This year, basically all medium- and heavy-duty truck companies will use natural gas heavy trucks as the main product in the next 3-5 years. Even a new lifting truck company will have a relatively high proportion of natural gas heavy trucks in the production planning of this year. It seems a bit too high. The author is worried that the car company that has been listed for less than three years can no longer repeat the mistakes made by previous “heavy price†heavy trucks. In the case of subjective and objective, it seems that it is not mature enough to sell more natural gas vehicles. Dig a pit and trap yourself.
Compared with the efficiency of diesel engines, natural gas engines still have a certain relative weakness. The so-called energy-saving is only in the alternative part of fuel, not in the efficiency of fuel use. Therefore, a natural gas vehicle is neither an angel nor a devil, but under certain time and space, it may be the mutual transformation of angels and Satan, and the pros and cons of both advantages and disadvantages coexist.
As we all know, natural gas vehicles have their advantages over energy-efficient cleaning and gas prices that are lower than those of fuel. However, since the natural gas vehicle's engine and related parts are slightly more complicated than the fuel machine, the price is correspondingly higher. For example, the new LNG heavy truck is 80,000 to 100,000 yuan more expensive than a diesel vehicle. Coupled with the cost of replacing gas tanks, the economy is less prominent.
At present, although many natural gas heavy truck companies have maintenance outlets, most service networks are under construction, including a joint after-sales service system established by vehicle manufacturers, engine plants, and gas suppliers.
There is still not much ability to repair natural gas heavy trucks, and problems need to be solved at the central or first-tier cities with maintenance capabilities. In addition to the maintenance stations in individual central cities and first-tier cities, there are professional technicians and maintenance technicians for natural gas vehicle maintenance. Apart from professional tools and spare parts, while other regions are still in a blank area, the manufacturer is just a system of long-term and huge projects, and there is no one for 3-5 years. The time is impossible to achieve.
In addition, natural gas heavy trucks are still popular stage products. Their filling stations are not spread out in remote areas of the country like fuel stations. Many areas do not have gas filling stations yet, if they are not added on the way The gas has climbed the nest and it is still not within the rescue scope of the after-sales service. Tens of tons or hundreds of tons of cargo will not be able to move. This is why the sky should not be called for failure. There are great risks.
At present, foreign CNG engines have been widely used in third-generation technologies. The more advanced LNG direct-injection technology has been used in a small number of trials. Its power, economy, and emissions are excellent, but its development is difficult and expensive. The cost is also high and domestic development has not yet begun. The first generation of natural gas vehicles is mechanical, the second generation is simple closed-loop control, and the third generation is electronically controlled injection CNG technology.
Electronically controlled CNG injection system uses high-pressure injection, through the throttle sensor, gas flow sensor, speed sensor, water temperature sensor, intake temperature sensor, pressure sensor and oxygen sensor through the central processing unit to control the ignition, air-fuel ratio. According to the author's understanding of the situation, the level of domestic natural gas heavy trucks is still in the second generation is a relatively simple technology closed-loop control phase. The use of electronically controlled jet CNG technology kits will also need to be purchased from Bosch, United Electronics, Delphi, and other key offshore component companies, and will continue to hold onto the throat and control the lifeline of the Chinese auto industry.
As far as the natural gas heavy truck products are concerned, they are also “arrogant†compared to fuel heavy trucks. For example, if an LNG vehicle's gas cylinder needs to maintain its “low temperature and vacuumâ€, the temperature will increase for a long time and the pressure in the tank will increase. This requires the driver to vent the gas when the vehicle is not in use and must be kept in open space when it is used. It is easy to cause major accidents.
Natural gas cylinders are high-pressure containers and are dangerous goods. The annual inspection is carried out by the Bureau of Quality Supervision, and the automobile itself is supervised by vehicle management agencies and public security agencies. This involves three departments, and the annual inspection process becomes quite troublesome and troublesome. When CNG's cylinders are inspected, they need to be disassembled for pressure testing, which is time-consuming and labor-intensive. LNG cylinders also did not identify specific agencies responsible for annual inspections, and even the operation of each place was inconsistent.
