🎓 Understanding the 4-stroke internal combustion engine: A quick guide for mechanics and electricians

Before you roll your eyes and mutter, “Ugh, not another boring engine explanation,” hear me out! Stick around, even if it’s just for a quick refresher. Modern vehicles still rely on some of the oldest engineering principles, and you’d be surprised how much has stayed the same. So, whether you’re a mechanic trying to bridge the gap between mechanical and electrical systems, or an electrician wanting to get a better handle on how electronics control mechanics, this article is for you.

🛠 How it works: The 4 strokes that keep you moving

As the name suggests, a 4-stroke engine runs through four distinct strokes in one full cycle: Inlet (Intake), Compression, Power, and Exhaust. The piston moves up and down in a rhythmic dance of mechanical genius, and here’s how it plays out:

1. Inlet/Intake stroke
   This is when fuel and air make their grand entrance. The intake valve opens, the exhaust valve stays shut, and the piston drops down. This creates a vacuum, which draws a fresh fuel-air mix from the carburettor. It’s like a vacuum cleaner but much cooler (and louder).
2. Compression stroke
   With the intake and exhaust valves now closed, the piston moves up, compressing the fuel-air mixture inside the combustion chamber. Think of it as the engine getting ready to fire up – it’s like winding up a spring before releasing all that pent-up energy.
3. Power stroke
   Just before the piston hits the top (Top Dead Center, or TDC), the spark plug does its thing and ignites the compressed fuel-air mixture. Boom! The explosion forces the piston down. This is the power stroke, and it’s the big moment when everything turns on. The explosion is so powerful, it keeps the piston moving, and with a little help from the flywheel, the engine keeps on rocking.
4. Exhaust stroke
   Now, the piston’s momentum carries it past Bottom Dead Center (BDC) and begins to move back up. The exhaust valve opens, and out go the spent combustion gases, pushed through the exhaust system. By the time the piston reaches the top again, the intake valve is opening and the exhaust valve is closing in a condition we call “rocking”, and the cycle starts over. It’s like the engine’s version of a never-ending treadmill.

⚖ The engine’s delicate balance: Why everything needs to be just right

Now, let’s break down why all of this matters. If any part of the cycle goes wrong, the engine won’t run. For instance, if no fuel is drawn in during the intake stroke (thanks to a blocked carburetor), there’s nothing to burn during the power stroke, and no explosion to create that downward force. No explosion? No power. Simple as that.

The same goes for the spark plug: If it doesn’t fire, the fuel/air mixture stays unburned, and without ignition, no power stroke. Even timing matters. If valves open or close at the wrong times, fuel can get pushed out during compression, leading to an incomplete combustion cycle and, once again, no explosion to propel the piston.

🚙 4-Stroke carburetor engine (Petrol)

This is the classic setup: Fuel and air mix in the carburetor, and the rest of the cycle is as described above: intake, compression, power, and exhaust. The key takeaway is that the carburetor is responsible for mixing the right amount of fuel and air to keep everything running smoothly.

🏎 4-Stroke fuel-injected engine (Petrol)

Fuel-injected engines work on the same basic principles, but with a twist: Instead of a carburettor, you’ve got injectors and a butterfly valve. These injectors spray pressurized fuel into the intake manifold, where it mixes with the air being sucked in through the butterfly valve. The rest of the cycle? Exactly the same as the carburetor version – intake, compression, power, and exhaust.

🚚 4-Stroke diesel engine

Now, here’s where things get interesting. Diesel engines work similarly to petrol engines, but with one crucial difference: Fuel is injected directly into the cylinder during the compression stroke. And forget about spark plugs – diesels rely on spontaneous combustion. As the air and fuel mixture is compressed, it gets so hot that it ignites on its own, causing the explosion that drives the piston down. This is why the power stroke in a diesel engine usually starts just after TDC.

📦 Wrapping up: The heartbeat of modern engines

And there you have it – the basic rundown of how a 4-stroke engine works, whether it’s petrol or diesel. It may seem simple on the surface, but when all the parts work together in harmony, they make your car or machine run like a well-oiled (sometimes literally) machine. Now go impress your friends with your newfound knowledge, and maybe even throw in a “TDC” or “BDC” for some added flair!