Diesel Engine Cold-Start: Challenges and Solutions

In the cold winter months, the issue of starting diesel engines has always been a significant challenge for both users and engineers. Whether it is diesel generator sets used for power generation or other equipment that relies on diesel engines, the ability to start quickly and reliably in low-temperature environments directly affects the availability and work efficiency of the equipment. This article will delve into the various factors that affect the cold-start performance of diesel engines and propose corresponding solutions to help readers better understand and address this challenge.

The starting performance of diesel engines in low-temperature environments is influenced by a combination of factors. These factors interact with each other to determine whether a diesel engine can start smoothly. The following is a detailed analysis of these influencing factors to better understand the complexity of cold starting.

The starter is one of the key components for starting a diesel engine. Parameters that measure the performance of a starter include electromagnetic power, output power, output torque, speed, and induced electromotive force. These parameters directly affect whether the starter can provide sufficient power to drive the diesel engine to start in low-temperature environments. The short-term working characteristics of the starter mean that it must output a large amount of power in a short time, and low-temperature environments can affect the performance of the starter in multiple ways.

Ambient temperature is the primary factor affecting the cold-start performance of diesel engines. When the ambient temperature drops, the physical properties of the fuel change significantly. The viscosity and density of the fuel increase, leading to poorer atomization and reduced fluidity. Fuel injected into the cylinder cannot atomize well, resulting in a rich mixture and reduced combustion efficiency. In addition, low temperatures can also reduce the airflow speed in the intake manifold, preventing the formation of a strong air vortex, which further affects the formation and combustion of the mixture. These factors collectively make it difficult to start diesel engines in low temperatures.

In low-temperature environments, the viscosity of lubricating oil increases significantly. The viscosity of lubricating oil increases with decreasing temperature, and the kinematic viscosity at 0°C can be thousands of times higher than at 100°C. The increase in lubricating oil viscosity leads to increased friction resistance in the diesel engine, resulting in a higher starting resistance torque. This not only requires the starter to output more power to overcome the resistance but also causes the diesel engine to have a lower speed during the initial start-up, further affecting the formation and combustion of the mixture.

The battery is the power source for the starter. In low-temperature environments, the viscosity and resistance of the battery's electrolyte increase, leading to a decrease in the battery's output voltage and starting current. This prevents the starter from obtaining enough energy to drive the diesel engine to start. The decline in battery performance is one of the important reasons for the difficulty in starting diesel engines in low temperatures.

At low temperatures, the wax in the fuel is prone to precipitation, which can sometimes cause blockages in the fuel filter and lines. In addition, the volatility and atomization properties of the fuel also deteriorate with decreasing temperature. Most of the fuel exists in liquid form in the cylinder, affecting the formation of the mixture and causing it to be too lean or too rich, which is not conducive to combustion.

The structure and design of diesel engines also affect their cold-start performance. For example, a low compression start temperature in the cylinder, increased heat transfer to the cylinder wall, and a low starting speed leading to increased air leakage all contribute to a drop in compression end temperature and pressure, which is not favorable for the formation and combustion of the mixture. Additionally, issues such as low fuel injection pressure and larger droplet size are exacerbated in low temperatures, affecting combustion efficiency.

The starting performance of diesel engines in low-temperature environments is influenced by a combination of factors. These factors interact with each other to determine whether a diesel engine can start smoothly. The following is a detailed analysis of these influencing factors to better understand the complexity of cold starting.

In low-temperature environments, the starting resistance torque of diesel engines increases, requiring the starter to output more power to overcome the resistance. At the same time, the decline in battery performance means it cannot provide sufficient energy. These factors collectively make it difficult to start diesel engines in low temperatures, and in some cases, they may not start at all.

In low-temperature environments, poor fuel atomization and poor mixture formation lead to reduced combustion efficiency. This not only results in a decrease in diesel engine power but also increases fuel consumption.

Due to incomplete combustion, the emission of pollutants from diesel engines during cold starts significantly increases. This not only causes environmental pollution but may also affect the service life of the diesel engine.

In low-temperature environments, the increased viscosity of lubricating oil leads to increased friction resistance in the diesel engine. This not only increases the burden on the starter but also increases the workload on the lubrication system, affecting lubrication effectiveness.

