1, what is a natural gas car?

Simply put, a natural gas vehicle is a gas-fueled vehicle that uses natural gas as fuel.

The methane content of natural gas is generally above 90%, which is a good fuel for automobile engines. At present, natural gas is recognized as the most realistic and mature alternative fuel for automobile gasoline and diesel in the world, and natural gas vehicles have been widely used in the world, China and our city.

At present, CNG vehicles are widely used in our city, which can burn compressed natural gas or gasoline respectively. In the future, CNG vehicles will be widely used. The pressure of compressed natural gas for vehicles is generally around 20MPa. Natural gas can be obtained by dehydration, desulfurization, purification and then multistage pressurization. Its use state is gas.

2. The main advantages and disadvantages of natural gas vehicles

(1) Natural gas vehicles are clean fuel vehicles. The emission pollution of natural gas vehicles is much lower than that of vehicles fueled by automobiles. The tail gas does not contain sulfide and lead, and carbon monoxide is reduced by 80%, hydrocarbons by 60% and nitrogen oxides by 70%. Therefore, many countries regard the development of natural gas vehicles as an important means to reduce air pollution.

(2) The economic benefits of natural gas vehicles are remarkable.

● It can reduce the operating cost of automobiles. At present, the price of natural gas is much lower than that of gasoline and diesel, and the fuel cost is generally saved by about 50%, which greatly reduces the operating cost. Because of the difference between oil and gas, the cost of changing cars can be recovered within one year.

● Maintenance costs can be saved. The engine uses natural gas as fuel, which has the advantages of stable operation, low noise and no carbon deposition. It can prolong the service life of the engine, save more than 50% of maintenance costs without frequent replacement of engine oil and spark plugs.

(3) It is safer than gasoline vehicles.

First of all, compared with gasoline, compressed natural gas itself is a safer fuel. This is manifested in:

High ignition point. The ignition point of natural gas is 650. C above, than gasoline ignition point (427. C) higher than 223. C, so it is not easy to ignite compared with gasoline.

Low density. The relative density with air is 0.48, and the leaked gas will be rapidly distributed in the air, so it is difficult to form the combustion concentration when it meets fire.

High octane number. It can reach 130, far higher than the best 96 cars at present, and has good explosion-proof performance.

The explosion limit is very narrow. Only 5~ 15%, it is difficult to form this condition in natural environment.

The release process is an endothermic process. When compressed natural gas is discharged from a container or pipeline, a low temperature zone will quickly form around the discharge hole, making it difficult for natural gas to burn.

Secondly, the accessories used in compressed natural gas vehicles are more demanding than gasoline vehicles. Show in:

The state has promulgated strict technical standards for natural gas vehicles. From the design of gas filling station, the manufacture of gas cylinders, the manufacture of parts of modified vehicles to the installation and debugging, strict technical standards have been formed in every link.

Strict safety measures are considered in the design. The safety factors of parts used in high-voltage systems are all above 1.5~4. The safety valve is installed on the pressure reducing regulator and gas cylinder, and the emergency gas cut-off device is installed in the control system.

Gas cylinders should be specially inspected before leaving the factory. After routine inspection, gas cylinders need to be inflated for fire prevention, explosion prevention, drop, shooting and other tests before leaving the factory for use.

Since the development of natural gas at home and abroad for 60 years, there has never been a car accident or death accident caused by explosion and combustion of natural gas, which proves that compressed natural gas vehicles are very safe and reliable.

(4) (4) The dynamic performance of CNG vehicles has slightly decreased. When burning natural gas, the dynamic performance decreases slightly by 5~ 15%.

(5) Large one-time investment in transformation. At present, it costs about 1 10,000 yuan to refit a CNG vehicle.

3. Brief introduction of 3.CNG automobile structure

CNG vehicles are modified with fixed gasoline vehicles, and a set of CNG vehicle compressed natural gas device is added under the condition of retaining the oil supply system of the original vehicle. The modified part consists of the following three systems.

(1) natural gas system. It is mainly composed of inflation valve, high-pressure cut-off valve, natural gas bottle, high-pressure pipeline, high-pressure connector, pressure gauge, pressure sensor, gas volume display and so on.

(2) Natural gas supply system. It is mainly composed of natural gas high-pressure electromagnetic valve, three-stage combined pressure reducing valve and mixer.

