What is Gasoline? Structure and Properties

Gasoline, boiling between 32-204 °C and a specific gravity of from 0.680 to 0.760 g / cm³ which is a hydrocarbon mixture having unique odor and colorless. The number of carbon in forming the gasoline varies between 4 hc 10. Although very few S coming from petroleum are the heavy and light hc (sulfur) and N (nitrogen) to which is a liquid under normal conditions hc. paraffinic in gasoline, ethylene, and the benzene include naphthenic hydrocarbons.

Gasoline, XIX. In the last quarter century it has been used in engine operating according to the Otto cycle. Fuel oil is one obtained by first refinery process after the discovery.

Gasoline Structure

Filling general formula CnHm closed by formula consists of expressed hc. additives to improve the structure and characteristics of gasoline are used for coloration. Besides resulting from the oil and a small amount of undesirable elements such as sulfur and nitrogen it is also included.

Gasoline HC structure;

– CnH2n + paraffinic hc depicted by two off formula,
– Cnhn represented by formula ethylenically closed (light) HC’s,
– CnH2n the naphthenic hc indicated by closed formula,
– CnH2n-6 has the benzenic hc indicated by closed formula.

Gasoline engines work best, respectively; benzenic HC’s, naphthenic and hc, hc, and finally provide ethylenically paraffinic HC’s. The higher the amount of the benzene in gasoline as is clear from this statement is, the better for gasoline engines. The main reason for this is that they have a high octane number of the benzene. The HC group is desired in the least amount of gasoline are paraffin structure. Heptane of the most commonly used paraffin wax is zero octane number explains why the need to lower the amount of gas.

Crude oil 3800C’n, “If heated above hydrocarbons are converted to smaller molecules break down hydrocarbons. This phenomenon is called cracking. For example, hexadecane C16 H34 molecule octane (C8 H18) and octane (C8 H16) is broken down into molecules. It allows more fuel to be produced this chemical change under heat and pressure oil. cracking heavy hydrocarbon constituent is applied to the first residue to it. In this way petroleum derived gas ratio of 40% – 60% interest. Another important aspect of the cracking process is improving the resistance to gasoline of the detonation. Also it provides for the removal of many side products.

Wanted in Gasoline Properties

The fuel used in the engine is required to have certain characteristics. Some of these features of a portion protecting a portion of the engine while improving the performance of the motor is also required for the vehicle’s safety. The features listed below must be present in gasoline.

– It should allow the engine to start easily in cold.
– Prevents the steam buffer.
– Able to respond to sudden engine power changes.
– Must be economic.
– It should be formed resin.
– Burning end will cause corrosion should not waste.
– It must not impair the ability of lubricating oil.
– It should have knock-resistant.

Cold Weather First Movement and Volatility

Gasoline and other liquid, still without gas called the ability to switch to the still volatile. Each liquid volatility varies depending on the temperature. The volatility of this liquid such as water we consider is increasing as it approaches the boiling point. The ability gasoline volatility is too high relative to water. This is due to start at as low as 32 ° C to the boiling point of the fuel. We mentioned that HC in different structures in the gas. boiling point ranges from 32 to 180 ° C for HC. The low temperature evaporation of fuel for use in spark-ignition engines are required. Liquid high boiling point is low volatility, high boiling point and low volatility.

Of light hydrocarbons present in the fuel at low temperatures is desired evaporation. a sufficient amount of fuel supply to the engine is cold, especially in the first movement is directly related to the volatility of the fuel. How well the volatility of fuel first move would have been easy at that rate. The volatility of the gasoline engine to ensure that a fuel according to various operating conditions.

Preventing Buffer Steam

The fact that a lot of volatility in the liquid fuel can be requested. Because heat engine, fuel system components and will increase the temperature of the fuel due to the rising temperatures will evaporate before they reach the engine, which will result in the fuel pump or a steam pipe plugs to occur. This is undesirable. Gasoline volatility is an expression of the vapor pressure of at most 37.5 ° C, 0.8 atmosphere (Reid to-steam) must be pressure. It is associated with the evaporation of gasoline volatility. Volatility is increasing the possibility of higher steam plugs occur. to prevent high volatility low volatility requesting steam buffer to cold weather, the first movement is required. an optimum volatility value is available according to engine operating conditions and the value of gas makes a good fuel.

Meeting of the engine’s sudden power change

Sudden transition to high speed gas when the pedal is pressed, the amount of air that sucks the engine suddenly increases. This engine air at the sudden increase should be given more fuel to the air inside to accelerate better. It must have high volatility of the fuel to provide fuel increase. Gasoline is a suitable fuel for engines is a volatility that can adapt to sudden changes in power.


