Gasoline expertise

World Fuel Charter Requirements for Motor Gasolines

The octane number is a measure of a gasoline's ability to resist spontaneous combustion; self-ignition can cause engine knocking. There are two laboratory test methods for measuring octane numbers: one determines the research octane number (RON) and the other determines the motor octane number (RON). OCHI correlates best with low velocity and medium knock conditions, and OCHM correlates with high temperature detonation and partial throttle conditions. RON values are usually greater than RHM values.

Cars are designed and tuned to a specific octane number. When a consumer uses petrol with an octane rating lower than the required octane rating, knocking occurs, which can cause serious engine damage. Engines equipped with knock sensors can operate at lower octane numbers, reducing the ignition timing; however, the fuel consumption will increase and the power will decrease, and at very low octane numbers the detonation will not disappear. Using gasoline with a higher octane rating than required will not improve the performance of the vehicle. The Fuel Charter establishes three octane grades for each category (91, 95 and 98 RON).

Normal combustion of the fuel gives the speed at which the flame spreads up to 35 m / s. This is in the normal state of the fuel. But under special conditions, the detonation process can occur when the combustion rate increases to 1500-2500 m / s. Detonation waves are reflected from the cylinder walls.

Detonation causes a ringing knock in the engine, shaking, black smoke with sparks in the exhaust gases can go. At this moment, engine parts suffer, their increased wear occurs, valves and pistons quickly burn out.

Combustion with detonation occurs from the combustion and decay of oxidation products of very fragile, decomposing substances, which at the same time have excess energy. And the higher the temperature, the sooner oxidation occurs. In the carburetor, with an unburned working mixture, portions of this mixture are exposed to particularly high temperatures, which leads to the formation of a large number of peroxides and the creation of detonation conditions. But if the composition contains hydrocarbons that do not create a lot of peroxide, then the combustion ends in a normal mode.
If the last portions contain a large amount of peroxide, then their concentration can become critical and lead to detonation and explosive decay. With a sharp increase in pressure, the occurrence of a shock wave, the mixture ignites. In this case, the mixture burns out at a speed equal to the propagation of the shock wave.

What increases the potential for detonation? Overheating, poor maintenance, when scale builds up on the jacket and, due to its low thermal conductivity, the temperature of the working mixture rises. At the same time, the humidity of the surrounding atmosphere contributes to the reduction of detonation. Detonation is also provoked by deposits in the piston crown and the formation of carbon deposits in the piston rings. The detonation resistance of gasoline is determined by its octane number.

Sulfur is a natural component of crude oil. If sulfur is not removed during the refining process, it will contaminate vehicle fuels. Sulfur has a significant impact on vehicle emissions, reducing catalyst performance and negatively affecting oxygen sensors. The reduction in sulfur concentration results in lower emissions from all vehicles equipped with catalytic converters.

Manufacturers are working hard to reduce fuel consumption while reducing carbon dioxide emissions. Running on a lean air / fuel ratio is the most promising way to achieve this reduction in gasoline-fueled vehicles. However, a new problem arises related to the quality of exhaust gas cleaning. While unburned hydrocarbons and CO are efficiently removed with existing catalysts during lean run, NOx is removed only during stoichiometric or rich run.

Lean NOx absorber catalysts work by chemically trapping NOx during lean burn operation. The NOx is then released and decomposed by the catalyst in a few seconds of rich operation. However, sulfur oxides are adsorbed more strongly and reduce the absorption capacity of the adsorbent for nitrogen oxides. Sulfur removal requires a longer run on a rich mixture, which negates the lean burn fuel economy benefits. However, when using gasolines that do not contain sulfur, the required NOx decomposition activity will be maintained.

Corrosive properties of gasoline . Gasoline, when it comes into contact with metal, can cause a serious change in it - corrosion. Therefore, various tanks, metal fuel tanks, parts in the carburetor suffer from corrosion damage, which inevitably occurs due to the content of organic acids, sulfur compounds and alkalis in the fuel.

Organic acids appear in it during transportation and storage due to oxidation. Petroleum acids have a particularly destructive force; they especially destroy parts with zinc and lead. When interacting with metal, organic matter forms soap flakes, which also settle on the elements of the power supply system in the engine and lead to its clogging.

Sulfur compounds are usually divided into active and inactive. The former include hydrogen sulfide, mercaptans, and elemental sulfur. The latter are disulfides, sulfides, and others. Metal parts are especially affected when active substances appear; they are the most dangerous and therefore unacceptable in gasoline. The latter by themselves do not have a destructive effect on the metal. But during fuel combustion, corrosive sulfur oxides can be formed. The proportion of sulfur varies in different grades in different ranges from 0.05 to - 12 percent, and with an increase in this number, engine wear becomes more and more likely, and metal corrosion from the effect of sulfur on parts reduces the performance and economy of the engine. Acids dissolved in water often get into fuel from dirty containers. Acids also lead to destruction, so they should not be in gasoline.

