Introduction to dimethyl ether urban buses

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SWB6116DME Methanol Engine Urban Bus Table of Contents 0. Introduction 1. Exterior view of the SWB6116DME methanol engine urban bus 2. Main technical specifications of the SWB6116DME methanol engine urban bus 3. Methanol storage and supply system 4. Additional information on vehicle operation 5. Additional information on vehicle maintenance 6. Safety technical requirements 7. Common faults in the fuel system and their solutions 0. Introduction Methanol is a versatile chemical product that can be produced from coal, natural gas, or biomass. The molecular formula of dimethyl ether is: CH3-O-CH3. Dimethyl ether is a highly flammable gas at room temperature and normal pressure, but it becomes liquid at room temperature and a pressure of 0.5 MPa. Due to its physicochemical properties that enable complete combustion and excellent compression ignition, dimethyl ether is being recognized and accepted by more and more people as a new type of high-quality, clean fuel. Research and development of dimethyl ether vehicles have also achieved certain results and progress. China’s energy structure is characterized by an abundance of coal, a shortage of oil, and limited natural gas reserves; as a result, it relies heavily on oil imports, which is detrimental to its energy security. Under certain conditions, using dimethyl ether as a substitute for diesel as a vehicle fuel can play a positive role in reducing dependence on petroleum and mitigating the pollution of the atmospheric environment caused by vehicle exhaust. Shanghai began researching the application of dimethyl ether in compression-ignition engines in the late 1990s. “During the 15th Five-Year Plan period, the development of dimethyl ether urban buses with complete independent intellectual property rights was completed. Building on the research results achieved during the 10th Five-Year Plan period, and with the support of various relevant municipal departments, SAIC Group developed the SWB6116DME urban bus by replacing the engine in the SWB6116 model with an SC8DR250Q3 dimethyl ether engine produced by Shanghai Diesel Engine Co., Ltd. It also developed a system for storing and transporting dimethyl ether fuel. This supplementary manual for the SWB6116DME dimethyl ether urban bus provides information on the vehicle’s exterior appearance and main technical parameters, the composition and working principle of the dimethyl ether storage and delivery system, additional details on vehicle operation and maintenance, common faults in the fuel system and their solutions, as well as safety requirements. For general requirements regarding vehicle operation and maintenance, please refer to the user manual for the SWB6116 urban bus. For the use and maintenance of the engine, please refer to the accompanying documents for that engine. Dimethyl ether vehicles are a new type of alternative fuel vehicle, and their technology is continuously being improved. Please read carefully the supplementary instructions for the SWB6116DME dimethyl ether urban bus, the operating instructions for the SWB6116 urban bus, the instructions for Shanghai Diesel Engine Co., Ltd.’s SC8DR250Q3 dimethyl ether engine, as well as the instructions for the dimethyl ether cylinders used in vehicles, and follow them accordingly. Please contact us promptly with any suggestions for product improvements or issues encountered during use. 2007-8-20 1. Exterior view of the SWB6116DME dimethyl ether urban bus Figure 1: Exterior view of the SWB6116DME dimethyl ether urban bus 2. Main technical parameters of the SWB6116DME dimethyl ether urban bus 2.1 Dimensional parameters Unit: millimeters Item Dimensional parameters Vehicle length 11,290±25 Vehicle width ≤2,500 Vehicle height (empty) ≤3,450 Axle spacing 5,800±10 Front suspension distance 2,360 Rear suspension distance 3,130 Front wheelbase 2,101 Rear wheelbase 1,860 2.2 Mass parameters Item Mass parameters Gross vehicle weight, kg (with air conditioning) Total weight 11,100 Front axle 3,100 Rear axle 8,000 Maximum designed total weight, kg Total weight 16,500 Front axle 5,800 Rear axle 10,700 Number of passengers, persons (with air conditioning) 77+1 Seats, number Passenger seats 23–48 Driver’s seat 1 Specific power, kW/t 11.15 Note: Allowable error for gross vehicle weight and maximum designed total weight is 3% of the rated value. 