Common Faults and Causes Analysis of Diesel Engine Intake and Exhaust Systems​

Abstract: The intake and exhaust system of a diesel engine refers to the entire intake and exhaust system, including the turbocharger system. As one of the five major systems of a diesel engine, the intake and exhaust system needs to operate reliably to provide it with clean and sufficient air when the diesel engine is operating normally. This article discusses the significance of analyzing the failure of the intake and exhaust system of a diesel engine, and analyzes the causes and mechanisms of some common intake and exhaust failures of diesel engines.

1. Working principle of intake and exhaust system

The intake and exhaust system is an important part of the diesel engine. Its main function is to effectively transport the fuel and exhaust gas of the diesel engine in and out. It achieves this function through a series of components and pipelines to ensure the normal operation of the diesel engine. The working principle of the exhaust system is shown in Figure 1, and the location of each component is shown in Figure 2.

1). Working principle of the air intake system

The main task of the intake system is to introduce air into the diesel engine for combustion. The intake system consists of an intake duct, an air filter, a throttle, an intake manifold, etc.

The air enters the intake filter through the intake duct. The function of the intake filter is to filter out impurities in the air and ensure that the air entering the diesel engine is clean. Then, the clean air enters the intake manifold through the throttle. The function of the throttle is to control the intake volume and adjust the opening and closing degree of the valve according to the working state of the diesel engine to achieve the best intake effect.

After entering the intake manifold, the air is distributed to different cylinders. Each cylinder has a combustion chamber, which contains components such as cylinders, pistons, and valves. After the air entering the combustion chamber is mixed with the fuel, it is compressed and ignited to produce an explosion, drive the piston to move, and thus generate power.

2). Working principle of exhaust system

The main task of the exhaust system is to discharge the exhaust gas generated by combustion out of the diesel engine and reduce the impact of the exhaust gas on the diesel engine. The exhaust system consists of an exhaust manifold, an exhaust pipe, a muffler, etc.

(1) After the exhaust gas is generated, it first enters the exhaust manifold. The function of the exhaust manifold is to collect the exhaust gas from different cylinders together and then discharge it through the exhaust pipe. The design of the exhaust manifold has an important impact on the emission of exhaust gas and the performance of the diesel engine. Reasonable exhaust manifold design can improve exhaust efficiency, reduce exhaust pressure loss, and increase the power output of the diesel engine.

(2) Subsequently, the exhaust gas enters the exhaust pipe. The main function of the exhaust pipe is to discharge the exhaust gas from the diesel engine as quickly as possible. The design of the exhaust pipe needs to take into account the fluidity of the exhaust gas and reduce noise. Generally, the exhaust pipe will adopt a curved design to reduce the pressure loss of the exhaust gas.

(3) The exhaust gas enters the muffler. The function of the muffler is to reduce the noise generated when the exhaust gas is discharged. There are usually a series of sound insulation materials and partitions inside the muffler to reduce noise through reflection, sound absorption and sound elimination.

In summary, the working principle of the intake and exhaust system is to guide and control the flow of air and exhaust gas inside and outside the diesel engine through reasonable design and installation to ensure the normal operation of the diesel engine. The intake system introduces clean air into the diesel engine for combustion, while the exhaust system discharges the exhaust gas generated by combustion and reduces noise. The coordinated work of these two systems ensures the efficient operation and environmental friendliness of the diesel engine. Through the above introduction, we can understand the working principle of the intake and exhaust system, which is an important guarantee for the normal operation of the diesel engine. The design and optimization of the intake and exhaust system has an important impact on the performance and emissions of the diesel engine. Only by understanding and mastering the working principle of the intake and exhaust system can we better perform the fault analysis of the intake and exhaust system of the diesel engine.

