Is it feasible to add 10% gasoline to prevent freezing in diesel vehicles?

These days, I heard an agricultural mechanic say that in order to prevent freezing in winter, it is best to add a little gasoline to diesel oil. I thought it was a joke, but it turned out that truck drivers and old farm hand often use it. As we all know, diesel vehicles add diesel and gasoline vehicles add gasoline. Generally, no one will mix gas, but why do diesel cars they drive have to add a little gasoline in winter? Can a diesel engine work with gasoline? Will there be any damage? Let's start with diesel engines and gasoline.

Agricultural machinery classroom | Diesel antifreeze

First of all, it is certain that there is not much problem in starting and running a diesel engine with a small amount of gasoline. Drivers add a little gasoline to diesel oil mainly to prevent icing, so why add gasoline to diesel oil to prevent icing? Isn't diesel itself used in winter?

Let's take a look at diesel: diesel is the fuel of diesel engine, which is divided into light diesel (boiling point range is about 180 ~ 370℃) and heavy diesel (boiling point range is about 350 ~ 4 10℃). The commonly used vehicle diesel oil is light diesel oil. The most important use of diesel oil is for diesel engines of vehicles and ships. Compared with gasoline, diesel has the characteristics of high energy density, low fuel consumption and low energy consumption, which makes some small cars and even high-performance cars start to switch to diesel.

Ignitability and fluidity are the most important properties of diesel oil, and their technical indexes are cetane number and freezing point respectively. Like motor gasoline, diesel has different brands. The brand of diesel oil is classified according to its freezing point. The freezing point of diesel oil is an important index to evaluate the fluidity of diesel oil, which indicates the lowest temperature at which fuel can be transported without heating. The freezing point of diesel oil refers to the highest temperature when oil is cooled to lose fluidity under specified conditions. When diesel oil is generally used, the freezing point of diesel oil is 3℃ ~ 5℃ lower than the ambient temperature (the cold filter point of diesel oil is generally higher than the freezing point 1℃ ~ 3℃). When the outside temperature reaches the cold filter point, diesel oil will precipitate crystals at low temperature, and when the crystals grow to a certain extent, the filter screen will be blocked. Therefore, with the change of seasons and regions, it is necessary to use different brands, that is, commercial diesel with different freezing points.

According to its freezing point, vehicle light diesel oil is divided into six grades: 5#, 0#, 10#, 20#, 35# and 50#. When we add diesel, we choose diesel according to the lowest temperature in the area where your vehicle is used. When the outside temperature is higher than 4℃, we choose 0# diesel. When the temperature is between 4℃ and -5℃, choose-10# diesel oil; When the temperature is from -5℃ to-14℃, choose -20# diesel oil; When the temperature is-14℃ to -29℃, choose -35# diesel oil; When the temperature is low, only -50 diesel can be selected, and -50 diesel is rarely seen. If the diesel brand used by the vehicle is higher than the above temperature, the fuel system in the engine may deposit wax and block the oil circuit, which will affect the normal operation of the engine.

Since there is diesel oil used at low temperature, why should we add gasoline to prevent freezing? In fact, this is the driver's helpless move. Take the most commonly used-10# diesel as an example. When the driver is driving, sometimes some gas stations don't have-10# diesel, only 0# diesel. If you can't get on the highway, it will be very dangerous, followed by pain, and what is more serious may be life-threatening. In desperation, drivers will be in danger. Because the freezing point of gasoline is very low (about -60℃), the freezing point of diesel oil will also become lower after adding gasoline, which will change 0# diesel oil into a similar unqualified-10# diesel oil in disguise.

So, will diesel cars with gasoline damage the vehicles? Generally speaking, diesel and gasoline can prevent freezing, and diesel engines can still be started. However, if gasoline is added too much, there will be no power, rough work, large jitter, slow speed and loud noise, which will seriously affect the normal use and even damage the diesel engine. Let's analyze why this happens.

The ignition point and combustion mode of diesel and gasoline are different, so the engine and fuel must be matched to work normally. So try to avoid mixing diesel and gasoline. Generally speaking, after the diesel engine is found to have added gasoline by mistake, it is necessary to stop adding diesel immediately, do not start the diesel engine, and completely discharge the gasoline before adding diesel. But if you only add a small amount of gasoline, you don't have to deal with it.

Let's analyze it in detail:

First, diesel engines and gasoline engines have different fuels, different ignition methods and different working principles. Diesel and gasoline are two completely different fuels. The spontaneous combustion temperature of diesel oil is low, about 220℃, and its viscosity is too high to volatilize. The spontaneous combustion temperature of gasoline is relatively high, about 4 15℃~530℃, with low viscosity and high volatility. The working principles of diesel engines and gasoline engines are also different. The ignition mode of diesel engine is compression ignition, and that of gasoline engine is ignition.

Second, the compression ratio is different. The compression ratio of diesel engine is much larger than that of gasoline engine. The compression ratio of diesel engine is generally between 16-22, and the high compression ratio can reach 26; The compression ratio of gasoline engines is relatively small, generally between 8- 1 1, and the high compression ratio can reach 14. Generally speaking, the higher the compression ratio of an engine, the higher the thermal efficiency, but why is the compression ratio of a gasoline engine so low? Mainly to avoid deflagration. The combustion characteristic of gasoline is that it burns very fast. When the compression ratio is too high, the compression of gasoline and air will be too intense, and the combustion will be too intense after being ignited by the spark plug, leading to deflagration. Deflagration is very harmful to the engine, so in the design of gasoline engine, the compression ratio will be controlled in a low range to avoid deflagration.

Third, the cylinder diameter and piston stroke are different, and the diesel engine has large cylinder diameter, long stroke and low speed; Gasoline engine has small cylinder diameter, short stroke and high speed. The cylinder diameter of gasoline engine is relatively small, generally less than 100mm, while the cylinder diameter of diesel engine can be made very large, and the cylinder diameter of some ships can reach more than 1 m, which is mainly related to the combustion characteristics of diesel oil and gasoline. Gasoline engine is an ignition mode. When the cylinder diameter is too large, the end mixture in the cylinder will burn before the flame front reaches, forming deflagration. The diesel engine is in compression ignition mode. When the mixture burns, it will form multiple flame centers and will not deflagrate, so the cylinder diameter of diesel engine is large. The greater the piston stroke of the engine, the greater the total torque, but the lower the speed. The combustion speed of diesel is slow and the compression ratio of diesel engine is large, so it tends to adopt long stroke and low speed in practical use; Gasoline combustion speed is fast, and the compression ratio of gasoline engine is small, so it tends to adopt short stroke and high speed in practical use. Due to the large compression ratio, high pressure and long stroke of diesel engines, the components of general diesel engines have been strengthened, and diesel engines look heavier and larger than gasoline engines.

Fourth, the combustion mode is different. Why do gasoline engines use spark plug ignition? The compression ratio of diesel engine is large. At the top dead center of compression, the in-cylinder temperature can reach about 500-800 degrees, and the ignition point of diesel oil is about 220 degrees. At this time, diesel oil can be injected for combustion. The compression ratio of gasoline engine is small. At the top dead center of compression, the in-cylinder temperature can reach about 300-400 degrees, and the ignition point of gasoline is about 427 degrees. At this time, the gasoline can't burn when injected, and the gasoline engine needs a spark plug to ignite.