Thermal Machines and Combustion Engine Mechanics

Thermal Machines and Energy Conversion

Thermal machines are systems designed to transform thermal energy into mechanical energy or vice versa.

Classification of Thermal Machines

External Combustion Engines

• Alternative: Steam engines utilizing single and double-effect mechanisms.
• Rotary: Closed-cycle systems such as steam turbines.

Internal Combustion Engines

• Alternative: Otto engines (4-stroke and 2-stroke) and Diesel engines (4-stroke and 2-stroke).
• Rotary: Wankel engines, open-cycle turbines, and gas turbines.

Heat Engine Fundamentals

A heat engine is a motor machine that converts thermal energy or heat into mechanical energy. In internal combustion machines, the fuel burns inside the machine, and the produced gases are responsible for driving the work. These systems incorporate a piston and a crank-connecting rod (biela) to transform reciprocating movement into rotation.

The Evolution of Steam Engines

James Watt, a Scottish engineer, improved the steam engine in 1769, making it safe and effective. In the local context, Francesc Salvà and Sant Francesc Ponç conducted several experiments. In 1805, Ponç built the first Catalan steam engine.

Operation and Components

The boiler consists of a repository that produces water vapor through heat generated by the combustion of fuel. The pressurized steam is then led to the cylinder through the distributor. This component distributes the steam to both sides of the cylinder, accelerating the force due to pressure.

• The Distributor: In double-effect engines, steam is introduced at both ends of the cylinder alternately. In simple-effect machines, steam is introduced at only one end.
• The Regulator: A shaft rotates at a speed proportional to the main axis of the machine. This axis is docked with two heavy metal balls. When the machine gains speed, centrifugal force moves the balls outward.

The displacement of the balls closes a steam valve to the cylinder, causing a decrease in the machine's speed. When the balls drop, the steam valve opens again to accelerate the steam engine.

Steam Turbines

Steam turbines are rotary machines that do not utilize the reciprocating mechanisms or cranks found in alternative engines.

Types of Turbines

• Action Turbines: Steam produced in the boiler flows to the turbine where a fixed shell directs it onto blades located on the periphery of a rotating roller.
• Action and Reaction Turbines: Steam hits the blades on a rotating rotor and turns it.

Gasoline vs. Diesel Engines

Advantages of Gasoline Engines

Gasoline engines are generally small and light, allowing for better acceleration and a lower initial cost compared to diesel engines.

Disadvantages and Comparisons

Diesel engines consume less fuel but can be more polluting. Gasoline is typically more expensive than diesel and requires more frequent maintenance.