25. How is combustion caused in gas engines?

**Giải thích:**<br /><br />Combustion in gas engines is initiated and sustained through a series of processes that involve the mixing of air and fuel, compression, ignition, and expansion. Here’s a detailed breakdown:<br /><br />1. **Air-Fuel Mixing:** The engine draws in air into the combustion chamber. Simultaneously, fuel is injected into this chamber. The air-fuel mixture is crucial for the combustion process.<br /><br />2. **Compression:** The piston compresses the air-fuel mixture in the combustion chamber. This compression increases the temperature of the mixture, making it ready for ignition.<br /><br />3. **Ignition:** At the top compression stroke, the spark plug (in spark-ignition engines) or the heat from the compression (in compression-ignition engines) ignites the air-fuel mixture.<br /><br />4. **Combustion:** The ignition source causes the air-fuel mixture to burn, releasing energy. This energy pushes the piston down, creating mechanical work.<br /><br />5. **Expansion:** As the piston moves down, it expands the gases produced by combustion, which helps to exhaust the burnt gases and draw in fresh air-fuel mixture for the next cycle.<br /><br />**Câu trả lời:**<br /><br />Combustion in gas engines is caused by the ignition of an air-fuel mixture within the combustion chamber, initiated by a spark plug or heat from compression, leading to a controlled explosion that produces mechanical work.