Method of ignition of the fuel mixture in a high-speed rocket engine

Definitions

The ratio of the amount of oxidizer to the amount of fuel in the combustion process or in a combustible fuel-oxidizer mixture is measured either as a mass ratio, or as a ratio of volumes, or as a ratio to the number of moles. Accordingly, a distinction is made between mass L 0 , {\displaystyle L_{0},} , volumetric LV {\displaystyle L_{V}} and molar LM {\displaystyle L_{M}} ratios:

L 0 = momf , {\displaystyle L_{0}={\frac {m_{o}}{m_{f}}},} LV = V o V f , {\displaystyle L_{V}={\frac { V_{o}}{V_{f}}},} LM = M o M f , {\displaystyle L_{M}={\frac {M_{o}}{M_{f}}},} where mo , mf {\displaystyle m_{o},\ m_{f}} - masses of oxidizer and fuel; V o , V f {\displaystyle V_{o},\V_{f}} - volumes of oxidizer and fuel; M o , M f {\displaystyle M_{o},\ M_{f}} - molar amount of oxidizer and fuel (number of moles).

For gaseous mixtures of fuel and oxidizer in accordance with Avogadro's law LM = LV. {\displaystyle L_{M}=L_{V}.}

If during a chemical combustion reaction there is neither a free oxidizer nor unburned fuel in the combustion products, then this ratio of fuel and oxidizer is called stoichiometric.

For example, the combustion reaction of hydrogen in oxygen with stoichiometric coefficients:

2 H 2 + O 2 ⟶ 2 H 2 O {\displaystyle {\ce {2H2 + O2 -> 2H2O}}} .

In this reaction, the combustion products (on the right side of the equation) contain neither fuel nor oxidizer, and for 2 moles of hydrogen, 1 mole of oxygen is required, or, according to Avogadro’s law, for 2 volumes of hydrogen, 1 volume of oxygen, or for 4 g of hydrogen, 32 g oxygen, that is, with complete combustion of hydrogen without excess oxygen: LV st = LM st = 1 / 2 = 0, 5, {\displaystyle L_{Vst}=L_{Mst}=1/2=0.5,} L 0 st = 32 / 4 = 8. {\displaystyle L_{0st}=32/4=8.} These numerical values ​​are called stoichiometric ratios.

Stoichiometric ratios depend on the type of fuel and oxidizer, for example, in the reaction of methane combustion in oxygen:

CH 4 + 2 O 2 ⟶ CO 2 + 2 H 2 O {\displaystyle {\ce {CH4 + 2O2 -> CO2 + 2H2O}}} LV st = LM st = 2 , {\displaystyle L_{Vst}=L_{ Mst}=2,} L 0 st = 64 / 16 = 4. {\displaystyle L_{0st}=64/16=4.}

The oxidizer excess ratio is the ratio of the actual oxidizer/fuel ratio to the stoichiometric one:

α = L 0 / L 0 st = LV / LV st = LM / LM st , {\displaystyle \alpha =L_{0}/L_{0st}=L_{V}/L_{Vst}=L_{M}/ L_{Mst},}

Moreover, α {\displaystyle \alpha } does not depend on how the oxidizer/fuel ratio is defined: mass, molar or volumetric. It is obvious that at the stoichiometric oxidizer/fuel ratio α = 1. {\displaystyle \alpha =1.}

Fuel/oxidizer mixtures for which α < 1 {\displaystyle \alpha <1} are called rich mixtures, and α > 1 {\displaystyle \alpha >1} are called lean mixtures.

In foreign scientific and technical literature, the excess oxidant coefficient is usually denoted by the letter λ. {\displaystyle \lambda .}

A parameter called excess fuel ratio

ϕ = 1 / α , {\displaystyle \phi =1/\alpha ,} the reciprocal of the oxidizer excess coefficient.

Fuel-air mixture

Gasoline and the atmosphere necessary for its combustion flow into the cylinders of an internal combustion engine in the form of an air-fuel mixture. The air-fuel composition is a composition of tiny particles of gasoline with air from the atmosphere, which is obtained by carefully mixing these two components. Obviously, before mixing, gasoline must be atomized, and then evaporated even before the moment of ignition.

There are three different methods of formation from compositions for piston engines:

1. Internal method, when the mixing procedure is carried out directly in the volume of the cylinder;

2. External method, when the composition is obtained outside the cylinder volume, for example, in the intake channel;

3. Combined or combination method of formation from compositions, in which the first stage of mixing flows outside the cylinder, and the second - from inside the cylinder.

