What are the most frequently asked questions about LNG heavy trucks?

-1. How many liters of diesel fuel does one cubic meter of natural gas equal? How to convert between natural gas and diesel?

The calorific value of one cubic meter of natural gas is equal to 0.86 liters of diesel fuel; one meter of natural gas produces as much power as 0.75-0.8 liters of diesel fuel.

-2. Some LNG filling stations measure in kilograms and some in cubic meters, which is more reasonable?

Measuring in kilograms and measuring in cubic meters are essentially the same, only the measurement unit is different, which is determined according to the local custom. The unit of measurement in different areas should be determined according to the customer's situation, market situation and other comprehensive analysis. The unit of cubic meter can be used to adjust the sales price according to the change of gasification rate, while kilogram is the more common unit of measurement.

The majority of LNG refueling stations use mass flow meters, which result in minimal discrepancies when selling by kilograms. If selling by volume, consideration needs to be given to the pricing based on the vaporization rate indicator to ensure customer interests are protected.

-3. Why is the LNG filling volume sometimes higher and sometimes lower?

Due to the difference in the origin of the gas source, the density, calorific value, gasification rate and temperature of LNG may be slightly different, the filling volume fluctuates slightly, which does not affect the accuracy of the filling metering.

-4. How is the refueling volume of LNG vehicles calculated? How do I know when I need to refuel?

(1) LNG is measured in the same way as gasoline and diesel oil, one is measured by volume, and the unit of measurement is cubic meter (the unit of measurement for gasoline and diesel oil is liter), and the other is measured by mass, and the unit of measurement is kilogram (the unit of measurement for gasoline and diesel oil is ton). Depending on the measurement habits of different regions, either cubic meters or kilograms can be chosen as the unit of measurement.

Regardless of the unit of measurement, the amount of gas refilled is the same, and the dispenser automatically measures it. The conversion relation is that 1 kilogram of LNG is equivalent to approximately 1.4 cubic meters of natural gas.

(2) The driver's cab of the LNG vehicle is equipped with an LNG liquid level display, which is the same as the fuel level display of a diesel vehicle. The liquid level display includes liquid level icon, liquid level scale, liquid level pointer and liquid level value (L). When the key switch is turned on, the display will be fully illuminated for 3 seconds and then start to display the values of various parameters of the gas cylinder, including the liquid level value and the gas cylinder pressure value.

Select the refueling time, when the liquid volume scale line is lower than the liquid volume warning line (the data is determined by the automobile manufacturer, the liquid volume warning line is generally 12.5% of the effective volume of the cylinder), the status light flashes to remind the customer to refill in time.

-5. How long does it take to refuel an LNG vehicle?

The time required to fill the same volume of LNG and diesel fuel is comparable. The maximum filling capacity of LNG dispenser is 150 to 200 L/min, and the normal filling time is 5 to 10 minutes.

-6.What is the driving range of the LNG heavy-duty truck?

The range of an LNG vehicle is determined by the volume of LNG cylinders and the 100km gas consumption of the vehicle, and can reach 400 to 1,000 kilometers, which is comparable to that of a diesel vehicle. For example, an LNG heavy truck equipped with two 450-liter cylinders can store about 500 cubic meters of natural gas and consume 50 cubic meters of gas per 100 kilometers, which gives it a range of more than 900 kilometers.

-7. What are the advantages of LNG vehicles over diesel vehicles?

(1) Longer mileage: LNG heavy trucks can travel more than 400Km on 450L of fuel, and the refueling time is short.

(2) Better economy: the vehicle saves fuel costs, simple equipment, low maintenance costs, and the vehicle overload effect is more prominent.

(3) High security: LNG's ignition point of 650 ℃, higher than gasoline, diesel; LNG's explosion limit of 5% -15%, the explosion limit is narrower than gasoline, diesel, and gasification density is very low, a slight leakage will be immediately volatile and diffuse, greatly reducing the risk of explosion.

(4) Clean and environmentally friendly: LNG components are pure, less CO emissions.

-8. Can natural gas vehicles use diesel fuel?

Currently, heavy-duty natural gas trucks can only use a single fuel, either compressed natural gas (CNG) or liquefied natural gas (LNG), and cannot use diesel.

-9. What is the gas consumption per 100 kilometers in actual operation of LNG vehicles and how does it compare to diesel?

In actual operation, the fuel consumption of LNG vehicles per 100 kilometers is approximately 50 cubic meters for heavy-duty LNG trucks with the same power as diesel trucks that consume 40 liters per 100 kilometers. This difference may vary depending on the quality of the gas source.

