What causes an engine deflagration?

It is a phenomenon that the combustible mixture accumulated in the furnace boring burns at the same time instantly, so that the pressure on the flue gas side of the furnace suddenly increases. In severe cases, the pressure generated by deflagration can exceed the allowable value of the design structure and cause damage to the water wall, rigid beam, furnace top and furnace wall. There must be three conditions for the occurrence of deflagration (i.e., the three elements of deflagration), all of which are indispensable.

First, there is the accumulation of fuel and combustion air; Second, the mixture of fuel and air has reached the concentration of deflagration; The third is to have enough ignition energy. In the start-up, operation and shutdown of the boiler, how to avoid the accumulation of fuel and combustion air is the key to prevent the deflagration of the furnace. Because the deflagration occurs instantly, and the flame propagation speed is very fast, up to hundreds of meters to thousands of meters per second, the spherical shape of the flame spreads in all directions, and the embers are burned within a few hundredths to tenths of a second, which is equivalent to the fuel being ignited at the same time, and the flue gas volume suddenly increases, so that the flue gas resistance is also very large, so it is too late to leak out and occur**.

Engine deflagration Once the engine deflagration occurs, it is extremely harmful, it causes deformation and damage to the moving parts such as engine cylinder walls, pistons, piston rings, valves, connecting rods and connecting rod bearings, and the specific reasons are usually as follows: 1) Excessive carbon accumulation. The heat storage and non-thermal conductivity of carbon deposition make the combustible mixture burn in advance due to the red-hot heat, and at the same time will reduce the vortex intensity generated by the mixture at the end of compression, prolong the combustion time, increase the tendency of spontaneous combustion, so it is easy to induce deflagration; 2) The engine is overheating.

When the engine is in high-power, overload condition or low-grade high-speed continuous driving for a long time, especially in the hot summer, the outside temperature is high, and the heat dissipation of the parts is poor, which is easy to cause the engine to overheat. When the overheating fault is serious and cannot be improved in time, the combustible mixture will be preheated when it enters the combustion chamber, causing the local mixture temperature to be too high, reaching the ignition point in advance, and burning itself before the normal ignition of the fuel, thus causing deflagration; 3) Improper use of fuel. The lower the grade of gasoline, the worse its anti-knock performance.

Gasoline that has been stored for too long or is poorly sealed will naturally decrease in octane and its anti-knock performance will deteriorate. If it is misused, it is easy to make the mixture incomplete, and the first combustion mixture is partially expanded, compressing the rest of the unburned mixture to reach the spontaneous ignition temperature, and suddenly all of it will cause high-pressure combustion; 4) The engine crank chamber is leaking. The self-tightening spring at the lip of the crankshaft oil seal of the two-stroke engine falls off or fails; The oil seal rubber becomes stiff when it ages, so that the spring self-tightening force cannot play a sealing role; During the repair of the engine, the oil seal is scratched or bruised; The carburetor adapter seat (intake pipe or intermediate gasket) is not tightened, etc., and the air leakage caused by the above parts will make the mixture thinner, thereby destroying the normal combustion, and it is easy to cause premature ignition and deflagration.

What is engine super knocking.

Engine "super knocking", also known as low-speed premature ignition, is an abnormal combustion phenomenon unique to supercharged direct-injection gasoline engines. When the engine inhales the mixture of fuel vapor and air, in the process of compression, due to the mixture of low ignition point substances in the fuel, it will cause the gas mixture to automatically deflagrate before the ignition of the spark plug, forming a new ignition point, and the flame spreads outward at a speed several times higher than the normal combustion, so that the cylinder wall is affected and vibrates, which is called detonation. To put it simply, knocking is a manifestation of abnormal pressure in the combustion chamber caused by abnormal combustion.

A phenomenon when detonation occurs.

The engine will emit a crisp and discontinuous metal knocking sound when a slight knock occurs, while a continuous metal knocking sound will occur when the engine will have a continuous metal knocking sound during a severe and continuous knock, and the engine power will also be significantly reduced.

What are the causes of detonation?

1 The air-fuel ratio is incorrect, and the mixture is too dilute to increase the combustion temperature, thereby increasing the engine temperature.

2. The octane number of fuel is too low, the octane number is an indicator of anti-detonation, the higher the octane number, the stronger the anti-detonation, and the lower the conversely, it is easy to detonation.

3. The cleanliness of the fuel is insufficient, and some physical substances and chemical impurities contained in the fuel, including some aromatic substances, will cause spontaneous combustion and detonation during the compression process of the engine.

4. Excessive carbon deposition in the combustion chamber, due to the serious carbon deposition, the actual volume of the cylinder becomes smaller, the compression ratio increases, and at the same time, the carbon deposition in the high-temperature environment will always burn red due to the poor heat dissipation ability, so that the high-temperature compressed mixture is not only ignited by the sequential spark plug, but also randomly ignited by the high-temperature carbon deposition in the cylinder, resulting in detonation.

5. The engine temperature is too high, the engine is too hot in the environment, the inlet air temperature is too high, or the engine cooling water circulation is poor, which will cause the engine to detonate at high temperature.