2.3 Mobility and off-road capability parameters Item Mobility and off-road capability parameters Minimum turning diameter, m ≤22 Approach angle, (°) ≥8 Departure angle, (°) ≥7.5 Minimum ground clearance, mm ≥145 2.4 Basic performance parameters Item Basic performance parameters Power Maximum speed (fully loaded), km/h ≥80 Minimum stable speed in direct gear, km/h ≤30 Braking distance at 50 km/h initial speed, m ≥750 Time to accelerate from rest to 50 km/h (fully loaded), s ≤30 Time to accelerate from 30 km/h to 70 km/h in direct gear (fully loaded), s ≤50 Maximum gradient, (%) ≥20 Fuel efficiency Fuel consumption at 50 km/h constant speed, kg/100km ≤30 Ride comfort Equivalent continuous noise level Leq, dB ≤113 2.5 Safety and environmental protection parameters Item Safety and environmental protection parameters Braking Braking distance, m Empty, pressure 600 kPa, speed 30 km/h ≤9 Fully loaded, rated operating pressure, speed 30 km/h ≤10 Percentage of total braking force relative to vehicle weight, (%) Empty ≥60 Fully loaded ≥50 Percentage of braking force on front axle relative to axle load, (%) Empty ≥60 Fully loaded ≥60 Percentage of friction force per wheel relative to axle load, (%) ≤5 Percentage difference between left and right braking forces relative to the greater of the two braking forces on that axle, (%) Front axle ≤20 Rear axle When braking force difference is greater than 60% of axle load, ≤24 When braking force difference is less than 60% of axle load, ≤8 No part of the vehicle shall exceed the width of the test track, m 3 Emission of exhaust pollutants Meets the requirements of GB 17691-2005, China Phase III Emission smoke density Meets the requirements of GB 3847-2005 Noise External noise during acceleration, dB(A) ≤83 Internal noise during constant speed driving, dB(A) ≤78 2.6 Technical parameters of major assemblies Item Model SWB6116DME Chassis model SWB6116DME Engine Model SC8DR250Q3 Type Six-cylinder, in-line, four-stroke, turbocharged with intercooler, compression ignition Maximum net power, kW/r/min 184/2,200 Maximum torque, N•m/r/min 958/1,200–1,400 Total displacement, L 8.27 Clutch Model 430 pull-type clutch Type Single-disc, dry Type Hydraulic remote control with pneumatic assistance Transmission Model QJ1205 Type Mechanical, manual, fully synchronized Control method Mechanical remote control Drive shaft type Open single-section with two universal joints Front axle Model EQ153 two-stage drop front axle assembly Type Steering bridge, knuckle-type, fully forged Maximum axle load, kg 7,000 Front wheel Alignment Front wheel camber (°) 0 Kingpin inclination, (°) 8 Kingpin caster, (°) 3.5 Front toe, mm 0–1.5 Rear axle Model RC25160 Type Single-stage reduction Maximum axle load, kg 11,300 Gear ratio 4.89 Steering gear Model 3411010-4E Type Integrated servo recirculating ball power steering Steering gear ratio 20.48:1 Steering wheel diameter, mm Φ450 Front wheel steering angle Inner wheel, (°) 55 Outer wheel, (°) 40 Suspension type Non-independent, air suspension, equipped with lateral stabilizer bar and double-action shock absorbers Braking system Type Dual-circuit, independent front and rear pneumatic braking Service braking Front disc and rear drum wheel brakes Parking braking Energy-storing spring pneumatic braking Wheels Rim 8.25×22.5 Tire 11R22.5 Frame Type, mm Channel steel, longitudinal beam cross-section 230×70×6, transverse beam cross-section 230×65×6 Outer frame width, mm Front 740, Rear 890 Electrical equipment Battery, A•h 6-Q-200 Generator, V/A 28/110 Liquid dimethyl ether cylinder Model CYEW350-140-2.0 Type Welded cylinder Capacity, L 3×140 2.7 Capacity parameters and filling specifications Filling location Unit Specification Capacity Remarks Engine lubrication system L CF-4 grade 15W/40 lubricant specifically for dimethyl ether engines (Great Wall) 25 Sinopec Great Wall Lubricants Group Co., Ltd. Engine cooling system 50% FDF-1 coolant additive 41 Product of Shanghai Automotive Research Institute Transmission GL4 grade 85W/90 gear oil 8.2 Use GL5 grade 75W/90 when winter temperature is below -10°C Rear axle main reducer GL5 grade 85W/90 gear oil 12 Use GL5 grade 75W/90 when winter temperature is below -10°C Steering system No. 8 hydraulic transmission fluid 4.8 Use No. 10 aviation hydraulic fluid (SY187-88) in northern regions Clutch assistance system JG3 brake fluid (GB10830) 1.5 3. Dimethyl ether storage and delivery system 3.1 Schematic diagram of the dimethyl ether storage and delivery system Figure 2: Schematic diagram of the working principle of the dimethyl ether storage and delivery system 3.2 Working principle of the dimethyl ether storage and delivery system The dimethyl ether storage and delivery system of the SWB6116DME dimethyl ether urban bus consists of a filling panel, a set of liquid dimethyl ether cylinders for use in vehicles, a pressure control assembly, and pipelines. The composition and working principle of each part are as follows: 1) Liquefied dimethyl ether cylinders and cylinder sets for vehicles: The SWB6116DME type dimethyl ether urban bus