For gasoline species, the internal combustion engine is the most popular method of external formation of compounds. Before mixing with the atmosphere, gasoline is atomized either by splashing or injection under pressure.

The spraying procedure is carried out in carburetors, and the injection procedure is carried out using special devices, namely injection, which are called nozzles.

For external formation from compositions, you simply need evaporated fuel, which includes condensed flammable gases and gasoline. Gasoline is a product of distillation of oil.

Gasoline consists of eighty-five percent carbon and fifteen percent hydrogen and is a light hydrocarbon fuel. When combined with the atmosphere, gasoline vapors create not only flammable but also explosive compounds, which is generally determined by the mass correspondence between gasoline and the atmosphere, as well as their partial pressure and temperature in the composition.

The correspondence of one to fourteen and seven for gasoline and the atmosphere is stoichiometric, since it meets the rules of the strictest numerical correspondence of the weight categories of substances taking part in the chemical combustion reaction. It is worth keeping in mind that the air-fuel composition made by the external method of formation from compositions is not yet a fuel-air charge for a piston engine.

From the point of formation of the composition to the combustion chamber in the cylinder, the fuel-air composition repeatedly changes its state of aggregation under the influence of alternating changes in pressure and temperature.

As a result, some of the gasoline vapor turns back into a liquid state, cooling, or vapor will again appear when gasoline films come into contact with the hot walls of the intake system and cylinder. As a result, it is not the stoichiometric composition that enters the combustion chamber, even if it is completely made at the place where the composition is formed, but a composition that differs from the optimal composition in the direction of decreasing or increasing the amount of gasoline.

From this it is clear that the mass composition of the air-fuel mixture made outside the cylinder can differ significantly from the composition compressed at the moment of ignition in the combustion chamber. This provision is the most important disadvantage of the method of external formation from compositions, which leads to additional losses of gasoline, loss of stability of the engine when changing its modes, as well as additional reasonable difficulties in the system of preparation and intake of the air-fuel composition.

In order to maintain the composition of the air-fuel charge close to stoichiometric compliance, the process of preparing the air-fuel composition must always be controlled by the method of increasing or decreasing the number of gasoline compositions supplied to the formation system. This is achieved most efficiently in modern gasoline injection systems with electronically controlled electromagnetic injectors.

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Air/fuel ratio and excess air ratio

The most commonly used oxidizer is atmospheric oxygen, so the concept of air/fuel ratio

- the ratio of the mass L 0 a {\displaystyle L_{0a}} or volume LV a {\displaystyle L_{Va}} of air to the mass or volume of fuel:
L 0 a = mamf , {\displaystyle L_{0a}={\frac {m_{a}}{m_{f}}},} LV a = V a V f , {\displaystyle L_{Va}={\frac {V_{a}}{V_{f}}},} where ma , mf {\displaystyle m_{a},\ m_{f}} - masses of air and fuel;
V a , V f {\displaystyle V_{a},\V_{f}} - volumes of air and fuel. Sometimes, when calculating using stoichiometric combustion equations, the molar ratio of air to fuel is used, and it is assumed that the molecular mass of air is approximately equal to 29 g/mol.

LM a = M a M f , {\displaystyle L_{Ma}={\frac {M_{a}}{M_{f}}},} where M a , M f {\displaystyle M_{a},\ M_ {f}} is the molar amount of air and fuel (number of moles).

Air contains other gases that do not participate in the combustion process, mainly nitrogen with a volume (and molar) concentration of about 78%. To calculate the stoichiometric air/fuel ratio, this nitrogen and other inert gases must be taken into account in the chemical reaction equation; to simplify the coefficients of the equation, we assume that in air there are 4 molecules (volume) of nitrogen per 1 molecule (volume) of oxygen, then the equation for the combustion of methane in air will:

CH 4 + 2 O 2 + 8 N 2 ⟶ CO 2 + 2 H 2 O + 8 N 2 {\displaystyle {\ce {CH4 + 2O2 + 8N2 -> CO2 + 2H2O + 8N2}}} ,

from which it follows that for 1 volume of methane, approximately 10 volumes of air are required for stoichiometric combustion in air, more precisely, 9.66 volumes; the discrepancy is due to the fact that the equation does not take into account argon in air with a concentration of about 1 vol. % and the exact volumetric value of the oxygen concentration in the air is 20.95%.

Stoichiometric air/fuel ratios for some fuels are given in the table for air at a temperature of 25°C and a pressure of 100 kPa.

The ratio of the actual volume or mass of air to the stoichiometric volume or mass of air is called the excess air ratio

α {\displaystyle \alpha } [1]:
α = L 0 a / L 0 ast = LV a / LV ast = LM / LM st . {\displaystyle \alpha =L_{0a}/L_{0ast}=L_{Va}/L_{Vast}=L_{M}/L_{Mst}.}

Why should you mix gasoline and oil?

