Unit 8. Conversion Systems

Transcription

1 Unit 8. Conversion Systems Objectives: After completing this unit the students should be able to: 1. Describe the Basic conversion systems 2. Describe main conversion kit types. 3. Describe how the CNG Bi-Fuel system works.

2 8.1 Conversion to CNG Overview Compressed natural gas or CNG has become the alternative fuel of choice for many people who wish to reduce their dependence on gasoline and other petroleum-based fuels as well as minimize the harmful emissions from their vehicles. If you want a CNG vehicle you can simply buy a Factory-ready compressed natural gas (CNG) vehicle that running on CNG such as the Honda Civic GX. There is another practical option convert an existing gasoline-powered vehicle so that it can run on compressed natural gas. Converting an older vehicle to CNG does have its pros and cons. It can be quite expensive to retrofit a CNG conversion kit. If the fuel savings achieved by converting to CNG can compensate for the initial cost, then the investment will be well worth the price, especially if CNG refueling stations are readily available. CNG conversion can also reduce maintenance costs since CNG is a clean-burning fuel. This means less expense in maintenance procedures such as engine tune-ups, oil changes and parts replacements which are common in gasoline and diesel powered vehicles. There are now a number of companies that offer natural gas conversion in the United States. They basically sell CNG conversion kits, CNG tanks and cylinders. They also provide installation of CNG kits and retrofitting a bi-fuel system into existing gasoline and diesel vehicles.

3 8.2 Conversion Systems: CNG conversion kits come with everything that is needed to convert a vehicle to CNG. These components must be high quality parts and from a reliable company. There are two types of CNG fuel systems available: a) Dedicated vehicles or conversions that run solely on CNG and normally have a fuel capacity equal to or larger than the original gasoline or diesel tank. b) Bi-fuel vehicles that have the ability to run on either CNG or gasoline/diesel. These bi-fuel vehicles typically retain their original gasoline/diesel tank and are retrofitted with an additional, smaller-capacity CNG tank. Advantages of Having a dual fuel system : c) Will ensure adequate fuel reserves in between natural gas fills. d) Compared to having only a gasoline engine, this additional fuel reserve will extend the vehicle s driving range. e) Drivers can switch from CNG to gasoline even while driving, idling or parked. f) Some CNG systems will automatically switch to gasoline when the natural gas level reaches a preset low pressure setting Types of conversion System Kits Conversion System kits can be classified into two main types: 1- Aspirated system Kit. 2- Sequential system Kit.

4 Fig. 8.1 CNG Conversion Kit Components for Aspirated kits 1- High Pressure CNG Tank 2- High Pressure Supply Line 3-2 Stage Pressure Regulator device 4- CNG Controller Switch (inside cab) 5- CNG Mixer (Aspirated Kit) 6- CNG Filler Valve 7- CNG Pressure gauge (for CNG fuel gauge inside car) 8- CNG Control Unit 9- Emulator

5 Fig 8.2 Aspirated Kit Diagram You also need an electric shut off valve or a quarter turn valve to isolate the high-pressure tank in case of an emergency. This valve goes between the tank and the rest of the system Description of aspirated (mixer) CNG systems. The 2 main components in an aspirated CNG system are the pressure regulator and the mixer. The addition of a controller system which includes an ECU and Stepper Motor to regulate natural gas flow was added when closed-loop fuel-injected engines came out in the 80 s.

6 Fig 8.3 Pressure Regulator The basic system with the regulator and the mixer still remains the most popular and most used system worldwide. An aspirated CNG system starts with the High Pressure CNG Tank, the tank is connected to the filler and the pressure regulator with high pressure steel tubing, and there may be a valve or high pressure filter between the tank and regulator. Fig 8.4 CNG Electronic Pressure Gauge On carbureted vehicles the in-cab controller switch will be the control for the system with a 3 way switch and manometer (electronic pressure gauge), this switch when operated will

