Analysis and transformation of carbon deposit in engine combustion

First, the causes of coke formation in fuel system

Some incorrect operations in daily operation and maintenance will lead to the rapid formation of coke, which can be summarized as follows: the engine often runs for a short time; Long-term driving at low temperature and low speed; Working at high temperature, high speed and overload for a long time; The engine intake valve is poorly sealed; Often run in dusty places; Low grade gasoline, engine knock; Gasoline contains a lot of water and gum.

The above situation can be attributed to two reasons: one is related to the engine operating conditions, such as the engine is often overloaded or running for a short time; The other is related to external conditions, such as poor fuel quality or poor working environment.

The formation of carbon deposit is analyzed according to the following two reasons.

The operating conditions and related conditions of the first engine are mainly because when the engine is overloaded, the oil seal of the engine intake valve is poor, and the air-fuel ratio cannot be guaranteed to be stable when the engine runs at low temperature or high temperature at high speed and low speed.

14.7 In the vicinity of the combustion chamber, the mixing of combustion gases cannot be guaranteed, resulting in some unburned fuel and lubricating oil infiltrating into the mixed combustion chamber. However, in the parts with low engine temperature, such as piston crown, fuel injector, spark plug and throttle valve, it gradually solidifies into solid interior, and coke will be formed through long-term accumulation.

Second, it is related to the external environment of the engine, such as poor fuel quality or poor working environment. In the case of poor fuel quality, it is actually very similar to the first case mentioned above. Because the air-fuel ratio is calculated according to the volume ratio of air to fuel, if the fuel quality is poor, the volume of fuel actually burned will decrease under the condition of the same volume of fuel entering the combustion chamber, which is equivalent to increasing the air-fuel ratio. At the same time, impurities, colloid, dust and silicide in the air are oxidized in the combustion chamber, which will also form the carbon deposition phenomenon of the engine after long-term accumulation.

Second, the composition and elements of carbon deposit

Carbon deposits are dense, loose and soft, and their composition varies with engine working conditions, fuel and the nature of impurities in lubricating oil entering the combustion chamber. It is found that the components of carbon deposition are: carbonaceous deposits generated by the combustion of fuel and lubricating oil; Lead compounds produced by foaming agent (tetraethyl lead) in gasoline; Fuel combustion of sulfur and metal forming salts; Metal oxides formed by combustion of lubricant additives; Air carries dust, sand, etc. Silicide; Formation and compounds of metal wear debris of engine parts.