Views:3 Author:Site Editor Publish Time: 2020-02-26 Origin:Site
On the basis of retaining the gasoline supply system of the vehicle, a CNG supply system is additionally added, and the CNG is depressurized and directly supplied to the engine. CNG or fuel can be selected through the fuel switching control device. This type of vehicle is called a gasoline / natural gas dual-fuel vehicle. Most international CNG vehicles belong to this category. Below we will introduce the fuel switching control principle of dual fuel vehicles.
Gasoline / natural gas dual-fuel vehicles can be divided into three types: open-loop mixer gas supply system, closed-loop mixer gas supply system with electronically controlled power valve, and electronically controlled gas injection. The special equipment differs mainly in the way of forming the mixed gas and the way of controlling the density of the mixed gas. And other few part like the injection whether single-point injection control or multi-point sequential injection control. The other special devices are the same. At present, the hybrid closed-loop control system is commonly adopted on EFI vehicles at home and abroad. After matching, the indicators of power performance, emission performance, and fuel economy can basically meet the requirements of use.
In the closed-loop control, the gas supply system adds a gas ECU, and by utilizing the oxygen sensor of the original vehicle, it achieves the closed-loop control of the air-fuel ratio. At the same time, a stepper motor power valve controlled by the gas ECU is added between the pressure regulator and the mixer. In this way, the engine can enable the engine to obtain the best air-fuel ratio under various operating conditions through gas ECU, the oxygen sensor and electronically controlled power valve. It works by shutting off the supply of natural gas when gasoline is used. And cutting off the supply of gasoline while natural gas is used. Either way, the mixture is premixed and ignited by an electric spark.
Compared with the electronically controlled gasoline injection engine, the functions of the main electronically controlled parts added to the dual fuel engine are:
Gas ECU, when working with gas, it will analyze and calculate according to the engine’s intake pressure signal and oxygen sensor signal, throttle position signal and speed signal to control the action of the stepper motor.
Fuel switching controller: it utilizes logic control unit to realize the fuel switching process between gas and gasoline, and indicates the fuel situation accordingly (displayed by the indicator light), and displays gas pressure inside the high-pressure gas cylinder when working with CNG so that the driver knows the amount of remaining gas.
Simulator (also known as Emulator): it controls gasoline injection. When the fuel is gasoline, the injector control circuit is turned on to keep the gasoline injection system working normally. When the gas is used, it cuts off the control circuit of the gasoline nozzle and simultaneously inputs the gasoline injection analog signal to the ECU to keep the normal operation of gasoline ECU.
Ignition advance regulator: When working with CNG, based on the ignition advance angle controlled by the gasoline ECU, a certain degree is automatically increased to compensate for the shortcoming of CNG slow combustion speed. While working with gasoline, it will restore the ignition time controlled by gasoline ECU.
Accessories of CNG circuit system
Ignition advance regulator
Stepper motor power valve: it executes the instructions of the gas ECU to control the gas supply and ensure that the air-fuel ratio of the mixture is near the theoretical value.
Pressure reducer: it adjusts the CNG with a high pressure output from the gas cylinder to the CNG that meets the needs of the engine.