P1  Schematic diagram of the diesel engine intake and exhaust system

P2  Diesel generator intake and exhaust system location diagram

1). Common fault analysis of supercharger system

The main components of the diesel engine supercharger system are composed of the intake manifold, exhaust manifold, turbocharger, etc., as shown in Figure 3. The turbocharger is an important circulation component of the diesel engine intake and exhaust system. During the operation of the diesel engine, the energy balance between the diesel engine, the exhaust turbine and the compressor must be maintained, that is, the energy generated by the exhaust gas discharged by the diesel engine at a certain power is absorbed by the turbine, and the energy of the turbine is transferred to the compressor, and the compressor transfers the energy to the compressed air, which can just meet the air volume required by the diesel engine at this power.

(1) Turbocharger surge

Turbocharger surge is one of the common faults in the intake and exhaust system. It is manifested by violent airflow fluctuations in the compressor, accompanied by a loud roar. The airflow is manifested in a periodic and strong pulse form, that is, the pressure, speed and flow of the airflow change sharply. When the supercharger surges, the main engine operating condition will decline and the speed will be automatically reduced. When the surge zone cannot be crossed, the main engine can only operate at a reduced power. It causes great economic losses. The main reasons are:

① The blockage of the flow channel of the supercharging system is the most common cause of supercharger surge;

② The diesel engine runs at low speed and high load;

③ The load of each cylinder of the diesel engine is seriously uneven;

④ The load of the diesel engine is fused;

⑤ The turbocharger and the diesel engine will be mismatched.

(2) Bearing burnout

Bearings are one of the important components in the supercharger. They ensure the normal and reliable operation of the supercharger, prevent the floating bearings of the rotor assembly from radially moving, and complete the complete positioning of the rotor, so that the rotor of the supercharger rotates in the designed position without rubbing against the intermediate body, volute, etc. Most of the bearing burnouts are caused by low lubricating oil pressure, insufficient or interrupted oil supply, dirty lubricating oil, or metal debris mixed in the oil.

(3) Abnormal noise from the turbocharger

The reason for the abnormal noise from the turbocharger may be that the impeller is damaged or the gap between the rotor impeller and the housing is too small, the bearings and thrust plates are severely worn, the rotor is too large to cause the outer edge of the impeller to rub against the housing, or the dry friction of moving parts such as bearings and sealing rings can cause abnormal noise from the supercharger.

(4) Turbocharger overheating

The reasons for supercharger overheating include excessive exhaust temperature, excessive lubricating oil return temperature, excessive cooling water temperature and reduced boost pressure, which lead to reduced air flow and excessive supercharger temperature.

2). Analysis of common faults of air valves

When the diesel engine is working, it will make a rhythmic and continuous “click, click” sound, which will increase and decrease with the speed of the diesel engine. Causes of failure:

(1) The clearance of the valve is too large due to wear or improper assembly.

(2) The valve spring is broken.

(3) The camshaft is seriously worn, causing the top and bottom of the cam to jump too much, thus making a sound.

If the diesel engine valve is not sealed tightly, it will produce black smoke, low-temperature white smoke or high-temperature black smoke, and there will be insufficient power. You can also hear the sound of leakage. Cause of failure: The contact surfaces of the exhaust valve system of modern diesel engines undergo complex working conditions and repeat movements under high temperature and pressure. The wear rate of the surface must be very low to meet the high requirements for diesel engine efficiency throughout its service life. In a four-stroke diesel engine, the intake valve opens to allow air to flow into the combustion chamber, and then closes to promote the compression and combustion of the fuel and air mixture. At this stage, the exhaust valve closes, then opens to allow the hot combustion products to flow out of the chamber, after which they close and repeat the process. The contact surfaces of the valves encounter complex and demanding contact conditions. Closing the valve involves relatively high impacts on the valve seat. In addition, the location close to the combustion also means being subjected to high temperatures, especially for the exhaust valves which are repeatedly passed by hot combustion residues, which can cause carbon deposits on the exhaust valves.

2). Analysis of common faults of air valves

When the diesel engine is working, it will make a rhythmic and continuous “click, click” sound, which will increase and decrease with the speed of the diesel engine. Causes of failure:

(1) The clearance of the valve is too large due to wear or improper assembly.

