The primary reason for diesel engines having more efficiency than gasoline engines is they _______________.

Explanation:

Diesel engines are known for their higher efficiency compared to gasoline engines. The primary reason for this efficiency difference lies in their higher compression ratio.

Compression Ratio:

• The compression ratio of an internal combustion engine is the ratio of the maximum volume of the combustion chamber to the minimum volume. In simpler terms, it is the ratio of the volume when the piston is at the bottom of its stroke (bottom dead center) to the volume when the piston is at the top of its stroke (top dead center).
• In diesel engines, the compression ratio is significantly higher than that of gasoline engines. Diesel engines typically have compression ratios ranging from 14:1 to 25:1, whereas gasoline engines usually have compression ratios between 8:1 and 12:1.

Importance of Higher Compression Ratio:

The higher compression ratio in diesel engines contributes to their greater efficiency in the following ways:

• Increased Thermal Efficiency: The thermal efficiency of an engine is directly related to its compression ratio. According to the thermodynamic principles of the Otto and Diesel cycles, higher compression ratios result in higher thermal efficiency. This means that a greater proportion of the energy from the fuel is converted into useful work, leading to better fuel economy and lower fuel consumption.
• Higher Combustion Temperature: The higher compression ratio in diesel engines leads to higher combustion temperatures. This is because compressing the air in the cylinder to a smaller volume increases its temperature. When the fuel is injected into the hot compressed air, it ignites spontaneously without the need for a spark plug, as is the case in gasoline engines. The higher combustion temperature ensures more complete combustion of the fuel, reducing unburned fuel and emissions.
• Improved Air-Fuel Mixing: The higher compression ratio results in better mixing of air and fuel. The diesel engine compresses only air during the compression stroke. Fuel is injected directly into the combustion chamber at high pressure, leading to a fine atomization of the fuel. The high temperature and pressure ensure that the fuel vaporizes quickly and mixes thoroughly with the air, leading to efficient combustion.