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The Main Parts of a Diesel Engine

The working principle of the diesel engine shares a handful of similarities with the working principle of a gasoline engine, but also a handful of differences. These differences include slight alterations to the way the engine’s six main systems—fuel, lubrication, air intake, exhaust, cooling, and electrical—function. Generally, the ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression. The diesel engine is referred to as a compression-ignition engine. This makes it unique from petrol and gas engines, which both use spark-plug ignition of the air-fuel mixture. The engine’s six different systems play their own, unique role in making sure everything is operating at peak condition. Let’s look at the main parts of a diesel engine and the reasons why they’re essential to a diesel engine’s health, longevity, and performance.

The Fuel System

A diesel engine’s fuel system is designed to inject a precise amount of atomized and pressurized fuel into the engine cylinders at the right time. When this rush of fuel is mixed with hot, compressed air, combustion occurs. In a diesel engine, fuel reaches the cylinder bore, or sleeve, through a specific path.

Fuel tank → Water separator → Feed pump → Filter → Injection pump → Injector nozzle → Cylinder

The fuel tank is for storing fuel. Most fuel tanks will have a fuel gauge that checks the fuel level and a drain plug that drains fuel. The water separator separates dirt, water, and any other contaminants from the fuel. The feed pump feeds fuel to the filter and injector pump. To open the nozzle, the fuel system has to pressurize the fuel. The pressure needed to inject fuel into the combustion chamber and offset the pressure of compression varies. Normally, it ranges from 350 to 450 PSI. The injection pump is in charge of handling this process. The injector nozzle atomizes the fuel or, in layman’s terms, breaks it up into small particles. Once the fuel enters the nozzle, it’s injected into the combustion chamber.

The Lubrication System

Lubrication has a variety of benefits, including:

  • Reduces wear-and-tear from surfaces rubbing together
  • Reduces the amount of power needed to overcome frictional resistance
  • Removes heat from the piston and other vital components
  • Separates the piston rings and cylinders
  • Removes foreign materials from the engine

The engine’s various components are lubricated under pressure feed. The oil is stored in the oil pump. The oil pump puts the oil through a strainer, then delivers it through a filter to the main gallery. The oil flows from the main gallery to the main bearings. After the oil lubricates the main bearings, some of the oil falls back to the sump, some of it splashes onto the cylinder’s walls, and the remaining oil travels through a hole to the crankpin. From the crankpin, the oil travels to the piston pin through a hole in the connecting rod web. There, it lubricates the piston rings. To lubricate the camshaft and timing gears, the oil is led through a second oil line through the main gallery. Lubricating the entire engine might seem like a long, winding process, but your engine is equipped with the parts it needs to do everything quickly and efficiently.

The Air Intake System

Similar to the fuel system, air flows into the cylinder’s bore, or sleeve, through a specific path.

Air filter → Turbocharger → Intake manifold → Inlet port → Inlet valve → Cylinder bore

The air filter keeps dust from entering the cylinder bore. Filters normally have pores, which are measured in microns, on the surface. As a general rule, the lower the micron value, the better the filtration. Most filter sets will contain outer and safety filters that allow for better filtration. The turbocharger compresses air from the air filter. When air is compressed, the oxygen molecules are packed closer together. This increase in air means more fuel can be added, which generates additional mechanical power and leads to a more efficient combustion process. The intake manifold transports air from the turbocharger to the inlet port. The inlet valve allows air into the cylinder bore. A camshaft controls when the valve opens and closes.

Exhaust System

Another one of the main parts of a diesel engine is the exhaust system. Using the following path, exhaust flows through the engine:

Cylinder bore → Exhaust valve → Exhaust port → Exhaust manifold → Turbocharger → Muffler

The exhaust is passed through the muffler, which cools it down. Exhaust gasses have a higher pressure than the atmosphere, so if they’re released without being cooled, they’ll make a loud, unpleasant sound.

Cooling System

As heat-generating sources, diesel engines need a way to regulate their temperature. They cool themselves down by circulating a water-based coolant through the water jacket. The coolant is circulated through pipes to the radiator. The radiator removes any heat, then returns the coolant back to the engine. The cooling system serves a large variety of purposes. It maintains optimal temperature, protects the engine and its components from overheating, and maintains the lubricating properties of the engine’s oil. There are two types of cooling and three types of water-cooling methods. The two types of cooling are:

  • Air Cooling
  • Water Cooling

The three types of water-cooling methods are:

  • Direct or Non-Direct Method
  • Thermosiphon Method
  • Forced Circulation Method

Electrical System

The engine’s electrical system is composed of the starter motor, alternator, and the battery. The starter motor rotates the flywheel. It receives its power supply from the battery. The starter motor’s pinion engages with the teeth of a flywheel ring and rotates. This rotates the crankshaft, which leads to the movement of pistons in the cylinders. The piston sucks air and fuel into the combustion chamber, which starts the engine. Once the engine reaches a certain RPM, the starter motor removes its pinion from the flywheel. The alternator is fixed on the engine and usually includes a pulley. The belt drives the shaft of the alternator. The alternator’s main job is to charge the batteries. In most engines, you’ll find two batteries. A fully-charged automotive battery should measure at 12.6 volts or above. When the engine is running, the voltage can jump to 13.7 or 14.7 volts.

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The Main Parts of a Diesel Engine