At the same time, when natural gas trucks are used as second-hand vehicles, they do not have to reduce their selling prices just like oil-fueled ones. Natural gas heavy trucks, however, are generally difficult to transfer to the “hot potatoâ€. From this, it can be seen that the natural gas heavy truck is more complicated and troublesome than the fuel heavy truck in use.
The most important thing is that natural gas heavy trucks have potential safety hazards when driving on long downhill sections under heavy load conditions. When the downhill slopes, they obviously feel that the braking effect is not given. This is due to the lack of pressure in the cylinder of the gas engine. Only the installation of a retarder to assist the brakes has increased the cost of a few thousand dollars, which has also increased the burden on users. However, it does not work if it is not installed, otherwise it will cause accidents in which cars are destroyed. The most important thing is: Natural gas prices will surely increase significantly this year or in the future, and this has become a development trend. This rising price of gas will be immediately equal to the refined oil price, and gas engine heavy trucks will lose their absolute advantage to a certain extent.
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With the development of China’s social economy, the problem of environmental pollution has become increasingly prominent. Today, China has become the most poisonous country in the world. Among them, lead, sulfur and other pollutants contained in the exhaust gas are one of the major causes of atmospheric pollution due to the low emission of automobile exhaust gas. According to estimates by the National Environmental Protection Center, the emissions of automobile exhaust will account for more than 65% of air pollution in 2010. Therefore, to solve the pollution problem caused by automobile exhaust emissions is the focus of the current energy-saving emission reduction work.
The biggest feature of natural gas vehicles is “cleanliness.†Compared with fuel vehicles, CO2 emissions in exhaust gas are reduced by approximately 20%, CO by approximately 97%, HC (hydrocarbons) by approximately 72%, and NOx (nitrogen oxides) by a decrease. About 30%, basically free from harmful substances such as lead, sulfides and benzenes. Especially LNG heavy trucks are known as true zero-emission vehicles.
On the technical level, the ignition temperature of natural gas is 650°C, which is higher than that of gasoline and diesel. The ignition energy is also higher than that of gasoline and diesel, so it is more difficult to ignite than gasoline and diesel. The explosive limit of natural gas is 5-15%, and the density is lower than that of air, so there is a slight leakage that is volatile diffusion; while the gasoline ignition point is 427°C, the explosion limit is 1.0%-7.6%; the diesel ignition point is 260°C, and the explosion limit is 0.5 %—4.1%. This shows that natural gas vehicles are safer than gasoline and diesel vehicles. At the same time, the octane number of natural gas is as high as 130, and the anti-riot performance of gasoline and diesel cannot be compared.
According to the different forms of natural gas used by gas vehicles, it can be divided into: compressed natural gas (CNG), the main component is methane, and the pressure is generally 20-30 MPa;
Liquefied natural gas (LNG) and natural gas are liquefied at ultra-low temperature (-162°C) under normal pressure. Natural gas is purified and then heated up by compression. Under the action of mixed refrigerants N2, C1, C2, C3, and C4, the heat is removed and removed. The throttling expansion results in liquid natural gas. At normal atmospheric pressure, the volume is approximately 1/625 of the same amount of gaseous natural gas, natural gas is liquefied to 1/625 of the standard volume, and the pressure of the insulated vessel is 0.05-0.5 MPa. Almost all sulfur, mercury, and other impurities are removed during the liquefaction of natural gas.
According to the different natural gas fuel conditions used, natural gas vehicles can be divided into:
1. Compressed natural gas (CNG) cars. It is a colorless, transparent, odorless, high-calorie, lighter-than-air gas. The main component is methane. Compressed natural gas refers to natural gas compressed to 20.7-24.8 MPa and is stored in on-board high-pressure cylinders. Because the components are simple, easy to complete combustion, coupled with low carbon content of the fuel, good anti-knocking performance, without dilution of the lubricating oil, can prolong the service life of the engine.
