Sometimes you may have seen fire coming out of the silencer of speeding vehicles. This phenomenon is called Back Fire.
When a back fire is mentioned, the thought that comes to many people is that it is an additional feature of a car. But a back fire is actually a byproduct of a trick used to overcome a weakness in turbocharged vehicles. Before talking about Back Fire, let’s first look at the operation of Turbo Charges
Operation of Turbochargers
To increase the power of an engine, the amount of fuel burned in the engine per unit time must increase. For that, it should be able to burn more fuel at the same time. As the power of an engine increases, the number of revolutions per minute (RPM) increases. As the RPM of the engine increases, the time that the valves remain open in the engine decreases. That is, due to the limitation of the time available to get air into the engine, it is not possible to get maximum power due to the decrease in the amount of air relative to the amount of fuel coming to the engine.
Turbochargers are used to overcome this disadvantage. A turbocharger takes the air in the atmosphere, compresses it and feeds it to the engine. As mentioned above, it is possible to burn more fuel in less time and get more power. The instantaneous compression of air by the turbocharger is an adiabatic process, so the temperature of the compressed air increases according to the first law of thermodynamics. To reduce the temperature of the compressed air, it is sent through a device called Inter Cooler. As the air cools, its density increases further. The power needed to operate the turbocharger is obtained by using the energy of the exhaust gas of the engine.
Turbo lag In order for turbo charging to work well, the engine must run at a significant speed. The reason for that is that the pressure of the exhaust gas (Exhaust gas pressure) needs to remain at a significant value.
When the vehicle decelerates at a significant speed, the exhaust gas pressure decreases due to the reduced rate of fuel combustion. Then the speed at which the turbocharger rotates decreases. As the vehicle accelerates again, the combustion rate of the engine increases and the exhaust gas pressure increases. But this increase process takes some time. During that time, the turbo charger is not working properly. The above time delay (turbo lag) is a disadvantage of turbo chargers. This drawback mostly affects racing cars. This is due to the lack of expected output power during turbo lag.
Anti lag strategy is used to overcome this drawback. The trick is to detect when the engine is decelerating with sensors and inject more fuel into the engine at that time. In this way, the intake of a higher ratio of fuel to air (Rich air fuel mixer) will not burn in the engine and will go into the exhaust manifold.
mixed with gases from burnt fuel.) Due to the high temperature in the exhaust air pipe, the unburnt fuel is combusted in that section to obtain the air pressure required for the proper operation of the turbocharger. Therefore, the turbo lag in the turbo charger can be reduced. That is, even if the engine is at a low RPM value, the turbo charging can be maintained at a significant RPM value.
Occurrence of Back Fire
As described in the above paragraph, the fire caused by the burning fuel in the exhaust manifold is called a Back Fire.
It can be understood that the occurrence of back fire is a side effect of the anti-lag process.
Back fire occurs when a vehicle with such devices is decelerated. In some cases, Back Fire is made for entertainment purposes. For that, Back Fire can be obtained by stepping on the accelerator pedal (accelerator) of the car and relaxing.
Turbocharged racing cars use a special device called a Rev-limiter to control the engine RPM from getting too high. What happens is that if the RPM of the engine exceeds a certain value, using various methods (disabling the spark plugs is one method) to maintain the RPM of the engine at some constant value. Thus reducing the RPM value is sensed by the engine sensors as the engine decelerates. Then, as described earlier, the system of providing more fuel will be implemented and back fire will start to occur. Back fire also occurs when the accelerator pedal is pressed continuously in such straight-sweeping vehicles.
Vehicles without a turbo charger can also be configured to backfire. (Possible under both carburetor and EFI) Backfire is often done by increasing the fuel to air ratio. (Rich air fuel mixer) causes combustion in the exhaust pipe.
Vehicles without turbo charging will unnecessarily increase the vehicle’s fuel consumption by setting them to backfire. Setting up a car that is often used for daily work to backfire is an act that wastes fuel. With a crisis facing our country, it is important to use fuel sparingly