uses a cylinder set consisting of 3 vehicle-grade liquefied dimethyl ether cylinders with a capacity of 140 liters each to store the fuel dimethyl ether. It can hold 336 liters of fuel. The cylinder bank is located at the rear of the roof. There is a shield outside the bottle set to prevent direct sunlight from hitting the gas cylinders. There are louvers at the front and back of the shield for ventilation. Inspection doors are provided on both sides and at the top of the shield for routine inspection, maintenance, and operation. Automotive liquefied dimethyl ether cylinders are pressure vessels designed specifically for the properties of dimethyl ether, used to store it. At room temperature, dimethyl ether in the cylinder exists in both liquid and gas states; the liquid dimethyl ether is located at the bottom of the cylinder, while the gas phase dimethyl ether is found in the upper part of the cylinder. The pressure of the gaseous phase is the saturated vapor pressure of dimethyl ether at the ambient temperature. The saturated vapor pressure of dimethyl ether rises rapidly as the temperature increases. The saturated vapor pressures of dimethyl ether at different temperatures are shown in the table below: Temperature (°C) Satured Vapor Pressure (MPa): -10 0.187, 0 0.264, 10 0.370, 20 0.506, 30 0.677, 40 0.887, 50 1.142, 60 1.458. Liquefied dimethyl ether cylinders for use in vehicles consist of a cylinder body, an integrated valve, a safety valve, and a shut-off valve that connects to the liquid. The bottle body is welded from steel plates and flanges. The integrated valve consists of a valve body, a liquid inlet valve (with a check valve), a charge-limiting valve, a level gauge, a liquid outlet valve, and a gas connection valve. When refueling the vehicle, with the liquid inlet valve on the cylinder open, dimethyl ether enters the cylinder through the inlet valve. To provide space for the liquid dimethyl ether in the cylinder to vaporize and prevent accidents caused by excessive pressure inside the cylinder, a fill-limiting device controlled by a float will stop fuel from entering the cylinder by closing the fill-limiting valve when the cylinder is 80% full, thereby ensuring safety. The fuel that returns from the engine also goes back to the cylinder through the inlet valve. The gauge on the gas cylinder shows the height of the liquid level inside it. The liquid level signal of the third cylinder counted from the front is also sent to the fuel gauge on the dashboard, allowing the driver to top up the fuel in a timely manner based on the information provided by the gauge. The liquid level signal is also sent to the fuel filling panel, so that the staff at the filling station can keep track of the filling progress. The liquid discharge valve is the outlet through which dimethyl ether is released from the cylinder; opening this valve allows dimethyl ether to be discharged. The safety valve is installed in the gas phase area of the cylinder. When the pressure inside the cylinder exceeds 2.3 MPa, the safety valve opens to release the high-pressure gaseous dimethyl ether, thereby preventing more serious accidents. The gas-phase and liquid-phase connections of the cylinders are linked through pipelines to connect the gas-phase and liquid-phase areas of the cylinder set respectively, thereby maintaining a balance in the liquid levels between the cylinders while the vehicle is refueling or in use. The gas and liquid phase connections are also equipped with stop valves to facilitate the maintenance and inspection of the cylinders. 2) Filling panel: The filling panel is located inside the trunk door at the rear right side of the vehicle. The panel is equipped with a quick-connect dimethyl ether filling port, a vibration-resistant pressure gauge, a level indicator, an overflow valve, and a vent valve. There are labels on the panel indicating the name of the component and warning messages. Behind the filling port on the panel, there is a manual stop valve. The quick-connect fuel filler port can be quickly connected to the filling gun at the fuel station. After opening the manual shut-off valve located behind the filling port, the check valve inside the filling port is pushed open by the pressure from the filler; as a result, dimethyl ether can flow into the cylinder through the filling port, the manual shut-off valve, the pipelines, and the inlet valve on the cylinder’s integrated valve. After filling is complete, the check valve inside the filling port closes automatically, preventing dimethyl ether in the pipeline from flowing out through the filling port. After fuel filling is complete, the manual shut-off valve located behind the filling port should be closed to prevent dimethyl ether leakage