In a spark ignition engine, a spark plug is used to ignite the air-fuel mixture. The spark plug generates a high-voltage spark that jumps across a gap between two electrodes, creating a flame front that spreads across the air-fuel mixture and causes it to burn.
In a diesel engine, the air-fuel mixture is ignited by compression. The air is compressed to a very high pressure, which causes it to heat up and spontaneously ignite the fuel. This process is known as diesel knock.
Diesel engines are typically more efficient than spark ignition engines, but they also produce more emissions. Spark ignition engines are more expensive to build than diesel engines, but they produce fewer emissions.
Here is a table that summarizes the key differences between spark ignition and diesel engines:
Feature | Spark Ignition Engine | Diesel Engine
Fuel | Gasoline | Diesel
Air-fuel mixture | Homogeneous | Heterogeneous
Ignition | Spark plug | Compression
Efficiency | Less efficient | More efficient
Emissions | Fewer emissions | More emissions
Cost to build | More expensive | Less expensive
