Research on carbon deposition in automotive fuel injectors

The formation of the intake valve carbon deposit has many aspects of the formation of the intake valve carbon deposit, in addition to its own structural effects, the first engine operating parameters, such as engine speed and load, intake port geometry and injector position And parameters, coolant temperature, intake air temperature, air-fuel ratio, compression ratio, ignition advance angle, etc. all have a certain correlation with the formation of intake valve carbon deposit, followed by fuel quality, fuel additives, and oil formation on carbon deposition. In addition, engine parameters, such as oil permeability, crankcase ventilation, valve temperature, and EGR rate, also affect the formation of carbon deposits.

The temperature is one of the most important factors that determine the formation of carbon deposits. The difference in carbon formation in different parts of the intake valve is mainly caused by temperature. The composition of carbon deposits is related to the temperature. The composition of carbon deposits at different temperatures will be different, and at the same time, the shape of carbon deposits and the position on the intake valve will be different. Inlet valve deposit is affected by many factors, the most important external cause is temperature.

The Englebent Institute at the Technical University of Karlsruhe, Germany, studied the evaporation conditions of the fuel at the intake valve and the associated carbon deposition mechanism. The oil droplet evaporation process of the hydrocarbon mixture on the hot surface was experimentally studied under the thermal conditions of the intake valve. It was concluded that coking occurs only when the valve temperature exceeds 180°C, and that the chemical coking reaction becomes slower at lower temperatures. On the other hand, at very high valve temperatures, when the Leidenfrost temperature is exceeded (Leidenfrost), oil film evaporation occurs on the hot air valve, forming a fuel vapor layer, and the fuel oil droplets are suspended in the fuel vapor layer. Above, heat transfer is hindered, the temperature of the fuel oil droplets does not rise above the boiling point, and carbon deposition does not occur at this time.

Yasuo Esaki designed a very effective and accurate device to simulate the formation of carbon deposits at intake valves at different temperatures. The result is shown as 3: The intake valve temperature affects the position and shape of the carbon deposit. The most important intake valve temperature range for carbon deposition is 200350°C. Almost all engine oils can flow at low intake valve temperatures and evaporate at high intake valve temperatures, leaving a small portion of the oil converted to carbon deposits. When the intake valve temperature is very high, the carbon deposit on the curved surface will decrease and move up along the valve stem.

The effect of gasoline and its additives on carbon deposition is very complex. It is not only the most important source of carbon deposition, but also has a certain dissolution effect on carbon deposition. In addition, it also acts as a cleaning agent for the cooling and flushing of intake valves. The main components of gasoline are olefins, aromatic hydrocarbons, and saturated hydrocarbons. Due to the thermal instability of olefins, olefins are oxidized and form a gum, which is the main component of the intake valve carbon deposit. The high content of olefins in gasoline makes it easy to form carbon deposits in the engine intake system. Olefin is mainly a product of catalytic cracking of crude oil. In China, due to technical and technological constraints, catalytic cracking is the main process for deep processing of crude oil in China. As a result, the olefin content is too high (up to 35% or 40%), while the United States, Japan, etc. National gasoline olefins content is generally 13% 20%. China National Petroleum Corporation Lanzhou Research and Development Center utilizes imported air system carbon deposition (ISD) simulation test equipment imported from the United States to study the effect of olefins and diolefin content on cleanliness performance. . Japanese researchers use the Toyota 1G-FE engine for intake valve carbon deposition tests. The analysis of the results demonstrated that the olefin content has a very large impact on the IVD. Increasing the olefin content in the gasoline significantly increases the amount of carbon in the intake valve.

CONCLUSIONS AND RECOMMENDATIONS (1) The intake valve carbon deposits mainly come from gasoline. The higher olefin content of gasoline makes it easier to produce carbon at the intake valve. Proper mixing and leakage of high viscosity oils have a certain inhibitory effect on the formation of intake valve carbon deposits. The intake valve temperature is the most important external cause of carbon deposition.

(2) There are many factors that form the carbon deposit of the intake valve. In addition to the above factors, the structure of the engine itself and the operating parameters of the engine also have a certain correlation with the formation of the carbon deposit in the intake valve. In addition, the engine parameters such as crankcase ventilation, EGR Rates, etc., also affect the generation of carbon deposits to some extent.