What is the difference between LNG and CNG vehicles?
In recent years, with the increasingly severe environmental situation, natural gas has been listed as the preferred clean energy source by many countries, and natural gas engine fuel vehicles have also become a hot topic of concern. In cities, many buses and taxis have switched from fuel to natural gas. Observant friends may also notice that some cars are labeled with LNG on the back, while others are labeled with CNG. Today, let's talk about the story of 'them'.
1¡¢ Same or similar points
1. The main component of the fuel used is methane, and the methane content of natural gas from major gas fields such as Xinjiang, Qinghai, Sichuan Chongqing, and Changqing, which are the main sources of pipeline natural gas in China, is mostly over 95%. After purifying natural gas according to GB18047 "Compressed Natural Gas for Vehicles" standard, each gas station provides very low hydrogen sulfide and trace water capacity in CNG, while methane in LNG is also above 95%, with hydrogen sulfide content below 4ppm. It can be seen that the two are very similar in terms of physical and chemical properties and calorific value indicators.
2. As engine fuel, CNG and LNG are very similar in terms of power, fuel economy, and exhaust emissions, with no significant difference. 3. The technical requirements for the supply pressure, flow rate, and mixing ratio before entering the engine cylinder are the same.
1. The ways of storing natural gas fuel are different. In short, CNG is stored under high pressure, while LNG is stored under low temperature. CNG is stored in high-pressure steel cylinders with a working pressure of 20Mpa or steel inner liner wrapped around cylinders, while LNG is stored in vacuum insulated low-temperature containers at a low temperature of -162 ¡æ. The working pressure of this low-temperature container is generally below 0.5Mpa, with a starting pressure of 1.6Mpa for the main safety valve and 2.4Mpa for the auxiliary safety valve, making it a low-temperature and low-pressure container.
2. The focus of safety prevention is different. The biggest focus of CNG cylinders is to prevent explosions caused by stress corrosion and other reasons. And LNG is designed to prevent the explosion of low strength low-temperature storage tanks caused by collisions or rear end collisions of vehicles; Secondly, it is necessary to prevent personnel frostbite accidents during LNG leakage; Thirdly, it is necessary to prevent the pressure in the gas storage tank from exceeding the safety valve due to prolonged shutdown time, which may lead to the release of natural gas; Fourthly, it is necessary to prevent safety hazards caused by a decrease in vacuum degree after a long period of use (such as 2 years) of the gas storage tank (which may also lead to a deterioration in fuel economy), and to promptly inspect and supplement the vacuum. From the analysis of the appeal, it can be seen that the general statement that LNG vehicles are safer than CNG is not appropriate. The correct statement should be that if both technical standards and operating procedures are followed, both are safe. Otherwise, it could lead to safety accidents.
Compared to CNG vehicles, The energy density of natural gas stored in LNG storage tanks is high, 2.5 times that of CNG cylinders of the same volume. The corresponding extension distance is generally over 600 kilometers. Especially suitable for replacing diesel heavy-duty trucks and long-distance diesel buses. In contrast, CNG vehicles, due to their low energy density, typically have a range of up to 250 kilometers and can only be used for short to medium distance transportation. They are particularly suitable for city buses, taxis, coaching cars, as well as private sedans and micro cars.
4¡¢ In terms of the number of natural gas vehicles, CNG vehicles have an absolute advantage
1. At the end of 2011, there were over 15 million CNG vehicles worldwide, while the ownership of LNG vehicles was less than 1% of that. Except for Russia, which has 50000 LNG heavy-duty trucks, there have been no reports abroad on which country has a fleet of over 10000 LNG vehicles.
1. The terminal price of LNG is generally 10% -20% higher than that of CNG, which is a major limiting factor.
2. The application field suitable for LNG vehicles is relatively narrow. Currently, private cars account for 60% -70% of the total number of vehicles in China, while private cars (sedans, trucks) using CNG account for as much as 70% -80% of the total number of CNG vehicles; Therefore, the number of CNG vehicles can grow at a rate of 300000 to 400000 in the past two years.
3. The purchase cost of new LNG heavy-duty trucks and LNG long-distance buses is about 20% higher than that of diesel vehicles of the same type; Often causing homeowners to hesitate.
4. Each LNG refueling station serves several times fewer vehicles than CNG, and its operational efficiency is far inferior to CNG refueling stations. The average number of service vehicles per gas station in China is slightly 700, while the average number of LNG refueling stations is only about 100. Only a few dozen vehicles actually come to refuel every day. Even in some places, there is a phenomenon of "having stations but no cars".
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