Is there more carbon deposition when idling frequently? I will smash this scam! Don't be misled again.

I tried a long live broadcast for the first time yesterday, and it didn't stop for three hours. Really tired! During the live broadcast, a cyclist asked what an "oxygen sensor" was. How many kinds are there? So I answered these two questions briefly. As the name implies, the oxygen sensor is used to detect the concentration of oxygen in gas.

In the automobile, the oxygen sensor has a function: to detect the oxygen content in the exhaust gas. Thus, the combustion state of the engine can be known. After the detection signal of oxygen sensor enters the computer, it becomes the basis of "stable air-fuel ratio" of the engine.

Usually there are two oxygen sensors on the car, which are called "front oxygen sensor" and "rear oxygen sensor" respectively. The task of the former is to provide the parameter basis for the above-mentioned "stable air-fuel ratio" of the engine, and the role of the latter is to detect the good or bad state of the three-way catalyst. (If the data of "pre-oxygen sensing" and "post-oxygen sensing" are completely consistent, the ternary system is broken. )

Will idling for a long time lead to carbon deposition?

Say "air-fuel ratio" first!

We won't say much about oxygen sensors. I wrote this article today because I passed the oxygen sensor, and then I touched on the topic of "air-fuel ratio", so I thought of another controversial topic: Will idling for a long time lead to carbon deposition? In fact, there are various opinions on this issue on the Internet, which puzzles riders, but none of them really tell the principle.

Therefore, I think it is necessary to elaborate seriously and let those messy remarks end as soon as possible. In order to make this clear, we need to popularize the knowledge of air-fuel ratio: the so-called air-fuel ratio is the weight ratio of air/fuel. What do you mean? For example, if you pour 1 g standard gasoline into a beaker and ignite it until the gasoline in the beaker is completely burned, you will consume 14.7~ 14.8 g air during the whole combustion process.

You are not mistaken! Any combustion needs oxygen, so this 14.7~ 14.8 is the "standard air-fuel ratio". (The textbook of the Soviet Union and China is 14.7, while that of Europe, America and Japan is usually 14.8), so if the air-fuel ratio is lower than 14.7, we call it "anoxic combustion" and higher than 14.8, we call it "peroxide combustion".

Idling for a long time will not cause carbon deposition at all.

In the state of "oxygen-deficient combustion", gasoline can't burn completely because of lack of oxygen, and eventually there will be insufficient combustion; On the other hand, if it is "peroxide combustion", because there is too much oxygen, nitrogen oxides in the tail gas will increase, which is also unfavorable to the environment. Therefore, once the engine is warmed up and the water temperature reaches the normal working temperature, the computer will order the engine to dilute the air-fuel ratio to 1.47~ 14.8 to ensure the cleanest exhaust gas and the best working condition of the three-way catalyst.

The above control principle is called "closed loop control". It usually takes no more than 2 minutes for the engine to complete the process from cold state to "hot state engine". In other words, after your car warms up for 2 minutes every morning, the engine is close to the "optimal air-fuel ratio" state! (Usually, the idling air-fuel ratio of the engine is calibrated at around 14), so we know that idling will not lead to insufficient gasoline combustion! Therefore, the statement that "idling for a long time leads to insufficient carbon deposition in combustion" is simply nonsense without scientific basis!

The operation that will really make the engine in a "low air-fuel ratio" state is actually "floor oil"! Because when the air-fuel ratio is reduced to about 12.5, the power and torque performance of the engine reach the peak state. Therefore, when we desperately accelerate the floor oil, the engine computer will "temporarily put aside environmental protection"! At this time, there will be insufficient combustion in the cylinder (so the frequent opening mode of "big foot throttle+big foot brake" will really lead to an increase in carbon deposition).

Oil again! When idling, the oil coking is serious!

Through the principle discussion, we finally know that there will be no problem of insufficient combustion when idling for a long time. So idling for a long time will not cause carbon deposition in the cylinder at all! What are the bad consequences of idling for a long time? -In fact, the problem caused by idling for a long time is "intake coking", not carbon deposition! As I said, coking is actually mainly caused by engine oil. Engine oil cokes at high temperature and becomes coke. So where does the oil come from?

Quite simply, it is the oil vapor brought by the crankcase ventilation (PCV) system. We know that when the engine is running, the vacuum in the intake pipe will generate suction, and the oil vapor in the crankcase will be sucked into the engine to participate in combustion (which is necessary for environmental protection). The higher the vacuum in the intake pipe of the engine, the greater the suction!

When the engine is idling, it is also the time when the vacuum degree of the engine intake pipe is the highest. Therefore, the suction of the engine PCV system is maximum at idle speed. The more oil and gas is sucked from the crankcase, the faster the oil stain is deposited in the engine intake system, and the coking speed is obviously greatly accelerated.

Therefore, there is no benefit in idling the engine for a long time, and it is still burning oil in vain. This is one of the reasons why the automatic start-stop system is becoming more and more popular. Ok, that's all for today. My mind kept jumping. I am a big tiger! See you tomorrow!

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.