How's diesel engine VS petrol engine? What are the differences?

 With the development of electronic control technology, the stratified lean burn mode of GDI has appeared in recent years. At present, the HCCI mode of gasoline is being studied both at home and abroad. Also, it is trying to combine the compression ignition mode of high speed 6cylinder diesel engine generator with the preformed mixture formation mode of gasoline engine to realize high efficiency and low pollution combustion. The differences between gasoline engine and diesel engine are mainly divided into the following three parts.

 

Mixture formation

 

Because the boiling point of gasoline is low and the evaporation is good, it is easy to form a prefabricated uniform mixture with air in the cylinder under the condition of normal temperature or slightly heating. Conventional gasoline engines usually use premixed gas before ignition. The boiling point of diesel oil is as high as 180-360 ℃, so it is not suitable for out of cylinder premixing. Even if the mixture can be gasified outside the cylinder after heating, the conventional powerful 12cylinder diesel engine will reduce the charge into the cylinder and consume additional energy for heating due to the decrease of air density caused by heating, which is unreasonable. Therefore, the conventional diesel engine adopts high-pressure injection in the fuel cylinder and the mixture with air atomization to form a mixture of concentration stratification.

 

Combustion mode

 

It is not allowed to carry out premixed gas pressure combustion near stoichiometric ratio after premixed gas is formed outside the cylinder of conventional gasoline engine. Because the pressure rise rate will be too high to be close to explosion, the external forced ignition combustion mode is suitable. Ignition combustion mode refers to ignition at high temperature near the spark plug and then flame propagation combustion in the mixture.

 

Because the ignition temperature of diesel is relatively low, the high speed 6cylinder diesel engine is not suitable for combustion in the short time when it starts to spray to spontaneous combustion. After the initial ignition and combustion of diesel engine, it is necessary to conduct the diffusion combustion of fuel injection, gasification and mixture at the same time.

 

Load regulation mode

 

The difference of mixture formation mode leads to the difference of load regulation mode. The coefficient of excess air ignited by gasoline homogeneous mixture is small. This way of adjusting the load by changing the throttle opening and controlling the mixture air intake is called load regulation. In the wide range of cyclic injection, there are suitable mixture in the injection beam of 4stroke electric starting diesel engine, so the diesel engine can be ignited by compression ignition in a wide range of average excess air coefficient.

 

In addition, the new motor 6cylinder diesel engine can adjust the load by the amount of cyclic injection. The intake volume of the cycle is basically the same and the average excess air coefficient will change with the load. This way of adjusting the load by changing the injection quantity (average excess air coefficient) is called load quality regulation.

 

These three differences lead to various differences in performance, design and structure between the two. The root of these differences is the differences in physical and chemical characteristics of gasoline and diesel fuel. It should be pointed out that the difference between the working modes of gasoline engine and 4stroke 6cylinder diesel engine is not only related to the fuel characteristics, but also depends on the level of scientific and technological development at that time.