Engine Cycles

Purpose:  In this lab, we will venture into the four processes that govern most of our modern day engines. These processes include isothermal, isochoric, isobarric, and adiabatic. We will go over the difference in each and go into greater depth of the first law of Thermodynamics.

Relationships Between Pressure, Volume, and Temperature

In the picture above, we predicted the relationships between pressure, volume, and temperature. It was predicted through question format. For example, we were asked in question 1 and 2 how pressure and volume relates to temperature and we said that pressure and volume are proportional to temperature by drawing a linear line.

Question 5 and 6 is a continuation of the previous picture in determining relationships between pressure, volume, and temperature. We were given certain values, and we had to predict whether pressure, volume, or temperature increases or decreases.

The Four Thermodynamic Processes

On the board, Professor Mason drew up the four thermodynamic processes without labeling them and had us figure out which was which.

In response to Professor Mason's unlabeled drawings, we labeled, from A to D, the four processes.The trick in this activity was differentiating between an isothermal process from an adiabatic process. We knew that for an isothermal process, there could be no change in temperature; therefore, the inverse proportionality between pressure and volume had to happen more gradually. This says that the slope of an adiabatic process is more steep than the slope in an isothermal process.

Real Example of an Engine

We knew that an engine is composed of cycles, but we had to come up with a practical example of an engine functioning in the real world.

Efficiency of an Engine

We found two ways of writing efficiency. One requires the work done while the other requires both the cold and hot heat. Efficiency is just another way of saying, how much actual energy could we use out of the energy we put in.

Finding Important Values in a Simple Engine

We began finding our first values at each point in a thermodynamic process. By knowing the minimum amount of given information, we were able to find the values at all points.

After all the values at each point were found, we proceeded to find internal energy. We found that the sum of the internal energy is zero.

Semi-successful Experiment

Professor Mason started an experiment to show us that all process enclose an area which we found to be the work done in the entire process. We were only able to get 3 sides of the rectangular process. We had to imagine the bottom line.

More Examples of Engine Cycles

We continued to solve for heat and work at each process but before we did this, we had to make an educated guess on where our cold heat and hot heat occur.

We get a more interesting diagram of an engine cycle and using what we knew about the givens, we solves for the remain values at each point. We proceeded to solving for internal energy, work, and heat. These were the same steps demonstrated in the simple thermodynamic cycle. This shows that the steps remain the same for any P-V diagram.

Conclusion:  We found that the relationship between pressure and volume is inversely proportional while the relationship between pressure and volume with temperature is proportional. This is important for predicting the behavior of an engine cycle. We know that isochoric and isobarric processes are obvious in their behavior but had to differentiate between isothermal and adiabatic processes. The differences were found in the steepness of the slope and why they are different in this way. From creating a theoretical model of an actual engine to looking at P-V diagrams, we gained a deeper understanding of the ways engines work.