What is the working principle of a diesel engine?
3 Answers
The working principle of a diesel engine is: to generate high heat by compressing air, then atomize and inject diesel fuel through the engine's fuel injector, creating an explosive expansion effect inside the engine, which drives the piston to work. The diesel engine consists of the engine block, crankshaft connecting rod mechanism, valve train, fuel supply system, lubrication system, cooling system, and starting system. Diesel engines are divided into: 1. Spark-ignition engines: Gasoline engines inject gasoline into the intake manifold, mix it with air to form a combustible mixture, which then enters the cylinder and is ignited by the spark plug to burn and expand, performing work; 2. Compression-ignition engines: Diesel engines directly inject diesel fuel into the engine cylinder through the fuel injection pump and injector, where it mixes uniformly with the compressed air in the cylinder, spontaneously igniting under high temperature and pressure, driving the piston to perform work.
Diesel engines don't use spark plugs for ignition, relying instead on compression ignition. Having driven a diesel vehicle for several years, here's how the starting process works: Air is drawn into the cylinder, the piston moves upward to compress the air, getting tighter and tighter until the temperature rises very high, around 500 degrees Celsius or more. Then, at the critical moment, the fuel injector sprays atomized diesel into the cylinder. The fuel ignites spontaneously upon contact with the hot air, creating an explosion. This force pushes the piston downward, turning the crankshaft and getting the entire engine running. In cold weather, the air compression isn't hot enough to ignite the fuel, so a glow plug is used to preheat the air for a short while. Compared to gasoline vehicles, diesel engines are about 30% more fuel-efficient, offer greater low-speed torque, and handle uphill loads with ease. However, they tend to be noisier and produce more vibration, which can be hard on the ears over time. Modern vehicles have improved significantly with turbocharging and noise control. For everyday driving, this design is robust and durable, reducing the hassle of frequent maintenance.
In my younger days, I worked on repairing old diesel engines, where the principle was that the air's temperature skyrocketed upon compression to ignite the diesel. Specifically, the engine compresses air into a very small volume, operating at a high compression ratio of 16:1 or above, making the air hot enough to ignite the injected diesel, which then spontaneously combusts to generate power in a cyclic operation. The entire process doesn't require an additional ignition system, making it structurally simple and reliable. The difficulty in starting lies in insufficient compression when cold, necessitating a preheating system or the injection of a small amount of ignition aid. The advantages are high efficiency and strong fuel economy, especially for long-distance travel where it saves money and requires fewer refuels. The downside is higher particulate emissions, but with technological advancements like optimized electronically controlled fuel injection systems, emissions have become cleaner. Diesel engines provide stable torque output, making them suitable for heavy-duty operations, such as farm tractors or trucks, where they are relied upon for their reliability.