in the event that the seal of the one-way valve in the filling port fails. The relief valve is used to regulate the pressure of dimethyl ether supplied to the engine; the engine can operate stably only when the supply pressure of dimethyl ether is stable and higher than the saturated vapor pressure of dimethyl ether at the operating temperature. The overflow valve is already adjusted at the time the vehicle leaves the factory. Fuel supply pressure adjustment should be carried out by professional maintenance personnel. The vibration-resistant pressure gauge indicates the pressure of dimethyl ether supplied to the engine, which is normally 1~1.2 MPa. When the ground temperature is 40°C or higher, the supply pressure should be set at the upper limit; when the ground temperature is below 40°C, it can be set at the lower limit, in order to prevent dimethyl ether from vaporizing within the fuel delivery lines, which could cause instability in the engine or even its shutdown. During the routine maintenance and operation of the vehicle, this pressure should be checked frequently; if any abnormalities are detected (excessively high or low pressure, or severe fluctuations), a professional technician should be consulted for inspection and adjustment. The liquid inside the surface glass acts as a damper to improve the reliability of the pressure gauge. If it is found that the liquid level inside the surface glass is below ½, the pressure gauge should be replaced. The relief valve is used to maintain the pipeline or, when necessary, to discharge dimethyl ether from it. The opening and closing directions of the valve are indicated on the panel. When using a relief valve, fire safety must be taken into account. The area around the vehicle should have good ventilation, the ground should be level, free of holes or sewers, and there should be no sources of fire that could ignite dimethyl ether. The level indicator on the panel shows the liquid level in the dimethyl ether tank via a set of light-emitting diodes. When all the light-emitting diodes are lit, it indicates that the tank is full; when they are all off, it means the tank is empty. This allows the staff at the filling station to keep track of the liquid level in the tanks while fuel is being added, thereby preventing overfilling in case the filling machine malfunctions. 3) Pressure control assembly: As mentioned above, dimethyl ether can remain in a liquid state only at a certain pressure. If a certain pressure cannot be maintained during the transport of dimethyl ether, it will vaporize, causing instability in the engine and leading to stalling. One of the main functions of the pressure control assembly is to maintain the pressure in the dimethyl ether delivery pipeline, ensuring the stable operation of the engine. The pressure control assembly is also installed inside the cylinder guard. The pressure control assembly consists of a common rail connector, solenoid valve, coarse filter, boost pump, and fine filter, and is integrated on the mounting bracket. When the key switch is in the ON position, the power is supplied, the solenoid valve opens, and the booster pump starts operating at the same time. At this point, the pipeline between the booster pump and the cylinder bank is opened, and the booster pump pressurizes the dimethyl ether from the cylinder bank before sending it to the engine. Its purpose is to keep dimethyl ether in the pipeline in a liquid state at all times. If the engine does not start after the power supply has been connected for 1 minute, the system will automatically turn off the power. The filter is used to remove solid and/or gum-like impurities from dimethyl ether, in order to protect the precision components of the booster pump and the engine’s fuel system. The power supply for the solenoid valve and the booster pump is controlled by the key switch on the console. The key switch is on in the ON position and off in the OFF position. Cutting off the power to the solenoid valve and the booster pump can stop the fuel supply to the engine, serving as an emergency measure. 