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Comparison between CNG and LPG applications
Sep 15, 2017

(CNGV) liquefied petroleum gas vehicle (LPG; / CNG switch, natural gas pressure after decompression regulator, natural; power source, power steering system, navigation system, air conditioner, lighting and; (CNGV) liquefied petroleum gas vehicle (LPGV) compressed natural gas (CNG) liquefaction (CNG) liquefied petroleum gas (LPGV) compressed natural gas (CNG) liquefied petroleum gas (LPGV) compressed natural gas (CNG) liquefied petroleum gas (CNG) The main advantages of liquefied petroleum gas (LPG) CNG and LPG are as follows: 

1) Natural gas and liquefied petroleum gas are gaseous at room temperature and are easily mixed with air to form a homogeneous combustible mixture. Combustion is complete and can greatly reduce CO, HC And the emission of particulates. In addition, the natural and liquefied petroleum gas flame temperature is low, so the NOx emissions are correspondingly reduced .

2) natural gas octane number of up to 130, liquefied petroleum gas octane number is also about 100, With natural gas or liquefied petroleum gas can improve the engine compression ratio, resulting in a higher engine thermal efficiency.

 3) cold start and low temperature operation performance is good, no need to enrich the mixture during warm up.

 4) wide combustion boundaries, lean characteristics of superior. Burning a lean mixture can reduce NOx generation and improve fuel economy. 

5) do not dilute the oil, you can extend the oil replacement cycle and engine life. LNG and LPG shortcomings are: 

1) because natural gas at room temperature, atmospheric pressure is a gas, so its poor storage and transportation performance. At present, widely used will be compressed natural gas into the car cylinder storage and transportation approach, these cylinders both increase the car weight, but also reduce the cargo space. Although liquefied natural gas (LNG) can be made by cryogenic liquefaction technology, the technology is complex and the production cost is high. 

 2) an inflatable driving range is short.

 3) CNG or LPG are gaseous into the cylinder, so that the engine charge coefficient is reduced; In addition, compared with gasoline or diesel, CNG or LPG theoretical mixed gas calorific value is small, therefore, burning CNG or LPG will make the engine power The Evaporator function --------- evaporate and decompress LPG. Since the saturated vapor pressure of LPG is not more than 1.43MPa (the temperature is 38 ℃ when the table pressure), much lower than the pressure inside the CNG cylinder, generally only need one or two decompression cylinders accessories cylinder accessories include All kinds of valves and liquid meter and so on. In the car with a cylinder, the more integrated these components constitute an integrated valve, it has limited filling, storage display, liquid, manual cut off and security protection and many other functions. When the LPG reaches 80% of the cylinder volume when the cylinder is filled with liquid, the limited filling valve in the integrated valve is automatically closed and the liquid filling is stopped. Use the level gauge in the integrated valve to indicate the LPG reserves in the cylinder. The integrated valve is fitted with a safety valve which automatically opens the air at a pressure of 2.5 ± 0.2 MPa. In addition, the outlet is also equipped with a safety valve, when the occurrence of gas pipeline rupture and a large number of LPG leakage, as long as the valve on both sides of the pressure difference of more than 0.1MPa,  the valve will automatically close the outlet. 3) Electronically controlled CNG injection system Although the use of stepper motor servo valve and proportional adjustment of the electronically controlled CNG closed-loop control system to improve the air-fuel ratio control accuracy, but the small air conditions of air-fuel ratio is still difficult to accurately and steadily control The Therefore, in recent years, electronically controlled CNG injection system has been rapid development.

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