(3) Oil-gas fuel conversion system. It is mainly composed of three-position oil-gas changeover switch, ignition time converter and gasoline solenoid valve.

Two safety devices, fusible plug and bursting disc, are installed at the bottle mouth of natural gas cylinder. When the cylinder temperature exceeds 100. C or when the pressure exceeds 26MPa, the safety device will automatically rupture and release the pressure; A safety valve is arranged on the pressure reducing valve; When installing gas cylinders and high-pressure pipelines, there are shockproof rubber pads, which are firmly clamped. Therefore, the system is safe and reliable to use.

When CNG vehicles use natural gas as fuel, the natural gas is mixed with air through a mixer after three-stage decompression, and the compressed natural gas is reduced from the rated intake pressure of 20MPa to negative pressure, and its vacuum degree is 49~69kPa. The cooperation of pressure reducing valve and mixer can meet the concentration requirements of mixed gas under different working conditions of engine.

The pressure reducing valve assembly is provided with an idle electromagnetic valve for providing idle gas for the engine; Compressed natural gas needs to expand to do work and absorb heat, so there is also a heating device using engine circulating water on the pressure reducing valve. In order to improve the operating performance of the car, the cab is equipped with an oil-gas fuel changeover switch to control the oil-gas solenoid valve and the ignition time converter in a unified way; The ignition time converter automatically converts the different ignition advance angles of the two fuels through the circuit system; Five traffic lights on the gas indicator on the dashboard show the gas storage capacity of the gas cylinder; The fuel changeover switch is also provided with an air supply button for starting the engine.

4. Working principle of compressed natural gas vehicle

The system is divided into three parts: natural gas loop, gasoline loop and control loop.

The filling station fills compressed natural gas into the gas cylinder to 20MPa through the inflation valve. When natural gas is used as fuel, the manual cut-off valve is opened and the oil-gas fuel switch installed in the cab is turned to the "gas" position. At this time, the natural gas solenoid valve is opened and the gasoline solenoid valve is closed. The 20MPa high-pressure natural gas in the gas storage tank enters a decompression regulator through a high-pressure pipeline for decompression, then enters a mixer through a low-pressure pipeline and a power valve, mixes with the air entering through an air cleaner, and then enters an engine cylinder for combustion through a carburetor channel. The pressure-reducing regulator cooperates with the mixer to generate different vacuum degrees according to the different working conditions of the engine, and automatically adjusts the air supply of the pressure-reducing regulator, so that the natural gas and air are evenly mixed, and the use requirements of the engine under different working conditions are met. Power valve is a device to adjust the cross-sectional area of natural gas pipeline, which can adjust the air-fuel ratio of mixed gas to make the air-fuel ratio reach the best state.

A gasoline solenoid valve is installed in the oil circuit, and other components remain unchanged. When using gasoline as fuel, the driver turns the oil-gas fuel switch to the "oil" position. At this time, the natural gas solenoid valve is closed and the gasoline solenoid valve is opened. Gasoline enters the carburetor through the gasoline solenoid valve and is sucked into the cylinder for combustion. The fuel transfer switch has three positions. When set in the middle position, the oil-gas solenoid valve is closed. This function is specially used to burn the remaining gasoline in the carburetor room when gasoline is changed to natural gas to avoid the phenomenon of mixed combustion of oil and gas.

5. The main technical performance of compressed natural gas vehicles

Using natural gas fuel, the main technical performance of the vehicle is as follows:

The rated power of the engine is not less than 85% of the original vehicle.

The maximum torque of the engine is not less than 90% of the original vehicle.

The maximum speed is not less than 90% of the original car.

The acceleration performance of the car is not less than 85% of the original car.

The minimum stable speed of direct gear is not higher than 5% of the original vehicle.

The rated inflation pressure of natural gas is 20MPa.

1 m3 natural gas can replace gasoline by more than 0.8kg.

The one-time mileage of gas-filled buses and trucks shall not be less than 180km.

Cars and mini-cars are not less than 200km.

CO content of automobile pollutants ≤ 1.5%.

HC content ≤ 1000PPM

Second, the modification of CNG vehicles

In order to ensure the safety and modification quality of CNG vehicles, the state and Chongqing Municipality have formulated strict management regulations on CNG vehicle modification. When a car is converted into a CNG car, it must be modified in a certified designated modification factory.