4) Pipelines: The dimethyl ether pipelines include the filling pipeline, the fuel delivery pipeline, the return pipeline for excess fuel, and the pipeline that connects the gas and liquid phases in the cylinder assembly. Except for the two sections of piping connected to the engine fuel injection pump and the section of piping for injector return, which are flexible pipes, all other piping is made of rigid stainless steel seamless tubes. Clamshell connectors are used between pipes and between pipes and components. All pipelines must be leak-free. At the time of departure from the factory, the vehicle underwent a leak test using nitrogen at 1.6 MPa. All joints are inspected using the bubble test; no bubbles should escape within at least 1 minute. The pipes located within the engine compartment are all wrapped in insulating material to prevent the high temperatures in that compartment from heating up dimethyl ether and thereby causing a significant reduction in the engine’s power output. To detect leaks in the fuel system promptly, the vehicle is equipped with 4 leak sensors located near the cylinder assembly, control panel, pressure control assembly, and engine fuel pump. When the dimethyl ether concentration around these sensors exceeds 1.2%, the leak alarm on the dashboard will emit audible and visual warning signals. The optical signal will also indicate the installation location of the alarm sensor. 4. Additional notes on vehicle operation: Since the combustion characteristics of dimethyl ether are very similar to those of diesel, and dimethyl ether engines are a variant of diesel engines, the operation of vehicles powered by dimethyl ether is almost identical to that of diesel vehicles. The main points to note are as follows: 4.1 Dimethyl ether and its filling: Since dimethyl ether has a much lower viscosity than diesel, it cannot provide lubrication for the precision components of the engine’s oil pump and injectors. Therefore, when the engine runs on dimethyl ether as fuel, trace amounts of additives must be added to it to prevent wear on the precision components of the fuel system. Therefore, when filling the vehicle with dimethyl ether, it is necessary to use dimethyl ether that has already been mixed with additives according to the specifications and concentrations specified by the engine manufacturer. Once the vehicle enters the dimethyl ether filling station and reaches the filling position, the engine should be turned off and the power supply switched off. Passengers in the vehicle must comply with the safety procedures at the fueling station, turn off their mobile phones, and are not allowed to smoke or use flashlights. When filling with dimethyl ether, the vehicle chassis should be connected to the grounding wire of the filler machine. After dimethyl ether has been filled, it is necessary to confirm that the filling gun and grounding wire have been removed, and that there are no abnormalities in the filling compartment. Only then should the shut-off valve behind the filling port be closed, the dust cover for the filling port installed, and the door of the filling compartment closed. 4.2 Engine start-up and shutdown: Dimethyl ether engines have good start-up performance, but this is only possible when the fuel supply is adequate (that is, when the pipeline between the booster pump and the engine’s injection pump is filled with liquid dimethyl ether). When starting a dimethyl ether engine for the first time each day, the power to the solenoid valve and the boost pump should be turned on first; the boost pump should operate for about half a minute before the engine is started. After the vehicle starts, check whether the pressure indicated by the gauge on the filling panel is within the normal range (1~1.2 MPa); only if it is normal can the vehicle be driven away. When shutting down the engine, it is necessary to first use the shutdown switch to operate the shutdown lever on the engine’s injection pump in order to stop the engine. Then turn off the power to the solenoid valve and the booster pump. Using this shutdown method allows the engine’s fuel supply lines to be filled with liquid dimethyl ether, facilitating the next start-up. 4.3 While the vehicle is in motion: The fuel gauge on the dashboard indicates the liquid level of dimethyl ether in the cylinder. Due to the different cross-sections of the steel cylinder and the fuel tank, once the dimethyl ether level drops to half, it will fall rapidly; therefore, fuel should be replenished in a timely manner to avoid disruptions in operation. On the left side of the dashboard, a leak detector is installed. In the event of a leak, the LED on the alarm will indicate the location of the leak, allowing prompt action to be taken. 4.4 Parking of vehicles: Dimethyl ether city buses should be parked in well-ventilated areas. The ground of the site should be level, free of pits and holes. Explosion-proof lighting and electrical equipment are used on the site, along with fire-fighting facilities. Smoking and any activities involving an open flame or sparks are prohibited on the ground of dimethyl ether city bus parking lots. 4.5 Reactivation of vehicles that have been out of use: When a vehicle is reactivated after several days of being unused, it is necessary to check whether the engine’s speed control function is working properly. Refer to the engine operation manual for the inspection method. If a problem is detected, professionals should clean the dimethyl ether residue from the plunger components of the fuel injection pump to ensure that the engine’s speed control function operates smoothly and reliably. It is recommended that for vehicles that are not in use temporarily, they be started once a day and run for a few minutes, so as to keep dimethyl ether in liquid form within the engine’s fuel supply system and prevent the additive from accumulating on the surfaces of precision components. 