The Hyperlogos

A vehicle's engine provides motive power by consuming fuel, as opposed to an electric motor which uses electrical energy (current and potential) in order to produce rotation.

Engines

There are two main types of engine; internal and external combustion. External combustion engines typically include stirling engines, which work strictly on heat, and steam engines, which use heat to boil water in order to produce steam pressure, which pushes cylinders. Steam can also be used to run a turbine engine. Internal combustion engines burn fuel inside of them, utilizing the change in phase (from liquid to gas) due to combustion to turn the engine.

External Combustion

External combustion engines use heat to generate energy. Most of them work with steam, whether they are reciprocating or rotary (turbine) because when matter changes state it tends to change dramatically in volume as well. However, the Stirling Engine uses the repeated heating and cooling of a gas in a sealed container.

Internal Combustion

Internal combustion engines are further divided into two primary types, compression ignition (CI) and spark ignition.

Compression Ignition

Diesel engines are compression ignition, and ignite fuel by compressing the intake charge to heat it, then injecting the fuel. Generally speaking, they cannot do this until they are up to operating temperature, so they use electrically-heated glow plugs to achieve the proper temperature. This creates a "hot spot" in the combustion chamber which touches off the fuel. However, since it only comes from one spot, usually at the side of the chamber, this produces an uneven burn which does not get the maximum energy return from burning the fuel. Once the engine comes up to temperature, the glow plugs are no longer necessary.

Spark Ignition

Your ordinary vehicle uses a four-stroke "Otto Cycle" motor (hence the name "auto" and "automobile", even though automobile means self-driving, which also makes sense) which works on a "suck-squish-bang-blow" principle. The intake charge in these engines is a fuel/air mixture, which is ignited with a spark.

Finally, there are two main types of spark ignition engine: Reciprocating, and rotary.

Rotary Engines

Rotary powerplants use a three-sided rotor on an eccentric crank in place of all of that; as it rotates, it approaches the cylinder walls, which causes compression to rise, at which point the fuel/air mixture can be ignited with a spark. Note that airplane engines that have cylinders arranged in a circle are also referred to as "rotary" engines but they are still a reciprocating design.

Reciprocating Engines

Reciprocating engines are the usual type where ignition in the combustion chamber pushes a piston, which exerts force on a crankshaft via a connecting rod. These come in two major types: four-stroke and two-stroke. Actually, there are several different cycles (even several different four-stroke cycles, for example) for internal combustion engines, but we won't go into them now, except to hit the high points.

Otto Cycle

The Otto cycle is the four-stroke combustion cycle that we have come to know and often understand. It can be most simply explained with the four-word phrase "suck, squish, bang, blow". (Like a great deal of automotive terminology, it is loaded with euphemism.) An explanation follows:

1. Suck is the intake stroke. During this stroke, the intake valve is open and the exhaust valve is closed. The cylinder moves away from the head, drawing in the fuel-air mixture.
2. Squish is the compression stroke. The intake and exhaust valves are both closed, and the piston moves towards the head, compressing the fuel-air mixture.
3. Bang is the ignition stroke. The spark plug is ignited by way of the coil, and this touches off the compressed fuel-air mixture. Compressing the mixture raises the level of heat and moves the gasoline molecules closer together, which makes it easier to ignite the mixture. This is the only power stroke of the four stroke cycle. During this stroke, the burning fuel/air mixture pushes the piston away from the head. Both valves are closed.
4. Blow is the exhaust stroke. During this stroke, the intake valve is closed, and the exhaust valve is opened. The piston travels towards the head, pushing the exhaust gases out through the exhaust valve port.

As there are four strokes and only one of them is a power stroke, we can see that only every other reciprocation the piston makes in a four stroke engine produces a power stroke. Consequently, we are only making power half as often as we (theoretically) could be.

Two-Stroke Engines

A two-stroke engine does in two strokes what a four-stroke engine does in four. The means for controlling fuel delivery vary, but what they have in common is that they use a technique called exhaust scavenging to draw the air-fuel mixture into the chamber. This allows them to combine the exhaust and intake strokes. In the simplest form of two-stroke, there are not even any valves to open and close, meaning that there are basically three moving parts not counting bearings and seals; the piston, connecting rod, and crank shaft.

After ignition, the piston travels away from the head and uncovers the exhaust port. This allows exhaust gases to begin flowing out of the engine. As it continues to move, it uncovers the intake port, allowing the fuel-air mixture to be drawn into the engine by the vacuum created by the departing exhaust charge. As the piston rises, the wave front of the exhaust pressure traveling into the exhaust system reaches a restriction in the exhaust and reflects back towards the exhaust port, pushing the now-escaping fuel/air mixture back into the chamber until the piston travels down far enough to close the ports. The fuel/air mixture is now ignited and the process begins again.

Two-stroke engines have almost twice the power to weight ratio of a four stroke engine, and they are much simpler, which makes them more reliable at a given power output than a four stroke engine of the same physical size. However, they have numerous drawbacks that make them unsuitable for many purposes and as such there have been few automobiles that utilize them. They have been common on dirt bikes for many years, as well as on personal watercraft.

The first problem is reliability. Two-stroke engines do twice as much work in the same time, and as such have to handle twice as much stress. The second problem is efficiency. Some exhaust gases are mixed into the fuel/air mixture, and some of the fuel/air mixture is lost in the exhaust system, resulting in unburned hydrocarbons (fuel) being expelled from the exhaust system. This brings us to the third problem, pollution. Besides spewing fuel into the atmosphere unburned, which is never a good thing, two stroke engines also require lubrication at several points where four stroke engines do not. As a result they must be designed to waste or burn more oil than four stroke engines. This is usually done by mixing the oil with the fuel (called "pre-mix") although some two stroke engines use oil injection instead. Throwing these petrochemicals into the environment is clearly a bad thing, which is why California is outlawing two-stroke engines of all types on all waterways in 2008.

Nearly all of the tiny little engines (of about .1 to 1 cubic inch of displacement) used in radio controlled cars and the like are two-strokes, although instead of running on gasoline, they typically utilize a fuel containing ten to twenty percent nitromethane.

Engines: