First, the engine power and its causes
(I) Automobiles use natural gas as fuel
A major problem in the use of natural gas vehicles is that the engine's power is significantly lower than when using gasoline. According to data, when using natural gas as a fuel, the car generally has to reduce its power by about 15%, and in some cases it drops even more. The result of the drop in power, on the one hand, leads to insufficient power when the vehicle is heavily loaded, climbs or accelerates, and on the other hand it leads to a relative increase in fuel consumption and increases in pollutant emissions.
(b) The decline in the power of natural gas vehicles is mainly due to the characteristics of the fuel itself and the structure of the engine.
In terms of fuel properties, gasoline is a liquid fuel, and natural gas is a gaseous fuel. When using gasoline, the volume of liquid gasoline is almost negligible compared with the intake volume, but when natural gas is used as the fuel, the volume of the fuel itself occupies a large proportion of the entire intake air, thus resulting in a decrease in the amount of air entering the cylinder. The coefficient decreases, causing the engine power to drop.
(C) In the engine construction, the main factor determining the engine power is the compression ratio of the engine.
The larger the compression ratio, the higher the thermal efficiency and the greater the effective power. At the same time, the greater the compression ratio, the greater the tendency of the engine to knock. Therefore, the engine compression ratio must also be compatible with the antiknock property of the fuel. The anti-knocking property of gasoline determines that the compression ratio of a gasoline engine cannot be too high, but the antiknock property of natural gas is very good, and it can be used to compress a relatively large engine, thereby increasing its power. The application of natural gas vehicles is still in its infancy, and the supply of natural gas is not as popular as gasoline. Under such circumstances, specially designed natural gas engine cars have not yet been fully promoted. Many of the natural gas vehicles currently in operation are dual-use fuel vehicles, either natural gas or gasoline. This type of dual-purpose fuel vehicle has little or no improvement in the compression ratio in order to meet the need for the use of gasoline. Therefore, the characteristics of high antiknock property of natural gas have not been fully utilized, resulting in a decrease in engine power.
Second, corrosion and early wear and its causes
When the car was fueled with natural gas, it was found that the components of the combustion chamber were corrosive, and even the crankshaft was corroded. Valves, piston rings, and cylinders were heavily worn. Compared with the use of gasoline, the automobile overhaul period was usually shortened by 1/3-1/2. This is another problem that natural gas vehicles face. The reason for the corrosion and early wear of natural gas vehicles is that natural gas contains trace amounts of sulfur compounds (hydrogen sulfide) that cause corrosion and wear on cylinders and cylinder walls, which reduces engine power, shortens the service life, and shortens the overhaul period of automobiles. legend:
Explanation: Trace sulfur compounds (hydrogen sulfide) cause engine corrosion
Third, improve the power of natural gas vehicle measures (a) increase the air-inflating factor
The decrease of the air-inflating coefficient is an important reason for the drop in the power of the natural gas vehicle. Theoretically speaking, increasing the air-inflating coefficient is a way to increase the power. However, the reduction of the air-inflating coefficient is determined by the nature of the natural gas itself. Obviously, this problem cannot be solved from the fuel side. The only solution is to adopt air intake pressurization measures. However, the intake pressure boost will undoubtedly increase the volume and quality of the engine, and there are certain difficulties in its implementation.
(B) appropriate increase in engine compression ratio
The octane number of natural gas is very high, and the antiknock property is very good. If natural gas is used directly on a gasoline engine, this advantage of natural gas cannot be fully utilized, and engine power can be increased. If the engine cylinder head is thinned and the compression ratio of the engine is increased, the power of the engine can be increased and the power loss can be partially compensated. This method is a method that people usually use. However, considering that most natural gas vehicles are dual-use fuel vehicles, the engine compression ratio cannot be increased too much, or knocking may occur if gasoline is used as fuel. Therefore, there is a limit to the improvement of the compression ratio and it should be determined according to the actual situation. For example, when a car originally using No. 70 gasoline is changed to a dual-use fuel car, the compression ratio can be increased to the compression ratio of No. 90 gasoline; when the original engine using No. 90 gasoline is changed to a dual-use fuel car, compression can be performed. Than to increase the use of 93 or 95 gasoline compression ratio. For a vehicle that runs on a fixed line like a city bus and has guaranteed natural gas supply, a single-fuel natural gas vehicle with a compression ratio suitable to the natural gas explosion resistance should be promoted, and the characteristics of high natural gas compression ratio should be fully utilized to improve the automobile engine. power.
