Diesel cycle and Otto cycle are two different thermodynamic cycles used in internal combustion engines. In Diesel cycle, air is compressed to a high pressure and then fuel is injected which ignites due to the high pressure and temperature. The heat released due to combustion is converted into mechanical work. On the other hand, in Otto cycle, a mixture of fuel and air is compressed and ignited by a spark plug which leads to the release of heat and conversion of heat into mechanical work.

Efficiency of Diesel cycle vs Otto cycle

The efficiency of an engine is defined as the ratio of the work output to the heat input. The efficiency of Diesel cycle is generally lower than the efficiency of Otto cycle. This is because the compression ratio of Diesel cycle is higher than that of Otto cycle which leads to higher heat losses due to increased surface area of the cylinder walls. However, the efficiency of Diesel cycle can approach that of Otto cycle under certain conditions.

Effect of cut-off on efficiency

Cut-off is the ratio of the volume of air to the total volume of the cylinder. It is an important parameter that affects the efficiency of the Diesel cycle. The efficiency of Diesel cycle approaches to Otto cycle efficiency when the cut-off is zero. This is because when the cut-off is zero, the air is compressed to a very high pressure which leads to a high temperature. When the fuel is injected, it ignites due to the high temperature and pressure which leads to a complete combustion of the fuel. This results in a higher efficiency of the engine which approaches that of Otto cycle.

Conclusion

In conclusion, the efficiency of Diesel cycle can approach that of Otto cycle when the cut-off is zero. This is because a zero cut-off leads to a high temperature and pressure which leads to complete combustion of the fuel and higher efficiency.