2. Liquefied natural gas (LNG) cars. It refers to liquid natural gas with a temperature of -162 degrees under normal pressure and is stored in a vehicle-mounted insulating gas cylinder. Liquefied natural gas (LNG) has a high ignition point and is highly safe for long-distance transportation and storage.
3. Liquefied petroleum gas (LPG) is a kind of hydrocarbon mixture that is gaseous under normal temperature and pressure. It is heavier than air, has a higher octane number, and has a uniform mixing, full combustion, no carbon deposition, and no dilution of lubricating oil. Such advantages can extend the service life of the engine, and it also has a large carrier gas and long mileage.
According to different fuel use conditions, natural gas vehicles can be divided into: dedicated fuel natural gas vehicles, engines use only natural gas as fuel; dual-use fuel natural gas vehicles can use either natural gas or gasoline as fuel. Dual-fuel natural gas vehicles can use liquid fuels and natural gas at the same time. Compressed natural gas (CNG) automotive fuel systems typically include: natural gas cylinders, vacuum regulators, various types of valves and fittings, mixers (or natural gas injection devices), and various types of electronic control devices.
Natural gas vehicle main components: pressure reducer, mixer or spray gauge; 1 set of open-loop anti-condensation device or gas computer; 1 set of transfer switch assembly; 1 power control valve or natural gas filter; high-pressure steel pipe φ6x1: 0.8 KG; air tube 1; exhaust pipe 1 meter; stable firmware package 1 package; low pressure pipe φ19: 1 meter; low pressure pipe φ160.3 meters; clamp φ16-274 only; clamp φ22-φ321 only; clamp φ341 Only; 1 inflatable valve. Gas cylinders and gas cylinder brackets.
Relative advantages of natural gas vehicles:
(1) Natural gas vehicles are clean fuel vehicles. Natural gas vehicles emit much less pollution than gasoline-powered cars. Sulfur and lead are not included in the tail gas, carbon monoxide is reduced by 80%, hydrocarbons are reduced by 60%, and nitrogen oxides are reduced by 70%. Therefore, many countries have already developed natural gas vehicles as an important means of reducing atmospheric pollution.
(2) Natural gas vehicles have significant economic benefits. Can reduce the cost of operating the car. At present, the price of natural gas is relatively lower than that of gasoline and diesel, and fuel costs are generally saved by about 30%, which greatly reduces operating costs. In addition, maintenance costs can also be saved. The engine uses natural gas as its fuel. It runs smoothly, has low noise and does not accumulate carbon. It can prolong the service life of the engine. It does not require frequent oil and spark plug replacement, which can save a small maintenance cost.
(3) Safer than gasoline cars. Compared with gasoline, compressed natural gas itself is a relatively safe fuel. This is reflected in the high ignition temperature, natural gas ignition point above 650.c, and 223.c higher than the gasoline ignition point (427.c), so it is less flammable than gasoline.
In addition, the density is low, and the relative density to air is 0.48. The leaked gas quickly dissipates in the air, and it is difficult to form a fire burning concentration. The octane number is high, up to 130, much higher than the current best octane number 96 car, anti-knock performance is good. In the past 60 years since natural gas was developed at home and abroad, the fact that natural gas explosions and combustion have caused car crashes has never proven to be a safe and reliable source of compressed natural gas vehicles.
Relative disadvantages of natural gas vehicles:
The accessories used in natural gas vehicles are more demanding than those for fuel vehicles. They are shown in the following: The state has issued strict technical standards for natural gas vehicles, from the design of gas filling stations, the production of gas cylinders, the manufacture of modified gas components, to the installation and commissioning, etc. Strict technical standards.
Strict safety measures are taken into consideration in the design. The safety factor of the components used in the high-pressure system is selected to be 1.5-4 or more. The safety valve is installed on the decompression regulator and the gas cylinder. In the control system, the emergency air-disconnection is installed. Device. The gas cylinder must undergo special inspection before leaving the factory. After the gas cylinder is routinely inspected, it must be inflated for fire, explosion, fall, gunshot, etc., and it can be used after being qualified.
