Study on combustion and emission characteristics of a micro‐rotary cam internal combustion engine

In this article, the construction principle of rotary engine and sliding vane internal combustion engine is carefully analyzed, and the concept of micro‐rotary cam internal combustion engine is proposed by integrating and innovating on them. Overall design, theoretical analysis, and model making of miniature rotary cam internal combustion engine and its supporting system. The effects of different air intake modes and different ignition advance angles on the combustion and emission characteristics of internal combustion engines were studied. Through the study of the flow field, combustion and emission characteristics of small rotating internal combustion engines, it is found that the intake form has a great influence on the cylinder smoothness of rotating internal combustion engines. The vortex formed by the end cover inlet air in the middle of the combustion chamber can fully mix the fuel and air in the cylinder, and the mixture is evenly distributed in the combustion chamber to effectively promote the spread of flame. Compared with the surrounding air intake structure, the heat release should be increased by 4.3%, and the total amount of HC and CO generated was 26.8% and 15.7% less, respectively. By studying the turbulent kinetic energy, combustion heat release, peak temperature and pressure in the cylinder, fuel consumption rate and emission characteristics of small rotary internal combustion engine, it is found that when the ignition advance angle of the small rotating internal combustion engine is 5°, the peak pressure in the cylinder is increased by 2.3% compared with other schemes, the fuel consumption rate is high, and the combustion is more complete. In addition, in terms of emission characteristics, the amount of CO and HC generated when the ignition advance angle is 5° are reduced by 35% and 35.3%, respectively.


INTRODUCTION
2][3][4] Car companies achieve energy conservation and emission reduction by reducing emissions or developing new energy vehicles, but reducing emissions will inevitably sacrifice the power of the car. 5In the family of internal combustion engines, the traditional reciprocating internal combustion engine can no longer meet people's use requirements, and people urgently need an engine with higher thermal efficiency, more complete combustion effect and cleaner exhaust emissions. 6,7A large number of scholars continued to explore a variety of internal combustion engines, and the rotary internal combustion engine was born. 8Geo et al. 9 studied the combustion, performance and emission characteristics of low-grade alcohol (i.e., ethanol) and high-grade alcohol (i.e., benzyl alcohol) mixed gasoline.Vedagiri et al. 10 studied the performance, combustion, and emissions parameters of diesel engines powered by grapeseed oil biodiesel (GSBD).Ganesan et al. 11 studied the emission characteristics of engines using neem oil methyl ester (N100) and higher alcohols; Yuvarajan 12 reduced viscosity and other related problems associated with biodiesel by adding nonpolluting additives.Subramanian et al. 13 studied how hydrogen and oxygen (HHO gas) are produced together in an electrolyzer and fed into the engine intake manifold before the carburetor.Bhanu Teja et al. 14 did a study.This work briefs the ability of sterculia foetida methyl ester (SFME) as an alternate fuel in determining the engine characteristics.Muthiya et al. 15 conducted extensive experimental work to identify suitable solutions to control CO 2 emissions.Rotary engines are mainly divided into uniform rotation engine, differential rotary engine, and planetary transmission rotary engine. 16,17Among them, compared with the other two internal combustion engines, differential internal combustion engines are the most widely studied. 18,19Constant speed engines mainly have problems such as cooling, wear and so on. 20,21Triangle rotor internal combustion engine due to the special structure form is difficult to achieve a good sealing effect, the current triangle rotor internal combustion engine combustion chamber adopts linear sealing structure, but there are still internal combustion engine burning oil, poor air tightness and other defects, based on the current problems of the triangle rotor internal combustion engine, it is difficult to solve it well by scientific means. 22,23ased on the above problems, this article proposes a small rotating internal combustion engine, and the combustion and emission characteristics of small internal combustion engines are studied.The small rotary internal combustion engine is an improvement and innovation for the low efficiency of the reciprocating internal combustion engine and the easy wear and burning of the rotary engine.It is found that small rotating internal combustion engines have great advantages over reciprocating internal combustion engines in terms of fuel consumption rate and exhaust emissions.Moreover, this new type of power unit has a simple structure without too many transmission mechanisms, so it can save the loss of force in the transmission process, but also increase the utilization rate of fuel, and has good development prospects in machinery such as micro-small aircraft, because its light and convenient is also suitable for individual combat.