Also to be economical fuel responsive to all engine operating conditions are required. disadvantage in terms of fuel economy leads to a loss of fuel caused by the fact that the more volatile gasoline evaporation. Besides high volatility, which brings with it the storage difficulties.

Resin Formation (glue and varnish)

Liquid fuels, reacts with oxygen creates depressions in the environment where they are stored. This is called resin to collapse. These depressions are not desirable because they may cause an obstruction in the fuel system. resin ratio in gasoline 5 mg / cm 3 should be less than ten. The resin adhesion of the valve motor and thereby cause plugging of the fuel channel. Gas too long waiting for a long time will increase if the formation of the resin should not be stored.


With spark-ignition engines, combustion should not end now that the effects of corrosion. Corrosive combustion increases in direct proportion to the amount of sulfur-end products. Therefore, the amount of sulfur in petrol should be no more than 0,001. A higher amount of sulfur, the end of combustion sülfiroz acid (H2SO3) causes formation. Adversely affects the life of such acids cause corrosion on metal surfaces in engine parts.

Effect of Lubricating Oil

Volatility of fuel used in the engine is not enough to be a part of the fuel into the cylinders is a liquid.The liquid phase of petrol, oil, causing the oil in the cylinder wall thinning will prevent the lubricating function. It also refines and viscosity of the oil sump to descend fall, thus causing the lubricant to fail to fulfill the task. As we have seen volatility is a very important feature. Gasoline is a fuel that can respond to changing demands for HC that contain volatility due to different content.

Knocking Resistance

In four-stroke engine with spark ignition, the second time at the end of the combustion mixture is ignited by the spark plugs stuck in the combustion chamber mixture of normal time, is called the normal combustion. Starting spark the flame burning until the mixture is completely turns the room, it appeared to be spreading to other parts of circular rings. flame speed that allows the spread of the flames, called flame spread rate. The normal flame propagation velocity occurs in higher pressure surges. This phenomenon is called a knock. Knock is related to the octane rating of the fuel. The number of high fuel octane knock resistance is high. The octane number of gasoline varies according to the motor being used.

Attending Gasoline Additives

Gasoline additives involved can be analyzed in two groups. additives used to raise the octane number of the gasoline as the first group can be classified as additives used for preventive means in the second group.

Boosting the number Octane Additives

During the production of gasoline cracking, reforming, polymerization, isomerization, using methods such as octane number is increased. after production in order to increase the octane number;

– Tetraethyl lead is a maximum of 0.8 liters of gasoline have allowed cm³ and an additive that increases the octane number up to 7-10. adverse effects to the engine components today need both for human health and the environment from damage caused by the use of very low, is banned in our country.
– By the addition of benzene octane number increases. Typically up to 10% benzene is added.
– Carbonyl iron pentane,
– Mono-methyl aniline
– Alcohols methanol and ethanol participating in octane number can be increased.

Other Additives

Cleaning the engine, giving color additives, gasoline additives are used for protection. These can be listed as follows:

– Phosphorus compounds to clean the combustion chamber and spark plug deposits and ethylene bromide,
– Detergents to prevent deposits in the carburetor and manifold,
– Prevention of fragmentation of the resin formation of tetraethyl lead and antioxidants,
– The upper part of the valve and cylinder lubricant light oils,
– Rust preventive anti-rust agents,
– Asint etilendibromit to prevent,
– To avoid icing 1% isopropylalcohol, 0.005% 0.2% glycols or ammonium salts of phosphates,
– 1% is used methylalcohol used to prevent freezing of the gas.

All companies to better quality and a clean gas in the fast evolving competitive environment uses different amounts of additives.

Octane Number

Octane number of the gasoline engine compression ratio, so the efficiency is a feature closely. The fuel knock resistance the higher the octane number is higher. Number of fuel with the structural and operating characteristics of the engine next to the physico-chemical properties octane varies. The octane number, we reported that depends on the ratio of iso-octane fuel. The way the octane number octane number (of control), motor octane number (MOS), the research octane number (AOS), it is possible for us to see in three different ways. (YOS), a motor running at normal road conditions, taking into account the knock limit of determination (MOS), experiments conducted under difficult conditions in the CFR engine is obtained as a result. (AOS) is the octane number obtained at the end of the experimental studies in more mild conditions.

A fuel that aos’s 85 (MOS) ‘s may be 75. The difference here is called fuel awareness and tests show to be affected by the change in şartlarl. Requirements of the tests done in the way of control is found to apply. (YOS) is usually (MOS) to small (AOS) than it is at a great value.

The engine knock in experiments are done to determine the octane number and are measured at the start of the knock tendency of the fuel octane number is determined by comparing the reference fuel.

