How Do Diesel Engines Work?

If you manage a bus fleet, knowing how diesel engines work can help you avoid common diesel engine problems and keep your vehicles back on the road. Take a look at the steps below to discover how diesels work and why they are famous for their power efficiency.

In the first step of the process, the diesel engine’s intake valve opens, and the piston moves downward in the cylinder. During this, air is drawn into the combustion chamber. The air pressure drops as the piston moves down, causing fresh air to be sucked into the cylinder.

Next, after opening, the intake valve closes. The piston moves up in the cylinder, and the air within the cylinder is compressed. It’s worth noting that diesel engines can compress air more effectively than petrol engines, which creates a substantial amount of heat. In fact, the compression raises the air’s temperature so much that it’s hot enough to ignite fuel once it is injected.

Prior to the piston reaching the top, diesel fuel is directly injected into the cylinder, causing it to mix with the compressed, hot air. This triggers the combustion of the fuel in the combustion chamber. This combustion creates a large amount of heat and pressure, with the expanding gas triggering the piston to be pushed back down. The force created at this point is capable of turning the crankshaft and, therefore, powers the entire diesel engine.

During the exhaust stroke, the exhaust valve opens, and the piston is moved back up. The piston pushes the combustion by-products out of the cylinder through the exhaust valve, effectively clearing the cylinder for the next cycle. The diesel engine returns to the intake stroke, meaning the process starts all over again.

The main differences between how diesel motors work and how petrol motors work are as follows:

A petrol engine pre-mixes the gas and air, igniting this with a spark. In contrast, a diesel engine injects fuel into the compressed air, and the compressed air’s heat causes the fuel to ignite spontaneously.

As we’ve mentioned, a diesel engine compresses air at a much higher ratio than a petrol engine, compressing at a ratio of around 14:1 to 23:1 compared to the petrol ratio of 8:1 to 12:1. Arguably, the diesel engine compression ratio results in better power generation efficiency. Check out our guide on how to test compression on a diesel engine.

In the petrol engine process, the fuel is delivered to the cylinder in the intake stroke. It is then compressed. If the air-fuel mixture is compressed too much, the mixture can ignite and trigger knocking. On the other hand, as diesels use direct fuel injection into the cylinder, a diesel engine only compresses air, which explains why the compression ratio can be much higher.

Diesel engine fuel is ignited by air compression, so, instead, diesel engines sometimes come with a glow plug. A glow plug aids in fuel ignition during cold temperatures, effectively helping start diesel engines in winter.

Because petrol engines don’t depend on the air and fuel spontaneously combusting, they do not need glow plugs. Instead, they come armed with spark plugs, which ignite the air-fuel mixture and take heat away from the combustion chamber.

To understand the process of how diesel engines work further, take a look at some of the key components involved and what they are used for.

1. Engine block: The engine block is the area in which all the other diesel engine components are placed.

2. Battery: The battery, charged by the alternator, supplies electrical power to start your diesel engine and ensure all electrical systems operate properly.

3. Cylinder: The cylinder is the home of air compression and fuel combustion. This is the central area where the piston moves up and down.

4. Cylinder head: The cylinder head contains key components like the intake and exhaust valves, as well as the fuel injectors. This part covers the cylinder’s top, sealing the cylinder for controlled combustion and directing the flow of exhaust gases and air. Cylinder head problems can disrupt the process, so you may consider remanufactured cylinder heads as a solution.

5. Piston: Pistons move up and down in the cylinder, converting energy from combustion into mechanical energy. The force effectively turns the crankshaft.

6. Crankshaft: The crankshaft converts the piston’s linear motion into rotational motion, driving the wheels of your bus fleet vehicles.

7. Valves: The intake valves open, allowing air into the combustion chamber, while the exhaust valves work to expel combustion gases. They determine the flow of air and gases within the engine, controlled by the camshaft.

8. Camshaft: The camshaft controls the timing of the opening and closing of the valves by pushing against the rocker arms connected to them. The camshaft rotates in line with the crankshaft, ensuring proper timing for efficient engine performance.

9. Fuel injector: The fuel injector does what it says on the tin – it injects diesel fuel directly into the combustion chamber at high pressure, ensuring it mixes with compressed air and ignites properly. Blocked injectors can cause your engine to overheat, so be mindful of this and schedule regular maintenance checks at Foxwood Diesel.

10. Connecting rod: The connecting rod connects the piston to the crankshaft, enabling the transmission of movement.

11. Glow plugs: Glow plugs heat the cylinder’s air in colder conditions, helping to start the engine by increasing the temperature of the compressed air.

12. Air filter: The air filter stops dirt and dust from getting into the diesel engine’s intake system, meaning only clean air can be drawn into the combustion chamber.

13. Exhaust system: The exhaust system draws the combustion-produced gases from the engine, helping to decrease harmful emissions and noise.

14. Oil system: The oil system transfers oil throughout the diesel engine, lubricating moving parts to decrease friction and enhance overall efficiency. If there’s an issue with the oil system, your fleet may be experiencing high oil consumption or an oil leak.

So, there you have it! Hopefully, you now understand how diesel engines work, which is crucial knowledge for keeping your bus fleet up and running. If you need assistance with diesel engine maintenance and would like to task our team with the job, please get in touch with us today. Foxwood Diesel is well-stocked with a variety of new and reconditioned parts and engines fit to get your fleet back on the road in no time.

Our diesel engine specialists are more than happy to talk you through how a diesel engine works, as well as common diesel engine myths and how you can keep your engine in good condition. For more insights into all things engines, please browse our blog!