Why is the efficiency of diesel engines higher than gasoline engines

Both gasoline and diesel engines belong to internal combustion engines, and both fuel is burned and the chemical energy in the fuel is converted into the mechanical energy that drives the vehicle forward by pushing the piston in the cylinder to move back and forth, so the working principle of the two is basically the same.

In the suction stroke, the gasoline engine sucks a mixture of gasoline and air into the cylinder, and the diesel engine sucks only air into the cylinder. At the end of the compression stroke, the diesel engine compresses the inhaled gas to a smaller volume, greater pressure, and higher temperature than the gasoline engine.

In the power stroke, the gasoline engine uses a spark plug to generate an electric spark to ignite the fuel. At the end of the compression stroke, the diesel engine injects mist diesel into the cylinder from the fuel injector, and the mist diesel burns immediately when it encounters high temperature hot air.

In a diesel engine, the gas pressure that pushes the piston to do work is greater and more efficient than that of a gasoline engine. The efficiency of the gasoline engine is 26-40, and the efficiency of the diesel engine is 34-45

As a fuel for daily use, diesel has the highest energy density, nearly 1 times higher than LNG and more than 10% higher than gasoline. In addition, the diesel engine also has the characteristics of high torque at low speeds. To sum up, diesel engines are more efficient than gasoline engines.

1.factors that widen the gap at high loads;

Under high load conditions, the mixture of gasoline engine is thicker, and the excess air coefficient = , while the average excess air coefficient of diesel engine = is generally thinner.

Although the compression ratio of the gasoline engine is low, its maximum combustion temperature is much higher than that of the diesel engine due to the thicker mixture and higher isocapacitance; In addition, the residual exhaust coefficient of gasoline engines is higher than that of diesel engines. The above two reasons make the isentropic index of the gasoline engine smaller than that of the diesel engine, and the high-temperature thermal decomposition is intensified, which makes the thermal efficiency of the gasoline engine decline much greater than that of the diesel engine relative to the theoretical cycle. Although the molecular coefficient of change of gasoline engine is higher than that of diesel engine, its influence is small and does not play a major role.

2.factors for further widening of the gap at low loads;

Due to the difference in the formation of the mixture and the way the load is regulated, the lower the load on the gasoline engine, the smaller the excess air coefficient. Diesel engines are the opposite. This further widens the gap between the thermal efficiency of the two.

The lower the load, the lower the air intake, and the higher the residual exhaust gas coefficient. The residual exhaust gas coefficient of the diesel engine remains roughly unchanged at low loads. In addition to having an impact on the isentropic index of the gasoline engine, this factor also reduces the combustion speed and thermal efficiency of the gasoline engine.

When the gasoline engine is high and low load, the temperature difference after combustion of the working fluid is smaller than that of the diesel engine, that is, the gasoline engine still maintains a higher combustion temperature at low load. This is because the gasoline engine is a volume-regulated load, and the excess air coefficient of the mixture does not change much at various loads. Although the amount of gas entering the cylinder is small at low load, the calorific value of the working fluid per unit mass does not change, so the temperature of the working fluid does not drop much after combustion.

The diesel engine is a mass-regulated load, and the excess air coefficient increases at low load, the calorific value of the working fluid per unit mass decreases, and the temperature of the working fluid decreases proportionally after combustion. This factor makes the temperature difference between the working fluid of the gasoline and diesel engines at low load more significant, which causes the gap between the thermal efficiency of the two to increase.

Through a comprehensive comparison of the theoretical cycle and the ideal cycle thermal efficiency of the steam and diesel engines, the essential reasons for the influence of two different combustion modes on the thermal efficiency are theoretically clarified. In recent years, the emergence of in-cylinder direct injection (GDI) and homogeneous compression ignition (HCCI) gasoline engines is a prominent embodiment of the application of these cycle theories.

The efficiency of the diesel engine is higher than that of the gasoline engine, the reason is that the gas pressure and temperature produced by the diesel engine after combustion in the cylinder are higher than that of the gasoline engine, the compression ratio of the diesel engine is much larger than that of gasoline, and the diesel combustion in the cylinder is more adequate than that of gasoline.

Both gasoline engines and diesel engines belong to the category of burning fuel and converting the chemical energy in the fuel into the mechanical energy that drives the vehicle forward by pushing the piston in the cylinder, so the working principle of the two is basically the same.

The gasoline engine sucks in a mixture of gasoline and air, and the diesel engine sucks in air. In the compression stroke, the diesel engine compresses the inhaled gas to a smaller volume, higher pressure, and higher temperature than the gasoline engine.

During the working stroke, the gasoline engine uses a spark plug to generate an electric spark. At the end of the compression stroke, the diesel engine injects mist diesel into the cylinder from the fuel injector, and the hail mist diesel is immediately burned when it encounters high temperature hot air. In a diesel engine, the gas pressure hole that pushes the piston to do the work is larger and more efficient than a gasoline engine.

The efficiency of the gasoline engine is 26-40, and the efficiency of the diesel engine is 34-45(Photo by Xu Shuanghe, Pacific Automobile Network).