How the CNG Automotive System Works

Compressed natural gas (CNG) automotive systems usually include: natural gas cylinders, pressure reducing Pressure regulator, various valves and pipe fittings, mixers (or natural gas injection devices), various electronic control devices, etc. The natural gas engine also includes forged aluminum alloy, high compression piston, nickel tungsten hardened alloy exhaust valve seat, and methane catalytic converter. CNG cars are modified using standardized vehicles, and a set of "compressed natural gas conversion device for vehicles" is added while retaining the original fuel supply system. The modification section consists of the following three system groups.

 (1) Natural gas system. Mainly composed of inflation valve, high-pressure shut-off valve, natural gas cylinder, high-pressure pipeline, high-pressure connector, pressure gauge, pressure sensor, and gas volume display.

 (2) Gas supply system. Mainly composed of gas high-pressure solenoid valve, three-stage combined pressure reducing valve, mixer, etc.

 (3) Oil gas fuel conversion system. It mainly consists of a three position oil gas conversion switch, an ignition time converter, and a gasoline solenoid valve.

 When the car uses CNG as fuel, the natural gas undergoes three stages of pressure reduction and is mixed with air through a mixer to enter the cylinder. The compressed natural gas is reduced from the rated intake pressure to negative pressure, with a vacuum degree of 49-69KPa. The combination of pressure reducing valve and mixer can meet the concentration requirements of mixed gases under different operating conditions of the engine.

The pressure reducing valve assembly is equipped with an idle valve to supply air for engine idle speed; During the pressure reducing process of the compressor, it needs to expand and do work to absorb heat from the outside, so there is also a heating device on the pressure reducing valve that utilizes the circulating water of the engine; To improve the operational performance of the vehicle, the driver's cab is equipped with an oil gas fuel conversion switch, which is used to agree to control the oil gas solenoid valve and ignition time converter. The ignition time converter is automatically converted by the circuit system to different ignition advance angles of the two fuels; The 5 traffic lights on the gas volume display on the dashboard display the gas storage capacity of the gas cylinder; The fuel conversion switch is also equipped with a gas supply button for the engine. Therefore, it has complete functions and is very convenient to operate. When the fuel conversion switch is placed in the natural gas position, the solenoid valve opens and the gasoline valve closes. The natural gas in the gas storage cylinder flows through the main valve, filter, and solenoid valve, enters the pressure reducer, undergoes multi-stage pressure reduction to negative pressure, and then enters the mixer through the power valve. It is mixed with the air from the air filter to ignite and drive the engine crankshaft to rotate.

The mixer can automatically adjust the air supply and evenly mix air and natural gas according to the different vacuum levels generated by the engine under different operating conditions, under the regulation of the pressure reducer, to meet the fuel supply requirements of the engine.

The power valve can change the low-pressure pipe and cross-sectional area of natural gas, adjust the shut-off of the mixed gas valve, restore the original vehicle's fuel supply system to normal fuel supply, and ensure normal engine operation. The control system mainly consists of a fuel conversion switch, which controls the switch of the gasoline solenoid valve and the gas solenoid valve to achieve fuel supply and gas supply selection.

 Refer to:https://afdc.energy.gov/vehicles/how-do-natural-gas-cars-work

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