1, vehicle modification procedure.

(1) Before vehicle modification, the vehicle owner shall apply to the local motor vehicle management department, and fill in the vehicle modification application form after the approval of the vehicle management department, and then the vehicle can be modified in the designated CNG vehicle modification enterprise.

(2) After the vehicle modification is completed, submit the vehicle modification certificate issued by the vehicle modification unit together with the modification application form to the vehicle management department to handle the motor vehicle transaction procedures.

(3)CNG vehicle drivers should be trained by the municipal vehicle management office and obtain a certificate. Only after being registered in the vehicle management department can you drive a natural gas car.

2. Technical requirements of modified vehicles

Before the vehicle is modified, the vehicle performance should be checked, mainly to check the starting performance and dynamic performance of the engine. The engine is required to have good starting performance and sensitive acceleration performance, and the maximum power and torque shall not be less than 90% of the engine design calibration value, otherwise the vehicle shall not be modified. The main technical performance indicators of the vehicle to be modified shall meet the requirements in the following table before modification.

Technical indicators

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The maximum power and torque of the engine (1) shall not be less than 90% of the engine design calibration value.

(2) Engine compression ratio >; 7.3

(3) the pressure of each cylinder >; 0.85MPa, the pressure difference shall not exceed 5% of the average cylinder pressure.

(4) Vacuum degree of intake pipe at idle speed

(5) When using gasoline, the engine runs smoothly under various speed conditions, and there should be no sudden explosion during sudden acceleration or deceleration, and the carburetor does not backfire, so as to stabilize the oil pressure.

electric current

No-load voltage of gas (1) battery >:12.4v; Starting voltage >; 8.5V

(2) The engine generates electricity normally; The starter works normally.

(3) Platinum voltage of distributor

Each assembly of the whole vehicle (1) works normally.

(2) The vehicle technology meets the requirements of GB 7258- 1997 Technical Conditions for Motor Vehicle Operation Safety.

3. Installation of refitted system

(1) Installation of natural gas cylinders.

The gas cylinder should be installed in the safe part of the car, which shall not affect the driving performance of the car. According to the specific situation of each vehicle type, it can be installed beside the frame, on the auxiliary longitudinal beam or between the cab and the trunk. Rubber gasket should be installed between the gas cylinder and the fixing clip, and the installation must be firm. After the gas cylinder is fastened, apply a force 8 times the weight of the gas cylinder along the longitudinal direction of the car, and it shall not be displaced or loosened.

(2) Installation of high-pressure pipeline

The high-pressure pipeline is connected with the gas cylinder through a sleeve-type high-pressure connector. Pipes between gas cylinders and near pressure reducing valves shall have seismic elbows. The distance between pipeline fixing clips should not be greater than 600mm, and rubber pads should be installed at the clips and through the orifice plate. Gas cylinders or pipe joints installed in the cab, passenger compartment or luggage compartment must be equipped with vents and other devices to exhaust the leaked gas from the cab or outside the cabin.

(3) Installation of pressure reducing valve

The pressure reducing valve should be installed on the front baffle of the cab or other parts of the engine with less vibration. The diaphragm of pressure reducing valve should be vertical to the ground, away from exhaust pipe and other heat sources, and as close as possible to carburetor. After the pressure reducing valve is installed, connect the startup circulating water to the water channel of the pressure reducing valve.

(4) Install other accessories

1) Install high-pressure cut-off valve, pressure gauge and connect high-pressure pipeline;

2) Install mixer and low-pressure pipeline, and connect pressure reducing valve and mixer;

3) Install a gasoline solenoid valve between the carburetor and the fuel transfer pump, and pay attention to the electromagnetic coil facing upwards;

4) Install an inflation valve at a proper position;

(5) Installation of electrical components

According to the number of selected electrical components, wiring and installation shall be carried out according to the requirements of relevant specifications. Pay attention to the following two points during installation:

1) Install the fuel change-over switch and gas volume display in the cab at a position convenient for operation and observation, and install the ignition time converter at an appropriate position;

2) Connect all electrical circuits according to the circuit diagram, and pay attention to the good grounding of electrical components.

Third, the debugging and use of CNG vehicles.