Overall structure of internal combustion engine
As shown in Figure 1A, a small rotating internal combustion engine is mainly composed of an intake system, an exhaust system, an ignition system, and an internal combustion engine body.Two spark plugs are distributed on both sides of the upper part of the cylinder block, the ignition system is composed of a control part, magnet, high-voltage battery pack, inductor and spark plug, the inductor is ignited by an induction magnet, the magnet is installed on the output shaft, and the output shaft rotates with the rotor and piston.The intake system is composed of a check valve, carburetor, and fuel tank, and the small rotating internal combustion engine has two intake systems distributed on the left and right sides of the end cap, and when the piston is running, the oil in the tank flows through the carburetor and mixes with air from the check valve to the cylinder block.The outer circumference of the internal combustion engine cylinder is distributed in the shape of a sheet, which can increase the heat dissipation area to achieve the effect of heat dissipation.The cylinder block of the internal combustion engine and the end covers at both ends are evenly distributed and fixed by 11 bolts, which can also play a sealing role while ensuring the safety of the internal combustion engine.The intermediate shaft and the rotor are connected with the rotor to move together, and a reversing device is installed on the side of the raised end cover, and the reversing device is connected to the output shaft to convert the left and right swing of the output shaft into rotation in the same direction.Figure 1B shows the assembly drawing of a small rotary internal combustion engine, the overall

How the internal combustion engine works
As shown in Figure 2, when the piston moves upwards counterclockwise, the inside of the cylinder block is divided into two chambers by the piston, and the left cavity produces a low-pressure environment due to the rapid counterclockwise rotation of the piston, when the pressure reaches a certain value, the check valve on the left side begins to open, and the left side begins to intake.The right cavity piston compresses the gas, so the pressure in the chamber increases until the spark plug ignites.At this time, the left gas begins to suck into the cylinder block, at this time the piston compresses the right gas, the spark plug sensor senses the position change of the piston, and when the piston compresses the right gas to reach the top dead center, it starts to control the ignition of the spark plug, and the combustible mixture in the right combustion chamber burns rapidly, and the expansion force generated by combustion pushes the piston clockwise.When the piston moves directly below, the high-pressure gas can break through the check valve of the exhaust port, and the exhaust gas generated by the combustion of the combustible mixture in the combustion chamber on the right is discharged from the exhaust port.The rotor runs clockwise to compress the combustible mixture of the left combustion chamber, and when the spark plug ignites when it reaches the left top dead center, the left combustion chamber begins to do work, so that repeated operation is the working principle of a small rotating internal combustion engine.

Meshing and boundary condition setting
The results of numerical simulations and calculation times are directly related to the scale of the mesh.According to the research experience of Junfa 24 and Pengfei, 25 it can be seen that the encryption scale of the grid and the basic grid scale are exponential: Based on the geometric scale of each computational domain of the small rotating internal combustion engine and the gradient changes of the physics in each computing domain during the operation of the internal combustion engine, the encryption level of each computing domain in this article is shown in Table 1.The rotating internal combustion engine mesh model shown in Figure 3 uses a smaller grid base size near the intake valves, and refines the mesh of the internal combustion engine model by combining adaptive encryption and fixed encryption in the computing basin.
The setting of boundary conditions directly affects the simulation results of numerical simulation.Pressure and solid wall temperature are generally used as boundary conditions in the simulation of internal combustion engines. 26Table 2 shows the specific boundary value settings utilized in the model.

F I G U R E 4
The average pressure in the cylinder under different grid sizes changes with the rotor rotation

Mesh agnostic validation
In order to ensure the accuracy of the simulated structure, the grid was verified independently of the structure.In this article, four combustion chamber body grid sizes are set, namely, 1, 2, 3 and 2 mm + grid adaptive encryption, the speed of the internal combustion engine is set to 4600 r/min, the inlet pressure is 0.35 bar, and the working process of the small rotating internal combustion engine is numerically simulated.The change law of the average pressure in the cylinder with the rotor rotation under different grid sizes Figure 4 shows the change law of the average pressure in the cylinder with the rotor rotation under different grid sizes, the cylinder pressure with a grid size of 3 mm in the figure is not much different from other grid sizes, and the range of changes in the cylinder pressure of the internal combustion engine is constantly shrinking as the grid size becomes smaller.From the figure, we can see that the pressure curve in the cylinder with a grid size of 1 mm and a grid size of 2 mm + grid size is close to coincide, which proves that the grid independence has been verified.In order to improve the efficiency of simulation, the combustion chamber body mesh size used in this article is 2 mm + mesh adaptive encryption.