Lead. Alkyl lead fuel additives have previously been used as inexpensive antiknock agents for gasoline. However, their harmful effects on health have led to the discontinuation of leaded gasoline in many markets. Consideration should still be given to the existing vehicle fleet, as older vehicles require lead (or lead replacement fuel additives) in the fuel to protect the engine. Gasolines with a low lead content (0.05 g / dm ³ ) are sold in the leaded gasoline markets. This reduces the risk of contamination and provides adequate engine protection. While the efficiency of automotive catalysts is increasing, resistance to lead poisoning remains very low, so that even slight lead contamination can destroy a modern catalyst. Therefore, the market for lead-free gasoline is very important in the long term.

Actual pitches. Oxidation of unsaturated gasoline hydrocarbons leads to the formation of resins, which are deposited on the walls in the combustion chamber and other parts with which the fuel comes into contact. These deposits are dark brown and sticky and can gradually interfere with engine performance. Accumulating in the carburetor, clogging up the pipelines, these substances can cause a lot of trouble for the car and even disable it.

When the engine is running, high-boiling gasoline fractions, together with their resins, are directed to the cylinders, and with constant heating of the pipeline walls, oxidation is more active, and harmful substances settle on the pipeline walls, polymerize, form deposits, narrow the useful lumen of the pipeline, and worsen evaporation.

Deposits are also deposited on the intake valves, due to which the valves hang. Deposits can also lead to detonation when the engine is compressed, and carbon deposits impair the transfer of heat from hot gases to the liquid in the cooling system.

There is a concept of the concentration of actual tar in mg per 100 ml of gasoline. In automotive fuel, their content is permissible 2 - 10 mg per 100 ml, if exceeded, the time before engine breakdown from increased carbon deposits decreases.

Ash-forming fuel additives can adversely and irreversibly affect the performance of catalysts and other components (eg oxygen sensor), resulting in increased emissions. Therefore, high quality gasoline should be used and the use of ash-forming fuel additives should be avoided.

Gasoline induction period. High chemical stability is the main indicator of high-quality gasoline. Chemical stability refers to how a fuel resists chemical changes during transport, storage and use. It is influenced by the composition, its non-hydrocarbon impurities, the presence of various added antioxidant additives.

Until the moment it is poured into the tank of a car, it goes a long way of transportation through oil depots, and earlier from the plant where it is produced. All the way gasoline undergoes oxidation as a result of mixing with oxygen. Most of the products formed during this remain dissolved in the fuel itself, but some fall out as a precipitate. Moreover, a certain amount of sludge and sediment can accumulate in the tanks, and this also accelerates the oxidative process. It is also influenced by the catalytic effect of a metal, for example, copper.

To prevent an unpleasant process, special antioxidants are used, they are also called inhibitors. Under the influence of molecular oxygen, these processes are suspended for some time. Therefore, modern gasoline usually contains such additives in small quantities - from about a thousandth to tenths of a percent.

The antioxidant inhibits the process for a certain moment, this time is called the induction period, after which the effect of oxygen increases again. The typical period is 600 to 1300 minutes. During accelerated oxidation, resins are formed to determine the induction period, and their amount indicates the stability of the fuel during long storage.

The chemical stability of motor gasoline is an indicator that allows you to determine their tendency to gum formation, and therefore to calculate the storage time. It depends on the chemical composition of the gasoline. The formation of tar, as well as the change in color and the appearance of a strong odor in the fuel and the oily layer at the bottom of the tank, is the result of oxidation. Gasolines with a high content of olefinic hydrocarbons, as well as those produced using cracking or pyrolysis, are more susceptible to oxidation. With the help of a special device, under a certain pressure and at a special temperature, the induction period is monitored - the time during which the fuel does not oxidize under these conditions. Accordingly, the indicators of the induction period allow us to conclude that it is prone to gum formation and oxidation, these indicators are directly proportional. The formation of resinous substances has a detrimental effect on the condition of the engine - resins are deposited on the intake pipes, gas distribution inlet valves, parts and walls of the power system and the combustion chamber. The oxidation state is calculated by an indicator called the residue (in mg), which is formed in 100 g of gasoline after its evaporation under special conditions. The higher the ambient temperature, the less stability, respectively, it is recommended to paint the tanks in light colors and fill the fuel to the maximum level. The use of additives increases the shelf life and induction period.

