What is the reason why the tail gas smells of gasoline after the car starts?

It is normal that the exhaust pipe will have a strong smell of gasoline after a cold start. Let's talk about the reasons for doing this today, so that car owners can feel at ease.

Do you know how gasoline burns in a cylinder? If you fill a cup with gasoline and light it with a lighter, you will find that the flame only burns on the surface of the gasoline, but the gasoline under the cup will not burn. In fact, it is not liquid gasoline that burns, but gasoline that evaporates into gas.

Similarly, after gasoline enters the cylinder, it must be evaporated and fully mixed with air to form a combustible gas with sufficient concentration before it can be ignited by a spark plug. If the gasoline is still liquid after entering the cylinder, the spark plug will not ignite.

We all know that the engine calculates the fuel injection quantity according to the intake air quantity combined with the theoretical air-fuel ratio. For example, if the engine inhales 14.7 grams of air and the air-fuel ratio is 14.7, then the fuel injector will inject 1 gram of gasoline. In this way, after the gasoline is completely volatilized, it just forms a mixture with air of appropriate concentration.

The volatility of gasoline decreases with the decrease of temperature. For example, the engine still inhales 14.7 grams of air when it is cold started. If the fuel injector still injects 1g gasoline with an air-fuel ratio of 14.7, 1g gasoline may not completely evaporate due to the deterioration of volatility. If half of the gasoline is evaporated, the remaining half is liquid gasoline. In this way, the actual mixture concentration is reduced, and the spark plug is not easy to ignite.

Therefore, during the cold start, the engine has rich control, and more oil is injected according to the actual temperature control. For example, if the engine inhales 14.7g of air, then we need to provide 1g of gasoline vapor, but at the current temperature, the evaporation rate of gasoline is only 10%, which means that if you spray 1g of gasoline, only 0. 1g can be evaporated. what am I supposed to do？ Only 10g gasoline can be sprayed, so 10% evaporation is enough.

This way, the tail gas will naturally smell of gasoline. During cold start, 65,438+04.7 g air and 65,438+00 g gasoline were injected into the cylinder, of which only 65,438+0 g gasoline was evaporated and mixed with air to participate in combustion. The remaining 9 grams of gasoline still exists in the cylinder in liquid state. When liquid gasoline is burned in the cylinder, it will be oxidized and carbonized at high temperature, but it can't be completely burned out. So it is discharged from the exhaust pipe together with the exhaust gas. So we smelled the obvious smell of gasoline. It's winter. If you pay attention when starting the engine in the morning, you will find that the exhaust gas has a strong smell of gasoline. It doesn't matter. Generally, there is only a smell for a period of time at the moment of starting, and it will not be so obvious after a period of time.

If the engine can still smell gasoline after reaching the normal operating temperature, there is a problem. First of all, check whether there is any leakage in the fuel system, because many interfaces of the fuel system are rubber pipes, which will harden in winter, and the vibration when the engine starts will easily loosen it, thus causing gasoline leakage.

If there is no leakage in the fuel system, it is basically a problem with the engine itself. Generally, this kind of problem will be accompanied by the lighting of the engine fault light, and it needs to be connected to a computer to find fault information before it can be handled.

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