(III) Use of Special Natural Gas Vehicle Engine Lubricants
Natural gas is a gaseous fuel, and no dilution of engine lubricating oil occurs during use. Therefore, a lower viscosity lubricating oil can be used, which can reduce the power loss caused by viscosity and improve the efficiency of the engine. At the same time, the engine oil for natural gas vehicles can effectively prevent the corrosion and wear of valve components such as valves and piston rings, and prevent the power loss caused by the cylinder pressure drop . On the CA6102 natural gas engine bench, the use of natural gas engine oil and the use of ESC30 Gasoline engine oils were subjected to comparative tests, external characteristics and load characteristics. The fuel used in the test was natural gas, and the fuel consumption was calculated as the volume of natural gas under standard conditions. Compared with the use of ESC30 gasoline engine oil, the use of natural gas engine oil can increase the engine's power and torque, reducing the fuel consumption rate of about 10%.
IV. Measures to reduce corrosion and wear (1) Natural gas desulfurization
As mentioned earlier, the root cause of corrosion and early wear of natural gas vehicles is due to the trace amount of hydrogen sulfide in natural gas. Therefore, desulfurization of natural gas is an important means to reduce corrosion and wear. However, desulfurization of natural gas makes it difficult to completely remove hydrogen sulfide. Therefore, the corrosion of natural gas to engines is difficult to completely avoid.
(b) Use of corrosion-resistant materials
The use of anti-sulfide corrosive metal materials to make engines is also an important measure to prevent corrosion. However, this method is only applicable to the manufacture of new engines, and it is powerless for existing engines.
(III) Use of Special Natural Gas Vehicle Engine Lubricants
The use of natural gas vehicle engine oil instead of currently used gasoline engine oil is an effective measure to prevent corrosion of natural gas vehicle engines. This method is not only simple and does not increase costs. Natural gas vehicle engine oils have a higher alkali number than gasoline engine oils and have a strong acid neutralization capacity. The 50,000 km driving test shows that natural gas-specific lubricating oil can effectively prevent corrosion of hydrogen sulfide, reduce engine wear, and prolong engine overhaul period by more than 1/2. At present, there are also some lubricant manufacturers in China that have conducted in-depth research on natural gas vehicle-specific lubricants. For example, the special-purpose engine oil for the Ernst CNG/gasoline dual-fuel engine developed and manufactured by Shaanxi General Petrochemical Co., Ltd. is aimed at a large number of The gasoline was converted to natural gas vehicles for R&D and production, and it obtained national patent technology in 2006, and achieved good social and economic benefits through the use of a large number of natural gas buses and rental cars.
V. Conclusion
1. The reason for the drop in the power of natural gas vehicles is due to the decrease of the air-intake coefficient and the relatively low engine compression;
2. The cause of early engine wear is due to trace amounts of sulfides in natural gas;
3, to improve the natural gas engine power measures are mainly air intake boost, increase engine compression ratio and the use of dedicated natural gas engine oil;
4. Ways to prevent corrosion and early wear include natural gas desulphurization, use of corrosion-resistant materials for the manufacture of engines and the use of dedicated natural gas engine oils;
5. The use of dedicated natural gas engine lubricating oils has a significant effect on increasing power and preventing engine corrosion and early wear, and is a simple, economical and effective measure.
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