1, CNG vehicle debugging

(1) natural gas leakage test

First, slowly inflate the natural gas to about 10MPa, check the relevant parts with leakage detection liquid, and then inflate it to 20MPa after confirming that there is no leakage, and further carefully check the leakage.

(2) Fuel conversion and commissioning

Start the engine with gasoline first, then turn the fuel switch to the middle position, cut off the supply of two fuels, and keep the engine speed at about 2000 rpm. When the remaining gasoline in the carburetor runs out and the engine starts to shake (or the sound changes), immediately switch the fuel to the natural gas position. The normal operation of the engine shows that natural gas burns well. If the engine is not working properly, adjust the ignition time or check other circuit systems.

(3) Ignition timing adjustment

Turn the fuel switch to "gas" position, start the engine, divide the distributor position according to the original adjustment experience, and fix the distributor after optimizing the ignition time. Then put the fuel switch in the "oil" position, and adjust it by adjusting the knob or digital adjustment on the ignition time converter until the best ignition time is reached.

(4) Idle speed and starting mode

1) Run the engine with gasoline, and adjust the idle speed of gasoline according to the original adjustment method of gasoline vehicle.

2) Run the engine with natural gas and adjust the idle speed adjusting handle on the pressure reducing valve until a stable minimum idle speed is obtained. The method is as follows: firstly, loosen the melody metal of the idle speed adjusting handle of the pressure reducing valve for about 65438 0.5 turns; If it is not ideal, fine-tune it with the adjusting screw of carburetor.

3) Start directly with natural gas after flameout, and see if it is easy and quick to start with natural gas. If the starting performance is poor, it should be readjusted.

(5) Acceleration mode

Run the engine with natural gas, let the engine run at idle speed, and then step on the accelerator repeatedly and quickly to see if the engine speed changes quickly and smoothly. If it is not satisfied, adjust the adjusting knob of the three-stage valve of the pressure reducing valve until it is satisfied.

(6) Adjust the air-fuel ratio between natural gas and air.

1) On the chassis dynamometer, the engine runs directly in gear with natural gas fuel, so that the engine is in the maximum torque state. Then use the exhaust gas diverter to detect the exhaust gas of the engine, adjust the adjusting screw of the power valve to make the CO value at 1.0~ 1.5%, and fix the adjusting screw of the power valve. Then, check and adjust the idle speed, starting and acceleration repeatedly.

2) During vehicle operation, the power valve can be directly adjusted according to experience to correct the air-fuel ratio of the engine.

(7) Loosen the fixing screw of the pressure sensor housing, micro-move the left and right housings (with sliding resistance inside), observe whether the pressure gauge and display light are on or off, and lock the fixing screw of the housing after adjustment.

2. Driving operation of compressed natural gas vehicles

CNG vehicle drivers must undergo technical training and obtain certificates before driving natural gas vehicles.

(1) Before starting the car: slowly open the valve of each natural gas bottle, then slowly open the high-pressure cut-off valve, observe the pressure gauge, understand the natural gas pressure, and check whether the pipe joint and pressure reducing valve are leaking. When opening the gas valve, people should not stand in front of the gas valve and gas cylinder.

(2) Natural gas start-up: Turn the fuel change-over switch to the "gas" position, turn the ignition switch to the "ignition" position, and the indicator light on the fuel change-over switch will light up, so that the operation can be started according to the normal operation procedure of the automobile.

(3) Conversion of natural gas into gasoline: Just turn the fuel switch from the "gas" position to the "oil" position once. During the transfer, the engine will stop slightly, so it is best not to transfer in a place with heavy traffic. If the conversion is carried out in the stopped state, the engine speed should be increased to avoid flameout.

(4) Conversion from gasoline to natural gas: First, turn the fuel switch from the "oil" position to the middle position. When the car will run out of oil in the carburetor oil chamber, that is, when the engine sound changes (about 1~2 minutes), immediately turn the switch to the "refueling" position. In the process of conversion, the engine will still stop slightly, so don't do it in places with heavy traffic.

(5) When driving with natural gas, pay attention to the gas indicator light on the instrument to understand the gas situation. When the green light is completely off and the red light is on, it means that the natural gas is about to run out.

(6) Mixed burning of oil and gas is strictly prohibited.

