The movements in a combustion engine are like a carefully choreographed dance. Not only are the countless engine parts moving all at the same time, but they’re also doing it in a perfectly timed sequence. When any part of the engine’s combustion sequence is disrupted, you end up with something called an engine detonation.

No, a detonation doesn’t mean that your engine goes off like a bomb. The term ‘detonation’ refers to a situation where the engine experiences a form of abnormal combustion. In plain English, it means that the combustion chamber in the engine goes ‘boom’ in a way that’s wrong and very bad.

But here’s where it gets interesting. There are three names for abnormal combustion in the engine: engine detonation, engine pre-ignition, and engine knocking. The problem of abnormal combustion gets very confusing because many people use those three terms interchangeably.

Are you confused yet? Don't worry. That's precisely what this article is going to clear up for you. Here, we're going to look at how you'd know if your engine is detonating. Before we get to that, though, we'll also explore engine knocking and pre-ignition.

By exploring all three, you’ll get a complete picture of abnormal combustion as a whole, and you’ll be able to tell when it’s happening to you.

What's the Difference between Engine Detonation, Knocking, and Pre-ignition?

At this point in the article, we know that there are three types of abnormal combustion in an engine: detonation, knocking, and pre-ignition. Now, let’s take a look at the differences between all three.

Engine Pre-Ignition

What it is: Engine pre-ignition is pretty straightforward since it’s all in the name. Basically, this is when the combustion chamber’s air and fuel mixture ignites much sooner than it should.

Remember: The air and fuel mixture is supposed to be compressed to a certain level before the spark plug ignites the mix so that it combusts. That doesn't happen in pre-ignition.

Instead, something causes the mixture to ignite even when it’s not yet compressed. Because the mixture combusts before it’s ready, the engine produces a lot less power than it should.

That might not sound like a big deal initially, but left unrepaired, it could give you an unstable drive while also causing damage to your engine.

What causes it: Several things can cause the air and fuel mixture to ignite prematurely. That could be an overheating spark plug, piston problems, or an imbalanced air-fuel mix.

Engine Knocking

What it is: Engine knocking can be confusing, thanks to the misleading name. Rather than explaining the cause, the term of this phenomenon refers to the sound you can hear when it happens. Because of this somewhat confusing name, people often mistake it with pre-ignition or even detonation.

Engine knocking is another type of abnormal combustion, but it’s not a case of the air-fuel mixture igniting prematurely (that’s ‘pre-ignition’). Instead, knocking is what happens when the mixture doesn’t ignite evenly.

Here's how combustion is supposed to happen: The spark plug generates a spark that ignites the air-fuel mixture. That ignition should occur at an optimum part of the process and spread out evenly starting from where the spark plug is and spreading its way out like a wave.

Engine knocking is when the combustion doesn’t start from the spark plug and spread out like it’s supposed to. Instead, random parts of the mixture start igniting before they should.

The end result? A knocking sound that gives this phenomenon its name.

What causes it: Engine knocking can be caused by problems like faulty spark plugs, carbon deposits building up inside the cylinders, and using fuel with an octane rating lower than your car’s minimum.

Engine Detonation

Now that we know about pre-ignition and knocking, how does engine detonation differ?

What it is: Engine detonation is the same as engine knocking. Read that again. That's right - they're one and the same. People generally use the terms detonation and knocking interchangeably, which is why the confusion about this topic still exists.

So, don’t be surprised if you come across people using ‘engine detonation’ to refer to engine knocking. Some may even use that term to refer to pre-ignition, as well.

Their Differences – in a Nutshell

Whatever the case might be, here is the summary of their differences:

1. Engine pre-ignition is uncontrollable combustion that happens before your spark plug is supposed to deliver the spark. 
2. Knocking or Detonation is also a form of uncontrollable combustion. However, this happens after the spark event has taken place.

How Do You Know If Your Engine Is Detonating?

Here are some tell-tale signs that your engine is detonating:

High Pitched Pinging or Knocking Sound

A typical engine produces a low, gentle hum. In the case of one that’s detonating, you’ll hear higher-pitched noises like pinging or knocking coming from the engine itself.

Rough Engine

For an engine to run correctly and deliver a smooth and continual supply of power, the combustion process must happen uninterrupted. Abnormal combustion that occurs when the engine is detonating will disrupt that.

So, what you’ll feel is that the engine is producing power very roughly when you press on the gas pedal.

Excessive Vibrations

That abnormal combustion and the rough engine will also result in excessive vibrations that you'll indeed feel throughout the car.

Power Loss

Again, an engine with a compromised combustion process will not be able to deliver power as it should. So, you’ll experience a loss of power when you try to accelerate and move the car forward.

Engine Damage

Any kind of abnormal combustion—whether detonation, knocking, or pre-ignition—will eventually lead to internal engine damage. That damage can happen in the form of melted spark plug electrodes, blown head gasket, or even cracked piston rings, just to name a few.

(Blog from carpart.com.au)