Analysis of advantages and disadvantages of natural gas heavy trucks and diesel heavy trucks


Natural Gas Heavy Truck Basic Concept

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, the 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 diesel vehicle's ignition point 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 vehicle is: When the vehicle is working, the high-pressure gas in the gas cylinder is depressurized through a pressure reducer, and finally it is ignited after the engine is mixed with air, and the generated energy provides power for the vehicle.

LNG is liquid natural gas, but it is not stored in the same state as CNG. When the liquid natural gas in the gas cylinder is gasified by the gasifier, it becomes a natural gas with a certain pressure in the gaseous state, and its working principle is the same as that of the CNG natural gas vehicle.

Because of the different fuel storage modes for CNG heavy trucks and LNG heavy trucks, the two models have their own advantages and disadvantages. The analysis results are shown in the table below. From the point of view of the product itself, compared with LNG heavy trucks, CNG heavy trucks usually require 12 cylinders, occupying a large space, requiring a high overall arrangement of the vehicles, and a longer refueling time. From the perspective of lightweighting heavy trucks, the development prospects of LNG heavy trucks are even broader.

Differences between natural gas engine heavy trucks and diesel engine heavy trucks The most obvious difference between natural gas heavy trucks and diesel vehicles is the difference in engines, which in turn causes several other differences:

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 waterways are different: LNG needs to absorb heat from the engine to convert LNG into a gasified natural gas supply engine, so it is necessary to connect the hot water of the engine 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.

With the economic development, environmental pollution has become increasingly prominent. Among them, due to the low emission location of automobile exhaust gas, lead, sulfur and other pollutants contained in its exhaust gas are the main causes of atmospheric pollution. According to the calculation of the National Environmental Protection Center, the emissions of automobile exhaust will account for 64% 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.

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 explosion limit of natural gas is 5 to 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% to 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.

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