The difference between gasoline and diesel, why not mix them?

It depends on the characteristics of diesel and gasoline. Diesel oil is a kind of light petroleum product, and the most important use of diesel oil is for diesel engines of vehicles and ships. Compared with gasoline, diesel has higher energy density and lower fuel consumption rate, but the exhaust gas contains more harmful components (NO, particulate matter, etc. ) First of all, we must talk about the characteristics of two fuels:

The volatilization speed of gasoline is faster than that of diesel, so gasoline can enter the cylinder as a mixed gas during the intake stroke, while diesel is not easy to volatilize to form a mixed gas, so it can only be directly injected into the cylinder before the start of the power stroke.

The auto-ignition point of diesel oil is lower than that of gasoline, so diesel oil can spontaneously ignite in a cylinder with high temperature and high pressure; If the gasoline engine adopts compression ignition mode, it must have a higher pressure, so as to obtain a higher temperature to ignite. However, because gasoline is volatile, it will absorb a lot of heat when it volatilizes, which increases the difficulty of compression ignition again, so ignition with spark plug is the most suitable way.

The burning speed of gasoline is faster than that of diesel, so it is too fierce to put gasoline in a high temperature and high pressure environment, and the body can't stand the tempering of this gunpowder smell, so the pressure of the cylinder should be reduced. When ignited by spark, the flame in the cylinder spreads and burns in the form of "wave", thus avoiding the impact caused by deflagration; However, in high temperature and high pressure air, diesel oil burns in many places at the same time to form flames, that is, it does work in the form of deflagration (similar to the "knock" of gasoline engines), and its working state is rough. However, due to the slow combustion of diesel, although the combustion began to be intense, the combustion time was still longer than that of gasoline.

Therefore, the gasoline engine changes the throttle opening through the accelerator pedal, controls the amount of mixed gas entering the cylinder, and realizes different power output; The control power output of diesel engine depends entirely on the fuel injection, which is a real throttle. If the throttle valve is cancelled, the engine intake will be more sufficient and the combustion will be more sufficient, which is one of the reasons for the high thermal efficiency of diesel engine.

Characteristics of two engines:

After the mixture in the gasoline engine is ignited, it burns instantly and bursts into energy, so it can be repeated for many times in unit time and output high power at high speed, so it can have higher performance and faster response speed with small volume and light weight, and a wide speed range can also bring better control feeling. The compression ratio of gasoline engine is often only half that of diesel engine, and the temperature and pressure in cylinder are much lower than that of diesel engine during power stroke, so the thermal efficiency is relatively low, which is also commonly known as "fuel consumption".

After diesel engine injects fuel, it takes a certain time to burn, which is suitable for full combustion of fuel at low speed and brings great torque. In order to resist the high pressure and large torque in the cylinder, the connecting rod of the cylinder and piston of diesel engine is stronger than that of gasoline engine, so it is larger than that of gasoline engine. But it is precisely because the diesel engine has the characteristics of high compression ratio and low speed that it can better convert heat into kinetic energy, so the thermal efficiency of the diesel engine is better, that is, the fuel consumption performance is better. This is why cars and racing cars usually use gasoline engines, while buses, trucks and other large vehicles use diesel engines.

Present situation of diesel engine

With the development of technology, the stability and volume of diesel engine have been greatly improved. The manufacturing process of high-strength aluminum cylinder block reduces the weight of the engine. Tail gas aftertreatment and particulate matter recovery can effectively reduce tail gas pollution; Fuel high-pressure rail injection and low compression ratio (compared with traditional diesel engines) can effectively suppress noise; The application of the balance shaft improves the ride comfort; VGT variable cross-section turbine and intercooler improve the engine power, and many excellent designs are gradually equipped on passenger cars, so that diesel engines have the capital to compete with gasoline engines, and their low-carbon emissions and excellent low-speed torque are accepted by many SUVs and even cars.

In Europe, the proportion of diesel vehicles in passenger cars has reached 40%, while domestic diesel engines mainly match SUV models. Recently, domestic independent brand diesel vehicles have also been listed. But at present, the quality of domestic diesel is not good enough, which leads to the neglect of diesel engines in China. The main problems are that the cetane number is not high enough (poor combustibility), the sulfur content is too high (damaging engine parts and increasing exhaust pollution), and there are too many polycyclic aromatic hydrocarbons (that is, there are too many impurities, and poor combustion will cause coking and carbon deposition). If the quality of diesel oil in China can be improved, I believe that in the face of soaring oil prices and environmental degradation, China people will gradually accept diesel vehicles.