7 turn off the gasoline through the use of an electronic shut-off in the fuel, as the gasoline runs out you switch to natural gas which is introduced through a mixer-plate above or below the carburetor. The natural gas is then regulated by manifold vacuum by the regulator. Fig 8.5 CNG Mixer On fuel injected vehicles the simple mixer system is the same with the addition of injector emulators, these are spliced in or plugged into the injector wires and turns off the injectors when the CNG system is turned on. Fig. 8.6 Injector emulator

8 A closed-loop controller is an addition to an aspirated system which uses the oxygen sensor along with the throttle position sensor and an RPM signal to operate a stepper motor (electronic valve) to control the amount of natural gas introduced into the system depending on a rich or lean condition. Fig 8.7 Closed-loop Controller Advantages of Aspirated CNG Systems 1) Affordable ($400 to $525 without tank) 2) Easier to install 3) Less components to fail 4) Can be used on carbureted vehicles 5) Tuning and setup simpler Disadvantages of Aspirated Systems 1) Slight power loss 2) Less fuel regulation (chance of check engine lights) 3) Old technology, works best on older vehicles

9 8.2.3 Components for Sequential Kits 1- High Pressure CNG Tank 2- High Pressure Supply Line 3-2 Stage Pressure regulator 4- CNG Controller Switch (inside cab) 5- CNG Injectors 6- CNG Filler Valve 7- CNG Pressure gauge (for CNG fuel gauge inside car) 8- CNG Control Unit Fig. 8.8 Sequential Kit Diagram You also need an electric shut off valve or a quarter turn valve to isolate the high-pressure tank in case of an emergency. This valve goes between the tank and the rest of the system.

10 Description of a Sequential Injection CNG system. The Sequential Injection system still has a high pressure tank, filler, filter and regulator, the regulator is different in that it puts out a steady pressure as opposed to variable pressure. Fig 8.9 CNG Pressure regulator (Sequential Kit) The Natural Gas is then injected by natural gas injectors which are controlled by the gasoline injector pulse.

11 Fig 8.10 CNG Injectors This system also uses its own MAP (manifold absolute pressure) sensor, natural gas pressure sensor, natural gas temperature sensor and coolant temperature sensor to operate and control the system.

12 Fig 8.11 CNG MAP Sensor Advantages of Sequential CNG Systems 1) More controlled CNG operation (fewer check engine lights) 2) Less power loss 3) Works good on newer vehicles 4) Modern system using multiple sensors to regulate Natural Gas Disadvantages of Sequential CNG Systems 1) More expensive ($2000 up without tank) 2) Harder to install (need to remove intake manifold in many cases) 3) Harder to tune, will need tuning software and tuning expertise

13 8.4 How a CNG/gasoline bi-fuel system works: Here are the step by step details: CNG is fed into the high pressure cylinders through the natural gas receptacle When the engine needs natural gas, CNG leaves the storage cylinders and passes through the master manual shut-off valve. CNG enters the engine chamber via the stainless steel high pressure line. The regulator accepts the CNG and reduces its pressure from 3,000 psi to approximate atmospheric pressure. The natural gas solenoid valve lets the natural gas flow from the regulator into the gas mixer or fuel injectors. This same solenoid valve also shuts off the natural gas when the engine is stopped. The carburetor has one primary function and that is to turn the liquid fuel into a vapor ' this process is called 'atomization' or 'ionization'. With CNG this process is eliminated. Fig 8.12 Bi-Fuel System When the CNG leaves the tank it is cold and semi-liquid. This state has to be changed in order for the gas to combust in the chamber. In order to vaporize the gas completely the gas from the tank is fed into a diaphragm chamber that is hooked up with the engine cooling system through water pipes.

14 Fig 8.13 CNG Tank Since the engine water circulates through the radiator and the engine it is boiling hot. This water is circulated around a diaphragm in an air tight chamber. When the water heats the diaphragm it in turn heats the gas within. This increases the pressure of the gas and it is fed to the internal combustion engine through the carburetor. Fig 8.14 Water Circulation (Reducer & Radiator) A fuel selection switch will be installed (usually on the dashboard) that will allow the driver to manually select either CNG or gasoline. Converting to CNG is easy and convenient by installing on of the branded CNG conversion kits.