Understanding Air Standard Cycles

Air standard cycles are theoretical cycles used to analyze the performance of internal combustion engines. They simplify the actual engine process by making assumptions like the working fluid being air throughout the cycle, specific heat capacities being constant, and the combustion and exhaust processes being replaced by heat addition and rejection processes.

Comparing Common Air Standard Cycles

Let's look at the heat addition processes in some common air standard cycles:

• Otto Cycle: This cycle models spark-ignition engines. Heat addition occurs at constant volume.
• Diesel Cycle: This cycle models compression-ignition engines. Heat addition occurs at constant pressure.
• Dual Cycle: This cycle is a combination of the Otto and Diesel cycles. Heat addition occurs partly at constant volume and partly at constant pressure.
• Brayton Cycle: This cycle models gas turbines. Heat addition and rejection occur at constant pressure.
• Rankine Cycle: This cycle models steam power plants. Heat addition and rejection occur at constant pressure, with phase changes involved.

Transforming Cycles by Removing Heat Addition

The question asks which cycle becomes an Otto cycle if constant pressure heat addition is removed. The Otto cycle is characterized by constant volume heat addition.

Let's consider the cycles mentioned:

• Brayton Cycle: Heat addition is entirely at constant pressure. Removing this would mean no heat addition, not an Otto cycle.
• Rankine Cycle: Heat addition involves phase change at constant pressure. Removing this is not relevant to transforming it into an Otto cycle.
• Diesel Cycle: Heat addition is entirely at constant pressure. Removing this would mean no heat addition, not an Otto cycle.
• Dual Cycle: Heat addition occurs partly at constant volume and partly at constant pressure. If the constant pressure heat addition part is removed from the Dual cycle, the remaining heat addition process is solely at constant volume. This remaining process is exactly the heat addition process of an Otto cycle.

Therefore, if the constant pressure heat addition phase is removed from a Dual cycle, you are left with only the constant volume heat addition phase, which is the defining characteristic of the heat addition in an Otto cycle.

Based on this comparison, the Dual cycle is the one from which an Otto cycle can be obtained by removing the constant pressure heat addition.