5. Additional Notes on Vehicle Maintenance 5.1 Routine and Periodic Inspections: In addition to the regular inspections for dimethyl ether-powered urban buses, the following additional checks are required. 1) Before starting the vehicle, in addition to the regular inspections, the filler cap should also be opened after the engine is started, in order to check the pressure indicator on the filling panel as well as to verify that there are no leaks or unusual odors in the dimethyl ether lines. If any problems are found, professional assistance should be sought promptly for repair. 2) Maintenance of the dimethyl ether filter: ① Coarse filter: Clean it once a month. Replace the filter element and seals every six months. ② Fine filter: Clean it once every three months. Replace the filter element and seals every six months. 3) The replacement cycle for seals is half a year. 4) After vehicle maintenance and the disassembly/installation of the fuel system, the integrity of the dimethyl ether storage and delivery system should be checked using the bubble test while the pressure in the dimethyl ether supply line is above 1 MPa. Each connection point should be observed for more than 1 minute; no bubbles escaping indicates normal operation. At the same time, check the fixing and protection of the pipelines. 5) During vehicle maintenance, check the installation condition of the liquefied dimethyl ether cylinder used in the vehicle; if it is loose, tighten it promptly to prevent the cylinder from shifting and causing the pipelines to break. 6) During vehicle maintenance, check the function of the solenoid valve and replace the seals in the fuel system as specified. Fix any abnormalities promptly. 7) The regular inspection of liquefied dimethyl ether cylinders for use in vehicles shall be carried out in accordance with the technical specifications of the cylinders. 8) Maintenance of the leak alarm: Before each day’s outing, after the power is turned on, press the self-check button on the alarm panel; the four red alarm lights flashing in sequence indicate that the alarm is functioning properly. During the first-level maintenance of the vehicle, clean the sensor filters to prevent malfunctions due to blockages. During maintenance, do not rinse the sensor directly with water. 5.2 Requirements for the maintenance workshop 1) The floor of the maintenance workshop for dimethyl ether urban buses should be level, free of pits, holes, or ditches. Exhaust fans should be installed on the exterior walls near the ground level. 2) Install explosion-proof electrical equipment in the repair shop. 3) Equipped with a lift for the repair of vehicle chassis. 4) Equipped with a workbench for the inspection and maintenance of equipment on the vehicle’s roof. 5) Equipped with lifting equipment and lifting tools for loading and unloading liquefied dimethyl ether cylinders from vehicles when necessary. 6) Install necessary fire-fighting equipment and combustible gas leak detection systems. 6. Safety Technical Requirements 1) Before using the SWB6116DME dimethyl ether urban bus, its drivers and maintenance personnel must carefully read this safety manual and the product operation instructions, so as to become familiar with the structure, working principles, usage methods, maintenance requirements of the vehicle’s dimethyl ether engine and fuel system, as well as the procedures to take in emergency situations. They must also undergo training and pass relevant assessments before they can operate the vehicle. 2) When filling vehicles with dimethyl ether, it is necessary to strictly follow the safety procedures at the filling station. Once the vehicle reaches the refueling area, it is necessary to turn off the engine, as well as the vehicle’s main power supply and mobile phone. Smoking and the use of flashlights are prohibited inside the fueling station. The driver must get out of the vehicle when refueling. All operations related to fuel filling are carried out by the staff at the fuel station. After fuel filling is complete, the ground wires and filling gun are removed; the control panel should be checked to ensure it is functioning properly. Then, the manual shut-off valve should be closed, a cover for the filling port should be installed, and the inflation chamber door should be closed. After that, the power supply can be reconnected, the engine started, and the filling station left. 3) Before filling the vehicle with dimethyl ether for the first time (including before filling an empty cylinder with dimethyl ether), the cylinder should have its air replaced with nitrogen. When filling with dimethyl ether for the first time, the cylinder certificate and the technical documents specified by the filling station must be carried. 