Effect of air intake structure on combustion characteristics of internal combustion engines
The intake structure of the rotating internal combustion engine is mainly divided into two forms: end cover intake and peripheral air intake, as shown in Figure 5, schematic diagram of different intake structures.Among them, Figure 5A represents the end cover air intake, the intake structure adopts the end cover punching, the combustible mixture enters the inside of the cylinder block from the end cover, the air flow direction is parallel to the rotor, the advantage of the structure The end cap intake has a schematic diagram of the perimeter air intake structure.(A) End cap air intake; (B) perimeter air intake is that the structure is simple and convenient to process and manufacture, and at the same time will not damage the structure and strength of the internal combustion engine cylinder block, but the end cover structure is compact and can provide the installation of the air intake pipe position is not much.Figure 5B represents the peripheral intake structure, the use of cylinder block punching, combustible mixture input from the cylinder block to the inside of the cylinder block, the direction of air flow is perpendicular to the rotor, the use of peripheral intake will also have its disadvantage, because it is input from the internal combustion engine cylinder block, so it is necessary to punch holes in the internal combustion engine cylinder block, which will affect the strength of the cylinder block.
The intake structure is also an important factor affecting the performance of the internal combustion engine, and many scholars at home and abroad have optimized the intake structure to improve the performance of the internal combustion engine and reduce the emissions of the internal combustion engine. 27In order to select the best intake structure, the influence of different intake structures on the flow field, combustion and emission characteristics of small rotating internal combustion engine cylinders is compared and analyzed, and the optimal internal combustion engine intake structure is finally selected by analyzing and studying the internal combustion engine flow field, combustion and emission aspects. 28,29As shown in Table 3, it is the specific parameters such as pressure and temperature of the intake air at different intake structures.The operating conditions of the small rotating internal combustion engine are set to: speed 3000 r/min, intake pressure 0.35 bar, equivalent ratio Φ = 0.8, The air-fuel ratio is 14.7.

Cumulative air intake
Figure 6 shows the comparison chart of cumulative air intake under different intake structures, and the black in the figure represents the end cover intake structure.Red represents the perimeter air intake structure.From the figure, we can see that the final intake volume of the end cover intake structure is 0.60 g, and the final intake volume of the peripheral air intake structure is 0.49 g.This means that the air intake volume when using the end cover structure is 22.4% more than when using the peripheral air intake.It can be seen that according to the analysis of cumulative air intake, the structure of end cap air intake is better than the structure of peripheral air intake.In order to explore the volumetric efficiency of different intake modes, the Figure 7 below shows the variation law of volumetric efficiency of different intake modes.From the figure, it can be seen that the volumetric efficiency of the end cover intake air is 0.8, and the volumetric efficiency of the peripheral intake air is 0.85.Compared to the end cover intake,

F I G U R E 7
Volumetric efficiency for different intake methods the volumetric efficiency of the perimeter intake is improved by 5.88%.It can be seen that the volumetric efficiency of the peripheral air intake is higher than that of the end cover air intake.

In-cylinder flow field analysis
Figure 8 shows the variation law of the inlet air field in the cylinder of the end cover intake air and the surrounding intake structure.The end cover intake structure is used to initially form vortex A in the middle of combustion when the piston has just begun to compress the gas in the early stage of intake, and the vortex A gradually develops in the middle of the intake period, while the vortex B is initially formed in the position of the inner wall of the combustion chamber, and the vortex A reaches the highest intensity in the late stage of air intake, and the position is gradually moved up from the middle position of the combustion chamber.The appearance and movement of vortex A and turbine B promote the full mixing of gases in various areas of the combustion chamber, providing favorable conditions for full combustion.Using the peripheral intake structure, vortex C is formed in the middle of the combustion chamber at the beginning of the air intake, and the vortex C gradually moves down in the middle of the intake and disappears in the late intake period.It can The law of change of the intake air field in the cylinder F I G U R E 9 Pressure change curves in cylinders with different intake structures be seen that compared with the surrounding air intake structure, the end cover intake structure is used to fully mix the gas in the cylinder during air intake, which provides favorable conditions for full combustion.