Natural gas heavy truck refers to a gas-fueled heavy-duty vehicle that uses natural gas as fuel (CNG is compressed natural gas; LNG is liquefied natural gas). According to different fuel use conditions, it can be divided into single-fuel natural gas vehicles (engines use only CNG or LNG as fuel), dual-fuel natural gas vehicles (using diesel + natural gas, or using gasoline + natural gas as a fuel vehicle). The most widely used at present is a single fuel compressed natural gas vehicle.
Difference between natural gas engine heavy truck and diesel engine heavy truck:
First, the fuels are different: natural gas vehicles are automobiles that use natural gas as fuel (cyanogeneous CNG and liquefied natural gas LNG), so their engines are natural gas-specific engines and fuel is stored in cylinders; diesel vehicles are diesel-based fuels. The car, whose engine is a conventional diesel engine, is stored in a fuel tank. Different fuels, the vehicle's fuel supply system will also have differences.
Second, the engine combustion products are different: natural gas vehicle combustion products are mainly water and carbon dioxide, the tail gas does not contain sulfides and lead, carbon monoxide is reduced by 80%, hydrocarbons are reduced by 60%, nitrogen oxides are reduced by 70%, and it is beneficial to protection. Environment; Exhaust and carbon dioxide emissions from diesel vehicles, as well as a large amount of CO (carbon monoxide), HC + NOx (hydrocarbons and nitrogen oxides), PM (particles, soot) and so on.
Third, the engine cooling waterway is different: LNG needs to absorb engine heat to convert LNG to LNG to the engine, so it is necessary to connect the engine's hot water through the rubber tube and the cylinder vaporizer.
Fourth, the exhaust system is different: The exhaust system of a general LNG vehicle is packaged with a catalytic converter. The three-way catalytic converter is the most important external purification device installed in the exhaust system of an automobile. It can convert harmful gases such as CO, HC, and NOx emitted from automobile exhaust into non-harmful carbon dioxide, water, and nitrogen through oxidation and reduction. .
Exhaust assembly sequence: exhaust pipe, exhaust brake butterfly valve, exhaust pipe, flexible hose, exhaust pipe, catalytic converter, muffler. Natural gas heavy truck refers to a gas-fueled heavy-duty vehicle that uses natural gas as fuel (CNG is compressed natural gas; LNG is liquefied natural gas). According to different fuel use conditions, it can be divided into single-fuel natural gas vehicles (engines use only CNG or LNG as fuel), dual-fuel natural gas vehicles (using diesel + natural gas, or using gasoline + natural gas as a fuel vehicle).
At present, domestic natural gas heavy trucks basically use a single fuel, that is, they can only use compressed natural gas (CNG) or liquefied natural gas (LNG), and diesel can not be used. Because the working principle of diesel and natural gas is quite different (the ignition point of diesel vehicles is 220°C, diesel is compression ignition type; the ignition point of natural gas is 650°C, natural gas is ignition type; the ignition point of gasoline is 427°C, and the ignition type is used) .
The working principle of CNG natural gas heavy truck is: When the vehicle is working, the high-pressure gas in the cylinder is decompressed by the pressure reducer, and finally it is ignited after the engine is mixed with air, and the generated energy provides power for the vehicle.
LNG LNG heavy-duty trucks are just different from CNG in terms of storage status. When liquid natural gas in gas cylinders is vaporized by a gasifier, it becomes a natural gas with a certain pressure in the gas state. Its working principle is the same as CNG natural gas vehicles.
Because CNG heavy trucks and LNG heavy trucks have different fuel storage methods, the two models have their own advantages and disadvantages. CNG heavy trucks usually require 12 cylinders, occupying a large space, requiring a high overall arrangement of the vehicles, and a longer refueling time. long. From the perspective of lightweighting heavy trucks, the development prospects of LNG heavy trucks are even broader.
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