4) If a dimethyl ether leak is detected while the vehicle is in motion (for example, if the leak alarm goes off), the vehicle should be stopped in a safe location. The main power supply of the vehicle must be turned off immediately, and the passengers should be evacuated. Afterwards, attempts should be made to close the various valves on the cylinders, after which professional personnel should be called to carry out repairs. 5) If a fire breaks out near the vehicle, it should be moved immediately to a location far away from the fire. If transfer is not possible, the passengers in the vehicle should be evacuated immediately and the main power supply of the vehicle turned off. If possible, close all the valves on the cylinder immediately to shut off all its inlets and outlets. 6) If the vehicle catches fire, the passengers should be evacuated immediately and the main power supply of the vehicle should be turned off. If possible, close the cylinder valve immediately to shut off all inlet and outlet ports of the cylinder. Then use a fire extinguisher to put out the fire. When using a fire extinguisher, point it at the location of the gas leak in order to dilute the gas concentration and extinguish the fire. 7) If the vehicle needs to be taken into the workshop for repair, do not fill it with dimethyl ether before entering the workshop. Before repairing the vehicle, the main power supply as well as the inlet and outlet valves for the gas cylinders and the shut-off valves on the gas-liquid pipelines must be turned off. If necessary, dimethyl ether in the pipelines should be released at a safe location through a vent valve. The dimethyl ether pressure in the pipeline between the cylinder and the engine can reach up to 1.0–1.2 MPa. To ensure safety, do not perform any operations on the dimethyl ether system under pressure. It is recommended to first turn off the vehicle’s main power supply as well as the valves for the inflow and outflow of gas cylinders. Then, at a safe location, slowly open the release valve on the filling panel to release any residual dimethyl ether in the pipelines. Only after the pressure gauge indicates 0 can work be done on the pipelines. To empty the fuel from the cylinder, liquid extraction must be used. 8) No items that could cause a fire shall be present around the dimethyl ether urban buses when they are in the maintenance workshop. Tasks such as welding and grinding on vehicles that may generate sparks must be carried out by specially trained personnel holding the necessary certificates, and protective measures must be taken. The maintenance area must have safety and fire prevention markings and be separated from the maintenance areas for other vehicles. There must be no open flames within 10 meters of the maintenance point. The maintenance area is equipped with explosion-proof electrical appliances and lighting, as well as fire-fighting equipment. Maintenance personnel must wear anti-static protective clothing, anti-static gloves, and anti-static shoes; they are not allowed to wear synthetic fiber clothing or shoes with metal studs. Non-professionals are not allowed to enter the maintenance area. During maintenance, hitting is strictly prohibited to prevent sparks. 9) Vehicles should be parked in well-ventilated dedicated parking areas for dimethyl ether vehicles. The site should use explosion-proof electrical equipment and lighting fixtures, have safety and fire prevention signs installed, and be equipped with fire-fighting equipment. Flammable and explosive items are not allowed in the area, and smoking is prohibited. 10) Dimethyl ether liquid can cause the temperature of the surrounding environment to drop due to rapid evaporation, so care should be taken to avoid frostbite. 11) Dimethyl ether is a weak **agent; it can enter the body through the respiratory tract, digestive tract, and skin. It irritates the skin and respiratory system and has an effect on the nervous system. Excess concentrations of dimethyl ether in the air can cause oxygen deficiency and lead to unconsciousness. Those who have inhaled dimethyl ether vapor should be moved away from the scene to a quiet place with fresh air and moderate temperature. Those experiencing breathing difficulties must receive artificial respiration or oxygen therapy immediately, and should be rushed to a hospital for treatment. 