What's with the car knocking at the door?

Carbon deposit is a kind of colloidal carbon that collects on engine parts such as valve, intake branch pipe and fuel nozzle. When the engine is working, some components in gasoline will condense into colloidal carbon, and the condensed colloidal carbon will accumulate continuously, which will affect the normal work of the engine precision management system.

The main causes of abnormal engine knock are as follows:

First, the ignition angle is too early: in order to make the piston gain power immediately after the compression top dead center ends and enter the power stroke, it is usually ignited in advance before the piston reaches the top dead center (because it takes some time from ignition to complete combustion). But premature ignition will make most of the oil and gas burn while the piston is still in the compression stroke. At this time, unburned oil and gas will spontaneously ignite under great pressure, resulting in knocking.

Second, the engine has too much carbon deposit: too much carbon deposit in the combustion chamber will not only increase the compression ratio (produce high pressure), but also produce high-temperature hot spots on the surface of carbon deposit, which will knock the engine.

Third, the engine temperature is too high: the engine temperature is too high in a too hot environment, or the engine cooling water circulation is not good, which will cause the engine to knock at high temperature.

4. Incorrect air-fuel ratio: If the air-fuel ratio is too thin, the combustion temperature will increase, and if the combustion temperature increases, the engine temperature will increase. Of course, it is easy to knock.

Verb (abbreviation for verb) The octane number of fuel is too low: Octane number is an indicator of the antiknock performance of fuel. The higher the octane number, the stronger the antiknock performance. The engine with high compression ratio has high combustion chamber pressure, and it is easy to knock if the fuel with low antiknock property is used.

Commonly used methods are: disassembly and washing, bottle washing and fuel additives.

1, disassembly and cleaning

This method is very direct and rude, but it is usually sent to 4s stores. Disassembly of the engine is complicated. No matter what parts are disassembled every time, their performance will be more or less affected. Need to hire a professional master to disassemble. Dismantling and washing can directly see the carbon deposit in the engine, and the cleaning will be cleaner. But the cost will be higher and technology will be needed.

2, infusion bag or infusion bottle cleaning

This method is also quite common. When the cleaning agent is discharged into the air inlet, the carbon deposit is diluted and softened into slurry, and then burned and discharged from the cylinder. General cleaning objects include air intake, throttle valve, intake valve, oil nozzle, cylinder interior and so on. , but the effect is not as obvious as unpacking and washing.

3. Fuel additives

One reason for carbon deposition is that the fuel is not completely burned and adheres to various parts of the engine, and carbon deposition is formed over time. The main function of additives is to drill into the pores of carbon deposits with strong surface activity, destroy its structure, gradually dissolve these carbon deposits from the metal surface, then burn them with fuel at high temperature, and then discharge them through waste gas. Effective fuel additives, such as PNF stock solution, are non-corrosive, can clean the whole oil circuit, impurities in the oil tank, moisture in the oil tank, high-pressure oil pump, built-in gasoline filter element, nozzle, piston top, intake valve and exhaust valve, and will not block the three components, so the safety is relatively high.