-10.Why is it necessary to periodically vent LNG tanks, and is it dangerous?

If a liquefied natural gas (LNG) vehicle is not used for a long time, the liquid inside the gas cylinder continuously vaporizes, causing the pressure inside the cylinder to increase. When the pressure exceeds a certain value, the secondary safety valve of the cylinder automatically opens to release pressure, ensuring the safety of the cylinder. In case the secondary safety valve fails or malfunctions, the main safety valve activates to protect the cylinder's safety.

In the event of accidents such as damage to the cylinder shell by external forces, vacuum failure, or a sudden increase in system pressure, the main and secondary safety valves open sequentially to release pressure, ensuring the safety of the vehicle. When venting the gas cylinder, since the main component is methane, which is lighter than air and easily dissipates, it does not easily accumulate and pose a danger.

-11. During the refueling process for natural gas vehicles, filling stations require that no one be seated in the vehicle because it is unsafe?

Comparative ignition points: Diesel has an ignition point of 220°C, while gasoline has an ignition point of 427°C. However, gasoline has strong volatility, and gasoline vapor has a lower ignition point than diesel. The ignition point of liquefied petroleum gas (LPG) is 490°C, and the ignition point of natural gas is 650°C. The density of liquefied petroleum gas (LPG) compared to air is 1.5 to 2, and in the event of a leak, it tends to settle downward, posing a safety hazard for potential explosions.

The density of natural gas (NG) compared to air is 0.58 to 0.79, and in the event of a leak, it quickly dissipates into the air, posing minimal safety hazards. The explosion limits for liquefied petroleum gas (LPG) are between 1.7% and 9.7%, while for natural gas (NG), they range from 5% to 15%, making explosions less likely. LNG has a lower filling pressure compared to CNG, approximately 1/40th of the filling pressure of CNG, making it less prone to leakage. The filling pressure for LNG is only 0.5 MPa, whereas for CNG, it is 20 MPa.

From the above, we can see that the safety indexes of LNG are higher than those of common fuels, so the safety of using LNG as fuel is higher than that of other fuels. However, from the point of view of better guaranteeing the safety of passengers, ensuring the control of open fire hazards in the filling station, and effectively controlling the safety risks, it is required that no one can sit in the vehicle when filling up at the filling station.

-12. Are LNG cylinders safe?

Before LNG storage tanks are shipped from the factory, they undergo special inspections. In addition to routine inspections, the tanks are also subjected to tests such as fire, explosion, drop, and gunshot tests. Only after passing these tests can they be used in the factory. LNG tanks for vehicles are designed as low-temperature, insulated pressure vessels with a double-layer (vacuum) structure.

The inner vessel is used to store the low-temperature liquid liquefied natural gas (LNG), with multiple layers of insulation material wrapped around its outer wall, providing excellent thermal insulation performance. Meanwhile, the interlayer (the space between the two layers of the container) is evacuated to a high vacuum, collectively forming an effective insulation system. The design of the outer shell and support system can withstand the external forces generated by the vehicle during operation.

The inner vessel is equipped with dual-level safety valves to provide protection in case of overpressure. In the event of overpressure, the primary safety valve (opening pressure approximately 1.6 MPa) is the first to open. Its function is to release pressure caused by abnormal heat loss due to insulation layer and support system failure, vacuum breakdown, and accelerated heat loss under conditions of fire.

The secondary safety valve (with an opening pressure typically above 2.4 MPa) is set at a higher pressure threshold compared to the primary safety valve. It activates when the primary safety valve fails or becomes blocked.

The protection of the shell under internal overpressure conditions is achieved through a circular vacuum plug. In case of a leak in the inner container (resulting in excessive pressure in the annular space), the vacuum plug will open to release pressure when it reaches 0.1 to 0.2 MPa. If the vacuum plug itself leaks, it can lead to vacuum failure, which can be identified by the appearance of large water droplets or frost on the outer shell. However, frosting or condensation at the end of the connected pipeline to the cylinder is normal. All pipelines and valve components are located at one end of the cylinder and are protected by protective rings or covers.

-13. Will LNG be prone to explode when the vehicle is involved in an accident or collision?

LNG is stored in insulated containers with pressures ranging from 0.05 to 0.5 MPa. Compared to CNG, LNG has lower storage pressure and lower density after vaporization (lighter than air), making it prone to rapid evaporation and dispersion in case of leakage, thus reducing the likelihood of combustion. The ignition point of LNG is 645°C, with an explosion limit of 5% to 15%. Liquid LNG is not easily ignited, making it safer than gasoline or diesel.