In-cylinder pressure analysis
Figure 9 shows the pressure curve in the cylinder of the two schemes, in which the pressure in the cylinder changes with the change of the rotation angle, and the abscissa represents the angle ordinate representing the pressure in the cylinder.The intake structure indicated by the red curve is the end cover intake, and the intake structure represented by the black curve is the peripheral air intake.The speed of the mixture entering the cylinder from the air duct is the same, so from the figure we can see that the pressure peak of the average pressure in the cylinder appears at the same corner, and the high-pressure mixture enters the combustion chamber and instantly fills the entire combustion chamber, at this time the pressure will be reduced, and the pressure in the cylinder will gradually increase as the rotor rotates to begin to compress the mixture.When the rotary piston compresses the gas, a high-pressure environment is formed, and the gas is active in the high-pressure environment and fully mixed, providing compression ignition conditions for the ignition of the spark plug. 30The spark plug ignites the mixture, the flame combustion instantly spreads to the entire combustion chamber, the gas combustion expands to do work, and the internal combustion engine has a peak of average pressure in the cylinder.
After that, the pressure in the cylinder showed a downward trend, which was due to the gas combustion expansion to push the shaft to do work, and the combustion chamber area gradually expanded with the rotation of the rotating piston, so that the pressure in the cylinder gradually decreased.From the figure, we can see that the peak pressure of the end cover intake structure is obviously higher than the peak pressure of the surrounding air intake structure, indicating that the pressure of the end cover intake structure is higher than that of the surrounding air intake structure in the work stage, and it can be seen that the peak pressure in the cylinder is high when the end cover air intake structure is high, and the work effect is good.

Analysis of flame propagation processes
Figure 10 shows the flame propagation process during combustion in the cylinder of a rotating internal combustion engine under two intake forms, and the flame propagation speed is determined by the turbulent flame propagation speed and the expansion velocity of the burned zone. 31From the figure, we can see that when the rotation angle is 50 • , the spark plug has ignited the mixture and generated a flame.The difference is that scheme 1 generates a flame mass in the middle part of the cylinder, that is, the lower part of the spark plug.Option 2 has two combustion centers in the cylinder, which speeds up the propagation of turbulent flames, thereby speeding up the spread and propagation of the flames.As the area of the burned area of the mixture combustion gradually increases, the spread speed of the flame to the rotation direction of the rotating piston is significantly faster than the spreading speed of the rotating piston in the opposite direction, which is due to the formation of a mainstream flow field in the cylinder with the same direction of movement as the rotating piston when the internal combustion engine is burning, and the flame spreading speed consistent with the rotation direction of the rotating piston is significantly higher than the spread speed in the opposite direction under the influence of the mainstream flow field.When the rotor angle is 56 • , the flame begins to spread around, and it can be seen from the figure that the diffusion range of the flame of scheme 2 is significantly larger than the flame diffusion range of scheme 1, which shows that the flame propagation speed is faster than that of the peripheral air intake structure of scheme 1 when the air intake structure of scheme 2 end cover is adopted.When the rotor angle is 62 • , the flame has basically spread to this combustion chamber, and the flame combustion is near the end when the rotor angle is 72 • .The comprehensive appeal adopts that the flame propagation speed of the perimeter intake structure is faster than that of the end cover intake structure.

