What on earth is that thing under my bonnet?

Among all the world’s uncertainties at least one matter seems settled: Batteries and electric motors will have a major role in powering the cars and trucks of our future. But as automotive technology becomes more diverse, it’s good to reflect on the technology most of us currently rely on.

Most NZ car owners (3.8 million of them in fact) rely on the same four-stroke internal combustion piston engines that have been in use for well over a century. Despite these engines having been around for so long, most people still open their bonnets and have no idea what’s going on under there – but that’s okay!

Whether your engine is powered by petrol, diesel, biofuels, compressed natural gas or something else, they all seem like pretty complex creatures. However, if we break it down, the basic physics are pretty easy to understand (but really not so basic or necessarily easy to understand after all!).

Combustion, also known as burning, is the basic chemical process of releasing energy from a fuel and air mixture.  In an internal combustion engine, the ignition and combustion of the fuel occurs within the engine itself. The engine then partially converts the energy from the combustion to work. The engine consists of a fixed cylinder (tube) and a moving piston inside it. The expanding combustion gases push the piston up and down, which in turn rotates the crankshaft. Ultimately, through a system of gears in the powertrain, this motion drives the vehicle’s wheels.

There are two kinds of internal combustion engines found in our cars today: the spark ignition gasoline engine and the compression ignition diesel engine. Most of these are four-stroke cycle engines, meaning four piston strokes are needed to complete a cycle. The cycle includes four distinct processes: intake, compression, combustion and power stroke, and exhaust.

‘Spark-ignition gasoline’ and ‘compression ignition diesel’ engines differ in how they supply and ignite the fuel.  In a spark ignition engine, the fuel is mixed with air and then inducted into the cylinder during the intake process. After the piston compresses the fuel-air mixture, the spark ignites it, causing combustion. The expansion of the combustion gases pushes the piston during the power stroke. In a diesel engine, only air is inducted into the engine and then compressed. Diesel engines then spray the fuel into the hot compressed air at a suitable, measured rate, causing it to ignite.

Few, that was a lot of information. Luckily, there’s an animated diagram for all us visual learners that does a pretty good job of laying out the basics of engines (still hardly seems basic right!?) Take a look!

Hopefully, the infographic of a simple 4-cylinder engine will help you understand what’s happening on those unhappy days when your car is laid up at a mechanic’s shop and maybe it will feel a bit better for your pocket too!

Regardless of when the uptake of alternative powered vehicles really starts to make up a material portion of NZ’s vehicle fleet, the internal combustion engine has done Kiwi’s a great service, and we expect it to continue to do so for a long time yet!

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