Question

For an ideal Diesel cycle, the heat addition is an:

• A. Isobaric process
• B. Isothermal process
• C. Isochoric process
• D. Isentropic process

Hint:

In the Diesel cycle, heat is added at constant pressure (isobaric), whereas in the Otto cycle, heat addition occurs at constant volume. The understanding of these processes is key to analyzing different types of thermodynamic cycles.

Answer 1

The Correct Option is A

The Diesel cycle is a thermodynamic cycle used in Diesel engines. It consists of four distinct processes: two adiabatic processes (compression and expansion) and two processes involving heat addition and rejection. In this case, we are concerned with the heat addition process in the cycle.
In the Diesel cycle, the heat addition process occurs at constant pressure. This is known as the isobaric process. During the isobaric phase, fuel is injected into the combustion chamber at a constant pressure, and combustion occurs, causing both the temperature and volume to increase. This is in contrast to the Otto cycle, which uses constant volume for heat addition.
Let’s break down the options and their meanings:
- Option (A) Isobaric process: An isobaric process is one in which the pressure remains constant while the temperature and volume can change. In the context of the Diesel cycle, this corresponds to the phase where heat is added to the system at constant pressure. This phase results in an increase in both the temperature and the volume of the gas, leading to the expansion of the gas as the fuel burns. Hence, this is the correct answer.
- Option (B) Isothermal process: An isothermal process occurs when the temperature remains constant. In the context of the Diesel cycle, the heat addition process does not occur at a constant temperature, so this is not applicable.
- Option (C) Isochoric process: An isochoric process happens when the volume remains constant. This process is more relevant to the heat rejection phase in certain types of engines but not to the heat addition process in the Diesel cycle.
- Option (D) Isentropic process: An isentropic process is one where the entropy remains constant. In the Diesel cycle, the compression and expansion processes are isentropic, but heat addition occurs at constant pressure, making this option incorrect.
Thus, the correct answer is (A) because heat addition in the Diesel cycle occurs at constant pressure, which is characteristic of the isobaric process.