Abstract
Experience proves that mechanical CNG conversion kits for NGV have several disadvantages. These include the unresponsiveness of CNG flow during the acceleration period due to the thermodynamic properties of the gas and the low pressure used at the output side of the pressure regulator. The other inconvenience is that the mechanical ignition timing setting can be optimized for one fuel only. The fuel change process from gasoline to gas cannot be obtained instantly, dual fuel operation is still occuring for an elapse of time that depends on the carburetor's fuel chamber volume and the operation condition of the engine. The reverse process of fuel change has other inconvenience due to the engine motoring condition (without any fuel entering the cylinder) that occurs during the filling period of the carburetor's fuel chamber. Electronically controlled CNG injection (ECCI) can eliminate these disadvantages and inconveniences. The only deficiency of the ECCI is that because of the injection system needs high gas pressure, some residual gas with sufficiently high pressure (±7 bars) still remains in the storage tank. But its economic and technical benefits can overcome this deficiency. The study and experiment carried out is stressed on the design and set up of the ECCI hardwsare and software system. The controlled parameter for this purpose is the amount of gas injected to the NGV cylinders at an exact time at any condition of the engine. Input parameters are limited to engine rpm, throttle position, ambient air pressure and temperature, inlet manifold pressure, and exhaust gas temperature. The electronic module consists of two principal parts: acquisition and analysis. Some subparts of the acquisition system have been designed to meet the acquisition requirements of the control system. The software analyzes the data acquired and direct the controlled output to the fuel injection CPU to excite a proper amount of fuel injected needed by the engine. ECCI proves to be reliable and effective mean to control CNG vehicles.