Not everyone knows how to dilute gasoline for a two-stroke Chinese scooter, and why there is a need to mix gasoline and oil in strictly defined proportions. The fact is that the design features and operating principle of a two-stroke engine do not allow the use of pure gasoline for its operation. Thanks to the oil introduced into the fuel mixture, lubrication is provided and friction in the crank mechanism is reduced.

Diluting gasoline with oil allows you to:

• increase the service life of the power plant;
• ensure effective lubrication of rubbing parts;
• avoid jamming of engine parts due to overheating;
• prevent possible damage during engine operation.

In addition, the use of gasoline mixed with oil in the required percentage allows you to avoid the occurrence of scuffing, which is the reason for repairs. A lack of oil can cause overheating of the elements of the cylinder-piston group and failure of the two-stroke engine.

An increased oil concentration will cause increased wear on the engine due to the formation of a thick layer of carbon deposits

That is why it is important to determine the proportion using the table, which indicates the required amount of oil for different volumes of gasoline

The reason for the formation of carbon deposits in the working chamber is the use of low-quality oil.

Excess air coefficient in various fuel-burning devices and engines

Dependence of power and specific fuel consumption for internal combustion engines with spark ignition on the excess air coefficient

Internal combustion engines

The excess air coefficient α {\displaystyle \alpha } is always equal to unity for a stoichiometric mixture. But practically in internal combustion engines (ICE) this coefficient differs from 1. For example, the optimal α {\displaystyle \alpha } for spark-ignition engines from the point of view of efficiency is 1.03-1.05, this excess is due to the fact that -due to imperfections in the mixing of fuel with air in the carburetor or cylinder of an engine with fuel injection, a slight increase in α {\displaystyle \alpha } is necessary for complete combustion of the fuel. On the other hand, the greatest engine power, all other things being equal, is achieved when operating on richer mixtures ( α = 0.83...0.88 {\displaystyle \alpha =0.83...0.88} The figure shows the dependence of engine power and efficiency with spark ignition from α {\displaystyle \alpha } and the air/fuel ratio for gasoline at certain values ​​of α {\displaystyle \alpha }... So, for gasoline, the stoichiometric air/fuel ratio by mass is 14.7, for a propane-butane mixture it is the ratio is 15.6.

In modern engines, maintaining α {\displaystyle \alpha } close to optimal is achieved using an automatic fuel/air ratio control system. The main sensor in such systems is the sensor for the concentration of free oxygen in the engine exhaust gases - the so-called lambda probe.

In diesel engines, to avoid strong soot formation, α {\displaystyle \alpha } is maintained at a level of 1.1…1.3[2].

Gas turbines

In the combustion chamber of a gas turbine, for example an aircraft engine, α {\displaystyle \alpha } is maintained close to 1. But in front of the turbine blades, in order to reduce the gas temperature, for reasons of the heat resistance of the blades, the gas from the combustion chamber is diluted with air taken from the turbine compressor, which reduces its temperature from approximately 1600 °C to 1300...1400 °C, therefore α {\displaystyle \alpha } in the turbine exhaust gases α {\displaystyle \alpha } is significantly greater than 1 and reaches 5.

Industrial, heating and domestic boilers

α {\displaystyle \alpha } in such boilers depends significantly on the type of fuel. In gas boilers of small power or productivity, α {\displaystyle \alpha } is 1.2...1.4, in large energy boilers burning natural gas - 1.03...1.1. In boilers operating on liquid and solid fuels, α {\displaystyle \alpha } is maintained within the range from 1.5 to 2…3 for complete combustion.

Stoichiometric composition - mixture

The stoichiometric composition of a mixture is a composition that exactly corresponds to the quantitative content of substances combined with each other during the combustion reaction.  

For the stoichiometric composition of the mixture (R - R3), powerful central initiation and other conditions of open technological installations possible in industry, the maximum excess explosion pressures (Diamax) were determined: 1) fast-burning mixtures.  

This equation is valid for the stoichiometric composition of the monomer mixture.  

The maximum value of ip does not correspond to the stoichiometric composition of the mixture, but refers to a richer mixture, which is explained by higher rates of chemical reactions in these mixtures due to a higher concentration of active centers arising during chain reactions. In table Table 16 shows the values ​​of IP for stoichiometric mixtures, as well as the maximum values ​​of IP and the corresponding mixture compositions.  

