With the continuous development of the shipping industry, more than 95% of the world's total trade and transportation are borne by the shipping industry, and its total energy consumption accounts for 3% of the total energy. The marine diesel engine is the heart of the ship's work, and it is also the main place for energy consumption and pollutants generation. So, what are the ways for modern diesel engines to save energy and reduce emissions?

1 Types and formation factors of pollutants produced by marine diesel engines

Ship diesel engines will generate a lot of waste during the start-up process, which is the process that fuel combustion must go through. It contains water vapor, carbon dioxide, and oxygen. There are also some gases that are harmful to the atmosphere, such as carbon monoxide, hydrocarbons, and sulfur oxygen compounds. The main factor leading to the existence of these pollutants is that they are not fully burned during the internal combustion process, which harms the environment.

2 Ways to save energy and reduce emissions for modern diesel engines

•  Improve the injection system

The performance of the injection system has a direct impact on the combustion of substances in the diesel engine. Improving the operation of the injection system can improve the efficiency of diesel engine operation, reduce fuel consumption, and control the emission of pollutants such as exhaust gas. At present, many ocean-going ships use low-speed diesel engines. The injection system of this type of machinery is a plunger pump injection system. Due to structural deficiencies, it is difficult to meet the low emission requirements of diesel engines. At the same time, some diesel engines have also joined the variable timing structure, but the number of ships used is small, and the reliability of operation needs to be improved. After the injection system is improved, it needs to have the following properties: First, there is a higher fuel injection pressure, and the pressure can be adjusted in time according to the ship's operating conditions; Second, accurately control the timing and amount of fuel injection to achieve flexible control of the amount of fuel; Third, the entire machine can be flexibly combined, and the closed-cylinder technology can be used flexibly. 
Based on the application of these three technical performances and the use of high-pressure common rail injection systems, the fuel injection volume and pressure generated by the injection can be flexibly adjusted, reducing the energy efficiency of the diesel engine, and meeting the development requirements of energy-saving, environmentally-friendly, and economical diesel engines.

•  Improve the ventilation process

Whether the ventilation of the diesel engine is perfect, directly affects the power of the internal combustion engine and the load generated by its operation. When a diesel engine is perfectly ventilated, a large amount of fresh air enters the cylinder, squeezing the exhaust gas out, and consumes very little unit power. It can be adopted as follows: control the air loss of the intake valve. In the process of intake of air by the intake valve, the flow loss may be increased due to insufficient flow cross-sectional area or large gas flow resistance. Therefore, in order to control the gas loss, the gas flow cross-sectional area of the intake valve can be appropriately increased to allow a large amount of gas to enter. At the same time, it is necessary to reduce the flow resistance and adjust the air distribution structure in the machine to ensure the normal use of the function while increasing the airflow;  The loss of flow resistance is controlled. When the exhaust system is discharged and discarded, the existing flow resistance will be used, and the smallest cross-section is at the position of the exhaust valve. If the valve lift is small, after the gas enters the exhaust passage from the valve gap, it will flow out in the form of jets, resulting in partial loss of resistance and kinetic energy. If the situation is the opposite, pressure energy will be generated. Therefore, the design of exhaust is to reduce the change of airflow cross-sectional area and increase the impulse of airflow. The temperature of the intake air is controlled. After the high-temperature gas enters the machine, the temperature of each part will increase. To control the temperature change, it is necessary to reduce the contact area between the fresh air and the parts.

•  Waste heat utilization

The temperature of the diesel engine gas can reach 400℃ after the exhaust gas, there is moderate temperature residual heat, and the displacement is 20 times that of the fuel oil, so a lot of energy can be found in the exhaust gas. In this regard, an abandoned boiler can be installed to reduce the temperature value, and a heat pipe boiler can be installed to collect the energy in the exhaust gas and reuse the heat energy.

•  Use the booster system and booster

In order to improve the efficiency of diesel engine operation, reduce harmful gas emissions, and meet the new requirements of international maritime affairs for marine diesel engine gas emissions, turbocharging technology can be used to improve the system to improve the performance of diesel engine operation.

First, develop two-stage turbocharging technology. At present, the diesel engines of many ships use the first-stage turbocharging technology. The pressure generated by this technology is small, which limits the volume of intake air and causes the fuel to be incompletely burned. In this way, not only the use of fuel is increased, but also the exhaust emissions of the fuel-burning engine are increased. For this, it is necessary to find the best way of boosting on the basis of existing technology.  The supercharging system uses two turbochargers and connects them in series. In the specific work, the exhaust gas is collected first, and energy is integrated from the exhaust gas. The energy is used to drive the supercharger with a smaller capacity first, and then the supercharger with smaller energy is used to drive the larger supercharger. In this process, the low-pressure supercharger can compress the surrounding air, transfer the air to the cooler, and finally to the compressor. Before this, the air has been compressed once. After the air is compressed twice, the volume of air entering the cylinder can be increased, the fuel can be fully burned, and the emission of harmful gases can be reduced.