Effect of Oxygenates Blending with Gasoline to Improve Fuel Properties

Transcription

1 792 CHINESE JOURNAL OF MECHANICAL ENGINEERING Vol. 25, No. 4, 2012 DOI: /CJME , available online at Effect of Oxygenates Blending with Gasoline to Improve Fuel Properties BABAZADEH SHAYAN Soheil 1, *, SEYEDPOUR Seyed Morteza 2, and OMMI Fathollah 1 1 Department of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran 2 Department of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran Received May 27, 2011; revised December 23, 2011; accepted February 7, 2012 Abstract: The purpose of this paper is to study the effect of oxygenate additives into gasoline for the improvement of physicochemical properties of blends. Methyl Tertiary Butyl Ether (MTBE), Methanol, Tertiary butyl alcohol (TBA), and Tertiary amyl alcohol (TAA) blend into unleaded gasoline with various blended rates of 2.5%, 5%, 7.5%, 10%, 15%, and 20%. Physicochemical properties of blends are analyzed by the standard American Society of Testing and Materials (ASTM) methods. Methanol, TBA, and TAA increase density of the mixtures, but MTBE decreases density. The addition of oxygenates lead to a distortion of the base gasoline s distillation curves. The Reid vapor pressure (RVP) of gasoline is found to increase with the addition of the oxygenated compounds. All oxygenates improve both motor and research octane numbers. Among these four additives, TBA shows the best fuel properties. Key words: gasoline oxygenates, distillation curve, reid vapor pressure, octane number 1 Introduction The Gasoline is a complex mixture of hydrocarbons obtained from crude oil distillation and processing, as well as the other organic chemicals derived from other energy sources. Modern gasoline is a heavily processed product that can also contain various synthetic components, added to improve its performance and meet the demands of today s advanced engine technology. Until recently, one such component was lead, which was added to gasoline to boost octane ratings and reduce engine wear. However, leaded gasoline cannot be used on cars equipped with the modern catalytic converters designed to reduce harmful exhaust emissions, as lead very rapidly and permanently annihilates the performance of the catalyst. With the reduction or removal of lead, the octane number, the ability of petrol to avoid engine knock, must be raised by other means, such as increasing the concentration of aromatics, optimizing the use of components such as alkylates and isomerates or lending high octane oxygenates. The additives used in the adulteration of commercial gasoline can be classified as oxygenated, aromatic, and light and heavy aliphatic hydrocarbons, the majority of these compounds being natural constituents of gasoline [1]. The addition of solvents changes the original composition of the fuel, affecting in physicochemical properties in different ways [2]. Distillation curves, vapor pressure and octane rating are properties closely related to the fuel composition and the characteristics of its components [3 5]. Simple * Corresponding author. soheil.babazadehshayan@gmail.com Chinese Mechanical Engineering Society and Springer-Verlag Berlin Heidelberg 2012 alcohols and ethers are used as gasoline additives to reduce pollutants from vehicle exhaust gases. Proponents of these oxygenates claim several advantages: they are octane enhancers [6], they have significant anti-knock properties important for unleaded fuels, they can be produced from renewable agricultural raw materials instead of fossil sources, they reduce carbon monoxide emission from vehicle exhaust. But also reducing the emission of carbon monoxide (CO) and unburned hydrocarbons, minimizing the emission of volatile organic compounds [7 11]. Methyl tert-butyl ether (MTBE) is the oxygenate most commonly employed to increase the octane number of gasoline [12]. Use of MTBE has become restricted due to its toxicity and contamination of groundwater [13 15]. In addition to MTBE, alcohols such as Methanol, Tertiary butyl alcohol (TBA), and Tertiary Amyl alcohol (TAA) have led to growing interest as oxygenated additives [16 17]. Even without the exact composition of the adulterant and the gasoline it is shown that each solvent has an effect on the physicochemical properties of gasoline of specific magnitude and behavior, depending on the concentration and chemical nature of the solvent. In this study, an investigation was carried out into density, volatility (distillation curves and Reid vapor pressure), and octane number of unleaded gasoline after the addition of different oxygenates in various proportions. 2 Experimental Procedure 2.1 Material Base gasoline composition was used to evaluate the effect of the gasoline formulations containing oxygenates