Exothermic analysis
Figure 11 shows the heat release curves for the two schemes.It can be seen from the figure that the combustion start moment of the two schemes is the same, when the rotor angle is close to 50 • , the mixture in the internal combustion Flame propagation process of different intake structures

F I G U R E 11
Heat release curve of flame propagation process of different intake structures engine cylinder begins to burn and release heat.The overall heat release of the end cover intake of scheme 1 at the rotor angle of about 98 • remains stable, indicating that the combustion is at the end at this time, and it can be seen from the figure that the combustion time of the internal combustion engine cylinder around the intake of scheme 2 is slightly earlier than that of scheme 1, which indicates that the combustion speed of the surrounding intake air of scheme 2 is faster than that of the end cover intake, but the heat release of the end cover intake structure is increased by 4.3% relative to the heat release of the surrounding air intake structure, which shows that the end cover intake air combustion is more complete and the combustion efficiency is higher.In addition, when the rotor angle is about 60 • , the heat release reaches 600 J (the center of gravity of the heat dissipation), and it can be seen from the theoretical cycle that most of the heat release is at the bottom dead center, which will not affect the thermal efficiency.Based on the above analysis of turbulence intensity, it can be seen that enhancing the turbulence intensity in the internal combustion cylinder can make the mixture fully mixed, the combustion is more complete, and the heat release during combustion of the internal combustion engine is higher, which can further improve the performance of the engine and enhance the practicality of small rotating internal combustion engine in the fields of small and medium-sized aircraft, individual combat and low-power generation.

Effect of ignition advance angle on combustion characteristics of internal combustion engines
The influence of different ignition advance angles on the performance of rotary engine was studied, and the smaller the ignition advance angle, the more conducive it is to the rotary piston compression of the internal combustion engine, and the mixture is rapidly burned and expanded under the condition of high pressure and full mixing.However, if the ignition advance angle is too small, the space of the combustion chamber will be too small, which will affect the normal progress of ignition, and in severe cases, it may also lead to the ignition failure of the internal combustion engine spark plug.Table 4 represents the parameters set for nozzles in the model.
Figure 12 shows the spray setting of a small rotating internal combustion engine.First set the parameters of the nozzle, and then build six injection vectors in the software to obtain six intake injection paths.The specific steps are: first create the origin and the landing point of the six nozzles in the global coordinates, then create six oil lines based on the origin and landing point, and finally rotate the six oil lines as a whole according to the nozzle installation angle, and the direction vector of the six oil lines is the nozzle spray direction.
In order to find out the optimal ignition advance angle, the range of ignition advance angle is set to 5 • to 13 • at intervals of 2 • , respectively, provided that other conditions remain consistent.The effects of ignition advance angle on the power, combustion and heat release of mixed mixture in the cylinder, heat release rate, average pressure peak, average temperature peak, and high-temperature zone range in the cylinder were studied, and the optimal ignition advance angle was found to provide a theoretical basis for the subsequent research and manufacture of internal combustion engines.In order to ensure the accuracy of the calculation results, set the working conditions to the same as in the previous section.The speed of the small rotary engine is set to 3000 r/min, the intake pressure is 1.01 bar, and the equivalent ratio is Φ = 0.8.The model parameters and boundary conditions remain the same as the model parameters and boundary conditions in the previous section.Table 5 shows the specific simulation calculation scheme.

4.2.1
In-cylinder flow field analysis Figure 14 shows the flow field in the cylinder after the intake compression.In the late stage of compression, when the ignition advance angle is 5 • , vortex B is formed in the middle of the right side of the combustion chamber, and the wide range of turbine B affects the flow field of the entire combustion chamber.When the ignition advance angle is 7 • , turbine D is formed in the middle of the right side of the combustion chamber, which is weaker than that of turbine B. When the ignition advance angle is 9 • , a vortex E is formed in the middle of the combustion chamber.When the ignition advance angle is 11 • , a vortex G is formed on the left side of the combustion chamber near the wall of the cylinder body.At an ignition advance angle of 13 • , vortex j and vortex K are formed in the middle of the combustion chamber.With the operation of the rotor to compress the gas, the flow field in the cylinder is greatly affected by the operation of the rotor, and in general, the vorticity of vortex B is greater than that of other ignition advance angles.