(7) Inflating: After the car enters the inflating position, pull the brake to prevent the car from moving when inflating. Turn off electrical equipment (including tape recorders, etc.). ), remove the dust plug of the inflation valve and insert it into the inflation tube for inflation. After inflation, take out the inflation tube, install the dust plug, and check whether there is air leakage at the joint. If there is no leakage, start the vehicle.

(8) Air leakage treatment: In case of air leakage when the car is running, the power supply should be cut off first, the engine should be turned off, and the bottle valve should be quickly closed before other treatment. When the gas cylinder cannot be closed due to a large amount of leakage of pipeline rupture gas, the site should be closed immediately to isolate the fire source. No one or vehicles are allowed to enter, and natural gas (lighter than air) should be treated after it is exhausted. In case of fire, in addition to immediately turning off the power supply and gas cylinders, the site should also be closed and put out with a fire extinguisher. Because there is a safety device on the gas cylinder, it will not explode and can be handled with confidence.

(9) When parking, close the high-pressure cut-off valve and the gas valve of the natural gas bottle.

(10) Stop:

1) When the driver leaves the car or stops temporarily for more than 10 minutes, turn off the power supply and air supply valve.

2) When parking for a long time, exhaust the coolant and fuel oil, use up the natural gas, disconnect the power supply, and place it in a ventilated, moisture-proof, fire-proof and sun-proof place.

3) If parked in the garage, it is forbidden to open the air supply valve and use gas to start the engine.

3. Rules for the safe use of compressed natural gas vehicles

(1) Strictly implement the safety operation procedures for gas filling. The gas cylinder inflation pressure shall not be higher than 20MPa. The natural gas used should be purified to meet the vehicle gas quality standards.

(2) It is forbidden to run out of gas when the equipment fails and the system leaks.

(3) When disassembling related high-voltage components, unsafe operation should be avoided. When opening the bottle valve, people are not allowed to stand in front of the valve port of the gas bottle. Cut-off valve should be opened slowly, then gradually after ventilation to prevent impact on instrument valve and other components.

(4) It is forbidden to check the air leakage with fire.

(5) No open flames are allowed near the cab and vehicles. Check whether there is any natural gas leakage at any time. Smoking in the cab is strictly prohibited in a fully enclosed state.

(6) Avoid collision between gas cylinders and pipelines and obstacles when driving. If air leakage is found in the air supply system, it should be eliminated in time and replaced with gasoline fuel.

(7) When the vehicle stops driving, it should be parked in the shade to prevent the sun from exposure.

(8) When repairing vehicles, it is forbidden to knock or collide with gas cylinders, pressure reducing valves and pipelines. The distance between gas cylinder and open flame shall not be less than 10m.

(9) If the car uses compressed natural gas for a long time, it should switch to gasoline for one hour regularly to run the engine to prevent the oil supply system from failing.

(10) accident handling:

1) Traffic accident treatment: disconnect the main power supply and close all air valves;

2) Fire accident treatment: disconnect the main power supply, close all air valves to isolate the site, and use fire extinguishers, sand, covers, etc. Put out the fire, and notify the fire department as appropriate, and call 1 19 to call the police.

4. Maintenance of 4.CNG cars

The maintenance of CNG devices should be combined with the maintenance of automobiles at all levels.

(1) Before each trip, check the fastening of all components, deal with loose fasteners in time, and check whether there is any leakage of gas, pipes and joints. If there is any leakage, handle it in time.

(2) Check the high-pressure pipeline filter element and solenoid valve core once a month, and adjust the pressure of pressure reducing valves at all levels.

(3) Repair the pressure reducing valve and gas supply system once every six months, and replace the damaged parts in time.

(4) According to the National Labor Bureau's Regulations on Gas Cylinder Safety Supervision, natural gas cylinders are inspected once every two years. Those who fail the test should be replaced in time, and a test card should be filled out after the test.

(5) Always keep the CNG system and air filter core clean and complete.

(6) When the natural gas pipeline needs to be dismantled due to engine maintenance, clean cotton cloth should be used to block all joints to prevent foreign objects from entering and damaging the valve port of the pressure reducer.

(7) When maintaining the vehicle, check the fastening of the inflation valve, pressure reducer and pipeline clamp. If it is found that it is loose, the clip is lost and doesn't work, it should be handled in time.

(8) When maintaining the vehicle, use a torque wrench to measure and check whether the installation and fastening of the cylinder meet the requirements.

