviimixture-forming to worsen. Combustion rate falls since the heat value of the fresh filling is low, so the flow of heat to the side walls increases and effective power decreases. Since alcohols have a high combustion rate at low temperatures, the yalue of the heat lost in the cooling systems through conduction and radiation becomes less. For that reason thermal efficiency in the engine increases when using alcohol. Volumetric efficiency is variable depending on factors such as the density and temperature of the mixture in the carburettor, the evaporation temperature of the fuel used, the distribution of mixture to the cylinders, the opening and closing times of the vacuum valves, piston speed and exhaust back-pressure. The temperature of the mixture in the carburettor and the evaporation characteristics of the fuel have to do vvith the type of fuel. These two factors come to the foreground in methanol mode. VVhen methanol ör a mixture of high rated methanol is used in the engine, the distribution of air-fuel mixture to the cylinders becomes uneven. Therefore volumetric efficiency is likely to fail. Since the alcohols have only öne boiling point, they completely evaporate and combust better compared to gasoline. in addition, alcohols have a lower heat value in comparison to conventional petroleum fuels, so they burn better and the rate of CO in combustion products declines. The advantages of alcohols can be summarised as follows: 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 110 compared vvith gasoline, which has an octane rating of 91-100. Alcohols act as an octane booster when they are mixed vvith gasoline. A mix of 10 percent methanol and gasoline vvould have an octane rating of 95. Alcohols with higher octane ratings vvould permit the use of engines vvith higher compression ratios. With higher compression ratios, more power can be obtained from an engine, in other words, povver output equivalent to that of a gasoline engine could be obtained from smaller engines povvered vvith alcohols. Alcohols, vvith their greater latent heat of vaporisation, result in more compression work from an engine. The increased cooling of the air-fuel mixture allovvs more mixture to be packed into the cylinders. The use of püre methanol could increase the povver output of engine by 10 percent compared -YVİİİwith the same engine fuelled 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 betvveen alcohols, gasoline mixtures, and püre gasoline. Alcohols have greater leaning capabilities than gasoline. The disadvantages of alcohols can be summarised as follovvs: 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 alcohols especially the tem plating in the fuel tank. Ethanol of small percentages mixed with gasoline will experience fewer problems, vvhereas püre methanol would cause serious problems including damage to the parts of the fuel system. Because alcohols do not vaporise as easily as gasoline at Iow temperatures, cold-starting problems might occur with the use of alcohols in cooler climates. Cold-starting problems with püre 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. Consequently, methanol can be produced from national sources and used as an altemative to gasoline in any possible petrol crises in the future. xi.\