CFR (cooperative fuel research) compression ratio to determine the octane number of the methods used can be replaced by a motor. This is called motor CFR engine. The octane number tested in different compression ratio in the fuel CFR engine to be measured. After detecting the start of the compression ratio, knocking is obtained by chemical means, i-octane and n-heptane mixture as the compression ratio of the mixture to initiate detonation ratio is determined. The results (MOS) as it gives the octane number of the fuel. Compression ratio is a schematic view of exchangeable CFR engine is provided below.

Knocking (Detanasyo’s)

In ignition internal combustion piston engine with spark plug at the end of the compression stroke of the cylinder air / fuel mixture with a spark and was going tutuşturuluy done business with the exposed pressure increase. After the spark flame, burning flame propagation speed of the waves begin to spread in the room in case approximately 25-40 m / sec. outside the flame front of the flame front propagates the flame front expands temperature and pressure generated by the spark plug is called growing yet unburned end gas mixture. Before reaching the core of the flame to the end gas is called end gas temperature and the resulting combustion pressure effect and to generate a second detonation flame fronts. The speed of the flame front formed by the last gas of 500-700 m / s. It is about. This collision of two high flame propagation speed of the flame front and brings along a lot faster than normal increase in pressure. This rapid increase in pressure creates the sound of a hammer vuruluyormuşça the engine piston and cylinder wall. This volume provides an understanding of the knock.

The following figure shows a schematic view is given of the progress and turbulent flame front of a normal flame front.

The progress of the flame front

The following is a result obtained by measuring the detonation pressure indicator device diagram is shown. The other form of combustion is shown schematically occurrence of knocking in the room.

Knock, and low efficiency in the engine, with rapid increase in pressure can damage engine components formed. the drawbacks of the knock can be listed as follows:

– The disturbing create a sound that can be heard by the driver.
– Due to the high pressure of riding sudden load on the piston surface therefore leads to high stress and mechanical damage.
– Due to the high pressure segment of the gas leak, leaking gases causing the deterioration of lubricating oil properties.
– Power and causes loss of efficiency.
– Knock it’s also a question of influence will affect the chemistry of the exhaust combustion gases.

Prevention of Knock

High compression ratios the tendency to knocking increases. Therefore, the compression ratio according to the octane rating indicating the fuel knock resistance should be determined. The engine pressure and temperature of the obtained mixture at elevated temperature and compression end pressure is high, which leads to a reduction of ignition delay detonation. Inlet pressure and temperature must be kept low. Engine speed, increasing the speed and changing the last gas combustion zone pressure and temperature affects the knock. The engine must run at the appropriate speed. It should be given the lowest possible ignition advance. Because increasing the pressure and temperature values increasing ignition advance reveal the knock tendency. The air mixture / fuel ratio also influence the knock. Poor tendency to knock in the mixture is greater. The fuel / air ratio should be at optimum value. the output pressure of the exhaust gas is influenced by detonation. High exhaust pressure increasing compression causes detonation last pressure remaining in the cylinder exhaust gases reduces the increase in the amount of knock tendency.Exhaust valve will always be warm. Spark plug, if the exhaust valve away from here for a second firing temperature, that could knock. Spark plugs should be as close as possible to the exhaust valves. The shape of the combustion chamber is important in the inking. Combustion chamber surface / volume ratio tends to decrease the knock becomes smaller. Such as global combustion chamber. Cylinders must be cooled in a good way. Uncooled hot spots formed in the cylinder increases the tendency to knock.


The fuel in the cylinder / ignition is called a premature ignition of air mixture before ignition spark. The cylinder can not be cooled well, wrong to be elected to the spark plugs, the valve plate is thinned, the accumulated heat causes it to heat accumulation in the specified areas, such as the incorrect installation of the door seal and cause premature ignition.

It will bring premature ignition engine knocking combustion occurs, and damage to the engine knock is similar to the effects of backfiring.

– The disturbing create a sound that can be heard by the driver.
– Due to the high pressure, sudden load bearing surface of the piston, which in turn leads to high stress and mechanical damage.
– Due to the high pressure segment of the gas leak, leaking gases causing the deterioration of lubricating oil properties.
– Power and causes loss of efficiency.
– Knock it’s also a question of influence will affect the chemistry of the exhaust combustion gases.

Prevention of Knock

The vast majority of the early ignition cylinder problem is caused because well chilled. So the first roller to prevent premature ignition must be cooled in a good way.

Carbon deposits formed in the cylinder and cause backfiring come to incandescent case. This carbon must be cleaned or avoid the formation of puddles. Suitable plugs must be used. Otherwise, the spark plug electrodes means overheat and cause premature ignition incandescent case.

Source: MEGEP

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