Analysis of turbulent kinetic energy in the cylinder
Figure 15 shows the turbulent kinetic energy distribution.It can be seen from the figure that the turbulent kinetic energy is 12.3 m 2 /s 2 when the ignition advance angle is 5 • in the late intake period, and the maximum turbulent kinetic energy is mainly concentrated in the lower right side of the combustion chamber.When the fire advance angle is 7 • , the turbulent kinetic energy is 9.6 m 2 /s 2 , and the maximum turbulent kinetic energy is mainly concentrated in the lower right side of the combustion chamber.When the fire advance angle is 9 • , the turbulent kinetic energy is 8.6 m 2 /s 2 , and the maximum turbulent kinetic energy is mainly concentrated in the lower right side of the combustion chamber.When the fire advance angle is 11 • , the turbulent kinetic energy is 8.3 m 2 /s 2 , and the maximum turbulent kinetic energy is mainly concentrated in the lower right side of the combustion chamber.When the fire advance angle is 13 • , the turbulent kinetic energy is 8.0 m 2 /s 2 , and the maximum turbulent kinetic energy is mainly concentrated in the lower right side of the combustion chamber.With the operation of the rotor, the air flow in the cylinder is less and less affected by the intake airflow, and it is more affected by the rotor operation.In the later stage of air intake, with the increase of ignition advance angle, the turbulent kinetic energy is smaller, compared with the fire advance angle of 13 • , the turbulent kinetic energy is increased by 34.9% when the ignition advance angle is 5 • .It can be seen that when the ignition advance angle is 5 • , the turbulent kinetic energy is the highest affected by the rotor operation, which is conducive to the full mixing of the gas in the cylinder and provides favorable conditions for the full combustion of the gas.

Exothermic analysis
Figure 16 shows the change curve of the accumulated heat release with the rotation angle of the rotor of the internal combustion engine, which can clearly react to the heat release process of the rotating internal combustion engine.The abscissa in the figure is the angle of the rotor of the internal combustion engine, and the ordinate represents the heat dissipation of the internal combustion engine.From the figure, we can see that the heat release curve is steeper when the ignition advance angle is 5 • , which indicates that the heat release rate is high.In addition, when the ignition advance angle is 5 • , the heat release reaches the peak first.This is because with the rotation of the internal combustion engine shaft, the internal combustion engine enters a period of rapid combustion, the combustion speed at this time is determined by the flow field in the cylinder and the chemical reaction rate of the fuel, and the high turbulent kinetic energy and high-temperature environment are conducive to accelerating the combustion speed of the mixture in the internal combustion engine and shortening the combustion cycle of the mixture.As can be seen from the figure, the heat release rate of the internal combustion engine mixture is highest when the ignition advance angle of the internal combustion engine is 5 • .From the previous analysis, it can be seen that when the ignition advance angle of the internal combustion engine is 5 • , the turbulent kinetic energy of the cylinder mixture is the highest, and the charge coefficient of the internal combustion engine is very high at this time, which improves the collision probability between the molecules of the mixture under the same volume, which is conducive to the full mixing of the mixture, and the higher turbulent kinetic energy and the high-temperature environment in the cylinder provide conditions for the rapid complete chemical reaction of the mixture and release higher heat.

4.2.4
Cylinder temperature and cylinder pressure analysis Figure 17 shows the variation of the temperature in the cylinder between different ignition advance angles and the rotation angle corresponding to the peak temperature.It can be seen from the figure that the peak temperature in the cylinder is the highest when the ignition advance angle is 5 • , which can reach 1800 K, which is 8.4% higher than the peak temperature at the ignition advance angle of 13 • .It can be seen from the figure that as the ignition advance angle decreases, the temperature peak in the cylinder is higher and higher, which is because the smaller the engine ignition advance angle, the greater the turbulent kinetic energy, and the large turbulent kinetic energy can be used to accelerate the propagation speed of the flame and promote the combustion of the mixture to improve the combustion chamber.The higher the peak temperature in the cylinder of the internal combustion engine, the faster the combustion rate of the mixture, and the completion of the heat release of the mixture makes the temperature in the cylinder quickly reach the peak and shorten the combustion cycle.
Figure 18 shows the change curve of the pressure in the cylinder of an internal combustion engine with the angle of rotation of the shaft.The abscissa represents the angle of the engine rotor, and the vertical coordinate represents the pressure in the engine cylinder.It can be seen from the figure that the peak pressure in the cylinder when the ignition advance angle of the internal combustion engine is 5 • is 1.05 MPa, and the peak pressure in the cylinder is 2.4% higher The main reason for this phenomenon is: the smaller the engine ignition advance angle, the greater the turbulent kinetic energy, and the greater the turbulent kinetic energy can accelerate the propagation of the flame, which causes the peak value when the engine ignition advance angle is 5 • slightly forward.The ignition angle of the internal combustion engine is small, and the ignition time of the internal combustion engine is behind, which is conducive to the rotary piston compressing the mixed gas, and the mixture is ignited under the condition of high pressure full mixing, rapid combustion expansion does work to promote the rotary piston to rotate, at this time the pressure in the cylinder rises sharply to reach the pressure peak.As the combustion gas expands, the work pushes the rotary piston to rotate, and the space of the combustion chamber gradually increases, and the pressure in the internal combustion engine cylinder is slowly decreasing.