2 CHINESE JOURNAL OF MECHANICAL ENGINEERING 793 (MTBE, Methanol, TBA, TAA). This gasoline compositions, was obtained from the Tehran Oil Refinery Company (TORC) located in the province of Tehran, Iran. Table 1 lists the physicochemical characteristics of this gasoline. Table 1. Characteristics of the base gasoline Characteristic Quantity Method ASTM Density /(g cm 3 )(at 16 C) D 4052 Low heat value /(kj kg 1 ) D 4809 Reid vapor pressure/ kpa (at 37.8 C, ) 59.2 D 323 Sulphur/wt % D 4294 Motor octane number 81.6 D 2700 Research octane number 85.3 D 2699 Antiknock index Oxygen in fuel/(g cm 3 ) 0 Distillation temperature/ D 86 Initial boiling point/ % Evaporated/ % Evaporated/ % Evaporated/ Final boiling point/ Analyzer, following the ASTM D 323 standard [24]. The octane ratings were measured by Zeltex ZX-440 XL liquid fuel analyzer, according to the ASTM D 2699 (RON) [25] and ASTM D 2700 (MON) [26] standards. 3 Result and Discussion 3.1 Relative density The graphs in Fig. 1 gives the densities of the base gasoline mixed with the oxygenated compounds (MTBE, Methanol, TBA, and TAA) in different volumetric concentrations. As can be seen in this figure, densities of the alcohol oxygenates-gasoline blends increases because of their high densities, while the densities of the MTBE oxygenates-gasoline blends decreases because of its low density. Changes in the density affect the quantity of fuel that is injected into the combustion chamber during each cycle, altering the ideal air-fuel burning ratio. In the case of a gasoline adulterated with a more dense additive, the burning will be incomplete, resulting in the emission of pollutants to the atmosphere. The properties for MTBE and the other Oxygenates used in this study are shown in Table 2 [18 21]. Table 2. Properties of the Oxygenates Property MTBE MeOH TBA TAA Chemical formula C 5H 12O CH 3OH C 4H 10O C 5H 12O Purity/% Oxygen/wt% Molecular weight/ (g mol 1 ) Density/(g cm 3 ) (at 16 C) Flash point/ Boiling temperature/ Ignition temperature/ Reid vapour pressure / kpa (at 37.8 ) Motor octane number Research octane number Methods The gasolines containing the aforementioned oxygenated compound additives were evaluated in terms of their characteristics of density, volatility (distillation curves and Reid vapor pressure), and octane number (RON and MON) using ASTM (American society for Testing and Materials) approved equipment. The relative densities (measured at 16 ) of the fuel samples and oxygenated compounds were determined using an Portable Density/Specific Gravity Meter KYOTO DA-130N, following the ASTM D 4052 standard [22]. The distillation characteristics were measured by Tanaka AD-6 automatic distillation analyzer, according to the ASTM D 86 [23] standard, Reid vapor pressures are measured by Tanaka AVP 30D automatic RVP Fig. 1. Relative densities of the base gasoline with oxygenates (2.5, 5, 7.5, 10, 15, 20 % (v/v)) 3.2 Volatility The Crude oil and the various petroleum fractions and products derived from it such as gasoline consist of a complex mixture of various components, mostly hydrocarbons. Some of these components are quite volatile, and some are not so volatile. It is fairly recognized that the different petroleum fractions and products have inherent volatility characteristics. Volatility is defined as the tendency or ability of a material to change from a liquid state to gaseous state. When dealing with petroleum products, the principal volatility characteristics that are significant are distillation, vapor pressure, and flammability Distillation curves Gasoline is a mixture of hundreds of hydrocarbon compounds, each with its distinctive boiling point. Therefore, gasoline boils over a range of temperatures and

3 794 BABAZADEH SHAYAN Soheil, et al: Effect of Oxygenates Blending with Gasoline to Improve Fuel PropertiesY its tendency to vaporize is characterized by determining a series of temperatures at which various percentages of the fuel have evaporated, as described in ASTM D86, Test Method for Distillation of Petroleum Products at Atmospheric Pressure. A plot of the results is commonly called the distillation curve. These temperatures characterize the volatility of the fuel s light, medium and heavy fractions. These fractions, in turn, affect the engine s different operating regimes. Figs. 2(a), (b), (c) and (d) present the distillation curves of the base gasoline and its blends with oxygenates (MTBE, Methanol, TBA, TAA) in the volumetric proportions of 2.5, 7.5, 10 and 20%, respectively. As can be seen in Fig. 2, the addition of oxygenates lead to a distortion of the base gasoline s distillation curves, which becomes more marked the higher the oxygenates content. All oxygenates decrease the distillation temperatures significantly. Fig. 2 indicates that, among the oxygenated compounds used as additives for base gasoline, methanol was the one that caused the most marked change in the distillation curve. Figs. 2(c) and (d) show the effect of adding more than 10% by volume of methanol into the base gasoline. Clearly, this results in the front end to the first region of the curve being heavily distorted in terms of significantly increasing the volatility of the fuel in these regions. Adding more than 10% volume of methanol into gasoline continues to increase the volatility of the blend as evidenced by further reductions of both the T50 and T90 distillation temperatures. The reductions seen in T50 and T90 between 10% and 20% methanol are greater than the reductions from base gasoline to the 10% methanol blend, demonstrating a non-linear trend. The front end of the distillation curve is important for cold starting with a more volatile curve lower temperatures providing easier starting. However, if it is too volatile, hot-starting and hot-fuel-handling driveability can be a problem. The midrange is important for cold starting and warm-up driveability. This in turn helps with short-trip fuel economy. In older vehicles with carburetors, too much midrange volatility can contribute toward carburetor icing. A high tail end of the distillation curve contributes to better fuel economy, but if too high it can contribute to combustion chamber and other engine deposits. A high tail end also can contribute to cold-start fuel dilution of the engine oil [29].

