Diesel engine or petrol? Intrigued on why there are two variants of combustion engines in the market? Which type of car do you own right now? If you love petrol engines and want to know more about its counterpart, then this post is for you.
I will discuss the very basics of diesel engine like its major parts, how it works, and some of its essential properties that every car guy should know. So lets get started!
Introduction of Diesel Engine?
The word “diesel” came from German mechanical engineer Rudolf Diesel, which is an internal combustion engine where the ignition of fuel is triggered by elevated temperature of the air inside the cylinder due to mechanical compression.
Thus, diesel engine is known as a compression-ignition engine or CI engine. In contrast, petrol or gasoline-powered motors uses spark plug-ignition from the air-fuel mixture.
First prototypes of diesel engines even use petrol as fuel and in 1901, the first diesel engine cylinders for commercial use has been produced. Since then, diesel-powered engines is used in many types of vehicles in many industries such as trucking, military vessels, commercial ships, agricultural tractors, generators and many more.
Modern Diesel Engine – How it Work
Diesel vehicles today are based on petrol engine designs. But to be able to withstand the higher pressures involved for efficient combustion, major components were strengthened and modified in diesel powered motors.
Fuel is pumped by the injectors and metering unit which are commonly located on the side of the engine block. This type of motor doesn’t need spark plugs (electric ignition) to ignite.
Major components of a diesel engine include pistons, connecting rods, crankshafts, bearing caps, glow plugs, fuel injectors, cylinders and many others.
The engine block is designed to be thicker compared to a petrol engine block. They have more bracing webs that provide more strength to absorb more heat, stress and abuse. Diesel engine blocks are commonly made of either iron or aluminum.
When it comes to injection, the fuel and air mixture in a diesel engine are introduced at different times during a cycle and have to mixed inside the cylinders. There are two types of injections in a diesel motor – direct injection and indirect injection.
In most vehicles today, direct injection engines are the most widely used. This type of injection system doesn’t use swirl chamber where the fuel is injected. But the fuel goes straight into the combustion chamber instead. In contrast, indirect injection uses a pre-combustion chamber (a spiral swirl chamber) into which the injector squirts the fuel before it goes into the combustion chamber itself.
As a four-stroke engine, diesel motors strikes four times for every single fuel injection. Here’s how it works:
- Suction Stroke:
- Compression Stroke
- Injection Stroke
- Exhaustion Stroke
Suction stroke (or also known as induction) is where the air is sucked inside the cylinder during suction stroke. Compression stroke is where the cylinder of the engine initiates to compress the air which elevates its temperature to a degree that the fuel can be ignited. A typical compression ratio is 20:1, compared with 9:1 for a petrol motor.
Injection stroke begins after the compression stroke and fuel is then sprayed through the injector. Because of the heated air, the fuel ignites once they come in contact with each other. Lastly, the gasses formed due to this ignition are exhausted from the outlet valve – exhaustion stroke.
Another difference between a petrol and diesel engine is the speed control. Petrol engines is throttled , meaning the amounts of air (in any given engine speed), that enters the chamber varies. In contrast, diesel engines is not throttled so the amount of air entering the combustion chamber is always the same.
Engine speed is controlled by the amount of fuel being injected into the chamber. Meaning more fuel in the chamber, makes the combustion to be more turbulent, fiercer, which thus results to more power production.
Starting and Stopping a Diesel Engine
To start a diesel engine, it required a diesel fuel and glow plugs.
Both diesel and petrol engines are started by an electric motor. For diesel motors, this begins through a compression-ignition cycle as they don’t have spark plugs to create ignition.
Problem with diesel engine is when they are exposed to a cold environment, they are quite difficult to start because the high temperature needed for combustion isn’t met.
To answer this issue, modern diesel engines have glow plugs which are small electric heaters that are directly powered by the car’s battery. These glow plugs are switched on for just a few seconds before attempting to start the engine.
And you won’t get ignition if you don’t have fuel, and diesel engine requires diesel fuel. This is a type of fuel that is less refined compared to a petrol fuel. This means that diesel fuel is heavier, more viscous and less volatile fuel.
Now how to stop a diesel motor?
When you stop a petrol engine, you just cut off the spark. But in diesel motors, you don’t cut the spark but rather cutting the fuel supply at the injector pump of the fuel metering and distribution unit. Of course, the engine will also stop if you cut the air supply.
A diesel engine stops much faster compared to a gasoline-powered engine due to its higher compression which enables the engine to have greater slowing-down effect. But failure to cut either the air or fuel supply will result in a diesel runaway where the engine will continuously run at high RPMS. Diesel blowby may be one of the main causes of this issue.
Conclusion
So that’s it! Diesel engines are powerful and economical as they are quite fuel efficient motors. Though emissions like black smoke may contribute to some people’s refusal to use diesel engine vehicles, diesel cars are still in-demand these days and are still evolving alongside the ever growing technological advancements in the automotive world.
With the introduction of hybrids and electric vehicles in the market, do you think diesel-powered cars will thrive? Leave your comment below!