7. Common Faults in the Fuel System and Their Solutions 7.1 Faults with the Filling Panel Fault symptoms Solution methods Leakage at the filling port Cut off the power supply. Close the ball valve behind the filling panel. Open the relief valve to release the remaining fuel in the pipeline. Replace the filling port. If the pressure indicated by the pressure gauge is too high or too low, adjust the relief valve while the engine is idling until the pressure indicates a normal and stable value. If the liquid level in the pressure gauge is below ½, cut off the power supply. Close the ball valve behind the filling panel. Open the relief valve to release the remaining fuel in the pipeline. Replace the pressure gauge; the relief valve is leaking; cut off the power supply. Close the ball valve behind the filling panel. Open the relief valve to release the remaining fuel in the pipeline. Replace the relief valve. 7.2 Pressure control assembly failures: Symptoms and solutions – Leakage in the coarse filter: Close the liquid outlet valves on the three cylinders, and replace the seals or the coarse filter assembly. Leakage in the fine filter: Close the liquid outlet valves on the three cylinders, and replace the seals or the fine filter assembly. Symptoms and solutions – Clogged filters lead to insufficient fuel supply, causing the engine to stall while in operation: Close the liquid outlet valves on the three cylinders, and clean or replace the filter elements. Low pressure indicated by the pressure gauge; adjusting the relief valve is ineffective or the booster pump is not working: Close the liquid outlet valves on the three cylinders, and replace the booster pump assembly. Leakage in the booster pump: Close the liquid outlet valves on the three cylinders, and replace the booster pump assembly. The solenoid valve cannot open: Close the liquid outlet valves on the three cylinders, and replace the solenoid valve coil or the entire valve assembly. External leakage from the solenoid valve: Close the liquid outlet valves on the three cylinders, tighten the bolts at the leaking area, or replace the seals. Internal leakage from the solenoid valve: Close the liquid outlet valves on the three cylinders, and replace the seals on the valve core or the valve core itself. 7.3 Liquefied dimethyl ether cylinders for vehicles 7.3.1 Integrated valves: Symptoms and solutions – Leakage at the connection between the inlet valve and the inlet pipe: Tighten the nuts at the connection or replace the coupling. Leakage at the connection between the outlet valve and the outlet pipe: Tighten the nuts at the connection or replace the coupling. Leakage at the connection between the gas-phase valve and the gas-phase pipe: Tighten the nuts at the connection or replace the coupling. Leakage when the inlet/outlet valves and gas-phase valve are in the open position: Close all the shut-off valves and liquid-phase valves on the cylinder assembly, remove any remaining fuel from the faulty cylinder, and replace the seals or shut-off valves. Abnormal fuel level indication on the dashboard: Check whether the screws holding the level sensor in place are loose, or replace the level sensor. 7.3.2 Safety valves: Symptoms and solutions – Leakage in the safety valve: Close all the shut-off valves and liquid-phase valves on the cylinder assembly, remove any remaining fuel from the faulty cylinder, and replace the safety valve. 7.3.3 Liquid equilibrium valves: Symptoms and solutions – Leakage at the connection between the liquid equilibrium valve and the cylinder: Close the liquid equilibrium valves on the three cylinders. Tighten the joint at the leakage point; there is a leak at the connection between the liquid equilibrium valve and the liquid equilibrium tube. Close the liquid equilibrium valves on the three cylinders as well. Tighten the collar nut or replace the collar. Leakage in the body of the liquid level balance valve: Close all stop valves and valves connected to the liquid on the cylinder bank, remove the remaining fuel from the faulty cylinder, and replace the liquid level balance valve. 7.4 Pipelines – Fault symptoms and solutions: Leakage detected at pipeline joints: Turn off the solenoid valve. Tighten the collet nut or replace the collet fitting. 7.5 Maintenance and troubleshooting work must comply with the safety technical requirements specified in Chapter 6. After each maintenance task, the integrity of the sealed areas that have been serviced must be checked using a testing fluid at a working pressure of over 1 MPa; only after it is confirmed that there are no leaks can the vehicle be put back into operation.