MTM (Methylcyclopentadienyl Manganese Tricarbonyl) is a manganese-based compound supplied as an octane increasing fuel additive for gasoline and a combustion improving fuel additive for diesel fuel. MTM combustion products form deposits on internal engine parts such as spark plugs, leading to intermittent ignition, engine malfunction and increased emissions. As a result, the number of complaints from consumers and manufacturer's warranty costs is growing.

Combustion products also accumulate on the catalyst. As soon as the catalyst becomes covered or clogged with them, its lifetime and efficiency are reduced. MTM combustion products accumulate on the catalyst surface, but the on-board diagnostics system may erroneously indicate that the catalyst is working properly. Thus, the catalyst malfunction will not be noticed and eliminated, while the car will operate with increased emissions of pollutants into the atmosphere.

Ferrocene has been used as a replacement for lead to increase octane for unleaded fuels in some markets. It contains iron, which accumulates on catalysts and other parts of the exhaust system in the form of iron oxide. Iron oxide acts as a physical barrier between the catalyst / oxygen sensor and the exhaust gases. As a result, the exhaust gas cleaning system is not able to function as required, resulting in increased emissions. Therefore, the use of ferrocene should be avoided in unleaded gasoline.

Silicon is not a natural component of gasoline. However, it sometimes appears in commercial gasoline when it gets into waste solvents containing silicon compounds used in oil refineries. This contamination has a significant negative impact on exhaust gas treatment systems. Silicon, even in low concentrations, can cause oxygen sensor failure and high levels of engine and catalyst deposits. This can lead to engine failure when using even less than one tank of such contaminated fuel. Therefore, gasoline should not contain detectable concentrations of silicon, nor should it be used as a component of any fuel additive to improve the performance of gasoline and engine.

Oxygenates such as MTBE and ethanol are often added to gasoline to increase octane or to cause a leaner stoichiometry to reduce carbon monoxide emissions. Leaner operation reduces carbon monoxide emissions in vehicles with carburetors and fuel systems without electronic feedback control. These emission reduction benefits are not fully realized in modern vehicles using electronic closed-loop control because the lean effect only occurs when the engine is running on a cold engine or during rapid acceleration. This overpopulation can cause an increase in emissions. Since ethanol has a higher heat of vaporization than ethers, a decrease in the driving performance of a car using gasoline with ethanol is due to the additional heat required to vaporize the gasoline. If oxygenates are used, esters are preferred. The use of methanol is not permitted. Methanol is a corrosive substance that can corrode metal parts of fuel systems and degrade polymers.

Olefinic hydrocarbons are unsaturated hydrocarbons, which are the high-octane components of gasoline. However, they can lead to the formation of deposits and increased emissions of reactive hydrocarbons that contribute to the formation of ozone and toxic compounds. Olefinic hydrocarbons are thermally unstable and can lead to the formation of gums and deposits in the intake system of the engine.

Aromatic hydrocarbons are fuel molecules that contain at least one benzene ring. They are high-octane and high-energy gasoline components. Combustion of aromatic hydrocarbons can lead to an increase in the carcinogenic benzene content in the exhaust gases and an increase in combustion chamber deposits. Reducing the volume fraction of aromatic hydrocarbons in gasoline significantly reduces emissions of toxic benzene and carbon dioxide.

Benzene is a natural component of crude oil and is a high octane catalytic reforming product. For humans, it is a strong carcinogen. It is released into the atmosphere as a result of evaporation and with exhaust gases.

Saturated steam pressure. Gasoline tends to evaporate, evaporation can be of two types - statistical and dynamic. The vapor pressure of gasoline must be seasonally controlled to account for the different levels of vaporization required at different temperatures. Vapor pressure must be tightly controlled at high temperatures to reduce the likelihood of hot fuel problems such as vapor lock or overloading of the charcoal filter (adsorber). Controlling vapor pressure at high temperatures is also important to reduce evaporative emissions. At lower temperatures, a higher vapor pressure is needed to allow easy starting and warm-up of the engine.

Static is when a stationary surface evaporates its vapors into stagnant air. This evaporation is typical for a closed tank environment. With dynamic evaporation, the fuel is blown with an air stream. This happens, for example, in internal combustion engines.

An enclosed space limits the rate of evaporation, and it is equal to the rate of condensation, therefore such a system is in equilibrium, the vapor is in the saturation density, its density is minimal.
The saturated vapor pressure is the pressure that vapor develops when in equilibrium with a liquid in a given temperature regime. Moreover, in simple liquids, it is determined only by the parameters of the liquid and temperatures, and in complex ones, which include gasoline, by the ratio of the volume of the liquid and vapor phases.