6 The ignition angle is too early, so that the piston can gain power as soon as it enters the power stroke after the compression stroke is completed, it is usually ignited before the piston reaches the top dead center. Ignition too early will cause most of the oil and gas to burn when the piston is still compressing the stroke, and the unburned oil and gas will be subjected to great pressure and spontaneous combustion, resulting in detonation.

The methods to solve detonation are as follows.

1. Use fuel that conforms to the compression ratio of the engine.

2. Avoid "drag gear" driving.

3. Regularly clean the carbon deposits and fuel injectors in the oil circuit.

4. Avoid high temperatures: check the coolant water level regularly, check and change the engine oil regularly, avoid long-term intense driving, and monitor the water temperature frequently when driving in summer.

5. Appropriate selection of high-quality fuel additives. For example, fuel additives containing PNF stock solution can solve the problem of engine knocking to a certain extent.

What is called "engine deflagration": that is, the exhaust valve is opened before the combustion expansion process of the engine ends, that is, the combustion occurs in the exhaust stroke. Causes:

1. The lag of the injection advance angle;

2. The exhaust advance angle is opened in advance;

3. Incomplete combustion;

4. Ignition lag;

Overall, the engine exhaust temperature is too high.

If the "deflagration" occurs in the compression stroke, a "fuel knock" will occur.

Excessive carbon deposits in the combustion chamber, blow-in gases in the crankcase, low gasoline grades, too large ignition advance angles, and overheated engines.

Mixture and timing issues.

During deflagration, the pressure shock wave hits the cylinder wall and destroys the oil film layer, resulting in the aggravation of the wear of the piston, cylinder and piston ring, and the violent and disorderly heat release during the deflagration also makes the temperature in the cylinder increase significantly, and the heat load and heat dissipation loss increase, and this abnormal combustion also deteriorates the power and economy.

1. Engine deflagration refers to the fact that due to the high pressure and temperature of the gas, the combustible mixture burns itself without ignition, and the flame spreads outward at a speed several times higher than the normal combustion, resulting in a sharp cylinder knocking sound.

Once the engine deflagration occurs, it is extremely harmful, which causes deformation and damage to the moving parts such as engine cylinder walls, pistons, piston rings, valves, connecting rods and connecting rod bearings.

2. Pre-ignition of the engine refers to the phenomenon that the mixture has been ignited by the hot spot in the combustion chamber and burned in advance before the ignition of the spark plug. For example, incandescent carbon particles, protruding metal spikes, overheated spark plugs or red-hot exhaust valves can ignite the mixture prematurely.

The result of premature engine ignition is accompanied by a sudden popping sound with a drop in power and overheating of the engine. If the premature combustion of the engine is not severe, it may not cause much harm. But severe premature ignition leads to severe flare-ups.

Solutions for deflagration.

1. Fuel of the specified grade should be used.

2. Select the best ignition advance angle, adjust the ignition timing, and appropriately postpone the ignition advance angle.

3. Avoid overheating the engine and prevent the engine from working under heavy load for a long time as much as possible.

4. Keep the cooling system working normally, and remove the carbon deposits on the piston top and combustion chamber in time.

5. Use a spark plug of the appropriate type.

6. Correct operation and timely gear shifting, do not shift into the high-speed gear too early when the car starts, and shift into the low-speed gear in time when going uphill.

Both pre-ignition and deflagration are serious hazards caused by exhaust valves or carbon deposits in the combustion chamber, and are in a state of high temperature and red-hot temperature.

The inner capital is relatively large.

There are two maximum capacity differences:

1) Deflagration is spontaneous ignition on the surface, which is generated after the ignition of the spark plug and the combustion of the mixture. That is to say, peroxide is generated in the work stroke, so that the moment of spontaneous combustion lags behind the ignition rake angle. Pre-ignition is also when the surface is in a hot state, but it causes spontaneous combustion before the spark plug ignites.

Pre-ignition occurs in the compression stroke, and the pre-ignition angle is larger than that of ignition.

2) The metal striking sound produced by pre-ignition and deflagration is different. The metal striking sound produced by pre-ignition is dull. The metal striking sound from the deflagration is high-pitched.

3) the method of differentiation is: when the ignition is cut off, the engine is immediately shut down, indicating that the phenomenon of abnormal combustion at this time is deflagration; After turning off the ignition switch, the engine is still running, indicating that the phenomenon of abnormal combustion of the engine at this time is premature ignition.

In the process of gas combustion, the gas of the main combustion center generates pressure on the surroundings, and the mixture of the gas far away from the combustion center is burned in advance under the power of pressure, resulting in deflagration.

It is related to the gas distribution phase of the engine, and the engine has an ignition advance angle under different circumstances, and the actual gas burns earlier than the set ignition advance angle, which is early ignition.

The deflagration of the gasoline engine is that the spark plug is ignited at the time specified by the engine, and the combustion gas in the cylinder is burned. The diesel engine is not injected with fuel at the specified time. The correct combustion is 5 to 12 degrees before the piston reaches the cylinder top dead center (different for every engine).

Before that, it was premature ignition.