4 CHINESE JOURNAL OF MECHANICAL ENGINEERING 795 addition of 2.5, 5, 7.5, 10, 15, 20 % v/v of Methanol, TBA, TAA, MTBE Fig. 2. Distillation curve of base gasoline and its blend with Methanol, TBA, TAA, and MTBE Reid vapor pressure The pressure exerted by gasoline vapors in a confined space, which is measured at 37.8, is called Reid vapor pressure. RVP is the most important indicator both volatility and emissions because of the relation of the existing volatile organic compounds in fuels. In addition to these, maximum increase of RVP occurs with 5%-10% addition of all oxygenates. Also, RVP is very important the driveability of the fuels in year around. Fig. 3 shows the effects of the all oxygenates on the RVP. Adding oxygenates into gasoline cause an increase in vapor pressure and depress the boiling temperature. Also, higher RVP values can be cause of the vapor lock and higher evaporative harmful emissions. That s why, RVP was limited more countries with federal legislations. As it seen in Fig. 3, methanol-gasoline blends has higher RVP. This means, methanol-gasoline blends more volatile than the other oxygenates. The vapor pressure profiles of the methanol-blended gasolines in Fig. 3 indicate a significant increase in the mixtures RVP for the initial fractions of added alcohol. For this reason, methanol is suitable for country that are in cold region. 3.3 Octane Number The critical fuel property of gasoline for internal combustion engine is resistance to engine knock, expressed as the octane number of the gasoline. During a normal (no knock) combustion cycle, a flame front travels smoothly from the point of ignition at the spark plug outward toward the cylinder walls. The octane (and auto-ignition temperature) of various hydrocarbons is related to their ability to withstand pre flame conditions without decomposing into species that could auto-ignite before the flame-front arrives. The RON and MON methods use two primary reference fuels, n-heptane and 2, 2, 4 trimethyl pentane, assigned octane numbers of 0 and 100, respectively. The knocking intensity of the test fuel is compared to that of reference fuel blends. The anti-knock index (AKI) is the average of the research octane number (RON, D 2699) and motor octane number (MON, D 2700), sometimes expressed as (RON+MON)/2 or (R+M)/2. Automotive octane ratings are determined in a standardized single-cylinder engine with a variable compression ratio (CR 4:1 to 18:1), operated under standard conditions Cooperative Fuels Research (CFR) engine. Fig. 4 and Fig. 5 depict the MON and RON profiles of gasoline mixed with the oxygenated compounds and their respective volumetric proportions respectively. Research and motor octane numbers of all blends clearly increase with both alcohol and ether oxygenates. As it seen in these figures, maximum increases have been found TBA and TAA blends. For research octane numbers, best octane booster is TAA and for motor octane numbers, best octane booster is TBA. In addition to these results, alcohol oxygenates have better results versus the ether oxygenates for both research and motor octane numbers. Fig. 3. Reid vapor pressure of base gasoline containing Fig. 4. Motor octane number (MON) graphs for base gasoline containing addition of 2.5, 5, 7.5, 10, 15, 20 % v/v of Methanol, TBA, TAA, MTBE

5 796 BABAZADEH SHAYAN Soheil, et al: Effect of Oxygenates Blending with Gasoline to Improve Fuel PropertiesY Fig. 5. Octane number (RON) graphs for base gasoline containing addition of 2.5, 5, 7.5, 10, 15, 20 % v/v of Methanol, TBA, TAA, MTBE 4 Conclusions (1) A study is carried out on the influence of the addition of the oxygenates MTBE, Methanol, TBA and TAA on the parameters density, distillation curves, Reid vapor pressure, and octane rating. (2) The addition of alcohols leads to mixtures increased density because of their higher density while addition of MTBE decreases the density because of their lower density. (3) The addition of all oxygenates leads to mixtures increased RVP, and the highest and lowest effect on the RVP are obtained by the addition of methanol and TBA respectively. 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6 CHINESE JOURNAL OF MECHANICAL ENGINEERING 797 Biographical notes BABAZADEH SHAYAN Soheil, born in 1984, is currently an engineer at Motor and Propulsion Laboratory of Tarbiat Modares University, Iran. He received his master degree on aerospace at Tarbiat Modares University, Iran, in Tel: ; SEYEDPOUR Seyed Morteza, born in 1984, is currently an engineer at Tara Sabalan Co., Iran. He received his master degree on biomechanical engineering at Iran University of Science and Technology, Iran, in Tel: ; OMMI Fathollah, born in 1952, is currently an associate professor at Tarbiat Modares University, Iran. He received his PhD degree from Moscow University of Technology, Iran, in His research interests include increase in the output of internal combustion engines through changes in the type and amount of fuel consumption, decrease in the pollutants of internal combustion engines of different vehicles, conversion of carburetor engines into injectors, designing different types of one-base and two-base injectors, design of different nozzles, study the subject of fluid fusion in aerosol space in one phase and two-phase state, the entire research grounds related to the engine and drives, Tarbiat Modares University, Iran. Tel: ;