(9) Remove the sludge on the cylinder surface at any time, so as not to affect the technical performance of cylinder valves and safety explosion-proof valves.

(10) Only after the gas in the system is released and all valves of the gas cylinder are closed can the gas device be maintained.

(1 1) When the high-pressure system fails, the driver shall not disassemble, modify, repair or adjust the pressure reducer by himself.

(12) Fill in and save the relevant technical data of compressed natural gas vehicles in accordance with relevant regulations and requirements.

Fourthly, the construction and management of CNG filling stations.

1, composition of gas station

(1) Natural gas purification and drying (including pressure regulating control system)

Natural gas transported by natural gas pipeline network cannot be directly used as automobile fuel, and can only be used as automobile fuel after dehydration, hydrocarbon removal, desulfurization and purification, dry noise treatment and meeting the requirements of relevant gas quality standards. The system mainly includes dehydration, hydrocarbon removal and desulfurization equipment and filters, noise dryer, natural gas recovery device and pressure regulator.

(2) Natural gas compression system

The purified and dried natural gas can enter the compression system for compression. The compressor system includes the following parts: intake buffer tank, compressor main engine, lubrication system, cooling system and others.

The function of the inlet buffer tank is to reduce the vibration of the unit caused by the pressure pulsation at the inlet of natural gas and avoid the damage of the unit parts.

The main compressor is the heart of the compressor system and the whole gas station. The compressor used in CNG filling station has high exhaust pressure and small exhaust capacity, and generally adopts reciprocating piston compressor.

The compressor lubrication system includes the lubrication of crankshaft main bearing, crankshaft connecting rod, crosshead, piston and cylinder. CNG compressors generally adopt forced lubrication.

The function of compressor cooling system is to ensure that the temperature of natural gas under the final exhaust pressure does not exceed the design requirements. The cooling system is divided into two parts: one part is the cooling of compressor gas; Part of it is the cooling of lubricating oil. Generally, there are two cooling methods, namely water cooling and air cooling.

Others include the adjustment of exhaust volume, motor speed control, air intake unloading control, safety valve, leakage gas recovery or venting device and other auxiliary components.

(3) Natural gas storage system

The gas cylinder group shall be arranged in the gas filling station. When the compressor works, firstly, the gas cylinder group is inflated, and when the pressure in the gas cylinder group reaches the set maximum pressure, the compressor automatically stops. At this time, if a car is inflated, the inflation procedure is carried out in sequence. First, use compressed natural gas in the gas cylinder group. When the natural gas pressure in the gas cylinder group drops to the set pressure, the compressor will automatically start to re-inflate the gas cylinder group.

The design storage pressure of gas cylinders in filling stations is the same as the compressor exhaust pressure, both of which are 25MPa. The total gas storage capacity varies according to the scale of filling stations, and the design volume of each filling station manufacturer is also different. But its principle is to ensure the high efficiency of filling stations and the economy of building stations.

(4) Control system

The control system includes power supply control, compressor operation control, gas storage control (priority/sequence system) and gas sales control.

Power supply control includes power supply in different areas, starting system of main motor, protection system of main motor and auxiliary circuit.

Compressor operation control is set with automatic start, automatic stop, automatic stop at fault point, emergency stop and other control items.

Gas storage control (priority/sequence system) realizes gas storage control of gas filling stations through priority/sequence control devices.

The gas selling control is mainly included in the gas selling system, and the automation program is high, and the program control panel is completed. The program control panel is a computer system, and the software consists of four parts, namely, the system self-check program; Unit price setting procedure; Opening and closing, solenoid valve and flow detection, measurement and pricing procedures; Display output program.

(5)CNG gas sales system

The gas sales system consists of a gas sales machine and its gas circuit system.

When the gas cylinders on the compressed natural gas vehicle are inflated, the high-pressure natural gas from the gas cylinder group of the filling station flows through the mass flowmeter of the vending machine, and the flowmeter sensor generates pulse signals, which are transmitted to the electronic device (microcomputer device) through the transmitter (detector). The transmitted pulse signal is recognized by the computer for measurement, pricing and display.

The gas circuit system of the automatic gas vending machine is responsible for the sequential control of the gas selling process, and automatically closes the solenoid valve after the gas selling.

2. Procedures for establishing procedures on site

3. Management of gas stations