If the process occurs near equilibrium, then the stoichiometric composition of the mixture should be optimal. Indeed, any deviation of the initial composition from the stoichiometric one will lead to a decrease in the equilibrium yield of reaction products, as can be seen from the following.  

When using this method of growing single crystals, it is necessary to take into account the possibility of a change in the stoichiometric composition of the mixture due to the increased volatility of one of the components, especially if the melt is kept for some time to remove air and gases.  

It is easy to show that when a reaction occurs near equilibrium, the stoichiometric composition of the mixture is optimal.  

The normal combustion rate depends on the heat of combustion or the composition of the gas mixture, and the maximum value does not correspond to the stoichiometric composition of the mixture, but refers to a richer mixture, which is explained by the excess of active centers generated during chain reactions.  

An experimental assessment of the temperature of the residual gases at the moment the intake valve opens shows that the limit for the appearance of a backfire at a stoichiometric mixture composition corresponds to approximately 700 C. With increasing rotation speed, the temperature of the residual gases increases and, accordingly, the limit for the appearance of a backfire shifts to the region of leaner mixtures. This is a fairly convincing argument for the assumption that the main cause of ignition at the intake is the contact of a fresh charge with residual gases at the moment the valves close.  

Since M M, i.e. the concentration of the mixture, provided that the fuel is evenly distributed throughout the volume, exceeds the stoichiometric value, the probability of an explosion becomes very high, since the lower concentration limit and the stoichiometric composition of the mixture are achieved at the early stage of evaporation and mixing of gas with air.  

Flow washers are calculated based on the conditions that the mixture flow rate must be equal to the nominal one, and the acetylene content in the mixture must be 33% by volume, which corresponds to the stoichiometric composition of the mixture.  

In table 2.6 shows the content of flammable substances in some gas or steam-air explosive mixtures, corresponding to the most easily flammable composition of the mixture when exposed to various ignition sources, as well as corresponding to the stoichiometric composition of the mixture and the composition of the mixture at which the explosion pressure is maximum.  

A significant advantage of this method of purifying converted gas is that it eliminates the presence of an external source of nitrogen (air-separation unit), which is necessary for washing the separated mixture from CO and dosing the resulting nitrogen-hydrogen mixture to achieve the stoichiometric composition of the mixture.  

Design

• A fuel tank that is removable and has a valve.
• Adjustment screw.
• Block with a wick.
• Removable grid.
• Reflector.
• Burner.

There is a reflector on the body; it is painted with powder dye. The heating of the building depends on it.

The burner is located in the center of the structure.

The fuel tank, located at the rear of the device, supplies fuel to the wick bowl by gravity.

The control valve sets the heating power.

They are mainly made of fire-resistant steel and can weigh up to 10 kg in weight. The compactness of the device allows it to be transported to various places.

Poor fuel assembly concept

- This is a fuel assembly with a reduced gasoline content and an increased air content.

The error code assigned to this error by the on-board computer is P0171. Literally, this code stands for very poor fuel supply. Sometimes poor FA is called low-calorie.

A poor fuel mixture shows itself with the following signs: very poor traction, especially noticeable on steep climbs, engine overheating, the injector makes popping sounds, and white or gray smoke comes out of the exhaust pipe.

Reasons for preparing a lean fuel assembly: fuel pump malfunction, use of gasoline with water or other impurities, fuel sensor malfunction, vacuum hoses or intake manifold malfunction, injectors supply too little gasoline, pressure sensor malfunction.

Signs of a rich mixture

The formation of a rich fuel mixture occurs with a chic set of manifestations.

1. The first and most important sign: the malfunction indicator issued by the car’s on-board computer lights up. Error code: P0172.
2. The car muffler makes a loud popping noise. This happens due to a lack of air in the engine cylinders and, as a result, the air burns out in the exhaust pipe.
3. Exhaust gases are black or gray. This occurs due to the fact that the fuel assembly burns not in the engine, but in the exhaust pipe; the exhaust gas does not undergo any purification by filters; when burning in the pipe, the amount of atmospheric air sharply increases.
4. The car is less dynamic, less powerful. This is explained by the slow combustion rate of the fuel mixture. As a result of slow fuel combustion, power failures occur. If the mixture is over-enriched, it is even possible that the car simply will not move.
5. Fuel consumption has increased sharply. It is explained by the inefficiency of using the fuel mixture: it tries to cover the low combustion rate with additional injection of liquid fuel.

Stoichiometric mixture

In stoichiometric gas-air mixtures, the explosion pressure does not exceed 10 ata.  

In the case of a stoichiometric mixture, in contrast to a mixture of a different composition (for example, an equimolecular mixture of H2 02), under certain reaction conditions, almost complete conversion of all starting substances into reaction products is often possible.  

