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The Internal Combustion engine, as used in all manner of vehicles and other tools, has been around for over a century and a quarter.  There are many types of I.C. engine – for example the petrol and Diesel two- and four-strokes – but for the purposes of this article, I shall be concentrating on the 4-stroke petrol variety.

The petrol-driven four-stroke engine, then, is widely attributed to one Nikolaus August Otto, a German engineer for whom the Otto cycle (being the four strokes the engine makes – induction, compression, ignition and exhaust – in order to work) is named.  However, he was working on the operation principle of Alphonse Beau de Rochas, and after the engine of Jean Joseph Etienne Lenoir.

A basic engine is quite straightforward in its construction: firsly, the engine housing, the block, is made typically of iron, aluminium or an alloy, dependent on whether the manufacturer considers lightness, strength or cost to be more important.  Other factors which influence the materials used include heat conductivity, propensity to warp and, of course, for what it will ultimately be used.

In relation to cost, obviously an iron block would serve best as this metal is relatively cheap, has the advantage of strength and is easy enough to work.  The problem is its weight – which may not be an issue for a bog-standard, work-a-day vehicle, but when performance or dexterity are required, it can be a liability.  Aluminium is more expensive but much lighter than iron.  However, it is also less robust and is more difficult to work than iron, as it tends to warp easier.  However, in an alloy it works well, providing lightness while the other metal provides strength.  That said, the resulting alloy may still be difficult to work, and will invariably be more expensive, than iron.

Within the block are cut the cylinders, usually four, although six, eight, twelve and even sixteen have been used, either in straight, vee, flat or ”W” formation.  There have also been three- and five cylinder engines, ’though three cylinders tends against smoothness because three is fewer than the strokes in the cycle, and therefore there is an inbalance in the timing of the ignition (and thus, power) stroke relative to the number of cylinders.  The Vee engine can be either 60 or 90 degrees between each bank, the deciding factor being the power it needs to produce versus the thermodynamic efficiency of the rest of the layout (engines run optimally in a certain range: too cold and more petrol will be required, resulting in a silting up of the engine, and increased wear as the oil doesn’t reach its optimum viscosity – too hot and anything from a blown gasket to total seizure can occur), while a flat engine has the banks at 180 degrees.  The W configuration has three banks – hence this is only useful for 6- and 12 cylinder engines (although it would theoretically be possible to have a W9 unit, this would be improbable given that, as with the 3-cyl engine, the four strokes cannot easily be distributed between them.)

The cylinders are lined with metal sleeves, within which the pistons are pushed up and down by connecting rods attached to the crankshaft – of which mechanism, more later.  But the sleeves themselves, the cylinder liners, are important in the cooling of the engine.  Depending on the architecture of the engine block, these liners may be known as wet-liners – where the engine’s coolant runs directly against the liner – or dry-liners, where the coolant chamber will be separated from the liner by the construction of the block.  Factors influencing this design choice include ease of manufacture and optimal operating temperature.

The pistons within the cylinders are connected to the connecting rods (con-rods, for short) by an arrangement of gudgeon pins and various other mechanisms so that, held upward, the con-rod has free movement of sufficient degree along one plain.  This is because the other end of the con-rod is connected to the crankshaft.  Now, the crankshaft is, basically, a rod which rotates along the length of the bottom of the engine, and corresponding to each piston is an eccentrically-placed portion of the rod so positioned that, when the rod is rotated, it drags the piston down to the bottom and then back up to the top of the cylinder.  This is what causes the cycle to be completed.

However, this is not the end of the matter, for we haven’t touched the top of the engine yet – the cylinder head.  This is where the combustion chamber, and the valves, reside.  For efficiency, the combustion chamber has a specific shape, so that the fuel-air mixture may be properly drawn into the cylinder as the piston goes down on the induction stroke, and then is compressed to exactly the right degree on the upward, compression stroke; then when the compressed mixture is ignited it is as per design specification and then on the upward stroke the spent fuel is dispensed with efficiently.  Of course, the induction and exhaust have to happen by some means, and those means are the valves.  Once upon a time – and indeed, until relatively recently – the side-valve was the configuration of choice.  This meant the valves would either be pushed up into an inlet in the side of the combustion-chamber, or pushed into the combustion-chamber itself from the side.  This was cheap to produce, but mechanically not very efficient because the hot gasses were more inclined to rise than move sideways.  And so the overhead valve was born.  Now, the overhead valve, or ohv engine, was still controlled from the side of the engine, for that was where the camshaft was, and so a pushrod arrangement was used.  The pushrod was pushed up by the camshaft, where it engaged with a rocker arrangement whose fulcrum was a rod atop the cylinder head: the result being that as one end was pushed up, the other was pushed down onto the waiting valve, held closed by strong springs.  This arrangement has been largely superceded on all but the most agricultural and primitive of engines by the over-head camshaft (ohc) arrangement, whereby the camshaft (or camshafts, for double overhead camshaft – dohc -arrangements) acts directly on the valves themselves or, failing that, via rockers.  The camshaft itself is a shaft, smaller in diameter than the crankshaft, on which there are numerous ovoid protuberances (cams), so placed that as the shaft rotates, the cams cause whatever is beneath them (or above them, in the case of pushrod or sidevalve engines) to be pushed.  Obviously, this camshaft is connected to the crankshaft, so that it spins half as fast as does the crankshaft – that way, each valve only opens once per cycle, and it works properly.  Of course, between those valve actions, the compressed mixture in the chamber is ignited, thus pushing the piston down and providing the power – and the source of that spark is the sparking plug.  This is also the work of the camshaft, for as well as the cams the camshaft also has a gear ring, from which the distributor is run.  The distributor distributes the electricity needed to fire the sparking plugs, and it does that by means of a rotor arm which spins off the gear on the camshaft and distributes the charge to each of the cylinders in turn.  For a four cylinder engine, the firing order is usually 1,3,4 2 – but according to the set-up of the engine it could be any combination, except a straight line, for this would set up un-necessary strains on the engine and thus shorten its life.

There is, of course, much more to an engine than the foregoing. I will be adding to the store of knowledge on all things automotive hereon – and much more besides – but for now, this is a large enough contribution.