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FUEL SYSTEM 1 1. INTRODUCTION: Compressed Natural Gas (CNG) is widely used as an alternative fuel in cars for lower emissions and fuel economy. In CNG fuel supply system, the CNG is stored in two high pressure cylinders that is mounted under driver & co driver seat of the vehicle. The storage pressure of CNG in cylinder is up to 260 bar. An electrical cylinder valve is mounted on each of the cylinder for the delivery of CNG to pressure regulator. A filler valve is used for filling CNG in cylinder. During filling one has to remove filler cap from the filler valve. A Low Pressure fuel filter is used in the fuel circuit located in between Pressure regulator & CNG gas rail. This unit filters oil & dust from low pressure CNG & cylinder corrosion to protect the CNG injectors. A Pressure gauge is mounted inside the front bonnet on high pressure line which displays pressure in the CNG cylinder. High pressure CNG is carried from the cylinder to the pressure regulator by SS tube along the under body of the vehicle. Pressure regulator is a unit that reduces pressure from CNG tank storage pressure (up to 260 bar) to 4 bar (at gas rail) pressure. High Pressure (HP) Sensor is fitted on inlet side of pressure regulator. It monitors the pressure in high pressure line. In case of any drop in pressure in HP line is observed, it immediately alerts the GAS ECU about the leakage and the Gas ECU will not allow the change over to “GAS” mode. The HP sensor also sends pressure signal to CNG ECU to show CNG level inside the cylinder on instrument cluster. Pressure regulator outlet is connected to LP filter then to gas rail through a low pressure line. Both the ends of low pressure line are having spring band clamp type arrangement. The Gas rail is fitted with a Pressure & Temperature sensor and has one inlet and two-outlet connections. Two gas injectors are mounted on the inlet manifold and connected to gas rail through rubber hoses to gas rail. Through gas injectors, the CNG is injected inside inlet manifold. The entire system of vehicle is controlled by a ECU that is mounted in engine compartment near wiper motor. The capacity of CNG tank is 16 liters (of water capacity) 2 nos and petrol is 15 liters. The layout of “fuel supply system” and pipe lines fitment” are shown in this chapter. The CNG fuel supply system mainly consists of the following components.  CNG Cylinder  Cylinder valve  Filler valve / Receptacle  Low pressure filter  Pressure regulator  Pressure gauge  High pressure sensor