When firing stoichiometric mixtures of Ce2O3: Si02 and 2Ce2O3: 3Si02, not pure silicates are formed, but mixtures of several compounds.  

In a stoichiometric mixture flame, methane is oxidized primarily directly, while in the case of a rich mixture flame, methyl radicals are formed and recombine to form ethane (C3Hb), which is then oxidized. Thus, a rather unexpected result is revealed: in order to have an acceptable mechanism for methane oxidation, an additional mechanism for ethane oxidation is required.  

What amount of stoichiometric mixture must be introduced into a vessel with a volume of 500 liters to obtain one mole of phosgene.  

High temperature X-ray photography of a stoichiometric mixture of Si Si02 was carried out by Brewer and Edwards, and later by others. No new lines were also found on samples made from a mixture of Si and Si02 calcined at 1300 C, followed by quenching and X-ray examination in a conventional chamber.  

Typically, in stoichiometric gas-air mixtures, the explosion pressure does not exceed 10 kgf/cm2 (abs.  

According to the equation, a stoichiometric mixture of carbon monoxide and air consists of 2 1 3 76 6 76 equal volumes.  

An example is a stoichiometric mixture of non-reacting substances, such as nickel and sulfur, subjected to isothermal compression.  

The exponent for a stoichiometric mixture below 60 ag is between 0 5 and 0 6; between 60 and 100 atm it decreases to 0 25 and then increases again. The graph also shows that with increasing polystyrene content, the burning rate quickly increases, passes through a maximum at -8% and then slowly decreases.  

The spontaneous reaction in a stoichiometric mixture corresponds to the second order in both nitrobenzene (section A) and p-xylene (section B); This is precisely what is evidenced by the constancy of the rate constant calculated from the kinetic equation of second-order reversible reactions.  

Let us consider the reaction times of a stoichiometric mixture at φ - 0 01 and - j - 0 01, which corresponds to a change in pressure by - - 1 i - 1/0 from the value pg Let p1 7 6 mm Hg. Art. Let us determine the reaction time at р р1 — — Др 7 6 — — 0 076 7 676 and РР.  

General concept

Delving into the concept of what a too rich mixture is (VAZ, Skoda, BMW, Chevrolet, etc.), a few words should be said about the fuel itself. It consists of gasoline (diesel) and air correlated in a certain proportion. Liquid fuel is supplied to the engine cylinders. This ratio largely depends on its quantity.

A rich mixture is one that contains more gasoline and less air than normal. Since there is not enough oxygen inside the combustion chamber, the engine process loses power. Because of this, gasoline burns out already in the muffler. Some auto mechanics call this state of fuel high-calorie.

These violations are reflected in the appearance of the spark plugs. A characteristic black soot appears on them. There may be several reasons for this state of the engine system. They must be found and eliminated.

Automatic diagnostic system

If your vehicle's diagnostic system indicates that a "Compound Too Rich" error has occurred, certain actions must be taken. To do this, you need to understand the principles of the scanner.

Air is supplied to the fuel when diagnosing the MAP sensor and lambda probe. Perhaps it is caused by deviations of these particular systems. However, in addition to them, problems may be associated with deviations in thermal clearances (engine with LPG), mechanical damage to sealing materials, insufficient compression or deviation during timing operation.

To understand why automatic diagnostics indicate such an error, the car owner can take several steps. First of all, you need to analyze the information that the scanner provides. Next, you can artificially simulate the conditions for the occurrence of such a malfunction.

The next step could be to check components and mechanisms, such as contacts, absence of suction, as well as the operability of systems related to the supply of fuel and oxygen to the combustion chamber.

The first signs of a carburetor malfunction

Due to untimely or unprofessional periodic maintenance of the chainsaw, as well as due to heavy load, difficulties in its operation may arise from time to time. For professional workers, such breakdowns can reduce their work efficiency and spoil their mood for the whole day.

The following signs indicate an incorrect carburetor setting:

1. The tool starts up problematically, after which it immediately stalls.
2. The chainsaw stalls when you press the gas.
3. Gasoline is consumed in large quantities, and it still remains in the cylinders and does not burn out completely, and the exhaust is excessively thick.
4. The carburetor settings installed at the manufacturer's factory are lost due to improper use or self-adjustment.
5. Debris has entered the air intake system. Because of this, she failed.
6. Engine pistons are used up. In this case, adjusting the carburetor will only temporarily solve the problem.

In the event that dirt gets into the carburetor, one adjustment will not do. Here you just need to clean it. When the pistons are used up, a major overhaul of the engine is required.