(2) The valve spring is broken.

(3) The camshaft is seriously worn, causing the top and bottom of the cam to jump too much, thus making a sound.

If the diesel engine valve is not sealed tightly, it will produce black smoke, low-temperature white smoke or high-temperature black smoke, and there will be insufficient power. You can also hear the sound of leakage. Cause of failure: The contact surfaces of the exhaust valve system of modern diesel engines undergo complex working conditions and repeat movements under high temperature and pressure. The wear rate of the surface must be very low to meet the high requirements for diesel engine efficiency throughout its service life. In a four-stroke diesel engine, the intake valve opens to allow air to flow into the combustion chamber, and then closes to promote the compression and combustion of the fuel and air mixture. At this stage, the exhaust valve closes, then opens to allow the hot combustion products to flow out of the chamber, after which they close and repeat the process. The contact surfaces of the valves encounter complex and demanding contact conditions. Closing the valve involves relatively high impacts on the valve seat. In addition, the location close to the combustion also means being subjected to high temperatures, especially for the exhaust valves which are repeatedly passed by hot combustion residues, which can cause carbon deposits on the exhaust valves.

3). Analysis of common faults of air filters

The air filter used in diesel engines can be divided into several types, such as inertial type, filtering type, and integrated type. It is a device that can remove particulate impurities and dust in the air and prevent pipeline blockage. It ensures that the air inhaled by the diesel engine is clean during operation, thereby reducing the wear between the cylinder liner and the piston and extending the working life of the diesel engine. If the inhaled air contains dust or other impurities, it will aggravate the wear of diesel engine parts, and also cause insufficient intake volume. The fuel cannot get enough oxygen and cannot be completely burned, which will reduce the power of the diesel engine, increase fuel consumption, reduce economic performance, blacken exhaust smoke, increase exhaust temperature, and increase cooling water temperature. Therefore, the air filter should be replaced and cleaned in time.

4). Common fault analysis of exhaust pipe

The exhaust gas discharged from the diesel engine exhaust pipe drives the turbocharger to operate. If the exhaust pipe is blocked (especially the muffler part, as shown in Figure 4), the exhaust will be blocked, the exhaust back pressure of the diesel engine will increase, the turbocharger will operate abnormally, the diesel engine will overheat, the speed will drop, the power will decrease, and the power will be insufficient. If there are too many deposits in the diesel engine exhaust pipe and the pipe is blocked, the diesel engine will have difficulty starting or even fail to start. The reason is that the incomplete combustion of the fuel produces a lot of black smoke or solid particles, which adhere to the exhaust pipe, causing the exhaust pipe to be blocked or even completely blocked.

P3  Diesel engine turbocharger structure diagram

P4  Diesel engine muffler 3D image

Summary:

The intake and exhaust system is one of the important systems of diesel engines. If the intake and exhaust system works well, the diesel engine will run well, and the exhaust temperature, intake temperature, turbocharger operation, fuel consumption and power output will remain normal. Therefore, it is very important to maintain the normal operation of the diesel engine intake and exhaust system, and it must be recognized and treated. Daily maintenance managers should pay attention to the daily maintenance of the diesel engine intake and exhaust system and perform regular inspections to ensure that the diesel engine is in the best working condition.

Share:

More Posts

Troubleshooting diesel engines by sound

Troubleshooting diesel engines by sound Understanding these four engine sounds will make it easier to identify engine problems. When the engine fails, different phenomena will

Cummins 4B/4BT/6BT/6BTA Specs

Cummins 4BT Specs Cummins 4B/4BT/6BT/6BTA engine advantages 1. Design and manufacture It is suitable for harsh working conditions and has strong capacity for high-intensity and

About Fjt

We has been specialized in service and supply of Cummins engines and parts over 15 years, mainly focus on Cummins engine models NT855, KTA19, KTA38, KTA50, QSM11, 4BTA, 6BTA, 6CTA etc.

Scroll to Top