4.2.5
Fuel consumption rate analysis  , the mass fraction of the intake fuel is very high, but as the combustion progresses, it can be seen from the figure that a part of IC8H18 remains after the combustion is over, which indicates that the combustion is incomplete.On the whole, the IC8H18 remaining after combustion is the least when the ignition advance angle is 5 • , which is 76.9% less than the remaining IC8H18 when the ignition advance angle is 7 • , and it can be seen that the combustion is complete and the combustion efficiency is high when the ignition advance angle is 5 • .

The intake structure analyzes the generation law of HC and CO in the cylinder
Figure 20 shows the CO and HC mass fractions.Compared with the two different intake structures, the CO mass fraction produced by the end cover inlet air is 0.032%, which is lower than the CO mass fraction of the peripheral intake air by 15.7%, which is due to the rapid combustion of the combustible mixture in the combustion chamber when the end cover inlet air is used to release a large amount of heat, and the high-temperature environment in the cylinder promotes the conversion of CO into CO 2 , so that the CO mass fraction produced when the end cover inlet structure is used is less.Similarly, the HC mass fraction produced by the end cover air intake structure is 0.3%, and the HC mass fraction generated by the peripheral air intake structure is 0.41%, which shows that the HC mass fraction produced when the end cover air intake is used is 26.8% lower, the combustion heat release is high, and the flame spreads to the cylinder body wall, which improves the combustion efficiency and produces less HC.

The intake structure analyzes the NO X generation law in the cylinder
It can be seen from the Figure 21 that as the angle of the shaft increases, the temperature in the cylinder is constantly rising, which is due to the acceleration of the flame propagation speed in the cylinder, which improves the combustion efficiency and thus increases the temperature in the cylinder.Since the generation of NO X during combustion of the internal combustion engine is affected by the temperature in the cylinder, the magnitude of the NO X generation curve is similar to the temperature curve in the cylinder of the internal combustion engine.From the figure, we can see that the NO X production volume begins to rise sharply when the rotor angle is 50 • , and the NO X production begins to gradually decrease as the combustion in the cylinder proceeds until the rotor angle is 80 • .The mass fraction of NO X produced by the peripheral intake air at the combustion time is 71% lower than that of the end cover intake structure, which is because the temperature in the cylinder is higher than the peripheral intake when the end cover intake structure is adopted, which shows that the use of peripheral intake air has certain advantages in reducing NO X .

Ignition advance angle analysis of HC and CO generation law in cylinder
Figure 22 shows a CO mass fraction plot.The generation of CO is mainly due to the incomplete combustion of the combustible mixture caused by the local lack of oxygen in the cylinder during combustion, and the fuel is not completely mixed with air when it enters the internal combustion engine cylinder, so a part of the fuel lacks oxygen during combustion to produce CO.It can be seen from the figure that when the ignition advance angle of the internal combustion engine is 5 • , the CO mass fraction produced is 0.033%, and the CO mass fraction produced is the lowest.The mass fraction of CO generated by the ignition advance angle of the internal combustion engine is 7 • and the mass fraction of CO generated in the cylinder when the ignition advance angle is 9 • remains about 0.036%.The main reasons for this phenomenon are: when the ignition advance angle is 5 • , the piston compresses the gas to increase the pressure in the cylinder, the gas is fully mixed with high activity in a high-pressure environment, and the total amount of CO produced by combustion is minimal.Gasoline mixes with air at ignition advance angles of 11 • and 13 • the most effective, so the amount of CO produced is higher than that of several other solutions.Compared to an ignition advance angle of 11 • , the mass fraction of CO produced with an ignition advance angle of 5 • can be reduced by 35%.
Figure 23 shows the HC mass fraction versus rotation angle.It can be seen from the figure that the HC mass fraction produced when the ignition advance angle is 11 • , which is because the flame cannot be transmitted to the wall in time,  , the HC mass fraction to be reduced is 35.3% lower, it can be seen that the flame propagated to the cylinder wall of the internal combustion engine in time when the ignition advance angle is 5 • , so that the combustible materials attached to the cylinder wall burn, effectively reducing the emission of HC.

