Turbochargers For Beginners
It might look like a snail but with a turbo, your car certainly won’t be.
I could have called this post “Turbochargers for Dummies” but (a) anybody who is curious about how something works and wants to know more is not a dummy and (b) I don’t want to imply that those who want to have a vehicle with a turbocharger are dummies.
In any description or review of a new vehicle that’s got an internal combustion engine (petrol or diesel) or even a hybrid engine, you’ll probably come across the mention of a turbocharger somewhere in there. However, what is the point of a turbocharger and how do they work? Are they just a fancy luxury or do they actually do something useful and valuable? If you’re new to the world of motoring or if turbos have just been something you’ve heard about over the years and never really thought about before, you could well be asking these questions. After all, nobody is born known about how a car works and it’s not something they teach you at school. (Maybe it should be something they teach at school – physics would certainly be a lot more interesting if you could see the practical applications.)
Back To Basics
Let’s start by going back to the basics of how an internal combustion engine (ICE) works. An ICE can be thought of as the offspring of a cannon and a spinning wheel. The cannon (the father of the engine) works by using a spark and a controlled explosion within a small space, which produces a massive amount of force that moves a load (in this case, the cannon ball) in a straight line. Mama Spinning Wheel uses a crankshaft (piston), a drive wheel and a gearing system to turn that linear motion into useful rotational motion.
In your typical four-stroke engine, which was invented in 1867 by Nikolaus Otto, the explosion part of the process involves four main motions, referred to as intake, compression, combustion and exhaust or, more simply, suck, squeeze, bang and blow. Get your mind out of the gutter.
Let’s look more closely at the intake stage of the cycle. During the intake phase, the piston and valves allow a combination of fuel (petrol or diesel) into the chamber. In a naturally aspirated engine, ordinary common or garden atmospheric pressure and suction push the air into the cylinder. However, to make the process go more quickly and use fuel more efficiently, one needs some way of compressing and forcing the air into where you want it rather than relying on, essentially, gravity and air pressure. This was a bit of a burning need when they started flying planes a bit higher than they did in, say, World War 1, and the atmospheric pressure was a lot less at altitude. Compressing the air and forcing it into the business bits of the ICE is what a turbocharger does.
How Turbos Work
The next question is how the turbocharger does the job of compressing air and forcing air into the cylinders? It uses a system originally developed in aeroplanes with turboprop engines. This uses a fan system to slurp and pump air into the cylinder – the shape of the fan does this by altering the air pressure around the blades. Seems ridiculously simple, right?
Bright sparks among you will have wondered what gets the fan moving to do this job of pumping the air in. After all, you don’t get anything for free. However, the original designers came up with a clever solution. After all, during the final phase of the Otto cycle – the exhaust or blow phase – the waste air and other exhaust products (hopefully, there won’t be too many of these) is shoved out of the engine. A basic turbocharger uses this exhaust air to drive the turbine part of the system. This means that a turbocharger has two main parts: the turbine that harnesses the exhaust stream, which is hitched up to the second part: the compressor that takes in clean air.
There is a third part to a basic turbocharger that does more than just hold the two spinning bits together. This is the intercooler. As anybody who’s used a bike pump has noticed, when you compress air, it gets hotter. The problem with this is that as things get hotter, the molecules inside it move more and it expands – meaning it’s less compressed. Cold air is denser than warm air, which means that it’s not just in your head if you find it harder going on the bike or jogging on a cold morning. The intercooler is a kind of miniature radiator system that dissipates the heat energy created by compressing the air to keep it nice and dense.
Why Use Turbochargers?
So why do you need to have a turbocharger and get that extra air into your car engine, given that you don’t have the problems of a fighter jet operating at altitude? Is there any advantage to it for the everyday motorist?
The answer is, of course, a great big yes. By shoving more air into the cylinders, the power delivered by the combustion (bang) part of the cycle is increased. Power is the amount of force delivered every second, so the faster the engine burns, the more powerful it is. This means that an otherwise small engine can get the oomph of something much bigger. Because adding a turbocharger involves less weight than adding another cylinder or increasing the size of the cylinders (the other ways to make an engine more powerful), this improves the power to weight ratio. It’s all about the POWER (I’m hearing Jeremy Clarkson inside my head at this point).
You may hear some people claim that turbochargers are more environmentally friendly than naturally aspirated engines. This is a bit controversial and it’s not as simple as Turbo Good, Natural Aspiration Bad. Quite simply, a 1.2 litre engine that is naturally aspirated will use less fuel than a turbocharged 1.2. However, the turbocharged 1.2 litre will deliver a lot more power than the naturally aspirated 1.2 and will produce the power of a naturally aspirated engine that’s a lot bigger. Because it has delivered the oomph of a bigger engine without the demands of the extra weight that would be involved, the small turbo engine will consume less fuel than the naturally aspirated big one. The turbocharger is a racing greyhound that needs to eat as many doggy bikkies as a big sooky mastiff but will win the race.
Of course, this is only a very basic introduction – for beginners – and turbocharger designs get a lot more complicated that that. You’ve got all kinds of fun variations like twin turbos, which can be in sequence or in parallel, as well as the issue of turbo lag and how to overcome it.
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