Four-stroke engine

In his travels, he encountered the internal combustion engine built in Paris by Belgian expatriate Jean Joseph Etienne Lenoir.

The Lenoir engine ran on illuminating gas made from coal, which had been developed in Paris by Philip Lebon.

[2] In testing a replica of the Lenoir engine in 1861, Otto became aware of the effects of compression on the fuel charge.

The Daimler Reitwagen used a hot-tube ignition system and the fuel known as Ligroin to become the world's first vehicle powered by an internal combustion engine.

The Atkinson cycle is designed to provide efficiency at the expense of power density, and is used in some modern hybrid electric applications.

[4] Due to the unique crankshaft design of the Atkinson, its expansion ratio can differ from its compression ratio and, with a power stroke longer than its compression stroke, the engine can achieve greater thermal efficiency than a traditional piston engine.

While Atkinson's original design is no more than a historical curiosity, many modern engines use unconventional valve timing to produce the effect of a shorter compression stroke/longer power stroke, thus realizing the fuel economy improvements the Atkinson cycle can provide.

[citation needed] Like Otto, it took more than a decade to produce the high-compression engine that could self-ignite fuel sprayed into the cylinder.

[clarification needed] The thermodynamic analysis of the actual four-stroke and two-stroke cycles is not a simple task.

Different fractions of petroleum have widely varying flash points (the temperatures at which the fuel may self-ignite).

The higher temperature more effectively evaporates fuels such as gasoline, which increases the efficiency of the compression engine.

The direct fuel injector injects gasoline under a very high pressure into the cylinder during the compression stroke, when the piston is closer to the top.

The amount of power generated by a piston engine is related to its size (cylinder volume), whether it is a two-stroke engine or four-stroke design, volumetric efficiency, losses, air-to-fuel ratio, the calorific value of the fuel, oxygen content of the air and speed (RPM).

This is commonly referred to as 'valve float', and it can result in piston to valve contact, severely damaging the engine.

The output power of an engine is dependent on the ability of intake (air–fuel mixture) and exhaust matter to move quickly through valve ports, typically located in the cylinder head.

To increase an engine's output power, irregularities in the intake and exhaust paths, such as casting flaws, can be removed, and, with the aid of an air flow bench, the radii of valve port turns and valve seat configuration can be modified to reduce resistance.

An internal combustion engine is on average capable of converting only 40-45% of supplied energy into mechanical work.

A large part of the waste energy is in the form of heat that is released to the environment through coolant, fins etc.

Supercharging increases the power output limits of an internal combustion engine relative to its displacement.

When idling, and at low-to-moderate speeds, the turbine produces little power from the small exhaust volume, the turbocharger has little effect and the engine operates nearly in a naturally aspirated manner.

When much more power output is required, the engine speed and throttle opening are increased until the exhaust gases are sufficient to 'spool up' the turbocharger's turbine to start compressing much more air than normal into the intake manifold.

Turbocharging allows for more efficient engine operation because it is driven by exhaust pressure that would otherwise be (mostly) wasted, but there is a design limitation known as turbo lag.

A longer rod reduces sidewise pressure of the piston on the cylinder wall and the stress forces, increasing engine life.

It has a series of cams along its length, each designed to open a valve during the appropriate part of an intake or exhaust stroke.

Most modern production engines use hydraulic lifters to automatically compensate for valve train component wear.

The Mack Truck company, decades ago, developed a turbine system that converted waste heat into kinetic energy that it fed back into the engine's transmission.

This is necessary for emission controls such as exhaust gas recirculation and catalytic converters that reduce smog and other atmospheric pollutants.

Some potential solutions to increase fuel efficiency to meet new mandates include firing after the piston is farthest from the crankshaft, known as top dead centre, and applying the Miller cycle.