Analysis of NO X generation law in cylinder with ignition advance angle
The main reasons for the production of NO X gas in internal combustion engines are: air-fuel ratio, cylinder temperature, and oxygen concentration.Figure 24 shows the NO X emission curve in the internal combustion engine as a function of rotation, the abscissa represents the angle of the internal combustion engine rotor, and the vertical coordinate represents the NO X emissions.It can be seen from the figure that the mass fraction of NO X in the internal combustion engine will gradually increase after an angle of 50 • , and NO X emissions will reach a peak at an angle of about 80 • , and then gradually decrease.The reasons for this phenomenon are mainly caused by: the spark plug has just ignited when the angle is 48 • , and the flame is in an early stage of development, when the distribution range of the flame in the cylinder is not very

F I G U R E 1
Internal structure diagram and assembly drawing of small rotating internal combustion engine.(A) Diagram of the internal structure of a small rotating internal combustion engine; (B) assembly drawing of a small rotating internal combustion engine F I G U R E 2 Diagram of the working principle of the internal combustion engine length of the internal combustion engine is 160 mm, the overall height is 97 mm, the cylinder diameter of the main part is 128 mm, and the width of the cylinder block is 25 mm.

cylinder 2 Near the spark plug 5 Speed and temperature adaptation 3 F I G U R E 3
Schematic diagram of rotating internal combustion engine mesh model with spray encryption.(A) Rotate the internal combustion engine mesh model; (B) spray encryption schematic SchemeIgnition advance angle Rotate speed (r/min) Equivalent ratio ()

Figure 13
Figure13shows the in-cylinder flow field with different ignition advance angles in the early stage of intake compression.It can be seen from the figure that when the ignition advance angle of 5 • in the early stage of intake air compression is

F I G U R E 14
Flow field in the cylinder after intake compression F I G U R E 15 Turbulent kinetic energy distribution map

F I G U R E 17
Temperature change in the cylinder between different ignition advance angles and rotation angles corresponding to peak temperatures F I G U R E 18 The change curve of the pressure in the cylinder with the angle of rotation of the shaft than that of other schemes.The internal pressure in the cylinder reaches peak first when the ignition advance angle of the internal combustion engine is 5 • , followed by the ignition advance of 7 • and the ignition advance angle of 9 • .It can be seen from the figure that as the ignition advance angle increases, the peak time of the internal combustion engine occurs later in the cylinder pressure.

Figure 19
Figure19shows the change of fuel mass fraction with rotation angle.In the figure, the content of IC8H18 is the highest when the ignition advance angle is 5 • , which indicates that the mass fraction of the intake fuel is the highest when the

F I G U R E 20
CO and HC mass fractions F I G U R E 21 NO X mass fractions

F
I G U R E 22 CO mass fractions F I G U R E 23 HC mass fractions resulting in the cylinder wall temperature of the internal combustion engine is too low, and some of the combustible materials attached to the cylinder wall are discharged from the internal combustion engine with the exhaust gas without combustion.An ignition advance angle of 7 • and an ignition advance angle of 9 • produce similar HC mass fractions.The HC mass fraction produced when the ignition advance angle is 5 • is the lowest, compared with the ignition advance angle of 11 Different intake structure parameters TA B L E 3 F I G U R E 6 Comparison chart of cumulative air intake under different intake structures