To ensure reliable starting of diesel engines in low-temperature environments, it is crucial to take effective measures in response to the above influencing factors and the problems caused by cold starts. The following are some common measures to help improve the cold-start performance of diesel engines.

To enhance the cold-start performance of diesel engines in low-temperature environments, the design of the starter can be optimized. For example, using a high-power-density electromagnetic drive system can increase the starter's output power and torque. Additionally, improving the cooling system of the starter ensures its normal operation in low-temperature environments.

Selecting lubricating oil suitable for low-temperature environments is an important measure to improve the cold-start performance of diesel engines. Low-temperature lubricating oil has a lower viscosity, which allows it to maintain good fluidity in low-temperature environments and reduces friction resistance. Moreover, regularly changing the lubricating oil to ensure its performance meets the requirements is key to ensuring the normal operation of the diesel engine.

In low-temperature environments, the performance of the battery is crucial for starting diesel engines. Using high-performance low-temperature batteries can effectively increase the battery's output voltage and starting current. Additionally, regularly inspecting and maintaining the battery to ensure it is in good working condition is an important measure to ensure the cold start of diesel engines.

Optimizing the performance of the fuel system can effectively improve the cold-start performance of diesel engines in low-temperature environments. For example, using an efficient fuel injection system can improve fuel atomization; employing a fuel heater can raise the fuel temperature and improve its fluidity; and regularly cleaning the fuel filter can prevent fuel blockages.

For diesel engines operating in extremely low-temperature environments, cold-start auxiliary devices can be used. For example, preheating devices can be used to preheat the diesel engine's cylinders and lubricating oil in advance, raising their temperature and reducing starting resistance. Starting fluid can also be used to increase the temperature and pressure inside the cylinder, aiding the diesel engine's start.

Rationally designing the structure of diesel engines can effectively improve their cold-start performance. For example, optimizing the compression ratio inside the cylinder can increase the temperature and pressure at the end of compression; improving the fuel injection system can increase fuel injection pressure and droplet atomization; and using an efficient combustion chamber design can improve combustion efficiency.

For diesel generator sets, the requirements for cold start are more stringent. According to relevant technical specifications, diesel generator sets with a power rating of no more than 250kw should be able to start smoothly within 30 minutes at an ambient temperature of -40°C (or -25°C) and be able to work with the specified load within 3 minutes after starting. For diesel generator sets with a power rating greater than 250kw, their cold-start time and load-carrying working time should be executed according to the Cummins technical specifications.

When conducting cold-start tests, the following points should be noted:

The fuel and lubricating oil used by the diesel generator set should comply with the product specifications.

The test can be conducted in a laboratory or natural environment.

For diesel generator sets with more than two starting methods, each starting method should be tested three times separately. After a successful start, the machine should be shut down, and the next start should not be attempted until 10 minutes have passed.

During the test, one person should record the data while another operates the diesel generator set. No adjustments or part replacements should be made during the starting process.

When starting the diesel generator set, the low-temperature starting measures specified in the product specifications should be used, and the preparation time for these measures should be included in the successful start time.

After the recorder issues the "start" command, the operator should immediately implement the low-temperature starting measures and start the diesel generator set.

After starting, if the diesel generator set establishes voltage, the control panel indicator light comes on, and it can stably operate with 25% of the rated load, it indicates a successful start. At this point, the ambient temperature, relative humidity, atmospheric pressure, and successful start time should be recorded.

Starting diesel engines in low-temperature environments is a complex issue involving the interaction of multiple factors. By optimizing starter design, using low-temperature lubricating oil, adopting high-performance batteries, optimizing the fuel system, using cold-start auxiliary devices, and rationally designing the diesel engine structure, the cold-start performance of diesel engines in low-temperature environments can be effectively improved. For diesel generator sets, strictly adhering to the technical specifications and test requirements for low-temperature starting is key to ensuring their reliable operation in low-temperature environments.

In summary, cold starting is a challenge that diesel engines must face in cold environments. By comprehensively applying various technologies and measures, this challenge can be effectively overcome to ensure the reliable operation of diesel engines in low-temperature environments. This is of great significance for improving the availability and work efficiency of equipment.