What's the difference between engine tempering and blasting? How to judge?

Engine tempering and shooting are two different faults, both of which are related to the concentration of mixed gas. Generally speaking, tempering is because the mixture is too thin, and shooting is because the mixture is too thick.

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Tempering refers to the phenomenon that the mixture burning in the cylinder runs backwards behind the intake valve and burns.

It stands to reason that the intake valve sucks air when the engine is working, and it is only possible for the cylinder to burn in the power stroke and exhaust stroke, and the intake valve should be closed at this time, so why does the flame run out of the intake valve? In fact, this is caused by valve overlap, which means that the intake valve and exhaust valve are opened at the same time in some cases when the engine is running, in order to make the intake and exhaust of the engine run more smoothly at high speed.

Tempering occurs at the end of the exhaust stroke and the beginning of the intake stroke. At the end of the exhaust stroke, the piston pushes the exhaust gas out of the cylinder, but some exhaust gas remains in the combustion chamber. At this time, the exhaust valve is closed later, and the intake valve is opened. The fresh air that enters the cylinder when the piston inhales can accelerate the discharge of the remaining exhaust gas. At this time, if the exhaust temperature is high or even burns, it is easy to ignite the mixed gas in the intake manifold, leading to tempering and blasting.

Generally, it is easy to backfire when the mixture is too thin, because the combustion speed is very slow when the mixture is too thin, and the exhaust gas may still burn when the valves overlap, which will ignite the intake mixture and cause backfire and ignition.

Exhaust pipe blasting

The main reason for the exhaust pipe shooting is that there is too much oil, and the unburned gasoline enters the exhaust system for combustion, and the combustion pressure is ejected from the exhaust pipe to make a shooting sound. Generally, it is easy to appear when the throttle is loose.

The specific reason is that the mixture is too thick when stepping on the accelerator, and the gasoline can't burn completely. At this time, although gasoline will enter the exhaust system, it will not burn because there is no air. When you release the throttle, the engine stops injecting fuel, but before the throttle is closed, some air has been sucked into the cylinder. Because the engine does not inject fuel, this part of the air is discharged into the exhaust system, and it starts to burn in the exhaust system after encountering gasoline that has not been burned before, resulting in an explosion.