What does this affect? The more volatility, the more likely there is a vapor lock in the engine system. That is why in hot regions and in high altitude conditions, a lot of vapors are generated to the detriment of the liquid component. The vapors are mixed with the fuel, come with an admixture of air formed during heating, and the total amount of fuel supplied is reduced. There are interruptions in the operation of the engine, its stops.
Summer pressure of saturated vapors should not exceed 66661 Pa (500 mm Hg), winter - no more than 93325 Pa. Therefore, it is prohibited to use winter gasoline in summer, as well as summer gasoline in winter.

The fractional composition is set either as a series of temperatures "T" (T50 is the temperature at which 50% of gasoline boils off), or as a series of values "I" (I100 is the percentage of gasoline evaporated at 100 degrees). An excessively high T50 (or low percentage of I100) can result in poor starting and poor performance during warm-up at moderate ambient temperatures. Control over the index of the starting period (IPP), calculated by the temperatures at which 10%, 50% and 90% of gasoline boil off, and the volume fraction of oxygen, can also be used as a guarantee of reliable cold start and engine warm-up.

Gasoline consists of various hydrocarbons with complex and unequal volatility. Evaporation depends on the chemical composition of the fuel, and is determined by the limits of the boiling point of both itself and its individual fractions. The quality of gasoline directly depends on how the fractions are correlated in it. It is they that affect the ease of starting the engine and acceleration, warm-up time and other characteristics.
Distinguish between starting, working and end fractions. The first is the lowest-boiling hydrocarbons, they occupy a tenth of the distillate. Up to 90 percent of the volume is made up of the working fraction, and the remaining 10 - the end fraction, until the end of the boil.

The ratio of fractions should be such that gasoline can provide good engine start, quick acceleration, low consumption and distribution of fuel among the cylinders with minimal wear of them and pistons. In this case, the ratio of fractions should be ideal. Otherwise, the lubricant will be washed with liquid fuel, and the engine oil will dilute in the crankcase. With a lack of low-boiling fractions, part of the non-evaporated fuel in an unheated engine will enter the cylinders in liquid form. Lack of lubrication will lead to premature wear of parts.

To prevent this all, there is a control system for the content of low-boiling hydrocarbons. It is currently based on three indicators:

• distillation start temperature - not less than 35 degrees in summer and no norm in winter;
• distillation temperature of 10 percent gasoline - no more than 70 degrees in summer and no more than 55 in winter;
• saturated steam pressure.

Warming up of the engine starts with start-up and continues until stability in operation. At the end, at idle speed, the fuel practically evaporates completely in the intake manifold. With a minimum distillation temperature of 50% and lighter composition, the engine heats up faster. Low-temperature fuel is more likely to evaporate in the intake manifold, the combustible mixture fills the cylinders better and the engine power increases.
Throttle response is improved when the cylinders are filled with a rich mixture during throttling. A lean mixture, when the power system does not partially evaporate, leads to engine shutdown.
The distillation temperature of 50% of summer fuel has an upper limit of 115 ° С, of winter fuel - up to 100 ° С. This allows you to get a quick warm-up and good engine throttle response.

The use of high temperature fuel at the end of boiling increases engine wear, increases salt deposits on parts, and increases fuel consumption. Therefore, for summer gasoline, the distillation temperature of 90% of the fuel should be no higher than 180 ° С, and for winter gasoline no more than 160 ° С. The end of the summer boil should not exceed 195 ° C, and the winter one - 185 ° C.

Steam plug. Excessive volatility of gasoline can cause fuel heating problems such as vapor lock, carbon filter overload and increased emissions. A vapor lock occurs when too much vapor is generated in the fuel system and the supply of fuel to the engine is reduced. This could result in loss of power, erratic engine performance, or engine stalling. Since the saturated vapor pressure and fractional composition are not sufficient in order to guarantee the stable operation of the car, it is necessary to establish a certain ratio of the vapor and liquid phases (vapor lock indicator).

Fuel additives to protect against deposits. Combustion of even very high quality gasoline can lead to the formation of deposits. Such deposits will increase engine emissions and adversely affect vehicle performance. High quality fuel contains fuel additives to protect against deposits on injectors and valves.

However, detergents typically increase combustion chamber deposits (CCS) levels when compared to the base fuel. Therefore, it is necessary to create optimal fuel additives to maximize the reduction of OCS, which will allow engine designers to improve the design of combustion chambers to reduce emissions and fuel consumption. Removal of OCS can reduce hydrocarbon emissions from the engine by up to 10%, CO - up to 4% and NOx - up to 15%.