Question

How is the rpm (revolutions per minute) of an actual four-stroke gasoline engine related to the number of thermodynamic cycles? What would your answer be for a two-stroke engine?

Short answer

Answer: For a four-stroke engine, the number of thermodynamic cycles per minute is half the number of revolutions per minute (C_4 = R_4 / 2). For a two-stroke engine, the number of thermodynamic cycles per minute is equal to the number of revolutions per minute (C_2 = R_2).

Step-by-step solution

Understand the difference between four-stroke and two-stroke engines

A four-stroke engine goes through four distinct stages in its working cycle: intake, compression, power, and exhaust. During the whole process, the crankshaft completes two revolutions for one thermodynamic cycle to occur. A two-stroke engine, on the other hand, goes through only two stages: compression (with simultaneous intake) and power (with simultaneous exhaust). Thus, the crankshaft completes one revolution for one thermodynamic cycle to occur.

Relate the engine's rpm to the number of thermodynamic cycles for a four-stroke engine

If we consider the rpm of a four-stroke engine, we know that the crankshaft completes two revolutions for one thermodynamic cycle. Now let's represent the rpm as R_4 and the number of thermodynamic cycles per minute as C_4. We can establish the following relation: C_4 = R_4 / 2 This is because the engine requires two revolutions per thermodynamic cycle.

Relate the engine's rpm to the number of thermodynamic cycles for a two-stroke engine

Since a two-stroke engine completes only one revolution of the crankshaft for one thermodynamic cycle, the number of thermodynamic cycles per minute (C_2) is equal to the number of revolutions per minute (R_2) of the engine: C_2 = R_2 As a summary: for a four-stroke engine, the number of thermodynamic cycles per minute is half the number of revolutions per minute, while for a two-stroke engine, the number of thermodynamic cycles per minute is equal to the number of revolutions per minute.