Heat Engines, Fuel Types & Emission Reduction Techniques

Machines and Heat Engines

Machines transform thermal-mechanical energy into thermal energy or vice versa.
Heat engines are machines that transform drive energy into heat or thermal-mechanical work.

External and Internal Combustion Engines

External combustion: Combustion occurs outside the machine. The external combustion burns and uses the machine's heat to vaporize water; the resulting gases drive a device to perform work.
Internal combustion: Fuel burns inside the engine, and the gaseous products are responsible for producing the driving work.

Reciprocating and Rotary Machines

Reciprocating (alternative) machines: Incorporate a plunger or piston that has an alternating rectilinear movement. A crank mechanism transforms rotary motion into reciprocating motion.
Rotary machines: Produce rotary motion directly.

Steps in the Steam Engine

1. 1 - Steam is produced in the boiler.
2. 2 - The water vapor goes to the cylinder at high pressure through a distributor or conduit.
3. 3 - The distributor channels the steam into the cylinder at pressure and causes the piston to move alternately.

Wankel Engine Characteristics

Wankel engine: Intake/admission, compression, combustion (explosion), and exhaust events occur in three phases per rotor cycle—typically described as three admissions, three compressions, three explosions, and three exhausts per cycle.

Otto Engine — Four-Stroke Cycle

Otto engine is a four-stroke engine that transforms combustion forces into reciprocating movement and then into rotary motion.

1. 1st stroke — Intake (admission): The intake valve opens via the camshaft driven by a timing chain. Pressure drop draws air from outside and fills the cylinder. Gasoline is injected electronically by an injector controlled by a microprocessor that meters the fuel.
2. 2nd stroke — Compression: The piston compresses the air–fuel mixture up to just before top dead center (TDC).
3. 3rd stroke — Power (explosion): The spark plug ignites the mixture, causing combustion and delivering power.
4. 4th stroke — Exhaust: The exhaust valve opens and the combustion gases exit, driving the crankshaft and continuing the cycle.

Combustibles and Fuel Types

COMBUSTIBLES
Highly flammable petrol (gasoline) is very volatile. The numbers 95 or 98 refer to the octane index that measures the anti-knock (antidetonation) properties.
Diesel oils: Diesel fuels are of similar hydrocarbon composition to gasoline but are denser and less volatile; they should be well filtered because any impurity could damage the diesel injection system.
Biofuels: Obtained from the transformation of biomass.

Biodiesel

Biodiesel: Produced from vegetable oils, including used cooking oils; it can be used pure or blended.

Bioalcohols

Bioalcohols: Produced from biomass. The most important are methanol and ethanol.

Acid Rain and Emissions

Acid rain occurs when sulfur oxides (SOx) and nitrogen oxides (NOx) react chemically in the atmosphere and are converted into acids that mix with water vapor in clouds, returning as acid precipitation.

Reducing Harmful Effects and Emissions

Reduce harmful effects: Improve engine performance so systems consume less fuel; improve components and reduce emission mechanisms. Develop alternative and new systems that do not pollute and are durable. Reduce heat losses so machines operate more efficiently and do not have to work harder or consume more energy. Enhance filtration and fuel quality control to protect injection systems and extend component life.

Notes on original phrasing and intent: The content preserves and clarifies the original technical points: external vs internal combustion, reciprocating vs rotary machines, steam engine steps, Wankel and Otto engine cycles, types of fuels (petrol, diesel, biodiesel, bioalcohols), the role of octane numbers, and the environmental impact of SOx and NOx producing acid rain. Where necessary, spelling, grammar, and capitalization have been corrected for clarity and SEO while retaining the complete subject matter of the original text.